Big displacement, or forced induction?

[MaineShark]

I'm usually an "all motor" kind of guy, but part of me does like the idea of forced induction.

So, I thought I'd post a hypothetical possibility, to see what people think about it.

My plans for the Shark include a new engine. Something in the 600-650 hp range, and as much torque as I can get.

So, there are two possible routes:

Large displacement: NA, bored and stroked "old school" SBC, sweeping something in the 427 to 454 range.

Forced induction: Supercharged LT1, bored and stroked to something much smaller, like in the 383 to 406 range.

(I figure the LT1-type block would handle forced induction a little better, due to its improved cooling system)

Thoughts?

Joe

[bossvette]

Joe
this may be the best "bang" for the Buck
http://www.greenwoodchevy.com/engine17.htm
Craig sr.

[grumpyvette]

heres a few other choices

http://media.gm.com/news/releases/021106_engine.html

http://www.sallee-chevrolet.com/Sneak/Previews.html

http://www.sallee-chevrolet.com/Chev...arts_pics.html

keep in mind that a supercharged sbc will be under conciderably more stress and far more likely to break than a much larger engine spinning slower under less stress, plus the resale value of a bbc corvette is normally higher
put another way, if you had a choice between a corvette with a factory built , fuel injected engine or a small block with a supercharger what would you want to buy, well 99% of the guys I know would take the efi/big block choice

[67HEAVEN]

Joe,

From a cost, reliability and brute-force-kick-in-the-seat feel, guess what my answer would be (and in my case will be).

[MaineShark]

No big blocks. Only small-blocks.

The question is between a big, supercharged small-block, and a huge, naturally-aspirated small-block. Small-blocks can be punched out to 454 safely, so that's not a problem.

And I'm going to build whatever engine I do, myself, so no crate engines

Joe

[Last Ride]

Joe--
I have often wondered this as well. On my short list of possibilities is a twin turbo LT1 (since I already have the LT1). I think you could get 600 HP out of a TT LT1 with only 350 CID. How important is streetability? I would think that a forced induction setup would be more streetable than a large SB. I am glad you posed this question!

[matchframe]

For a normally aspirated small block, about the best HP you can get is about 540-550 HP. That is a displacement of 427. Bill Mitchell's Hardcore series of engines might be a good pattern to follow. http://www.theengineshop.com/engine.shtml To get into the 600 HP range with a normal aspirated engine, you would have to go Big Block and punch it out into the 500 range displacement. Otherwise, forced induction with big displacement is the only way to get a small block to produce over 600 HP.

Bill

[MaineShark]

That limited run of 454 SBC's (with the same bore and stroke as the 454 BBC - how cool is that?) that Mitchell did, produced about 610 on 91 octane, so tweaking it a bit and using 93 to cover the difference should make close to 650 a possibility...

Last Ride sort of hit the main question: is a smaller, supercharged engine going to be a better daily driver than a larger, naturally-aspirated engine? The supercharged setup does have the disadvantage of extra weight, so it would actually have to produce a bit more power, to compensate...

(I'm planning on going with sidepipes, so the only possible system is a supercharger, not turbos...)

Joe

[Bob_K]

Go displacement. Then you can always supercharge it later on as well.

[matchframe]

I have been thinking about the large on large displacements of these small blocks; I wonder what the durability would be?

These blocks were designed to be roughly .060 over bored 350 or 400 CIDs.

If they are bored that close to the water jackets, and stroked to the limit, do you think they might have the life span of something like the LT-1 350 if they are used as a daily driver? Then if you use forced induction that would put more pressure and heat on the already thin cylinders.

Just wondering!

Bill

I like the idea of the big small block. Why not build big now, and if your needs and budget allow throw a huffer on later?
Good Luck.

[Tom Bryant]

Keep in mind that these 427 and 454 small blocks use Motown blocks, not Chevy. There isn't enough room in a Chevy block for that long of an arm. With that in mind the cost for a production based 454 big block vs. the all custom 454 small block becomes real lop sided in favor of the BB.

Tom

[MaineShark]

Originally posted by Bob_K
Go displacement. Then you can always supercharge it later on as well.

There's the rub. You really can't. If you build the engine properly as a NA engine, it will have compression that is way too high for forced induction. If you have room for a supercharer, later on, then you really weren't running a very efficient NA combination.

