my boss loaned me a book on 4 stroke engine performance and it was quite informative. one thing i was able to do was calculate the required intake valve size for my 3.4, which is 1.82 and the head appears to be able to hold that size valve easily. then came the exhaust valve, the author mentioned that previous designers used an exhaust valve around 80 percent of the intake valve but because of recent(eg. 1984) advances it seems that the exhaust valve should be more like 60-65 percent of the intake valve on a street motor.

this does not equal 1.46, meaning that on both the 2.8 and 3.4 the ehxuast valve is apparently way to big. further research into what a too large exhasut valve does is that it apparently scavanges all of the exhaust out and some of the intake charge, as well as decresing fuel economy.

on paper 60 percent of 1.82 is 1.092 and impossible to fit in our heads. the small valve version of our heads has a 1.30 valve which is roughly 71 percent and im guessing should decrease some of this negative scavanging. so in theory i could use a small valve head and fit a 1.82 intake valve in it and leave the stock exhaust valve to get a better performaning engine(plus porting of course).

i was wondering what other peoples opinions on this was. mabye theres other information(more up to date) out there? im hoping this could be a nice discussion on head theory and not why i should be using a 3800.

I would think that on the primitive (relatively speaking) iron 60° heads that combustion chamber shape and intake/exhaust port design will have a much bigger effect on efficiency than mere valve size.

JazzMan

after you get youre bore and stroke the next thing you size is the intake valve. assuming the head isnt pure crap(it isnt) this is the biggest factor of cyl head flow since its a valve and thats what valves do. the combustion chamber is of decent design and can use some unshrouding and looks like it can handle some serious reshaping but thats not what im asking about.

quote Originally posted by megafreakindeth: im hoping this could be a nice discussion on head theory and not why i should be using a 3800.

I understand, and will not try to sell you on a 3800 here.

quote Originally posted by megafreakindeth: my boss loaned me a book on 4 stroke engine performance and it was quite informative. one thing i was able to do was calculate the required intake valve size for my 3.4, which is 1.82....

First, to illustrate how that number came about, can you post the mathematical formula that presumably led to it?

theres a table for 2 and 4valve engines in the book. you need the cylinder volume, mine is 576. the chart lists that in the 500-599 range you need a 1.75-1.85 valve so thus i arrived at 1.82.
im not saying this is the word of god but it certainly shatters my previous understanding of building performance so im trying to understand it better.

they also outline a method for determing the peak hp point of a given inlet valve but my math was pretty off here so i have to go over it again. math wasnt a strong point for me. here it is

rpm=(GSxKxVa)/CV
gs is gas speed, for a sports style wedge head(ours) the gas speed is apparently 210 ft per second
K is a constant of 5900 for a 2v engine dont know what it means
Va is valve area in sqare inches
CV is cylinder volume, note, only 1 cylinder

the books full title is Performance Tuning in Theory and Practice, 4 strokes, by A. Graham Bell

quote Originally posted by megafreakindeth: (210 * 5 900 * 8.16) / 576 = 17 552.5 rpm which totally makes no sense to me because its not gonna spin that high

I'll agree with that!

Let's return to the "576" you've used in the above equation as well as in your previous post:

quote Originally posted by megafreakindeth: theres a table for 2 and 4valve engines in the book. you need the cylinder volume, mine is 576. the chart lists that in the 500-599 range you need a 1.75-1.85 valve so thus i arrived at 1.82.. here it is rpm=(GSxKxVa)/CV gs is gas speed, for a sports style wedge head(ours) the gas speed is apparently 210 ft per second K is a constant of 5900 for a 2v engine dont know what it means Va is valve area in sqare inches CV is cylinder volume, note, only 1 cylinder

You've indicated that the "576" is the cylinder volume of only one cylinder. If that is the case, my question is, expressed in what type of units? It's certainly not 576 cubic inches, or 576 liters. Is it 576cc per cylinder? That at least would get you close to the displacement in ccs of your (6 cylinders X 576cc per cylinder =) 3.4L, or 3400cc-displacement engine.

In any case, if the intake valve diameter of your 3.4L engine is supposed to be 1.82 inches, how did you arrive at its valve area being 8.16 inches? Shouldn't the latter be (pi X the radius squared = 3.1416 X 0.91 X 0.91 =) 2.60 inches?

If so, then in turn that at least would drop the calculated optimum RPM way lower than the 17,553 RPM which you've readily acknowledged makes no sense, down to a more plausible ([210 x 5,900 x 2.60]/576 =) 5,593 RPM, would it not?

quote Originally posted by project34: You've indicated that the "576" is the cylinder volume of only one cylinder. If that is the case, my question is, expressed in what type of units? It's certainly not 576 cubic inches, or 576 liters. Is it 576cc per cylinder? That at least would get you close to the displacement in ccs of your (6 cylinders X 576cc per cylinder =) 3.4L, or 3400cc-displacement engine.

