engine size autocross

[c3rocket]

I hope this is in the right place to post I was wondering about what motor I should put in my 69 vette flared 315 squared t56 willwood big brake kit borgeson box t56 6 speed .I know everybody will say ls all the way and I agree but I not want to spend the 16 grand to do it meaning changing all my pulley set up and custom exhaust, this car is primarily used for autocross I was thinking about a blue print 427 or 454 small block the 454 makes 580 hp at 6000 and 570 trq at 4600 not bad for the price with a msd ignition all said and done about 10 grand with a warranty and my second option would be a destroked 406 to a 377 that would have a dart shp block scat crank and rods afr heads and make about 560 hp and 500 trq and rev to 7000 all day long long any thoughts will be appreciated. thanks .

[Vimes]

I don't know if you'd be happy adding big block weight to the nose. Autocrossing is handling first and foremost and adding weight to the nose is going to make it more prone to plowing during hard cornering. A Dart aluminim small block would be a better option IMO, and all your existing external parts (accessories, headers, ect) would bolt right on. In fact, nobody would need to even know you made a change.

This is an engine I always wanted to build, at least until the LS came along - a short stroke long rod 350. This link (http://purplesagetradingpost.com/sumner/techinfo/350%20chevy%20engine.html) goes over a Chevy 350 (The 350 Engine Chevrolet Should Have Built) that uses a bored out small block 400 with a 327's 3.25 stroke crank to make 350 cubes, and uses long rods which will allow 87 octane on 11:1 compression. This article is pretty old but even back then they were able to get 412HP at 5700RPM and 435TQ at 3500RPM, and more importantly the engine made over 400TQ from 2800RPM to 5200RPM. I think using a Dart aluminum block, modern heads, a lightened crank and a modern aftermarket fuel injection setup you could probably get closer to 500HP/TQ without the huge weight penalty of a big block. Plus, a short stroke engine winds up in a big hurry when you hit the go pedal, which is lots of fun.

[c3rocket]

The motor would be a 377 from a dart shp 400 block and with afr heads and all the good parts makes about 560 to 570 hp at 6800 rpm with about 500 trq, or I go with a blueprint 454 small block with a good intake and carb and ignition and will run at about 580 hp at 6000 rpm and 570 trq at 4600 either way they are about the same price 10 grand .

[68Formula]

Close or Wide ratio T56, and what rearend ratio?

[68Formula]

Also one hint (granted I'm no expert so hopefully more will jump in) since Autocross tracks are pretty short, I think a broad and flat torque curve works best. You'll mostly be using a couple gears if you have it setup right. Broader minimizes the gear changes as you setup transitioning from corner to corner (big savings in time and keeps the tire loading changes less abrupt). And flatter keeps the power very predictable for the driver regardless of the track.

So just looking at the Blueprint engines, the 427 seems to have power that is both slightly wider and a little more flat than the 454. With the torque it puts out, you could throttle out of a corner at 2600rpm and go up to 6200rpm without shifting if you needed to.

I'm not sure if a de-stroked would be preferred or not. It'll rev faster, but you'll want steep gearing to make it strong coming off a corner, and then really spin it up before the next corner.

[c3rocket]

370 rear gear t56 is 266 first and I think a .64 6th 30 inch tall tire .

[c3rocket]

I do agree with the torque curve on the 427 I am in first gear the whole time at good guys autocross and 1st and second at another venue but with that much power I could stay in second the whole time and even lug it a bit in the turns barely throttle my little 350 I have to rev the piss out of it its gutless.

[c3rocket]

Am I wrong to look at it like when I ride my dirt bikes and my 4 stroke is awesome cuz I can stay in 3rd or 4th while my buddies 2 stroke he is 2 to 3 gears versus 1 of mine .

[c3rocket]

This is my other ride and it is machine in a half and I like the power curve in it and I think it would do well in autocross .195733195733

[c3rocket]

Here's my 69 vette t56 borgeson box 315 squared vansteele front and ride tech rear suspension .

[short&wide65]

Those are both great looking Corvettes! I have a strong want for a 70-72 Corvette that I could autocross. Seeing yours isn't helping. lol. I had to pass on a cheap local red on red 72 last summer with a non numbers matching 350 and a bad rear subframe. The perfect project. But I have 65 GMC I have to finish first.


