that sounds about right for the correction. 5000 feet is about a 15-18% loss anyway you slice it. sometimes the temp can bring it down, but I would say that you are in the right range for a GT with the screens removed. remember, with a vented air box, we got the same HP , but when we did the velociy stack adapter, we lost 5hp . removed it, and it came back. could only work with the non vented air box. next time, remove the top of the air cleaner and see what the numbers look like.

I was talking Z06 C5,so 330 to 350 plus is the norm to the ground.

Vipers, I was talking 450hp rated versions, like the GTS, etc.
I was at the dyno when the stock viper with only a cat back did 440 and 440 torque to the rear wheels. dont know the year, but it was the GTS I think.

mk

 

Don't know what the c5's and vipers dyno at but I do know what happens when you put them stock side by side at our local drag strip. I don't know what model the vipers were, they were both stock and they made the c5 look like a pinto with mono.

Jim

 

Stock ls1 c5's dyno at 285-295hp at the wheels all freggin day long. Ls6 c5's do anywhere from 340-350hp at the wheels all day long. A 400hp RT-10 viper will put down anywhere from 330-350hp at the wheels. At well running GTS model with put down 20 to 30 more than that. And the new 500hp viper is good for 420+. When you are talking about certain car's you need to specify mark jumped the gun and assumed you were talking about a ls6 not a ls1.

Btw very very nice number's. Considering its just light bolt on at this point you can be very proud of your dyno session. Now its time for some FI. Screw type(roots type) supercharger or turbo would be great. I am not a huge fan of centrifical blower's cause they are basically a turbo with a belt. You get the loss of hp that comes with running a belt driven blower so it costs you hp plus cen. blower's still have lag just like a turbo. Not to mention because of all of this they aren't as effecient and normally don't have near the powerband range that a turbo does. But, hey to each their own.

Grats on your #'s. Take her to the track.

 

The stock ss camaro with only the "super queit" blower made 420rwhp with 8 lbs of boost.I then put a comp cam 212/218 @50 thousands with a 524/529 lift in along with home ported heads ,Mac headers,z06 intack manifold,3.5 inch exhaust and guess what? I lost 3lbs of boost.This was because of the overlap of the cam and the better flowing heads and manifold.I then ran it at 5 lbs and got the 528 hp.This was with vortech s smallest pulley!I found a custom pulley and I am now geting my desired 8.5 lbsof boost.I have just installed a comp 220/224 529/534 lift cam and a 12 bolt rear end with 3.91 gears instead of the stock 3.42. The car is just crazy fast.I think I have finally found out what too fast is.I took it out to 2nd creek road racing course where my friend was running a gt1 viper.I was running p zero slicks all around and the car was almost uncontrolable.It was doing renditions of a john force burn outs along both straightaways.My speed at the end of the front straight was 9 mph faster than the gt1 viper!Then I had to brake and .Big problems

 

Sounds like a "Performance Driving" class might be a good investment...

 

Thanks for the details! So now let’s try to predict just how fast ‘crazy fast’ actually is horsepower-wise, since you haven’t dyno-ed it yet at 8.5 lbs of boost. I’m getting cabin-fever over here in the cold of Wisconsin, and need something ‘fun’ to do!

The following will be approximations only and represent best-case scenarios to keep it simple (..no thermal losses), but should suffice to at least get us some decent ballpark numbers to think about.

What we want to do is predict the engine’s final configuration horsepower numbers at 8.5 lbs of boost, assuming a manual transmission is used throughout.

The first statement says 420 rwhp was generated at 8 lbs of boost, so let’s ‘see’ what that engine did NA.

First let’s find out what the crank hp is at 8 lbs:

Crank HP = (rwhp) / (trans loss)
Crank HP = (420rwhp) / (.85) = 494 crank hp at 8 psi

So the engine is putting out 494 hp at the crank. Now we can use that number to calc the engine’s NA crank hp by using it's Pressure Ratio (PR).

Blown HP = (NA HP) x (PR)

Solving for NA HP we get:
NA HP = (Blown HP) / (PR)

But first, let’s find what the PR is:
PR = (14.7psi + boost) / 14.7psi
PR = (14.7psi + 8psi) / 14.7psi = 1.54 Bar

So our PR is 1.54 Bar, or in other words, a little over ½ an extra atmosphere.

Now we have everything needed to ‘guess-timate’ the engine’s NA HP:

NA HP = (Blown HP) / (PR)
NA HP = (494 crank HP) / (1.54) = 320.8 HP at the crank

And at the rear wheels we get:

NA Rwhp = (crank hp) x (trans loss)
NA Rwhp = (320.8 crank hp) x .85 = 272.68 rwhp


Alright, so now let’s do the same for the modified engine which puts out 528 rwhp at 5 psi. In other words, how much horsepower does the modded engine put out without the blower?

Crank HP = (rwhp) / (trans loss)
Crank HP = (528 rwhp) / (.85) = 621.2 crank hp (..nice!)

PR = (14.7psi + boost) / 14.7psi
PR = (14.7psi + 5psi) / 14.7psi = 1.34

NA HP = (Blown HP) / (PR)
NA HP = (621.2 crank HP) / (1.34) = 463.6 HP at the crank

NA rwhp = (crank hp) x (trans loss)
NA rwhp = (463.6 crank HP) x (.85) = 394.1 rwhp

So the modded engine if it were dyno-ed NA is predicted to put out 394.1 rwhp. The number appears reasonable considering that bone-stock Z06 LS6's dyno between 340 – 360 rwhp, and this engine has an LS6 intake, ported heads (..LS1?), a hotter cam and complete exhaust system.

