I have a 3.4 DOHC engine that I just performed a compression test on. Two of the cylinders had very little compression. When I squirted oil into them, their numbers shot up well beyond the other 4 cylinders. This tells me that those two's rings are shot and the engine as a whole needs a rebuild. I was already planning on having the heads done. Now it looks like I'll have to have the bottom end done too. The engine has 91,000 miles on it.

I know the crank should be remachined. I plan to install the bearings, pistons and rings myself. I will buy a scale and balance the pistons and rods myself too.

So my question is: What is the absolute minimum that a machine shop has to do in order to do a bottom end rebuild?

Before having any machine work done on the engine, have the block and heads checked for defects. There's no sense having machine work done on bad parts.

You'll need to have the cylinders honed (or bored, depending on wear), if you're going to replace the piston rings. It would also be a good idea to have the crankshaft bores in the block checked for concentricity, and line bored if necessary.

That's what I would consider the bare minimum for rebuilding an engine. That's assuming everything else is in perfect working order. If you have the appropriate tools, you can do most of the assembly yourself.

[This message has been edited by Blacktree (edited 10-28-2007).]

No real telling until it is apart.

The crank journals may be ok and maybe not. Magnafluxing is a really good idea in case there are hairline cracks in either the block or the heads. I would magnaflux before doing much more.

If the crank journals look like glass with no score marks, you may do ok with new bearings, mains and sleeve. However, a sloppy rebuild can be a huge waste of money. Having a well equipped machine shop tell you what you've got is a good idea instead of your eye ball or your home set of calipers.

Having the shop hone the cylinder bores is a much more accurate process than buying a honing attachement for your drill. Also, having your valve seats machined for a good 3 side or 5 side cut is way better than lapping them. Having the valve springs load tested is good, but, you may want to just buy new ones.

No short cuts are recommended.

Example, my rings looked ok and my compression was around 124-125 before I took it apart. I did the head work, and got the valves re-seated, but, the rings and bores looked ok so I didn't replace them. Sho' nuff, the rings should have been replaced, so my compression is still 125 after a whole lot of work.

Arn

Bare minimum, hmm. If I were to build a motor (probably have done about 500), I would have EVERYTHING checked at least! Heads for cracks, if OK then surface and true. Complete valve job to include checking valve guide wear. Deck the block, and bore,hone and true the cylinders. True the cam and crank journals. True the crank and/or polish/turn it. Balance ALL components. All of your effots will be rewarded. Building an engine is not simple or cheap, but properly done will make for a very happy motoring experience!

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carpe diem

My experience comes from years of experience as a scooter mechanic,some as an auto mechanic.a rebuild engine has NEW pistons,, it is expensive to rebuild an engine, the main focus is the block, the only part you can get by on "good enough" is the crank bearing surfaces they must be round and in spec you want the spec on the bearing to be in limit,, the danger is not from the journals but from the crank itself and the rods,, an engine that has been run hard must have new rods,and bolts, the rods strech..balance is optional but I love E balance!! of course a balanced engine should have reground journals.. a new oil pump is a must,(hmmm wonder who scrimped here) if you must skimp do it on the head,, a rebuild engine has a new cam a rebuild engine has a new timing chain,,most old engines need a timing chain,but heck it runs,, you can get by with old lifters ect but you may pay for this some day ..use steel no alumiinum rockers.. I build my own engines to "tight"but my break in period is design for this never scrimp on the block,if you scrimp then just buy a rebuild kit and put it in,, if you gap the rings and they are close to the outer limit,do not kid your self,, bore it,,if you rering the lip at the top of the bore must be removed completely when using a ring compressor push piston in in perfect PERFECT alignment,scrub cylinder walls with fresh oil and a white rag to remove grit its in the cross hatch and pores,a tedious task that pays off!! use old stlye break in procedure

91k miles and it needs rings that badly! Is such the norm those engines? I got like 130k out my old 1969 340 cuda engine before it started to smoke a lil and that car was at the drag strip a lot. I can understand it for back, with how poorly engines were made. Anyway, as for balaning; I would send the crank, rods, pistons and flywheel/pressure plate to good balancer. I've had that done on few engines and you can really notice the dif.