Also one hint (granted I'm no expert so hopefully more will jump in) since Autocross tracks are pretty short, I think a broad and flat torque curve works best. You'll mostly be using a couple gears if you have it setup right. Broader minimizes the gear changes as you setup transitioning from corner to corner (big savings in time and keeps the tire loading changes less abrupt). And flatter keeps the power very predictable for the driver regardless of the track.

So just looking at the Blueprint engines, the 427 seems to have power that is both slightly wider and a little more flat than the 454. With the torque it puts out, you could throttle out of a corner at 2600rpm and go up to 6200rpm without shifting if you needed to.

I'm not sure if a de-stroked would be preferred or not. It'll rev faster, but you'll want steep gearing to make it strong coming off a corner, and then really spin it up before the next corner.


I do agree with the torque curve on the 427 I am in first gear the whole time at good guys autocross and 1st and second at another venue but with that much power I could stay in second the whole time and even lug it a bit in the turns barely throttle my little 350 I have to rev the piss out of it its gutless.

In my opinion (I'm no expert either) I would want a destroked engine because any of the cars I've co-driven at autocross with a flat torque curve overwhelm the rear tires coming out of corner too easily. Moving the powerband up makes it easier to get on the power sooner.

[68Formula]

There's also a BluePrint 400, which has the same bore, but shorter stroke than the 427. About 75ft-lb less torque on the lower end, still very flat, and looks like you could easily spin it up to 6500 (if they say the valvetrain is up to it).

https://static1.pt-content.com/images/pt/2022/01/BP4002CT1dynochart_590x-1.jpg?v=1626803557

[Jonathonar89]

I would 99% of the time take the cubic inches. So many people are into the destroke idea but RPM capability has a lot to do with valvetrain stability more than bottom end. Look at LS engines for comparison. 6.2-7.0 liter LS engines make better power than 4.8-5.3 engines but the architecture is nearly the same.

Don’t feel like you have to go LS. Traditional V8’s can work very well and, IMO, it’s nicer buying things like radiator hoses and other parts that were originally designed for your car and bolt in. Do what feels right for yourself. Big Blocks are awesome just as LS engines are.

[c3rocket]

I would think about a lsx but do you still have to change exhaust where headers bolt to the heads .

[dontlifttoshift]

High revving engines tend to be peaky. There is no torque and then suddenly it will blow the tires off as the RPMs come up. It is difficult to drive a car like that.

Take the engine with the flattest torque curve as it is the most predictable to drive.

[ryeguy2006a]

Soo... I'm going to be that LS guy I guess. If you are planning to AutoX the car a lot, I see no better option than the LS motor. Adding lightness to vehicles seems to be the best method for being competitive in that setting. It's hard to get much lighter than an aluminum LS engine. If you are going to be all in for the 454 SBC at $10k, I'm confident that you could piece together an LS swap for around that price. GM has a Crate LS3 430HP engine for $5k. (Granted, you may have to wait given the shortage) I'd grab a Summit Cam kit, Terminator X Max, stock loaded LS3 intake and find someone selling C6 Vette accessories. I'm sure someone makes mounts, oil pan and headers for a C3. Not sure what you are doing for a fuel system, but I ran a stock 5th gen Camaro fuel pump assembly that was modified by Vaporworx that was pretty inexpensive.

There are literally a million different combinations that could be suggested for an "LS" swap, but I think this one would meet all of your goals. 2 year warranty, and not kill the bank.

Even if you aren't making the same power as the 454 SBC, you are much lighter up front and the LS motors love to rev. LS3 Vette/Camaro guys usually make 450 rwhp with H/C/I. Then if that isn't enough, swap on an LSA supercharger. :evil:

Keep us posted on what you end up doing.

[short&wide65]

I would 99% of the time take the cubic inches. So many people are into the destroke idea but RPM capability has a lot to do with valvetrain stability more than bottom end. Look at LS engines for comparison. 6.2-7.0 liter LS engines make better power than 4.8-5.3 engines but the architecture is nearly the same.

The key is combining them both. I'm currently considering a 6.2 block with a 4.8 crank for a total of 5.5 litres that'll rev to 8000 rpm and make about 600 horsepower naturally aspirated.

https://www.motortrend.com/how-to/4-8l-crank-ls3-block-how-to-build-an-8000-rpm-ls-stroker/


High revving engines tend to be peaky. There is no torque and then suddenly it will blow the tires off as the RPMs come up. It is difficult to drive a car like that.

Take the engine with the flattest torque curve as it is the most predictable to drive.