Yes its in CC's i have dohc pistons so theyre larger, i think its 93mm.

quote Originally posted by project34: In any case, if the intake valve diameter of your 3.4L engine is supposed to be 1.82 inches, how did you arrive at its valve area being 8.16 inches? Shouldn't the latter be (pi X the radius squared = 3.1416 X 0.91 X 0.91 =) 2.60 inches? If so, then in turn that at least would drop the calculated optimum RPM way lower than the 17,553 RPM which you've readily acknowledged makes no sense, down to a more plausible ([210 x 5,900 x 2.60]/576 =) 5,593 RPM, would it not?

ah so my math was wrong i did 3.14x.91=whatever, then squared that answer. like i said math isnt the best for me. 5593 rpms is much more realistic and attainable right now.

[This message has been edited by megafreakindeth (edited 11-29-2007).]

quote Originally posted by megafreakindeth: ah so my math was wrong i did 3.14x.91=whatever, then squared that answer. like i said math isnt the best for me. 5593 rpms is much more realistic and attainable right now.

No problem. At least now we've a theoretical "peak-power" RPM figure for your 3.4L, 5593 RPM, which is much more plausible than the erroneous 17553 RPM figure was.

i found my ti-83 plus so i can do math now(and play tetris). i think the 60% intake/exhaust ratio is supposed to be based off of surface area and not diameter, it just makes more sense. some people say the ratio should be anywhere from 60-80 percent but with 60 youll see ill have to buy the least amount of parts and budget speaks more than performance(hence my lack of turbo)

going with my 1.82in valve i got a surface area of 2.60in sq. as a test i took 60 percent of that and got a surface area of 1.56, i then divided that by pi to get .49 and then the square root of that was .7. thus the 60 percent ratio for a 1.82 valve is 1.4in. this also allows for the stock 1.46 exhaust valve to be used with a simple oversized intake valve.

the surface area of the stock big exhaust valve is 1.67. 60% larger is 2.78. so an intake valve 60 percent larger than the exhaust valve in the head would be 1.87 in which is real close to my 1.82. btw i measured the distance between the intake and xhaust valve, theres 2mm to play with so my .12in increase wont do much to worry, unless the valves open towards one another.

in the book the advantages of using larger valves than nessesary means that a lower duration cam will flow as good as a higher duration cam with proper valves, this means easier idle(plus i have a 260 cam in there now, swapping heads is easier than cams) and less strain on the motor. this means that my peak rpm will be 5979.89 rpms which is perfect. its amazing that a .05in larger valve causes a 500rpm jump in peak power, that gives you 500 rpm to shift, it couldnt work out better....unless this is all wrong...again....

for a 2.8 the CV is 472(according to desktop dyno, 88mm bore 76mm stroke). the book states that for a 450-499 CV you need a 1.70 to 1.75 in valve so that would be 1.72 ideal. thats a 2.32 SA intake valve and a 1.39SA exhaust valve. 1.39 is the surface area of a 1.32 in exhaust valve(somehow 1.3 is a magic number and is the surface area of its diameter) this means a small valve head outfitted with the big valve heads intake valves, leaving the stock exhaust valve should flow the correct amount of air into the cylinder and wont scavange some of your air fuel into the exhaust resulting in more power more gas milage(in theory). peak power should be 6300 rpms.

for the 3.1 liter guys DD2k3 says youve got a CV of 524. the good book says thats a 1.77 intake valve.

so then a trick flow head for 2.8s and 3.1s is a small valve head with 1.75 intake valves while a 3.4 needs a big valve head with a bigger intake valve. not that the heads on them now arent good(cept small valve heads) but if youre losing some of your air charge out your exhaust then youre losing power, this may also lower your dynamic compression. if its not nessesary to use that large of a valve then why should you?

for porting the exhaust the guy recommends the port be enlarged to the diameter of the valve. a quick check of the port as it is now measures 1.18. theres some meat there to remove to reach 1.46 but judging by the profile the gasket left this may all have to be removed from the floor. the author says that removing metal on the roof of the port improves flow the best so i may start by opening the port up at the roof closest to the valve and gently curve down to where the gasket is. this should work because the headers point down so it will remove bends through the system. i have a set of heads i messed up so ill see what it takes to grind out the port to 1.46 before i work on my other set.

quote Originally posted by megafreakindeth: i found my ti-83 plus so i can do math now(and play tetris). i think the 60% intake/exhaust ratio is supposed to be based off of surface area and not diameter, it just makes more sense.

First, let's assume you're right, that author Bell is talking about it being desirable that the exhaust valve has 60% of the area --- rather than the diameter --- of the intake valve. And by the way, I agree with you; in the context of that write-up, area rather than diameter makes more sense to me as well.

