I've been reminded recently about Quad 4's.
I have a W41 engine sitting around waiting to be rebuilt and was thinking about what I could do with it.
I'd like to build it N/A and stroke it to 2.5 litres. I understand that there won't be much W41 left on it when I'm done with that, so I may just buy the extra parts and build a second engine, then sell the W41 as a W41.
Anyway, I've heard that the Twin Cam blocks can be bored out to Q4 bore size. Is this true? That seems like a huge overbore to me, but if they were cast with the same bore OD as the Q4's, which some of what I've read indicates, there's no reason it shouldn't be possible.
That's the big thing. I want to be reasonably sure that what I want to do can be done before I go to the trouble of buying a TC core engine to rip apart.
Other stuff would be 086 head compatibility with TC block, valvetrain mods, double roller timing chain, balance shaft delete, etc.
Quad 4 stuff
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The Dark Side of Will
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There's been a good bit of discussion about it on Quad4forums. You basically use a Quad4 block for the larger bore, then use a Twin Cam crank. The crank journals for the 2.4 are larger, so you can either line bore the 2.3 block and use 2.4 main caps and bearings, or you can turn the 2.4 crank down to the size of the 2.3 mains. You can either run 2.4L rods and have custom pistons made with a smaller compression height, or have shorter rods made. The 2.3L and 2.4L blocks have the same deck height though, so a piston made to 2.4L specs with a significant overbore would be about right, except that I'm sure the 086 head has a smaller combustion chamber since the 2.4 has similar compression ratios with a larger stroke, and I think both engines have flat top pistons. I know you have to do something with the oil pump and drive gear on the crank, but I'm not sure what.
The 2.4 crank is lighter, but the 2.4 rods are thinner and probably weaker. Unless you are running an aftermarket ECU, something has to be done about the crank trigger wheel.
If you need, I can give you some specs on the 086 head that I used when designing my pistons.
Oh, also -- if you run like a .030 overbore on the Q4 block (that's what I ran on my first block), then it's supposed to be a 2.6L when finished. I haven't done the math though. I got most of my information from this thread: http://www.quad4forums.com/forums/showthread.php?t=2036
I was considering a stroker, but came across a good deal for a forged 2.3L crank that I couldn't turn down.
The 2.4 crank is lighter, but the 2.4 rods are thinner and probably weaker. Unless you are running an aftermarket ECU, something has to be done about the crank trigger wheel.
If you need, I can give you some specs on the 086 head that I used when designing my pistons.
Oh, also -- if you run like a .030 overbore on the Q4 block (that's what I ran on my first block), then it's supposed to be a 2.6L when finished. I haven't done the math though. I got most of my information from this thread: http://www.quad4forums.com/forums/showthread.php?t=2036
I was considering a stroker, but came across a good deal for a forged 2.3L crank that I couldn't turn down.
'87 BMW M6 / '88 BMW M5 / '90 Audi Coupe Quattro / '88 Fiero GT 2.3L Quad4 - 400whp; pump gas
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The Dark Side of Will
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I read that thread a long time ago. I thought the upshot of it was that you shouldn't turn the crank because it ends up being excessively weak.
I would think the most expedient way would be to bore the hell out of the TC block, as long as it can take it.
The second most expedient method would probably be to bore the mains on the Q4 block, but since I haven't pulled one apart, I don't know how feasible that is. Does the Q4 block have clearance for the TC crank?
What about using TC cam carriers with W41 cams because of the smaller lighter valve lifters?
The OBDI computer *should* be adaptible to the TC crank sensor with a change to the spark reference angle in the code. I know that some of the Q4 masks have been hacked.
I would think the most expedient way would be to bore the hell out of the TC block, as long as it can take it.
The second most expedient method would probably be to bore the mains on the Q4 block, but since I haven't pulled one apart, I don't know how feasible that is. Does the Q4 block have clearance for the TC crank?
What about using TC cam carriers with W41 cams because of the smaller lighter valve lifters?
The OBDI computer *should* be adaptible to the TC crank sensor with a change to the spark reference angle in the code. I know that some of the Q4 masks have been hacked.
I wish I could pull some info off of the top of my head for you -- I remember my dad talking about a lead he had on a 2.4L engine, but I don't know if he ever picked it up (yes, we end up with lots of free engine cores that way haha). If he did, I can take some measurements for you when I finish exams if you can't get access to an engine. Personally, I think I would overbore the mains in the 2.3L block. That way, you don't have to deal with the balance shaft or modifications to the block/head to run an 086. I wasn't aware that the TC lifters were a smaller diameter than the Q4 lifters, and I haven't looked at the TC carriers for any significant length of time. Check Quad4forums to see if people might be using 2.3L HO cams in their Twin Cam 2.4 engines. That would at least let you know that the cam centerlines are the same height (assuming valve stem height and lifter height are the same). Good luck -- keep us posted!