If you own a (modified) C6 Corvette.

I don't get this.

Many 928 owners have worked long and hard and spent serious $$$ and R&D hours to create mods and methods to make our 928's lay down big horsepower.

Carl has posted the numbers on his supercharged stroker he built for Bonneville, which has put down the highest recorded HP numbers by any 928 block to date.

I've purposely started a new thread, because I don't want this taken to be a comment on Carl's build in any way, which is quite an accomplishment.

But, check out the specs on this vette.
http://www.planetlsx.com/vehicles/It..._Boom_Pow/135#

It has a de-stroked LS7, the displacement has been reduced to 400c.i., it too has 8.5 c/r, and 18 psi of boost, yet it made 1265 rwhp / 1103 rwtq.
I believe these are the same short block dimensions and boost levels as the 928MS engine.

At only 8 psi, the bowtie still made 835 rwhp / 673 rwtq, besting our 928 HP king with 10 less PSI of boost.

So, what is going on here? The 928MS motor has clearly taken every advantage possible to create as much HP as possible. The vette has done the same. The article mentions that the vette heads flow upwards of 400 cfm, which I believe is about 15% higher than the best 928 heads have flowed.
So is that where the answer lies?
If we were able to bolt on a set of 400 cfm heads would the Bonneville car instantly gain a 40% increase in RWHP and be a 1000 rwhp monster?

The reason I'm asking at all, is that it seems that we 928 owners really have to work hard for our horsepower. I know the rational is that our engines are so well optimized from the factory that there isn't much left on the table. Still, it makes me wonder why the 928 motor seems resistant to making big power easily.

Comments?

 

For engines to yield such high horsepower, I can only see these factors contributing to it:

1) Maximum Airflow and Exhaust Flow for the Cylinder Heads

2) Optimized Intake with runner lengths to yield both horsepower and torque

3) Forced Induction with Intercooler

4) Standalone Engine Management

5) Free-flowing exhaust system

6) Engine Design and Durability - I see this as crucial. A good durable block that can withstand heat, power and the speed it runs at to yield maximum power


Look at a Toyota Supra. That I6 can put out over a 1,000 RWHP if modified correctly. I don't want to know how much money it costs to make any 6 or 8 cylinder yield over 1,000 HP.


For a 928, I believe a 1,000 horsepower out of the 32-valve motor is capable, but how long will it last? There needs to be some serious thought put into improving the durability of the engine with the issues that have been highlighted with oiling issues before considering such a dramatic increase in power. Forced induction and a lower compression does appear to be the easiest route to yield such high numbers.

 

Paging Dr. Greg Brown, Dr. Brown, line 1.

 

Setting aside the turbo vs supercharger debate for just a moment.......

1. More aggressive cams
2. Higher flowing heads
3. More aggressive tune

I'm also sure that intake is helping too.

If Carl had the R&D $$$ that has been sunk into the LS platform by the big tuners, no doubt he would be seeing or surpassing those numbers.

The Chevy tuners pump out 6.5 - 7 liter engines without boost all day long that push the 500-550rwhp mark without an overly aggressive camshaft.
The engines from KATECH Racing accomplish this for about $20,000 and are proven to be ultra reliable on the track (even with a wet sump).

Look at Mike Simard's engine. The biggest difference between his engine and previous strokers (other than the 1/2 liter) is the intake manifold.
He sailed past the 600rwhp mark.

Put 18psi through Mike's engine (after lowering the compression a bit) you will see numbers like this.
Especially after he installs a set of his new cams and larger valves.


Todd proved beyond any doubt how inadequate the stock intake manifold is when trying to make big HP.

Those Chevy engines above are with intake manifolds that are stock or slightly modified that still resemble the stock design. Pop on some ITB's with some really aggressive camshafts......

 

You can only compare horsepower if tested on the same day, with the same dyno, with the same type of tires (if testing rear wheel horsepower), at the same pressures.

Horsepower claims are significantly "inflated"...and it keeps getting worse. That is driven by the people that want to "brag" about horsepower. If one dyno, in town, won't give you want you desire to hear, there's one right down the street, that will. This forces the guy with the original dyno to "recalibrate" his dyno to get better numbers. Remember the gas price wars? Some thing, but with inflated dyno numbers.

