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New idea for an engine

1802 Views 30 Replies 10 Participants Last post by  KEINoze
I just saw an F54 with L24 rods and crank at a Z car meet yesterday.
Gave me an interesting idea for a new engine:

F54 (bored out for . . .)
KA24 pistons
L24 rods & crank

This gives a really good bore x stroke combo for high end power.
Adding in an HKS cam, lighter pulleys, and flywheel would make for a high revving L-series.
Has anybody tried this? Think it'll work?

Pics of the meet

Post Edited (Nov 15, 9:17pm)
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Yep, been done...

and written up in Sport Z magazine.
The stock bore and L24 crank makes for a revvy L26 of a short-stroke configuration.
Be ready to blow your pistons, though, this combination will make power over 6500rpm---a place where cast pistons don't live for long...

Same can be done with an L20A crankshaft on a L28 bore making a really rev-happy L25 which was the combination for the 330hp L engine used in the GTU competitions when Paul Neuman was driving in the #33 Cannon Car...
According to L-Engine, if you use KA24 pistons, you will be a little over 4mm in the hole... Bad compression. I'm actually going to be running L24 crank and rods with flat tops with the current engine I'm building... SSHHHHH... Don't tell anyone.
Once again i am awwed at tonyd's knowledge of everything...
This isn't a new idea. It is, however, a bad idea. Basically, a "destroker" sacrifices displacement for rev potential. The problem with this idea is that you LOSE more displacementwise than you GAIN in rev potential, because displacement is LINEARLY related to stroke, while max rev potential varies with the SQUARE ROOT of stroke. Basically, if you go from 79mm stroke to 73.7, you lose 7% of your displacement. 7% less torque EVERYWHERE in the rev range. But you only gain ~3.5% potential revs up top! So basically you've got ~3.5% LESS peak power potential AND 7% less torque.
The L28 alredy has more bore than stroke and revs fairly well. It just seems wrong to "loose" displacement in hopes of more power through revving. YMMV.

Thank you Tony for that input!
Also Dan for the numbers.

The whole point of my idea was to have an engine making high end power. Obviously I'm sacrificing some torque and low end potential.
Plus, I was thinking about boring out the F54 to increase bore.
It's a high budget buildup to have a high revving L-series. I don't intend to do it anytime soon but seeing that most parts from any L-series is interchangeable I couldn't resist thinking about it.

The V10 F1 engines of the 2004 season have something around a 60mm stroke with over 100mm bore.
There's a reason they idle around 4k rpm and make peak horsepower at around 18k.
The bore and stroke on those tell you why they only have around 250lbs-ft of torque while having close to 1000hp.
They use the best engineers in the world to make an engine to produce the max output with limited cylinder numbers and displacement.

Same with a light F1 car, it doesn't really make sense to have a torquey engine on the lightweight Z. Light cars benefit more from a high revving, high horsepower engine. I'm not criticizing 3.1 stroker owners. It's just that my personal preference is with high revving engines.
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Just a note, F1 engines are probably the worst street engine you could have. I guess as long as you don't mind idling as 4000rpm or rebuilding after every 500 miles.
There's just one problem...

with the L-Cranks you get into serious harmonics much above 8500, and a stock L28 will rev there just fine with only head work, a cam, and induction to support it.
Our Bonneville car did that.
The 2 liter we are running should go to 9, but we have three spare cranks in expectation of the breakage or crackingthat will inevitably develop when wound that tight...

So it's not like you will be able to rev to 12K or anything likethat, you WILL be below 9K, and you don't need any special destroke job to do that.

The GTU cars that competed in Trans-Am needed an engine below 2.5 L, so the L20A crank and L28 bore gave them the MAXIMUM displacement within the rules allowable overbore for "production" blocks---which is why they used it. In that case, within the structure of the rules, it gave the MOST displacement, and revved high, which you have to do to make power with a small engine. Given their situation, it was a novel approach, and worked well on thetracks they ran on. There was a comparo between the two in Road and Track I believe where they showed the performance differences between the 2.5 and the 2.8 engines in two different racing cars (maybe it was a 2.4...)
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>"The whole point of my idea was to have an engine making high end power."

Destroker will lose you high-end power, see above. For the sake of a couple of hundred rpm up top.

>"Plus, I was thinking about boring out the F54 to increase bore."

To make up for the lost displacement. But you're STILL at a displacement deficit compared to what you'd have with the L28 (or LD28) crank.

F1 engine designers have a displacement limit, and a clean sheet of paper (whatever bore x stroke they want). We are for the most part limited to what Nissan made, ultimately. And most of us don't have a displacement limit (and most of us that *do* are still forced to stick with stock or near-stock bore x stroke anyway). Maximum performance for us means maximizing displacement, regardless of what may be perceived as "low-performance" bore/stroke ratios.

>"Light cars benefit more from a high revving, high horsepower engine."