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thought I would put my 2 cents in I had a engine shop first make sure the block and heads or any part you are going to reuse are crack free new over sized pistons so you can get the bores straight and true then have the crank turned and polished rods resized with new bolts valve job with new valve guides and valves new cams and lifters never use used lifters on new cams they will kill a new cam most times unless it is a roller cam .
Last balance it let the shop do it unless you have a balance machine to spin the crank then clean it clean it clean it take your time puting it together and check all your clearances over and over a good rebuilt engine takes time to rebuild if you just fly through it then most of the time you wont get a strong rebuild .
oh forgot new oil pump timing chain gaskets ect.

quote Originally posted by Francis T: 91k miles and it needs rings that badly! Is such the norm those engines? I got like 130k out my old 1969 340 cuda engine before it started to smoke a lil and that car was at the drag strip a lot. I can understand it for back, with how poorly engines were made. Anyway, as for balaning; I would send the crank, rods, pistons and flywheel/pressure plate to good balancer. I've had that done on few engines and you can really notice the dif.

I was shocked how bad the rings were myself. My guess is the previous owner never changed the oil and/or ran it low on oil. I have never seen such bad compression from rings on an engine with just 91k miles before (not that I'm an engine expert). I usually see spun bearings and blown head gaskets before the rings go completely like this.

I contacted my credit card company. They say that I should just contact the junk yard and have them pay the shipping back. If they refuse to pay the shipping, then I still tried to return it and they will credit my card. It will cost the junk yard more than it is worth to get this blown engine back so I'll see what they want to do with it tomorrow. No matter what happens, I'm still eating the shipping costs to get it here in the first place: $280. Thank goodness I don't have to pay another $280 to send it back.

From everyone's response it sounds like it may just be better for me to buy a rebuilt short block and have it shipped here or just buy a long block. My local machine shop wants $1900 ($1750 + tax) to rebuilt this type of engine. The laundry list that many have posted makes it sound like a garage engine rebuild is next to impossible.

My Dad sure will be disappointed since he and my uncles rebuild a seized Nova V8 in the late 60s in their garage. They unseized it by packing the cylinders with dry ice until they could pull the pistons out. They they replaced all the bearings, rings, honed the block and did all the work in their garage. My uncle drove it for another 25 years and 200,000 miles until they finally got a new truck two years ago.

How are you doing a compression test?

I would think that a full report on how you did the test, and what your results were would help us suggest what you should do next. You very well might have no problems running with what you have.

For example, I tried doing a compression test turning it over by hand, and I got the same results you got.

quote Originally posted by darkhorizon: How are you doing a compression test? I would think that a full report on how you did the test, and what your results were would help us suggest what you should do next. You very well might have no problems running with what you have. For example, I tried doing a compression test turning it over by hand, and I got the same results you got.

I turned it over by hand. I considered putting my impact wrench on it but I did not want to chance getting the crank bolt stuck or sheering it off.

My results:

#1 61 psi
#2 23 psi
#3 63 psi
#4 60 psi
#5 65 psi
#6 21 psi


I then poured about 2 table spoons of oil in each cylinder:

#1 115 psi
#2 112 psi
#3 110 psi
#4 113 psi
#5 115 psi
#6 110 psi


While turning the crank by hand with a 1/2" breaker bar, I could definitely feel which cylinders were compressing and which were not. I turned the crank around twice for each cylinder. My compression guage has a peak hold so I just took the highest reading for each cylinder. As soon as I put oil in all the cylinders, they were all pretty much even.

#2 and #6 spark plugs had oil on the side electrode in addition to the rest of the plug when I pulled them. They said they had performed a compression test on the engine and got 150 psi across the board on all the cylinders. I find that hard to believe since the two cylinders with bad compression also had the plugs with oil on them. The plugs were not marked and I seriously doubt that they took the time to make sure the plugs were placed back in their original cylinders.

Bottom line, they posted a fake compression test on the engine listing and then lied to me when I asked about it over the phone before I bought the engine.


I know the test is supposed to be done on a warm engine and the starter is supposed to be used. That is not possible in my situation. I have the engine on an engine stand and it won't be started or even hooked up to a transmission for a few more months. I only have 1 month to check the engine and/or deal with any disputes with the seller. I can't see how the compression could be 90+ psi off just because I turned the engine by hand cold. Even so, it should have been evenly off on the compression, not 4 even and the other two cylinders doing their own thing. The numbers I got for the leak down is what I expected to get for the first pass. The compression should not double (or quadruple) when I add oil even if the block is cold.

[This message has been edited by Doug85GT (edited 10-28-2007).]

