Well, crap. I damaged the engine. Probably a spun bearing, maybe broke a piston?
It seems like a little code change made for a destructive result, I lowered the "Boost fuel cutoff limit" variable a couple of counts below where I found the MAP sensor actually maxes out. I did that so that if the boost ever maxed out what the sensor could handle, it would kill the fuel. Turns out though, that having the boost set close to that point allowed me to hit that fuel cut point too easily.
As soon as it happened, it was too late. A few VERY loud backfires and the engine instantly started to sound like a diesel. Still ran just fine, but I'm not going to test it out. Looks like I'll have to ready a bottom end for it. Not sure if I'm going to go all out and assemble a forged bottom end, or if I'll just toss my old bottom end back into service. I don't have the time or the money to work on it at the moment, so it's parked for the time being. It wasn't the power that broke it surprisingly.
Damn, that sucks :-(. It was not a good weekend for cars.. we had the same thing happen in the Impreza I was co-driving at Prescott Rally on Saturday. Broke a piston and rod and cracked open the block when the motor leaned out.
How does the fuel cut operate? Does it just shut off fuel until the MAP goes below the cutoff pressure, without any hysteresis? If so it's probably not safe to use.. you're basically going to end up with a lean condition right around the cutoff pressure as the fuel cutoff cycles on and off.
[This message has been edited by Steven Snyder (edited 10-07-2014).]
It cuts off at 14.7 PSI, and restores at 8. So it did have a huge hysteresis, but it was violent when it kicked in.
I think that the fuel cutoff, combined with the high boost pressure and cylinder temps caused it to try to eat itself. Maybe it was when the fuel started coming back in? I don't know. I'm probably going to slap another bottom end in whenever I get the chance, unless I broke a piston and damaged a head. But I think I only spun a bearing though.
I'm shooting for middle of November to swap it in, but thats a maybe as of now. I have to pass emmissions in late November / early December. Which, coincidentially is around the time my wife should be giving birth to our first. So, it's not exactly a high priority at the moment. Perhaps a forged bottom end could be in the works over a slightly longer timeframe.
Lower! I'd really like to be at 9.0:1 and run something like 20 Lbs of boost. I'm probably at 9.4-9.5:1 or so right now due to the early heads with late pistons. But I'm also tempted to just toss in my old bottom end for the time being.
As far as code goes, I've done most of the re-code for 3 bar I believe. It's untested though. But, I did find that the computer is limited to 255 kPa, as when it figures out BPW, It takes the filtered map input, then it does some simple math to figure out exactly how many kPa that is, then figures out how much fuel building from that number. But, the figured kPa is a 8 bit (byte) value, so its limited to 255 kPa, which is still like 22.4 lbs of boost I suppose I could fix the code so that it figures a 16 bit (word) value before doing the BPW calcs... Really open up that $8F to its fullest 29 PSI of boost potential.
Converting to 3 bar didn't seem all that hard. The only real challenge is rescaling all the values that use the 2 bar RAM variables, and there was a little bit of math that needed to be fixed so it could calculate the 1 bar RAM variables correctly. Unfortunately, the code liked to use the native LSLA (multiply by 2) or LSRA (divide by 2) where as I had to change it to a LDAA "$03", then MULtiply to figure out the single bar value. This calc took up extra space so I had to move it to the custom code section. No biggie. But it was annoying that I couldn't just change a couple of numbers. I've really re-worked the heck out of 8F, but honestly the code hasn't let me down!
The only thing that I was having some trouble with code wise, was the transitioning from Quasi-Asynchronous Pulse to Normal mode and back. The engine always has a hiccup when the transition occurs, usually right at 19% throttle. I found that I could skew the injectors output based on BPW in a table to try to linearize the transitions, it helped substantially, but it's far from gone. This is one of those things that sucks about large injetors. The ECM wasn't meant to operate them in Quasi-Asynchronous Pulse for idle and part throttle. It was meant only for extreme vacuum, like when decelerating from high speeds. So there was some drawbacks.
That being said, the drivability was downright good. I had it down to where stalls were minimal, and I was working on fixing that last detail with stalling when the engine let go. I really regret setting up that boost fuel cutoff value. I had it set so high that it couldn't be achieved. Didn't have any problem till I set that lower Oh well, thats how it goes! I will rebuild!