I've autocrossed a C6 Corvette Z06 and in no way was it peaky at all. It also wasn't difficult to drive and is very competitive. I liked how easy it was to drive at autocross, even on a tight course.

[dontlifttoshift]

In attempting to contradict me you are making my point, thanks! The LS7, even cammed to match the theoretical HP output of you 5.5 liter screamer, will be waaaay easier to drive......because flat and predictable torque curve. The LS7 is awesome but it's a pretty mild engine.

From the link you posted
the 339-inch motor produced 607 hp at 7,900 rpm and 466 lb-ft of torque at 6,200 rpm. That's going to suck to autocross

[short&wide65]

In attempting to contradict me you are making my point, thanks! The LS7, even cammed to match the theoretical HP output of you 5.5 liter screamer, will be waaaay easier to drive......because flat and predictable torque curve. The LS7 is awesome but it's a pretty mild engine.

From the link you posted That's going to suck to autocross

While I agree that upon first glance the engine at the link I posted could be considered peaky, I'm not looking to build an exact copy. Those horsepower and torque numbers are also on an engine dyno so they are gross, not net so once it's in a car, it's probably close to the LS7's 505 horsepower.

The LS7 makes 475 lb-ft at 4800 RPM, which is still pretty high. I've also autocrossed a 2008 BMW M3 V8 which only makes 295 lb-ft at 3900 rpm. It makes 414 horsepower at 8500 RPM and was also really good to autocross.

I disagree that a higher torque peak can't still have a flat and predicable curve. I want a responsive engine that revs and not a burnout machine.

[SSLance]

Everyone has been after me to LS swap my SBC for years. Even when I hurt it couple years ago, it still made WAY more sense to freshen up the SBC than to LS swap it.

I feed and control my Fastburn 383 with a Holley Terminator 4bbl system and I'd challenge anyone to tell me it's not an LS if they drove it without looking under the hood. Well except for the killer torque it makes from 2,000 rom and up that is. It pulls out of holes way harder than any LS3 I've driven. I haven't dyno'd mine but paper calculator shows 525 hp (peak 5400), 550 ft lb (peak 4700) and it's VERY driveable and has beaten a ton of LS swapped cars over the years.

[c3rocket]

Thanks for the advice guys I only autocross this thing 10 times a year tops and what about a lsx 427 but I think I would still have to swap exhaust out.I auto cross with a fast bunch of guys and 2 of them have small block chevys and there about the fastest out there a ls would be nice but I would have to scrap all the stuff I all ready did for the car like a complete march serpentine pulley set up and my quick time bellhousing and custom side pipes.

[dontlifttoshift]

In case images don't show up. https://www.m3post.com/forums/showthread.php?t=102981 Here's the M3 on a chassis dyno. Kansas has more peaks than this torque curve. So yeah, great engine for autocross.

https://static1.pt-content.com/images/pt/2022/01/attachmentphpattachmentid118723stc1d1198-1.jpg

Go back to the OP. The 427 will be easier to drive than the 377, it makes more power everywhere, will require less maintenance, be more fun and driveable on the street and he won't have to regear the car to get it to dig off a slow corner

[c3rocket]

I have everything set up already with my march serpentine pulley set up and my quick time bellhousing also my custom side pipes and I only autocross 10 times tops a year and I think it will just be easier to put a 396 up the the 454 blueprint maybe with fuel injection a couple of guys in the group I autocross with are very fast and run small block chevy motors and I am not trying to be the fastest guy out on the coarse .

[Vimes]

Thanks for the advice guys I only autocross this thing 10 times a year tops and what about a lsx 427 but I think I would still have to swap exhaust out.I auto cross with a fast bunch of guys and 2 of them have small block chevys and there about the fastest out there a ls would be nice but I would have to scrap all the stuff I all ready did for the car like a complete march serpentine pulley set up and my quick time bellhousing and custom side pipes.

You'll have to swap the exhaust out with a big block anyway so I wouldn't let that stop you from doing an LS. A small block is EIIEEIIE, while an LS and a big block are both EIEIEIEI, with E being exhaust and I being intake. Your exhaust will not bolt to a big block. And, depending on how large your exhaust runners are you might need to change the exhaust anyway if you go with a big cube engine.