Remember the L-88 427 Chevy engines, from about 1969? 425 claimed horsepower. Everyone thought that Chevy might have understated those numbers and they "thought" that those engines really made about 500hp.
I had a buddy that assembled one of those...with original pieces. It makes 700hp, at the rear wheels, by today's standards....go figure.

My really good stroker engines (with stock style intakes) make about 420 at the rear wheels..with a "correctly" calibrated dyno....the only numbers I choose to deal with. It is simply amazing to watch one of those strokers "suck the doorknobs" off of a "600 horsepower" supercharged thing.

Figure that out.

 

I'll see if I can bring Todd's red car to Kansas once Andy's car is finished.
I won't use the launch control to keep it fair.

I miss Heartland Park Topeka

Yes there are always going to be variances in dyno's from around the world.

But, some of us have been at the dyno where boosted Chevy's came damn close to the 1,000rwhp mark (with less boost than the above example) and the same day my friends KATECH 427 ZO6 put down 505rwhp without boost.

During the same dyno "event", stock 928's put down fully acceptable numbers for stock cars or those with X-pipes etc...

 

What Greg Brown does is truly amazing. He is getting tons of power out of a 35 year old design
that the factory quit R&D on over 15 years ago.
He and others have had to re engineer / overcome
a lot. Can't really compare the two.
The Chevy engine continues to evolve & has many
more builders / vendors working with it, plus a good
solid design as a starting point.
A friend recently bought an ls3 Katech long block
for his 05 c6 Corvette. It made 531 hp & 480 torque
on the Katech dyno prior to shipping-( engine dyno, not a chassis dyno.)
Installed, it made rwp 485 on a Dynojet
Long block cost well under $10k (all new parts- not a rebuild)

 

This is easy to predict the outcome...whoever gets traction first is going to win.

 

+1

The past 4-5 years we have seen the 928 performance mark jump light-years ahead of where it was sitting somewhat stagnant for almost 30 years.

Greg, Louie and others have always had the skills to make big HP, but it takes someone to come forward with the cash to make it happen.

The Chevy tuners benefit from millions of potential customers to buy their parts, they can gamble on the R&D costs.

 

So, we 928 owners are just more honest about our performance numbers?

 

No. Not to start a war...but what you are seeing is much more efficient compressors. The boost level for those dyno pulls isn't really relevant. As turbos get bigger, they get more efficient. A big turbo running at 5 pounds can make more power than a smaller turbo running double that pressure.

I'm building a LS1 based 6.4L engine with a GT4294R turbo. If that engine doesn't make 800whp at 15 psi I'll be seriously disappointed. Cram enough air into anything and it will make big power numbers.

 

HP really is a simple formula.....

1: displacement (more is always better)
2: airflow (cams-heads-intake-exhaust)
3: Boost
4: RPM

928 engines can be made quite large in terms of displacement...& can get good airflow, upwards of 330cfm....they also take boost pretty well....RPM is the weak point...they don't take high RPM well...which does limit their peak HP #'s.....

 

Well...JT's rear turbo (5.0 with 9:1 CR) made 615hp at 16psi........ And Colin is putting his aggressive cams into his 928.....and will add a rear turbo to that..and running megasquirt.... I expect some big numbers there too

 

Wait, are you trying to tell me that "X psi" doesn't always equal "Y hp"?

Nonsense.......

 

yeh what can be said, the Porsche engine has several design features that limit what can be done, without major expensive reengineering. the LSX happens to be quite a good primative tool.

At the end of the day, What are you going to do with 1000 hp, I had an exciting moment in my 928 when it lit up and stepped sideways at 70 mph, with its measly 340 hp. A 1200hp 7 litre twin turbo Monaro was in a local W/shop recently and the guys said it was undrivable, anything more than 1/4 throttle and it broke into wheelspin! a standard one is going to be easier to drive and quicker in most instances.

Look at what John Kuhn has done, that is dollar for dollar, the best thing for a 928. He has maximised the output from the stock engine without changing its parameters.

Cheers Roy