With a cold hand turned motor, I am surprised you got numbers that high on the other cylinders. A sitting, non run motor almost always will have wierd compression numbers.
if this is a screw in guage, how fast did it hit those numbers? 1 crank? 3 cranks?
If the leakdown times were similar for all cylinders, then you likely don;t really have a problem.
The problem with a sitting engine is not knowing how well oiled the cylinder walls are, they will dry out over time.
You might have a couple of rings that were gummed up from sitting.
There are alot of things to consider, not the least of which is the money you spent on the motor and shipping. doing a full rebuild is expensive to do it right. Don't balance it yourself, spend the couple hundred and have it precision balanced. all pistons the same has little to do with the important piston/rod to counterwieght balance, and the crank overall balance.
I understand your misgivings on the motor, if it were me I'd find a way to fire the motor, even on the stand, (not an easy task, but might be doable) even a short burst would show alot. At the very least get a flywheel on it and use the starter, crank it for a while with no plugs in to blow some of the oil out, then re-try the tests. Check how fast the cylinders come up, watch each step up on the guage and count cranks. should be up in 3. One of the things I see is that it may have also been a valve issue, with that mileage, some carbon can flake off in shipping and be sitting in a seat.

If given that the compression test was not conclusive, it still does not explain how there was oil on the two plugs that were also in the two bad cylinders. The other spark plugs all showed normal brown and a little white coloring. Those two were black, thick gunk on them and had oil even on the side electrobe. That tells me that it was burning oil even when it was running the last time.

I am convinced that the engine is bad.

quote Originally posted by tjm4fun: With a cold hand turned motor, I am surprised you got numbers that high on the other cylinders. A sitting, non run motor almost always will have wierd compression numbers. if this is a screw in guage, how fast did it hit those numbers? 1 crank? 3 cranks? If the leakdown times were similar for all cylinders, then you likely don;t really have a problem. The problem with a sitting engine is not knowing how well oiled the cylinder walls are, they will dry out over time. You might have a couple of rings that were gummed up from sitting. There are alot of things to consider, not the least of which is the money you spent on the motor and shipping. doing a full rebuild is expensive to do it right. Don't balance it yourself, spend the couple hundred and have it precision balanced. all pistons the same has little to do with the important piston/rod to counterwieght balance, and the crank overall balance. I understand your misgivings on the motor, if it were me I'd find a way to fire the motor, even on the stand, (not an easy task, but might be doable) even a short burst would show alot. At the very least get a flywheel on it and use the starter, crank it for a while with no plugs in to blow some of the oil out, then re-try the tests. Check how fast the cylinders come up, watch each step up on the guage and count cranks. should be up in 3. One of the things I see is that it may have also been a valve issue, with that mileage, some carbon can flake off in shipping and be sitting in a seat.

BY HAND! Da.. that explains a lot, lol. Well at least he's tryign to do it himself and learning as her goes.
BTW: you can get a even every low milage engine for salavge with poor compression. I some guys swear by engine swaps and they can be a great way to go if you dont get one from wreak where the engine was at an angle and running with no oilnear the pickup. Best to have an engine pulled from a wreak you can see. I've been told (dont know if its true) that really bad front and rear end wreaks may be ones to avoid as the thrust bearings may be bad.

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I figured that, I couldnt even attempt to get those sort of compression readings dry turning it over by hand, I might of saw 15psi really going at it with a ratcheting wrench on the balancer.

YOUR MOTOR IS FINE, dont convince yourself otherwise with a hand crank compression test. I am serious, I did this excat thing with my motor, and got FAR worse results, I got absolutly 0 compression in 2 cylinders, that I determined to be valve seat issues, because proper velocity cant go up and seat a valve that has been open for a length of time. My motor sat for YEARS and with a few of the valve springs open, the springs fatigued a bit.

Please do not give this another thought, I am telling you there is no doubts that your motor is in perfect shape, compression wise.

How does that explain the oil on the two plugs?

Also, this goes to everyone, please educate me here. Why is it that hand cranking the engine is such a bad thing? Why is it that the cylinders seal better when they are spun faster with a starter as opposed to by a breaker bar? Would it make a difference if I turned the crank with my impact wrench (besides maybe breaking the 15mm bolt)?

quote Originally posted by darkhorizon: I figured that, I couldnt even attempt to get those sort of compression readings dry turning it over by hand, I might of saw 15psi really going at it with a ratcheting wrench on the balancer. YOUR MOTOR IS FINE, dont convince yourself otherwise with a hand crank compression test. I am serious, I did this excat thing with my motor, and got FAR worse results, I got absolutly 0 compression in 2 cylinders, that I determined to be valve seat issues, because proper velocity cant go up and seat a valve that has been open for a length of time. My motor sat for YEARS and with a few of the valve springs open, the springs fatigued a bit. Please do not give this another thought, I am telling you there is no doubts that your motor is in perfect shape, compression wise.