If you're set on part re-use your best bet would be to stick with a small block. You could just do up an aluminum 400 small block and it'll bolt right into where your current engine is. Or, stroke the same 400 out to a 427. I've never used these guys before (their link was first in my search) so can't say they're good or bad, but they offer an aluminum small block 427 short block (https://www.tristarengines.com/performance/gm/smallblock/prostar-427/pro-startm-427-cid-small-block-chevy-shortblock-featuring-darttm-shp-block) for 5500 bucks. And, Chevy Hardcore (https://www.chevyhardcore.com/tech-stories/engine/427-cubic-inch-small-block/) goes over their build that they claim is a streetable 600HP, but there's no dyno along with it. They did say you want an aftermarket 400 block for this as factory 400s are prone to cracking out when you stroke/bore them to the limit. For autocross, and just general fun-to-drive, I'd be looking at aftermarket aluminum anyway.

[dontlifttoshift]

Big block was never on the table.


I was thinking about a blue print 427 or 454 small block the 454 makes 580 hp at 6000 and 570 trq at 4600 .

[short&wide65]

In case images don't show up. https://www.m3post.com/forums/showthread.php?t=102981 Here's the M3 on a chassis dyno. Kansas has more peaks than this torque curve. So yeah, great engine for autocross.

Funny, because it is the car to have the SCCA's FS class where it routinely beats the Camaros and Mustangs in the class. You obviously haven't driven one.

[dontlifttoshift]

I have, along with the Mustang in FS trim and the Camaro 1LE trim in BS trim.

Nonetheless, in your need to argue you inferred sarcasm where there wasn't any. My apparently unclear post agreed with your comment about how great the M3 engine is for autocross and it supports my assertation that a flat predictable torque curve is better to drive.

[short&wide65]

Nonetheless, in your need to argue you inferred sarcasm where there wasn't any. My apparently unclear post agreed with your comment about how great the M3 engine is for autocross and it supports my assertation that a flat predictable torque curve is better to drive.

I’m not trying to argue at all. You said that a destroked high revving engine can’t have a flat torque curve and I disagreed.

[c3rocket]

Well with out having to change any thing I really like the small block 454.I have a detuned little 350 making 600 hp and and 600 trq at 4300 and love it and its very manageable and predictable here it is .

[c3rocket]

The 454 small block will be close to that very user friendly.

[68Formula]

Vacuum on the BP SBC 427 and 454 are extremely low (values are listed on their dyno graphs). You'll likely need manual brakes, hydroboost, or a cam with less overlap. I would not be surprised if that's also the reason they don't offer the Sniper EFI as a package on that one (insufficient vacuum for speed density).

On the 400 they claim 10.5" Hg @ 950rpm. Still low, but might work with power brakes. It's also offered with Sniper EFI. Torque is really flat and really wide. And if you went the EFI programmable timing map you can fine tune the power(take some out the bottom to soften it if necessary, or take some on the mid-range and really make the torque flat and predictable) even more. Or setup two tunes, so you have one specifically for autocross, and a second one for street/strip. The bore is the same size as the 427 and 454 so no bore valve shrouding. And it could rev a little quicker as it less stroke than the larger two.

Since the image won't seem to post for me, I'll just post the link for reference: https://cdn.shopify.com/s/files/1/2160/9839/products/BP4002CTC1-dyno-chart_5ac62cb4-8a9c-4657-ad31-a3609a98541f_1349x.jpg?v=1626803310

https://static1.pt-content.com/images/pt/2022/01/BP4002CTC1dynochart_5ac62cb48a9c4657ad31-1.jpg?v=1626803310

[c3rocket]

My car is manual brakes with a willwood big brake kit and will be using a e vac system for the crank case .I would run a fuel injection if I know it will not be a pain in the ass to fine tune .

[Vimes]

Big block was never on the table.

Missed a word - my bad.

[c3rocket]

I know late but here's a update I ended up going with a 434 small block from skip white racing with flat top pistons and the shorter of the two they offer team g intake it has dart shp block and afr 220 heads toped off with a holley xp 950 did 652 hp and 608 trq and I can run my ac and has vacuum, the only problem I am having auto crossing is in turns and stopping in the stop zone it cuts out so now I am putting in a new fuel tank with the sniper stealth fuel injection .

[Hopperj7]

For autocross, you really do not need as much power as you think. I had a friend who raced a bone stock LS1 in his first gen Camaro and always killed it. Too much power and you risk losing control or fighting the car.

[BonzoHansen]

...,the only problem I am having auto crossing is in turns and stopping in the stop zone it cuts .

I have that same issue on hard stops. Not turning though.