Got a couple of things on order for a forged bottom end. First things first, Crankshaft! GM - 12577484 which is the forged steel crankshaft from the LX9 (3500) and LZ8 (3900) engines. It's going to add a bit of weight, but it will make up for that with brute strength. With my lathe and mill I have the facilities to machine a new timing reluctor onto that crank. Should be a cake walk.
Connecting rods. Thought long and hard about them. The forged crank has a 2.25" crank pin diameter, and .864" journal width. There aren't a heck of a lot of rods intended for a 2.25" crankpin.
But, There was the 4.3 even fire motor, surprisingly, it has a 2.25" crankpin. They wanted to increase the crankshafts strength with the split throws, the best way to do that was to enlarge the crankpins so that they had more overlap. Thus the 2.25" crankpins.
However, 4.3L rods have two little issues. Their big end is wider, .930" as opposed to .864" and the Piston pin is fatter, .927" as opposed to .9055" (23mm). But the other good thing is the length is 5.7". Just like the stock rods for the 3.4 DOHC.
So the rods will have to be narrowed to fit. And since I will have to do custom forged pistons anyway, I can specify the .927" pins. Probably cheaper too as they are common to SBC's.
So I am going with Eagle CRS570063D rods. They advertise them as for applications up to 750HP.
One other issue would be which bearings to use. But I think I have my answer. Turns out that the 4.3's bearings aren't anywhere near as fat as the journals width, In fact its .753" Where the crank pin is still .864" So that leaves .110"overall, or .055" of clearance on either side of the shell. They needed to be narrow on the 4.3L since the journals have radiused fillets on the edges. But on the forged crank, it has recessed (rolled) fillets. So a fatter bearing won't collide with the fillets. So stock 4.3L bearings will be used.
That should be a good recipe for a forged bottom end, good up to 750 HP since that's what the rods are rated to. I don't plan on pushing that kind of power, but I think I could see this engine going into the 500 ish range with this setup. I think this engine was easily at or above 450 with 14.2 PSI. Certainly accelerated like it was!
I'll likely have to make some small clearance notches in the block for these rods though, they'll probably swing just a little wider than the original rods. It'll be tight for sure!
I wasn't having problems with detonation so much. In fact the engine ran pretty darn well! I wasn't data logging at the time though.
I will tear down the engine later on, but in the short term I will be building the bottom end components and testing clearances and stuff. Of course, I will open the engine up eventually and show off what I had accomplished destruction wise.
Interesting rods, I didn't know about them. I like the length, but I'd be concerned about their big end width, they are .019" narrower than the crank pin, they would have fairly excessive side clearance. Not to say they wouldn't work, but it is way outside typical clearance. Also, are those rods "offset"? That's my only issue with the 4.3l's rods. Luckily they need to be narrowed from .930" to .858", and that gives me ample clearance to try to remove the offset, but then things get awkard with the bearing tangs, I might have to flip and re-tang the rods. I want the piston centered squarely over the rod, otherwise there is a bending force applied to the rod. I mean chevy offset the rods on the 4.3 for the same reason.
But my next thing is getting pistons made. And I'm conflicted about which piston manufacturer to use. I have no idea how to compare and pick the best or most cost-effective. I'll probably have to send a sample piston in. Ive found all the custom piston forms to be inadequate for locating the valve reliefs. I basically need a stock piston to be forged, slightly dished with a .927" sbc pin.
Interesting rods, I didn't know about them. I like the length, but I'd be concerned about their big end width, they are .019" narrower than the crank pin, they would have fairly excessive side clearance. Not to say they wouldn't work, but it is way outside typical clearance. Also, are those rods "offset"? That's my only issue with the 4.3l's rods. Luckily they need to be narrowed from .930" to .858", and that gives me ample clearance to try to remove the offset, but then things get awkard with the bearing tangs, I might have to flip and re-tang the rods. I want the piston centered squarely over the rod, otherwise there is a bending force applied to the rod. I mean chevy offset the rods on the 4.3 for the same reason.
But my next thing is getting pistons made. And I'm conflicted about which piston manufacturer to use. I have no idea how to compare and pick the best or most cost-effective. I'll probably have to send a sample piston in. Ive found all the custom piston forms to be inadequate for locating the valve reliefs. I basically need a stock piston to be forged, slightly dished with a .927" sbc pin.
gonna be honest, don't know too much on the rods, I bought them in a package deal with a bunch of other parts, race shop that built my engine didn't seem to think it would be a problem at all.
have you looked into other smallblock chevy rods? you'll end up with 2 spares in the cost of a build, that's nothing.