[This message has been edited by Doug85GT (edited 10-29-2007).]

Just a post to describe the many ways you contradicted yourself here.

quote I know the test is supposed to be done on a warm engine and the starter is supposed to be used. That is not possible in my situation. I have the engine on an engine stand and it won't be started or even hooked up to a transmission for a few more months

quote The compression should not double (or quadruple) when I add oil even if the block is cold.

quote I can't see how the compression could be 90+ psi off just because I turned the engine by hand cold.

As I said before, you are lucky to get compression on a cold engine, that has been sitting, and even shipped cross country. You know the test you are doing is wrong, and therefore the results of the test are invalid, yet you are still using them to say that the junkyard is LYING to you when you have 100% no proof, and have not done even a semi accurate test.

quote Even so, it should have been evenly off on the compression, not 4 even and the other two cylinders doing their own thing. The numbers I got for the leak down is what I expected to get for the first pass.

Didnt I already say that valve spring fatiuge among other things related to a valve being open for a length of time? TMJ said something along the lines of some small peice of somthing in the valve sticking it slighly open, even to the point that oil fills that gap getting the PSI results you are looking for (110psi hand cranking is A TON for any motor, you will never get that 150psi, even on a brand new crate motor).

quote Originally posted by darkhorizon: Didnt I already say that valve spring fatiuge among other things related to a valve being open for a length of time? TMJ said something along the lines of some small peice of somthing in the valve sticking it slighly open, even to the point that oil fills that gap getting the PSI results you are looking for (110psi hand cranking is A TON for any motor, you will never get that 150psi, even on a brand new crate motor).

Sorry but you are completely wrong here if you are going to point to the valves. The leakdown test showed EVEN compression. That eliminates anything head related. The leak is in the bottom end only.


No one has yet to explain the oil on the two plugs which just happen to be in the same two cylinders that showed low compression.

quote Originally posted by Doug85GT: How does that explain the oil on the two plugs?

it is impossible to get the reading you got with just a bit of oil in the cylinder, and have failure enough for oil to splash up into the combustion chamber. To get oil on a spark plug, you would need a a valve seal to leak oil down through the exhaust valve, into the combustion chamber, all while it is not running. You will never see oil on a plug coming up from under the piston when it is running, because it will instantly burn off, I dont care how much oil there is, it is going to burn and char, and just look like soot or a lean condition on the plug.

simply put, if there is a piston there (you made 100+psi compression, so I assume there is a piston there), there is no way for volumes of oil to go up through there, and collect on a plug.

It is also very common after a motor sits in a yard, has stock plugs, and has not been cleaned, to have oil leak out of valve covers and the like, and get down by the plug from the outside. Many times I have picked out all sorts of junk including oil just to get a socket on a sparkplug.

If I was to guess, I would say they sat them in something oily when they took them out, or it tipped over and leaked oil out onto them through a valve cover, or something, or it was something other than oil. The LAST thing I would think when I saw that was bad compression.

EDIT

BTW even compression rules out anything RING related, having compression at all is all a head is there, 1psi = good head. In terms of this situation, a hand crank compression test, there are PLENTY of very small variables that the valve seats can play, so many that I dont think I could stop thinking of them.

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Ultimate 3800 swap thread

[This message has been edited by darkhorizon (edited 10-29-2007).]

1. There is no oil in the spark plug holes. They were clean. So no oil leaked in past the spark plugs.
2. The oil on the plugs is BURNED on.
3. There is even compression on the leak down test but uneven on the standard test. That means rings not heads.

quote Originally posted by darkhorizon: it is impossible to get the reading you got with just a bit of oil in the cylinder, and have failure enough for oil to splash up into the combustion chamber. To get oil on a spark plug, you would need a a valve seal to leak oil down through the exhaust valve, into the combustion chamber, all while it is not running. You will never see oil on a plug coming up from under the piston when it is running, because it will instantly burn off, I dont care how much oil there is, it is going to burn and char, and just look like soot or a lean condition on the plug. simply put, if there is a piston there (you made 100+psi compression, so I assume there is a piston there), there is no way for volumes of oil to go up through there, and collect on a plug. It is also very common after a motor sits in a yard, has stock plugs, and has not been cleaned, to have oil leak out of valve covers and the like, and get down by the plug from the outside. Many times I have picked out all sorts of junk including oil just to get a socket on a sparkplug. If I was to guess, I would say they sat them in something oily when they took them out, or it tipped over and leaked oil out onto them through a valve cover, or something, or it was something other than oil. The LAST thing I would think when I saw that was bad compression. EDIT BTW even compression rules out anything RING related, having compression at all is all a head is there, 1psi = good head. In terms of this situation, a hand crank compression test, there are PLENTY of very small variables that the valve seats can play, so many that I dont think I could stop thinking of them.

