ive done some reading, did a search on here and cant come to any conclusion. is a bigger block better for boost? i.e= 8psi on a ls1 vs 8psi on a ls7 seems like a no brainer. but if a 6cyl GN can smoke many v-8's, even some with boost, what gives?

nick from victory racing has been helping me choose an engine, but on my current budget. i think the ls7 is going to be the engine to beat for the next few years as its (ONLY) my opinion that a procharged ls7 will destroy the next cobra. so if you had a decent amount of money, and a procharger was your goal, would you go for a worked ls1/ls6, 370,402/408 stroker, or 427 for boost? obviously the expense rises in that order.

 

I dont think the Ls7 in the Zo6 is going to have any problem with the new cobra coming out......the Ls7 is already quicker then the ford GT...slap a ATI F1 on it and its all over for the fords

but back to what you are saying... if it were me...
I like different stuff.. I would destroke a Ls1/Ls6 down to 302ci ....and help it breath with some twin gt42's.....

 

GNs can run 30psi of boost where most V8s run less than 15... stock motors rarely see over 6psi unless the owner is out to break it.

The thing with larger motors(383, 408, 427) is you need a larger blower to get the same boost you would out of a 350. So there is cost associated with that if your goal is to make big boost in a large displacement motor. Power when it comes to boost is all about bigger is better. There is a limit to how much boost a motor can take no matter how well its put together... 30 psi is A LOT! Youre probably talking 800+ rwhp in an LSx. So in order to make the MOST power you gotta put together the biggest motor and build it to withstand the greatest boost. That probably sounds obvious but you never said what your goal was.

I dont see why anybody would want/need over 600 rwhp for a street motor. If 600 was my goal then Id build a 383 with some ported LS1 heads and 10 psi. I dont keep up with LS1 stuff so I cant say with 100% certainty that would meet the 600 rwhp mark though from what ive seen those motors do NA I have a feeling my combo would be sufficient.

 

Cubes makes it easier to make power from a given engine... i.e.- less boost is needed to make the same amount of power. On the flipside, as mentioned above, you'll need to increase the blower or turbo size to get back into optimum efficiency range (determined by the cfm the turbo/blower pushes and the pressure ratio).

30psi is a lot on any engine. Most 900rwhp supras you see are pushing well over 30psi (40 in some cases). At 60psi+ and nitrous, Marko D's supra dyno'd 1500rwhp. It was at ~35psi with nitrous when he was at the 1200rwhp level. he was also buzzing that little engine to over 9000rpm to do it.

Look at some of the V8s. Rick Intrau's 398 LT1 hit 1240rwhp with 23psi of boost and turning 8500rpm (no nitrous). Even though the rpm range was close to the supra, the bigger LT1 didn't need 35psi and nitrous the hit 1200rwhp+. Another shining example is Rob Reiger's old 390 gen1 small block chevy (stroked 350, not a big block), which now resides in chris chow's turbo buick. With 35psi, that engine made a little over 1800hp at the crank turning about 8000rpm... also without nitrous. Chris detuned the engine a little when he got it, pushing about 27psi, but still dyno's around 1200rwhp. The nitty-gritty of it is that you don't need as high of peak cylinder pressures (given by more boost) to make power since you're already dealing with a larger volume of intake charge on each stroke.

As a side note, Rob now has a 552ci BBC with twin T-100 turbos. Makes over 2600hp with race gas alone and around 20psi of boost. Dan millen is running a 370 cubic inch windsor in his mustang and needs in the high 20s of boost to make 2100hp in the same manner. If Rob were to run those boost levels with the BBC, 2800-3000hp wouldn't be out of the question if the engine holds together.

When talking max effort FI builds, block strength is your main issue. But more cubes makes it a little easier since you don't have to run higher levels of boost to make the same amount of power. Higher boost levels also opens the door to more tuning issues due to the higher IATs (compression makes heat, no two ways about it, and heat makes detonation harder to contain). You also have to have stronger (i.e.- more expensive) intake manifold gaskets and head gaskets to deal with the higher manifold pressures and cylinder pressures (which gets into IMEPs, BMEPs, etc).

 

I think a LS 402-408 with a YSi or F1 will be plenty, I dont see a need to pony all the extra money for the 427. A 402 with a good tune and streetable boost should make 700hp at the wheels or better.

 

Don't forget about fuel! You can run 8-10psi on most engines without resorting to race gas -- premium will do fine. When you start getting into the higher pressures, you'll need race gas to avoid detonation.

I run my GN around town at 12lbs of boost on 93 octane, but at the track we put 108 in and up the boost to 19. I haven't taken it to a dyno, but it shaves a good half-second off the ET. The stock GN block is extremely strong, so it's pretty easy to get the boost up without having to worry about it, which is why you see so many GNs that can smoke a blown LS1.

 

12psi? You should be able to run 15-16psi at any time on 93 octane (ECM makes ~14psi right off the showroom floor). I used to run ~16psi on 93 pump with no problems with both the stock turbo and eventually the TA-49 that replaced it. Alcohol injection netted 25psi without detonation on 93 (a friend of mine with a nearly identical setup dyno'd 394rwhp at 23psi). And FWIW, the stock "109" blocks tend to crack at about 600 crank hp, although many have seen 700hp at the crank with a block girdle. After that you must go with a "stage" block if you want to stay with a buick V6.

20psi on a well-tuned turbocharged 350 (with optimum sized turbo/s, of course) and you're looking at 700rwhp minimum. It's been done too many times to argue otherwise.

 

12psi is a happy compromise between fuel economy and power. It smokes my Z28 without any trouble at that boost level. I'm sure we could run more.

 

Don't forget that most V8's on boost are running superchargers where as the Buick is using a turbo. The turbo will make better power through out the RPM band where the supercharger will only make peak power at redline. Also, the V6 is generally a bit lighter than an iron small block.

If you're building a supercharged V8, then by all means up the displacement since it'll help with the low end where the blower won't be putting out full boost. With a turbo motor, displacement isn't as crucial since you can up the boost with a **** inside the car if need be.

 

I think an LS1 with 30 psi would be well over 1000 rwhp. . .

Anyway, it depends on supercharger versus turbo. With a supercharger, a bigger engine, heads, and cam will only help power - unless the compressor reaches choke flow. With a turbo, engine size doesn't seem to matter much at all. People are making the same hp with 180 cid motors as 355 cid motors all running the same turbocharger. The turbocharger selection and boost level seem to affect power much more than displacement due to the backpressure characteristics.

 

An LS1 with 30# would certainly be over 1000hp.