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Destroke?

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Guest Anonymous

Can someone explain to me the basics on DESTROKING an L28? Something about 240 crank, rods w/other pistons? What are the advantages?

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Guest eric-z

yeah, you can destroke the L28 by using the L24 crank, rods, then same pistons as you've got in the L28. You will get a little higher red line and I think a better rod/stroke ratio but other than that it doesn't appear to be a good Idea. if you decrease the stroke then you loose displacement which ultimately means your going to loose power. I think it is that every 4% increase in redline you get like a 10% decrease in power(incorrect numbers???) so loss in power outweighs the extra rpm.

 

I asked the same question a while ago, this is what I got out of it. tell me if I've got something wrong though. I kinda want to do it just to be different... maybe bore it out to gain back some lost displacement, but it would have to be on a turbo engine.

 

eric

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Guest Anonymous

Thanks for the reply. That is pretty much what I had in mind. I thought about using an old E31 in my garage with full port and big valves. Still toyaing with the idea. Just seems like you could take advantage of a large cam with this combo and some ARP bolts!

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Guest Anonymous

im pretty sure they destroke formula 1 engines to get such high rpms out of em. maybe search for something about formula 1 engines to see what you can find

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Less side loading on the rings enables higher safe RPM levels, but the rest of the engine is going to have to be pretty stout from the bottom to the valve springs. Without a hideously huge McNasty cam in it, it would be a waste of effort, small cams wont make high end power. One huge disadvantage to high RPM (and horsepower) engines on street cars, bearing wire and therefore overall engine life.

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It's the reduced piston acceleration that allows for higher rpm with a shorter stroke. As mentioned above, though, you lose more torque than the increased rpm would make up for. Basically, this is a very good way to lose torque EVERYwhere, and lose peak power as well, while having a *marginally* higher redline.

 

Another thing worthy of your consideration is that with greater displacement you can tune more for high-rpm power, while still maintaining enough low-rpm grunt for streetability.

 

Displacement rules.

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If you use Engine Analyzer they will calculate the piston velocity for you :) I was always getting warnings with my 7k RPM LT1 setup on stock pistons, but even at somewhat extended duty I did ok (not open road though, that would push it alot harder).

 

If you are going to open it up though I'd convert to full floater wrist pins, for peace of mind maybe more than real need, if your going to rev it though its a good idea I think.

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Bringing this thread back from the dead... (10 years!)

I am just wondering what a destroked L28 TURBO would be like.

Is it just a dumb idea, or would the extra revs get you more boost? I would think having the turbo would help to outweigh the loss of power/torque from the shorter stroke, as well as giving the turbo more headroom to spool higher. With appropriate head work and other supporting mods as well of course. Just something I've been thinking about, not sure if I would ever want to try it yet...

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Well shortening the stroke would give a better stroke/bore ratio right? But I get that's not a huge deal and not worth doing a bunch of work just to shoot for a ratio.

But if one were to take an L28et, put a balanced L24 crank and prepped L24 pistons in it, add say a mildly massaged P90, plus some engine management and ignition upgrades, would it be any worse than say a stock bottomed L28 with just electronic upgrades?

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Sure, in an acedemic world with all things equal, I'll agree that a better stroke bore ratio might be of some benefit. But that said, given head work engine management and ignition it would still be better to have more displacement. If you want to do something different, do it. Just don't claim some performance gain on some acedemic point without an apples to apples comparison.

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Yeah I'm not trying to advocate the idea because I think it's better than what people have been having huge success with for years or anything.

I just thought it was interesting and wanted to see what people thought the difference of what the OP proposed would have with a turbo engine would be like.

Whether or not I'd actually do it myself I'm not sure... the fact that my 260 has an L24 has always put me off because it's a smaller displacement than what it had originally, and this setup up^^ would yield just about 2.6 liters apprently. Just thought that was neat. I got a long ways to go before I make decisions like that though

Edited by 9/73-E31-260z

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I would say go for it, bore it out a little bit and get nice pistons and some high strength rods, and a gnarly cam and valve springs that can handle it, and build a 10k revving monster. You will have great throttle response, and high end power. Could you build an engine that is cheaper and makes more power, probably. But there is definatly a cool factor to pulling up to a light and sounding like an F1 car.