Your tests are flawed and you know it. Collect proper data, then make assumptions on that. Ill just say right now that i have never had a motor turned over by a starter that had perfect dry compression, yet I have never had any problems with these motors I tested.

If your only goal is to swindle the junkyard, you know you have no proper information to attack with, and proceeding on in the credit card battle, is quite immoral in my opinion.

Easy for you to say. It isn't your engine and you are not doing the work. You conviently side stepped the oil issue and you can't explain why I get even compression with a leakdown. Your theory about the issue being in the heads fails to explain the observation. You also do not explain the difference between hand turning the engine and turning it with a starter. The only difference that I can see is one is faster than the other.

I am ready to have the engine shipped back to the junk yard. You are in no position to make any moral judgement. The last resort of someone who is wrong is to resort to personal attacks. Good job.

quote Originally posted by darkhorizon: Your tests are flawed and you know it. Collect proper data, then make assumptions on that. Ill just say right now that i have never had a motor turned over by a starter that had perfect dry compression, yet I have never had any problems with these motors I tested. If your only goal is to swindle the junkyard, you know you have no proper information to attack with, and proceeding on in the credit card battle, is quite immoral in my opinion.

It is fairly easy for me to say, I built my car, with my motor, and I did fairly extensive research after I messed with my compression tester and found results very similar to yours.

I never side stepped any issue. oil doesnt look black when burned onto a plug.

http://www.spark-plugs.co.u...hnical/diagnosis.htm

quote Deposits Insualtor nose and electrodes encrusted with a build of deposits - usually off white in colour. This is often caused by oil leakage through the piston rings or valve seals. Could be due to the wrong viscosity of oil being used

The difference between hand cranking and starter cranking was discussed, just re read.

quote Originally posted by darkhorizon: It is fairly easy for me to say, I built my car, with my motor, and I did fairly extensive research after I messed with my compression tester and found results very similar to yours. I never side stepped any issue. oil doesnt look black when burned onto a plug. http://www.spark-plugs.co.u...hnical/diagnosis.htm The difference between hand cranking and starter cranking was discussed, just re read.

Even in your picture it shows black burnt oil deposits on the plug which the plugs on this engine also show. At best it means that there are multiple problems with this engine. BTW, what you quoted DIRECTLY contradicts your statement about oil past the rings not able to get on the plugs.

quote This is often caused by oil leakage through the piston rings or valve seals.

VS.

quote Originally posted by darkhorizon: You will never see oil on a plug coming up from under the piston when it is running, because it will instantly burn off, I dont care how much oil there is, it is going to burn and char, and just look like soot or a lean condition on the plug.

And thanks for posting that picture. The other plugs have that same white deposit which I mentioned in my earlier post. That means the engine is burning oil for sure. You were too busy saying I screwed up the compression test to notice when I mentioned the white deposits. This engine is definately going back to that junkyard at their expense.

At this point, it is clear your advice isn't worth the electrons that make it appear on my screen.

Why hand cranking for compresion wont work with even new rings and new bores and pistons you will get about 10 to 15 precent leak by on the rings so by turnig that slow the compresion will leak by the best test would be a leak down test if you have a leak down guage you are suposed to do it with a warm engine but it will work on a cold engine it will find any big problems with the engine as fare as how well it is seald up

quote Originally posted by engine man: Why hand cranking for compresion wont work with even new rings and new bores and pistons you will get about 10 to 15 precent leak by on the rings so by turnig that slow the compresion will leak by the best test would be a leak down test if you have a leak down guage you are suposed to do it with a warm engine but it will work on a cold engine it will find any big problems with the engine as fare as how well it is seald up

thank you.

quote Originally posted by engine man: Why hand cranking for compresion wont work with even new rings and new bores and pistons you will get about 10 to 15 precent leak by on the rings so by turnig that slow the compresion will leak by the best test would be a leak down test if you have a leak down guage you are suposed to do it with a warm engine but it will work on a cold engine it will find any big problems with the engine as fare as how well it is seald up

I'll buy a leakdown tester tonight and run the test. I'll post up the numbers from it.