[This message has been edited by ericjon262 (edited 10-16-2014).]
EricJohn, if there is too much endplay its going to bleed off a lot of oil pressure. OTOH, out of the box those are usually wider, so they may have fit perfectly.
EricJohn, if there is too much endplay its going to bleed off a lot of oil pressure. OTOH, out of the box those are usually wider, so they may have fit perfectly.
well, considering the rods are the final destination for the oil before returning to the pan, I bet it'll be fine.
Just did a little reading on side clearance. Apparently 20 or 30 thou is no biggie. Doesn't effect oil consumption, because it has to squeeze through a 0.001 ish clearance first so the 0.008" clearance from the factory is effectively wide open. Learn something new everyday. Eagle sells rod/crank combos that run mid .020"s for side clearance and no one has issues with that.
Either way, I'm sticking with the 4.3l rods I have now. I have the equipment I need to modify them so I don't even need to leave the garage to fit these rods.
Just did a little reading on side clearance. Apparently 20 or 30 thou is no biggie. Doesn't effect oil consumption, because it has to squeeze through a 0.001 ish clearance first so the 0.008" clearance from the factory is effectively wide open. Learn something new everyday. Eagle sells rod/crank combos that run mid .020"s for side clearance and no one has issues with that.
Exactly. Really, the only limit on big end side clearance is that it's less than small end side clearance.
Rods can be bushed down to run smaller piston pins. The smaller pins can be used with shorter compression height pistons without getting into the oil ring. Shorter compression height = longer rods. But you're sticking with what you have...
I used CP pistons in my Northstar. CP does a better job with surface finish inside the ring grooves than most of the "usual suspects". If you get a gapless TOP ring package from Total Seal, then you can have CP cut your ring grooves to those rings and run .001 ring side clearance.
Caveat: For some bore sizes Total Seal gets rings from "normal" ring manufacturers and modifies them to make them gapless. For their basic offerings, you're subject to the suppliers QC. My first set of rings had a couple of rings with .0012 thickness variation around the ring. Obviously that means I couldn't run .001 side clearance with those rings. I had to have the rings lapped (TS' "Diamond Finish" process) to get their tolerances down to what I wanted in order to have CP cut the tightest grooves they could cut. The diamond finish step is fairly expensive at $100+ per ring. It only matters on the top rings, of course.
[This message has been edited by Will (edited 10-17-2014).]
Since I'm going to need custom pistons anyway, I'm now considering getting a pair of total seal sets for a VW Beetle engine "Totalseal-9200C". They have 92mm bores, and the rings are very reasonably priced, and with some simple sizing changes will fit the pistons beautifully. They do run a gapless 2nd, and a conventional top ring. That's fine with me. I'm strongly considering CP as well. They just seem like professionals, hell bent on providing a perfect product.
Since I'm going to need custom pistons anyway, I'm now considering getting a pair of total seal sets for a VW Beetle engine "Totalseal-9200C". They have 92mm bores, and the rings are very reasonably priced, and with some simple sizing changes will fit the pistons beautifully. They do run a gapless 2nd, and a conventional top ring. That's fine with me. I'm strongly considering CP as well. They just seem like professionals, hell bent on providing a perfect product.
Call Total Seal and discuss exactly what your finished bore size will be... CP only sells to businesses (at least they did a few years ago), so you'll need to know what shop you'll have order the pistons. You can call CP directly and convey the specifics of your order, but that order will have to be placed through a shop.
quote
Originally posted by Fierobsessed: They do run a gapless 2nd, and a conventional top ring.
Don't do that... it's dumb. I have no idea why they ever started selling gapless 2nd's.
Some gas gets by the top ring via the gap. That blow-by gas collects between the top and 2nd rings (hence some piston designs have an accumulator groove in the 2nd ring land to increase the available volume and reduce the pressure). The 2nd ring needs a wider gap than the top so that the top ring's blow by can escape into the crank case faster than the top ring lets it by. If the 2nd ring is gapless, the top ring's blow by builds up between the two rings until there's enough pressure to unseat the top ring under certain load conditions.