What is a "benefit" depends on what is desired. If low-end torque is desired (street), large displacement fills the bill. If maximum high-rpm power is desired (competition), large displacement fills that bill, too.

I don't see the point to being able to rev 250rpm higher (if that) while GIVING AWAY a measure of peak high-rpm power and even more torque. You're revving *slightly* higher but defeating the goal of maximum performance!

IF you don't care about ultimate performance, and ONLY care about being able to rev a little bit higher, then the destroker makes some sense. But that goal doesn't make any sense to me.
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WOW, a stock L28 bottom end can handle 8500?!
I've limited my 3.1 to 7000 based on what I've *heard* to be a reliable limit for the KA pistons in a 96mm stroke KA motor of 6500rpm. But I have also gone to 7300 rev-limit on occasion as that gives similar peak piston acceleration as what KA pistons see in a KA motor at 7000rpm (redline in my '91 240SX, which hasn't had any piston failures yet).

Can stock L-series cranks, pistons and rods really *reliably* handle 8000 rpm+ without special treatment or with just shot-peening or other readily applicable treatment?
Thanks again for the input Tony!
I forgot that you were running a 2 liter L-series. I guess I got the best answer from the best man.
I would love to read the Road & Track comparo test. Remember which issue it was in?

I guess in an everyday car, a stock L28 with the proper head and intake setup would be enough for 8k.
Actually, anything above 8k in most road cars today seems like you're pushing it.
Maybe I should give Tomei a call and see what they have for L-series engines. Maybe Tony beat me to it and found out they don't have cranks for the L-series. Tomei makes some wonderful things for engines . . .
They also sell full complete race engines too.

For people saying it's not a good idea, why do you say so?
Is it because of everyday practicality issues? Is it because it'll reduce torque output? Is it because it's more complex than just swapping in a normal F54? Is it because you think the L-series is just too old?

****, I've seen KPGC10 Skyline GT-R's with 30 year old S20's revving over 9k without a problem.
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"For people saying it's not a good idea, why do you say so?"

LESS POWER, REDUCED PERFORMANCE. That is why it's a bad idea. Just because you're giving up "everyday practicality" and torque does NOT mean you're automatically gaining anything in terms of ultimate power output. You're LOSING power by destroking.
Yeah, I should clarify...

The bottom end did indeed use stock crank and rods.
We ran this engine for over four seasons.

Though free-floaters with teflon buttons would be the way we woudl do it over, and have built the L20A engine.

But yeah, standard Preparation Regimen: polish stress relieve, shot peen ,and balance the **** out of it electronically with the entire rotating assembly there.

We would shift at 8500rpm as our power peak was at 8250rpm.

Though, oddly we found that our fastest times resulted from skippin two gears while running up through thegears, the "close ratio direct-drive tranny was more for road racing, it didn't need to be as closely spaced as the [ismaller displacement engines[/i] apparently!

But yeah, just MAKE SURE YOU HAVE A REAL BALANCER ON IT AND MAKE SURE IT"S PROPERLY INSTALLED! The first crank was wrecked when the balancer vibrated off. We did not have the option of the new BHJ Dampener. I would go with that unit in a heartbeat over the NISMO unit we had used. Big nut, and THICK washer to hold the crank pulley FIRMLY on the snout!

I wish I had more video of the car making passes singing along for almost a mile straight at 8200.....8300....8400.....8500........

Never went "Boom" but after thatfirstseason when the crank pulley got welded to the snout so we could try and finish the season, we rebalanced it, installed a new crank, and ran it for another four seasons!

So "stock" is stock, but with common sense preparation and a good balance job!
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Hold on for Tomei!

Though if you DO call, I want to order THREE of their adjustable CAm Gears for the L-Engines!

The nice Kamearei tensioner assembly for the cam drive may well be available here soon for a resonable "US" cost. I will let the manufacturer break that news. I don't want to steal his thunder!
Oh, and don't forget the old Crower Crank...

I would give my eye teeth for one of the Crower-Crank Stroker 3.5 Crankshafts HKS was selling in the 80's!

I took ONE ride in a 3.5 bottom end, with an OS TC24B-1 Head on it with triple 50 Mikuinis in 1986 and am still having anal spasms from the experience!

Give me torque ANY day. And if it's a revver, that works too!
As a related aside, I've had built, but not yet installed or run a semi-similar franken-combo L28:

L28 crank, L24 (9mm) rods, forged Ross flat tops with wrist pins drilled higher to piston deck to compensate for longer L24 rods.

It's my own conception that I haven't yet seen in any other Z car. Any thoughts? I wanted to be "different" and thought this combo would rev a bit easier and perhaps give me a good torque/rev combo.

Thanks for thoughts guys.
Go talk to them...

Since you are in SoCal, Crower is in San Diego, Chula Vista I think.
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