I called the junkyard. When I called to buy the engine I was told it was 150 psi across all cylinders. I asked for the actual numbers today and here are their numbers on the compression test:

#1 160
#2 120
#3 180
#4 170
#5 120
#6 150


10% variance from highest to lowest would mean the lowest would have to be 160 or better. Even going buy their numbers, the engine is unacceptable.

As promised, I bought a leak down tester and performed the test on the engine. I tried a harbor freight tester first but it would only zero out at 15 psi. That did not sound like enough pressure to do a good test so instead I went to an air tool shop and bought a 2nd 100 psi gage and screwed it in place of the percentage loss gage.

I set my compressor to 100 psi then hooked the gages up to the engine. Here is what I got:

#1 5 psi drop Air exiting crank case
#2 5 psi drop Air exiting the Exhaust and Crank Case
#3 4 psi drop Crank Case
#4 5 psi drop Crank Case
#5 4 psi drop Crank Case
#6 5 psi Crank Case with some Intake Leak

Those drops from 100 psi translate directly into percentages. There were two cylinders that have valve issues; one intake and the other exhaust. But otherwise it appears I have a very healthy engine. I plan to port the heads and have a valve job done. That should fix the minor leakage I found during the testing.


My earlier posts were very skeptical and I apologize if I offended anyone. I am just not the kind of person to take someone's word that something won't work. I need an explanation why before I believe. engine man was the only one who explained that air leaks past the piston rings too fast to get an accurate test by hand. He also suggested the leak down test which no one else even mentioned. I am now a big believer in a leak down test.

[This message has been edited by Doug85GT (edited 10-30-2007).]

Ok to do the test right you must put the piston on top dead center with the valves closed for the cylinder being tested if you dont do that you will get bad readings and I am happy to help and from what you posted it sounds like it is seald up pretty good

[This message has been edited by engine man (edited 10-30-2007).]

I made sure they were TDC. If the engine moved when I applied the air pressure, I shut off the air and tried to get it to the right spot. It took a little getting used to at first but I got pretty easy towards the end. I only took a reading if the engine stayed in position for more than 20 seconds with 100 psi applied. Then I listened to the intake, exhaust and oil fill to tell where the air was coming out.

Thanks for the suggestion on the leakdown test.

quote Originally posted by engine man: Ok to do the test right you must put the piston on top dead center with the valves closed for the cylinder being tested if you dont do that you will get bad readings and I am happy to help and from what you posted it sounds like it is seald up pretty good

I wont say I told you so because I am a nice guy.

I see you want to port the heads you should buy this book it will help you understand where and why to remove material http://www.amazon.com/Chevr...rkshop/dp/0879385472 it is for a small block chevy but it still will give you a understanding of what you want to do .
I just pulled a head of my 3.4 DOHC and the exaust looks very restrictive the valve guide area needs to be ground it looks like it comes down and chokes the flow off

Actually, there's a thread in here that covers the porting of 3400TDC heads. It has plenty of photos and technical details, too.

LINK

Yes there is but is the guy a professinal cylinder head porter if not his recomndations my not be worth any thing i see he is more woried about the port floor and from what i read most of your flow is at the top of the port and he is thinking of playing with the short side radius thats good if you have a flow bench and can conferm what you are doing is working and not hurting flow

That is my understanding too. You don't touch the floor unless you either have a flow bench, you really know what you are doing, or there is a really obvious obstruction. I am only going to do a basic port job, mostly to remove casting flaws and port matching. I have a few books that discuss porting an engine. When I get the heads off, I'll see what else I feel comfortable doing.

quote Originally posted by engine man: Yes there is but is the guy a professinal cylinder head porter if not his recomndations my not be worth any thing i see he is more woried about the port floor and from what i read most of your flow is at the top of the port and he is thinking of playing with the short side radius thats good if you have a flow bench and can conferm what you are doing is working and not hurting flow

4 valve heads are a bit less picky, I wouldnt worry so much about design as I would overall size in this head, but turbulance and fluid dynamic would be fully realized.

A well shaped port is inportant due to if you make the port just big the low end power in the engine will be a pig due to low port vilocity and fuel drop out so size and shape of the port matters even in a 4 valve per cylinder engine if you get the shap wrong it will hurt flow due to turbulance I would have the valves back cut about 20 degrees this should help low lift numbers and unshrouding the valves by laying the combustion chambr back to the head gasket where the valve is closest to it that will help low lift flow