Get a gapless top and conventional 2nd. (IIRC, TS sells that as an "upgrade" to most of their sets anyway...)
[This message has been edited by Will (edited 10-21-2014).]
I started a dialogue with Ben at WOT-Tech, He has a piston design that is nearly drop in for my needs, just needs valve reliefs cut. It's the 3400 piston, with a flat top, .927" pin. He says he can get top gapless top rings for them too. I might just go that route. Tell ya' what though. It's going to be one expensive set of pistons!
Right now, I'm waiting on the rod bearings, so I can finalize my dimensions that I need to cut the rods to. I've decided that I am going to flip the rods, narrow only one side so that the rods are no longer (just barely) offset, and re-tang the rod and cap for the bearings being shifted to the new rod centerline. Definitely sharing that experience when I get there.
The "Boost fuel cutoff limit" feature seems to be a bit dangerous, though I would have never thought it was as it seems like a good idea in the perfect world. I wonder if it better to pull spark and leave fuel 100% untouched for any sort of RPM/Boost/whatever limiting feature.
[This message has been edited by brian89gp (edited 10-23-2014).]
The "Boost fuel cutoff limit" feature seems to be a bit dangerous, though I would have never thought it was as it seems like a good idea in the perfect world. I wonder if it better to pull spark and leave fuel 100% untouched for any sort of RPM/Boost/whatever limiting feature.
Got some of the fun stuff done today. I took those rods, and performed 3 machining operations on them to make them work with the 3.4 DOHC with the 3.9's forged crank.
First, I had to crunch some numbers, or really... let AutoCAD do the figuring. On the left is an overhead view of the edge of the rod with bearing as it came from eagle. On the right, what needed to happen to make it work
Since these rods are offset (clearly shown in the drawing 0.065") I had to take 0.074" off of one side of the rod to take it down from the 0.930" to the 0.856" that was needed to fit the crank, this would eliminate most, but not quite all of the offset of the rod.
Off to the lathe! It was a bit out of balance, so I had to cut pretty slow, but it did an excellent job.
Done with that.
Putting the bearings in showed that although they would work, the bearing wouldn't be centered on the cranl journal, nor the rod.
I felt it best to flip and re-tang the rods so that the bearings would be centered. This was a pretty easy job for the milling machine. I used a 3mm x 25mm slot cutter to do the dirty work. I spaced it 0.126" off the mill table, then clamped the rod to the table and took a .055" deep cut into the edge of the rod. Then did the same for the cap.
Once that was done, I put the crank into my old block, and attempted to fit the rods in so I could check block clearances. I ran into a small snag there...
The big end of the rods are bigger than the bores! OUCH! I thought perhaps I could drop the rods into the bottom end, and slip the pistons into the bore and insert the pins right at the deck. But with the rods in, the pin bore was below the deck so the pins would have never gone in.
So after some contemplation on what to do, I settled on using the lathe to narrow the edges of the rods. I didn't have to take much off.
The big ends now measure right at 3.603, they fit into the 3.622 bore comfortably now.
Custom pistons are on order, I decided to send a crown design to the manufacturer in order to demonstrate the location of the reliefs, the angles of the reliefs, and the location and size of the dish that I needed. Basically, its the stock 3.4 DOHC piston with a 5cc dish added to it to drop the compression from 9.5:1 to 9.0:1 The only deviation to this drawing was a relieving of the thin material near the relief cuts, just as they did from GM. I also went and had them do the ceramic coated crown, and coated skirts. I'm excited to see how these come out!
It might take a month or so to get them made. They should be the key to making this engine capable of well beyond 500 hp.
Originally posted by Fierobsessed: Off to the lathe! It was a bit out of balance, so I had to cut pretty slow, but it did an excellent job.
Done with that.
I hadn't ever put much thought into HOW rods should be narrowed... but it would be fairly tough to clamp them down to a mill table. This is a really cool way of doing it.
At the end of the day they are just chunks of metal that need some material removed. I locked my table down and used the compound to set the cut depth. No magic here at all. I actually just youtube'd rod narrowing. Costa Mesa R&D (fiatnutz) always has helpful hints on how to do this type of machining. They had two of these operations on their channel. The narrowing of the big end to fit in the bore was the most difficult, just because there wasn't any nice way to mount the rods in the chuck, but the 4 jaw chuck was able to grab the rod on the edges of the journal, lots of little adjustments to get it located right, but once the cuts were done, the rods looked factory.
