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ok some some help on my destroker math


trowa47

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ok so this is what i have

 

so a l28 block overbore 1mm

 

p90 head 1mm gasket

 

l20a crank so a 69.7 stroke

 

ok and so I think, I need to gets some rods made 140mm long and some flat tops with a pin hight of 32.97

 

and with ozdat math this gives me

 

Displacement:2.486 litres

Deck Clearance:0.030 mm

Rod/Stroke Ratio:2.009

Bore/Stroke Ratio:0.801

Static Compression Ratio:7.591

 

this is going to be a turbo car

 

so any help would be cool is a deck clearance of 0.030mm ok ? and any thing any one can tell me

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Any deck clearance will be fine so long as it's not negetive. I've looked at destroking an L28 before as well. Except I was planning to use an L24 crank and rods with L28 flat tops, L26 "C" stamp cam and an E88 head. A friend wanted an engine for a turbo project with high compression and could wind out to at least 8k. I figured going that route and keeping moderate boost, say 12psi, would be fairly quick, reliable and have a crap load of top end. Might want to think about trying that instead of custom rods and pistons. it'd be cheaper.

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L20B Rods would work well, that is what we are running in our L20A Powered Bonneville Car. That car's Peak Power occurs at 8750rpm, and our shiftpoints are between 9300, and 9500rpms.

 

Matter of fact, we are taking that to the Dyno this afternoon to recal the ECU for the new headers and full exhaust we put on the car in the off season, and then it's off to the races next weekend up at El Mirage.

 

Maybe I should charge the video camera and see if I can capture the sounds....muahahahaha

 

Anyway, I digress. We were able to get a tolerable ring stack using the L20B rods in the engine, of course we have custom pistons made---I'd say that is the route you're headed anyway. Make sure you verify the deck height on your block so you don't run into a previously decked unit that has your pistons popping up, say, a few thou from a previous deckheight alteration from a warped block.

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L20B Rods would work well, that is what we are running in our L20A Powered Bonneville Car. That car's Peak Power occurs at 8750rpm, and our shiftpoints are between 9300, and 9500rpms.

 

Matter of fact, we are taking that to the Dyno this afternoon to recal the ECU for the new headers and full exhaust we put on the car in the off season, and then it's off to the races next weekend up at El Mirage.

 

Maybe I should charge the video camera and see if I can capture the sounds....muahahahaha

 

Anyway, I digress. We were able to get a tolerable ring stack using the L20B rods in the engine, of course we have custom pistons made---I'd say that is the route you're headed anyway. Make sure you verify the deck height on your block so you don't run into a previously decked unit that has your pistons popping up, say, a few thou from a previous deckheight alteration from a warped block.

 

Very good advice on getting deck height measurements. No telling what's been done to your block in the last ~30 years (unless maybe you've owned it that whole time)...

 

Tony - is your Bonneville car turbocharged? IME it's not a trivial matter to get a turbo'ed engine to make power at really high rpm (it can be done, but the normal tricks like long duration/overlap on the cam don't necessarily work). Getting an L-series head to breathe at 9000rpm with cam timing that works for forced induction sounds like a challenge to me. Any thoughts on this?

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I am planning a similar engine, but I was going to use LD28 rods because I finally have a source. If I can find L20B rods, I would rather have those to keep the rotating mass down. I was also planning to bore it out a bit more than you are, 89-90mm.

 

Tony D - We Definately want to hear that engine at full song!

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