However, nobody goes to a parts store searching for an exhaust valve having a certain area. Rather, as you know, they might look for valves having a certain diameter, but probably not for valves having a certain area. So how does one solve for the diameter of the exhaust valve needed if one only knows the diameter of the intake valve? Well, one could figure that out by doing exactly what you did:

quote Originally posted by megafreakindeth: going with my 1.82in valve i got a surface area of 2.60in sq. as a test i took 60 percent of that and got a surface area of 1.56, i then divided that by pi to get .49 and then the square root of that was .7. thus the 60 percent ratio for a 1.82 valve is 1.4in.

What you did isn't wrong; it's just that solving that mathematical problem can be made much easier than all that. Basically, all you need figure is what all that always "reduces" to, which is (rightly or wrongly), the assertion that...

• The exhaust valve diameter should be about 77-1/2% the diameter of the intake valve.

Why? The calculations you're using above at one point multiply things by pi, and then later divide things by pi (which cancels out). They also square the radius of the valve and then later take the square root of what's been squared (which also cancels out). There's nothing "wrong" with doing that; it just isn't necessary. I'll spare you the detailed mathematical proof of my reduction of Bell's "60% statement," and point out only that the 77-1/2% "valve diameter figure" I mention happens to be the square root of the 60% "valve area figure" he does.

I'm not trying to give you a rough time here mega, especially since you've very readily acknowledged that you're not that great at math in the first place. I'm merely pointing out that author Bell's contention --- whether right or wrong --- just isn't anywhere near as complicated as he apparently makes it appear to be at first glance, is it?

...o god...
i do things slowly and repetativly so i can check and make sure im not messing up. its confusing in the book because he doesnt specify if he means 60 percent of the intake valve diameter or area. im just assuming that a head designed for a 2.8 being used on a 3.4 with a much bigger bore probably needs some recalibrating to get optimum performance, i dont want to blow the doors off my car with 3.4 power i just think it would be neat to have everything done right for the motor.

now im gonna reread what you wrote and try and digest it

I think you're being a bit harsh with and unforgiving of yourself:

quote Originally posted by megafreakindeth: ah, yes. i get it now, what your saying is i did my math right but at the 9th or 10th grade level i was last paying attention in.

I didn't intend to suggest that, largely because I'm not that well-versed in cruelty. I only wanted to point out that the math needed wasn't anywhere near as complicated as it might have first seemed.

Earlier you mentioned:

quote Originally posted by megafreakindeth: i do things slowly and repetativly so i can check and make sure im not messing up.... now im gonna reread what you wrote and try and digest it

That to me seems a far more useful plan of attack than that of some people I've seen at work who do things very quickly and equally wrongly. I can see in advance the "train wreck" that's about to ensue with their erroneous thinking. The only question in their minds is whether that train wreck --- because of their adamant insistence on it --- will happen exactly on schedule!

I'd argue that fault here lies with author Bell, not with you:

quote Originally posted by megafreakindeth: its confusing in the book because he doesnt specify if he means 60 percent of the intake valve diameter or area.

Two points are in order here:
1. Why did he have to make things so unclear in his book?
2. Why didn't he just say that in his opinion, what all this boils down to is:

• The exhaust valve diameter should be about 77-1/2% the diameter of the intake valve.

That would have made things a lot easier, wouldn't it?

quote Originally posted by JazzMan: I would think that on the primitive (relatively speaking) iron 60° heads that combustion chamber shape and intake/exhaust port design will have a much bigger effect on efficiency than mere valve size. JazzMan

I second this completely. You can put the biggest valve you can fit in there, but it won't make a difference if your air charge is too turbulent and spinning off the upper and lower floors of the intake port. Reading the book is good, but from my experience, after reading the book you need to go flow bench test (and that gets kind of expensive). I recommend any and everything by Smokey.

Just FYI, the exhaust valves in the Fiero 2.8 cyl heads have approximately 68% the surface area of the intake valves. That's not far off from the 60-65% figure.

Also, if that book was written in 1984, it's out of date. If it were me, I'd be looking for more recent (and possibly more accurate) information before jumping into an engine build.

quote Originally posted by megafreakindeth: ...it seems that the exhaust valve should be more like 60-65 percent of the intake valve on a street motor.

Given that for whatever reason, author Bell in his book apparently chose to refer to valve area rather than the more commonly used, valve diameter, the aforementioned "60-65 percent" statement in turn simply means the diameter of the exhaust valve should be about 77-1/2% to 80-1/2% the diameter of the intake valve (which are the square roots of 60% and 65%, respectively).

The cylinder heads from the Fiero 2.8L (which, mildly ported, are what I have on my 3.4L swap) have the same diameter intake and exhaust valves as in GM's 3.4L crate engine: 1.72 and 1.42 inches, respectively. That in turn translates into an exhaust valve having a diameter about 82-1/2% that of the intake valve, in effect quite close to what author Bell essentially recommended with regard to area, as Blacktree pointed out:

quote Originally posted by Blacktree: Just FYI, the exhaust valves in the Fiero 2.8 cyl heads have approximately 68% the surface area of the intake valves. That's not far off from the 60-65% figure.

In fairness, however, I suppose this in turn begs the question, "What should be the diameter of the intake valve?"