Wow that's awesome, what speed did you have the spindle spinning with the rod on it like that? I know if that was me I would have kept my face as far away from the plane that rod was spinning on as possible I had a chunk of delrin break off in a lathe and launch itself one time, did some damage to the wall. Connecting rod would go through the wall haha
Finally an update, Custom pistons are here, and they are pretty! I purchased these through WOT-Tech, sent them the dimensions for the crown design and the compression height, and they came through beautifully!
Of course I Immediately popped the rod in, and slid the pin through.
I had machined one of my original pistons to make it like the drawing in my last post. It was really nice to see how they faithfully reproduced my dimensions. They also widened out the radiuses in the corners of the dish and valve reliefs. The pistons are ceramic coated on the top, and graphite impregnated on the skirts. The pins are .927 for the rods I'm using.
I only have one issue, that I had a feeling that it might come up and bite me. There is only .037" of clearance between the rods width and the inside of the piston total. That would be fine if the rod wasn't still .028" offset. So I'm going to have to mill just a little bit of metal off of one side of the small end of the rod to buy me the clearance required.
I'm probably not going to get to install these for a while. More big life news. I'll be a father by Monday.
[This message has been edited by Fierobsessed (edited 11-29-2014).]
Bit of a late update, but... It's a girl! Adelyn, 6lb 11oz born 12/02/14 at 12:27AM
So, now that that's all going on, I've found I have a lot more time to THINK, rather than time to DO.
And lately, my thinking has been about balancing this new rotating assembly. The new forged crank is quite a bit heavier than the old cast crank. My new rods are just a bit heavier than stock rods. The piston and pins gained just a little bit of weight too I think.
I researched balancing methods for this type of engine, and one engine balancing company states that specifically for the 3.4 DOHC and the other internally balanced 60 degree V6's that bob weights weighing 100% of the big end of the rod with bearings (rotating mass)+ 46% of the weight of the piston, wrist pin, locks, rings and the small end of the rod (reciprocating mass) must be used on all crank pins to balance the crankshaft. Externally balanced GM 60 V6's use 100% of the rotating + 50% of the reciprocating mass. As do practically all v8's.
I wonder if the internally balanced 60 degree engines were actually under balanced to 100% + 46% as a compromise. And I have a strange feeling that this forged crank out of a 3900 engine is designed for 100% + 50%. Just because it's soooo heavy. But this info is scarce to find. I'm wondering if any of you know what is best in this particular setup, since I have to balance it anyway.
[This message has been edited by Fierobsessed (edited 12-25-2014).]
Im going to take a guess and assume the 4% underbalance could be for some weight of the oil, but it depends on the weight of the reciprocating mass. Consider the older buick V6's with a 36.6% bob weight, that was meant to reduce some of the secondary imbalance to add creature comfort, and they didn't need to rev that high to notice an obvious primary imbalance. If you weigh in the new reciprocating mass and its much heavier than before, consider a 50% balance, and since its going into a street car, I don't believe there is a need to overbalance. HTH
Congrats on the new baby girl! We are expecting our third(boy) NLT 24 Dec(C-sec).
[This message has been edited by sleevePAPA (edited 12-22-2014).]
Last run for this engine... Sounds kinda awful. Had to do the fuel pressure let off.
I'm working on getting the bottom end parts all together. I still have to do yet another machining operation on the rods, I have to narrow the small end of the rods to fit inside the pistons better. And, I need to make a reluctor ring that fits the crank with the 7 timing notches.
One thing... I found documentation that the notches are 60 degrees apart, with the one odd one being 10 degrees out. My old 3.4 DOHC it actually measured out to 4.25 degrees. It might not matter at all where that notch is, as long as its close to that one 60 degree notch. I was thinking about having the ring water jet cut, but I think I'll just machine it myself.
I suppose I could fix the code so that it figures a 16 bit (word) value before doing the BPW calcs... Really open up that $8F to its fullest 29 PSI of boost potential.
Oh well, thats how it goes! I will rebuild!
The only deviation to this drawing was a relieving of the thin material near the relief cuts, just as they did from GM. I also went and had them do the ceramic coated crown, and coated skirts. I'm excited to see how these come out!