Originally posted by Tom Bryant
Keep in mind that these 427 and 454 small blocks use Motown blocks, not Chevy. There isn't enough room in a Chevy block for that long of an arm.

Well, you could fit that arm in a Chevy Rocket block, but I think that still has wet head bolts, which limits the overbore, so you certainly can't match the 4.250 bore that the big block uses, like you can with the Motown small-block.

Originally posted by Tom Bryant
With that in mind the cost for a production based 454 big block vs. the all custom 454 small block becomes real lop sided in favor of the BB.

Well, the Mitchell 454 cost $10,000 with iron heads, $10,500 with aluminum heads.

Yeah, a big block's cheaper, but it's also like carrying a rather large extra passenger, when it comes to weight.

The complexity and potential reliability problems (can't really do a service overbore during a rebuild) of the very large small-blocks is what makes me think that forced induction might be useful. On the other hand, forced induction puts a lot of stress on the engine, so what effect does it have on reliability, itself?

And, like you said, cost is also a factor: is it more sensible, financially, to build a smaller-displacement block, and shell out for a supercharger, than to build the more radical large-displacement block?

Joe

[Last Ride]

Joe--
All I can tell you is that if you decide to go with a modern LT1 (or even LS1), there will be plenty of room for forced induction. The LT1 should not be too hard to find, and probably not that expensive any more. The LS1 is getting more plentiful each day. I have not yet fully researched the supercharger or the twin turbo yet, but it will add some weight to the front end. What are you doing with your suspension? If you modernize it a la Vette Brakes or something similar, go with an aluminum radiator, and things like that, you might not have as much of a weight penalty as you would think. The thing that makes me want to go twin turbo over supercharger is the fact that the turbos will not drag on the motor as much when not under boost. Boost can be controlled in the car to dial it up or down as well. I like the idea of a supercharger because this car is not a daily driver, and the installation would be easier. I want decent mileage, but I don't know if I want it bad enough to go with the TT when I could hit similar power goals with a supercharger. Just out of curiousity, why would going with sidepipes not allow you to do twin turbos? I thought less exhaust was better when it came to turbos.

Bryan

[MaineShark]

Originally posted by Last Ride
it will add some weight to the front end. What are you doing with your suspension? If you modernize it a la Vette Brakes or something similar, go with an aluminum radiator, and things like that, you might not have as much of a weight penalty as you would think.

Yeah, but if you did the same things, without adding the supercharger, you'd save even more

Just playing Devil's Advocate.

Originally posted by Last Ride
The thing that makes me want to go twin turbo over supercharger is the fact that the turbos will not drag on the motor as much when not under boost. Boost can be controlled in the car to dial it up or down as well. I like the idea of a supercharger because this car is not a daily driver, and the installation would be easier. I want decent mileage, but I don't know if I want it bad enough to go with the TT when I could hit similar power goals with a supercharger.

Now, I'd say it's really the other way around: tubo setups are less "daily driver friendly" than superchargers.

Originally posted by Last Ride
Just out of curiousity, why would going with sidepipes not allow you to do twin turbos?

Mechanically, there's no reasonable way to connect the outlet of the turbo to a sidepipe. The single pipe would be too large to fit under the frame rail without severely compromising ground clearance. The traditional sidepipe setup uses the four separate tubes of the long-tube header, and doesn't have the collector until after the pipes get out from under the car.

Originally posted by Last Ride
I thought less exhaust was better when it came to turbos.

If you're looking for high HP numbers, then yes. But to get the turbos to spool up in a reasonable manner actually requires a more restrictive exhaust than the typical high-performance setup might be. Too little backpressure will push the turbo lag into the unreasonable range.

My primary reasons for avoiding turbos:
Lag
Heat
Sidepipes
Lag
Inconvenient cool-down period
Heat
Lack of room
Did I mention heat and lag?

We already have enough cooling problems, without trying to find room for a huge intercooler to cool the very hot air exiting the turbo.

But we're getting a little far afield

On another topic: I doubt it, but I figured I'd ask: is anyone making aftermarket LT1-type blocks, that might be more overbore-tolerant? If not, does anyone know how far that block can safely be bored and stroked? I figure 383 is no trouble, but how about going farther?

Joe