 

Just remember high revs mean stuff wears faster which will mean more rebuilds and more money. Last I checked F1s had a ridiculously small stroke, like 5/8ths of an inch. But they also go through their entire engine before each race.

 

A turbo set up right will wont give u more power than a striker turbo it will just shift the power band higher.

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I would say go for it, bore it out a little bit and get nice pistons and some high strength rods, and a gnarly cam and valve springs that can handle it, and build a 10k revving monster. You will have great throttle response, and high end power. Could you build an engine that is cheaper and makes more power, probably. But there is definatly a cool factor to pulling up to a light and sounding like an F1 car.

 

Just remember high revs mean stuff wears faster which will mean more rebuilds and more money. Last I checked F1s had a ridiculously small stroke, like 5/8ths of an inch. But they also go through their entire engine before each race.

 

A turbo set up right will wont give u more power than a striker turbo it will just shift the power band higher.

 

So what is the point of your post?  Have you built any L-series engine or are you parroting the internets?

 

Bore it out?  Start with the L28 block.

Custom pistons?  Put them in the L28 block.

High strength rod?  Factory rods are all the strength you need.

Gnarly cam?  Which head?  Like the N42 or P90 (L28 heads).

10K redline?  L28 can do that.

Great throttle response and high end power?  Built L28 will give you that.

Cool factor?  Got me there, really cool to spend a lot of time and money on less power.

 

Current F1 engines have mandated durability rules of multiple races.  It was to drive down cost.  When was the last time a F1 car blew a motor?

 

The correct turbo set up will give you more power period, otherwise it is not the correct turbo for the engine. Comparing turbo'd stokers and non-strokers is apples and oranges. 

 

Given max built engines, properly done, I will take more displacement. 

 

If you have to play within class rules, now you get trickly with rod lengths, bores, strokes.....ect.

 

Only reason to destroke an L28 is to play in class rules like the Bob Sharp 2.5L engines.

Edited by ctc

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I thought current F1 rules were each team is allowed six engines per season, period. At least that's what I heard...

And I wouldn't try for something like that exactly (10, 000 rpm is anything but practical... unless your name is Takumi Fujiwara xD)

And shortening the stroke would add some durability and longevity due to the reduction in piston speed right? (Or correct me if I'm wrong...)

Would it cost about the same to rebuild an L28 into this 2.6 liter destroked design as rebuilding a standard L28?

Not exactly with no regard to the power difference but would it cost the same?

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Would it cost about the same to rebuild an L28 into this 2.6 liter destroked design as rebuilding a standard L28?

Not exactly with no regard to the power difference but would it cost the same?

 

Assuming you have access to the parts, I assume it would cost the same.  If you need to buy the additional parts, that will be additional cost.  Make sure you have the cam sized to the new displacement and head flow.

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Woah sorry I pissed in your boots apparently.

 

I was stating general terms, not posting a build sheet. I've only built one L28 (p90a head) and it was a rebuild not built for more power, so no I don't know if the stock rods would hold, apparently now I know.

 

People do mods that I don't necessarily agree with, but if its safe ill condone anyone to work on their project.

 

And yea cool to me is something that has a personal touch to it. Are u telling me that if someone was willing to bore out an L28 and destroke it, you would have no interest in seeing how it comes out?

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I've seen that thread, and a few others. I thought they were all interesting but they were all on N/A builds so that's why I brought this thread back to see what kind of an impact the proposed setup would have on a turbo engine.

And if what CTC says is true, or even if it costs more but not by much, maybe someday I'll try it out. Have a fairly unique engine, the 2.6 liters my car was supposed to have, and even a few more revs maybe.

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