Now we have what we need to solve what we’re really after, the numbers the modified engine is putting out at 8.5 psi. Using the result from above as well as the same calcs:

NA HP = (Blown HP) / (PR)

This time we want to solve for ‘Blown HP’, so we rearrange:

NA HP = (Blown HP) / (PR)
Blown HP = (NA HP) x (PR)

As before, we need to know the PR:

PR = (14.7psi + boost) / 14.7psi
PR = (14.7psi + 8.5psi) / 14.7psi = 1.58

Alright, we have it all to solve crank HP:

Blown HP = (NA HP) x (PR)
Blown HP = (463.6 crank HP) x (1.58) = 732.5 crank HP (..!)

At the rear wheels:

rwhp = (crank hp) x (trans loss)
rwhp = (732.5 crank HP) x (.85) = 622.6 rwhp (..!)

WOW!

Remember though, these numbers are a little optimistic since I did not calculate using density ratio, volumetric efficiency ratio, ideal temp gain, real temp gain, etc.

Sounds like a nice problem to solve, and one that’s relatively easy to do so with a brake upgrade.

Congratulations!


**EDIT**
Aw man, I just re-read the original post and saw that he's running 8.5 psi versus 8.0 (..I fixed those numbers) and a bigger cam! Oh well, the guess-timate will be bigger yet...

 

Interesting calculations.They are probably a little optimistic but its fun to read high numbers anyway.The shop with the dyno had a print out with a 99 ss with a similar engine setup as mine.I think it had a GM hot cam with a 525 lift on both intake and exhaust(need more on the exhaust)and a 218/227? duration at 50.Its overlap was 112 which is a little choppier than the 114 that my cam has and not as good for blower aplications.He also had an intercooled procharger with 8-9 lbs of boost.His numbers were602 rwhp corrected. I think his car is a low 10 second car at sea level and I have seen him run a 10.77 sec at Bandimer at an altitude of 5800 ft.I am looking forward to supercharging the 928 gt but I think that these cams have more lift and duration on the intake which I think is backward for a blown car.Any insight? Thanks

 

I ran 292rwhp with stock intake, and with the toilet seat intake, something like 299.

 

try and run with out the topcover and toilet seat. I bet you crack 300!

However, it seems the toilet seat works best with the stock air box and no mods. we lost 7hp. (as I REALLY wanted it to work!!) but without it, it ran stronger. again, I had some serious vents to the windshield too.

MK

 

I take it you mean the cams have a lobe seperation angle of 112 versus 114. But you are right in that all else being equal, the narrower seperation angle increases overlap and would make for a choppier idle.

As for which one is best for a blower application, a back to back dyno run with each one installed would be great to see and compare!

In the meantime though, when there is overlap, some fuel will flow out the open exhaust valve which certainly doesn't help power, especially at low speeds. However, that fuel performed a useful function by sweeping over the piston crown removing heat from it, as well as cooling the exhaust valve and combustion chamber as the charge passes into the exhaust system, all of which contribute to the reliability of the engine as another mechanism at work to keep detonation at arms length.

That's FAST!

I would have to say there's no need to worry about that since the 928 32v cams are extremely mild, even the 'performance' GT ones that you have. As a matter of fact, your GT is better equipped than the S4 based solely upon it's better/hotter cam. NONE of the 32v cams have ANY overlap at their rated 1mm (.039") of lift.

If you are still concerned, I would gladly swap my S4 cams for your GT's!

The only 'disadvantage' the GT has is that according to the factory brochures, the GT is 'guaranteed' to have the stated 10:1 compression ratio whereas the S4's compression ratio can be anywhere from 9.4:1 to 10:1. That 0.6 point of compression makes quite a difference and allows one to run more boost safely. But of course, one would have to measure it to be able to take advantage of it if the lower compression is there.

By the way, did you do anything to your SS internals? What compression ratio are you running?

 

The ss internals are all stock even down to the valve dimples that I left on the top of the pistons after a missed shift 15000 miles ago.The motor is bulletproof and has 47000 miles on it and has been supercharged for about 30000 miles.As far as the high compression of the gt motors,I dont think it will be a problem because of the altitude that I live at(9300 ft).Thanks for the Info on the overlap and the 928 cams.I wonder if advancing the intake cams and retarding the exhaust cams would held in a blown aplication?

 

The compression for the ls1 is 10 to 1. or 10.1 to 1, I cant remember which one. Also, the motor has been bulletproof but the rest of the drivtrain has not been and it has been an ongoing struggle to keep it alive with the horsepower.I have gone through 3 ,10 bolts and 1 ,12 bolt rear ends.I have gone through just as many clutchs and the t 56 transmission is making noise.I have also gone through several axles.I hope the gt does better from a high horsepower reliability standpoint.

 

Very impressive, especially considering it's a stock block!

You are right, and I was not clear. A 'verified' 10:1 engine can be supercharged successfully at any altitude. What I meant to say was that an S4 engine will be more forgiving because of it's moving target static compression ratio which can be less than 10:1.

I would have to say 'yes' since a forced induction engine is merely a reflection of it's NA 'counterpart'. If NA and dynoing reveals a horsepower increase as a result of re-timing the cams, those gains will be reflected when the blower is bolted on, and will make more power than before the change.

By the way, according to my spreadsheet calcs, your GT engine in it's current state of tune at 8 psi should put out 542.6 rwhp.
Well, admittedly the jury is still out.

The racer stroker guys have had big problems with drivetrains. I'm hoping the 'problem' is the stroker's big power-chunk delivery down low in conjunction with the big meats on back for hookup where there's no tire spin which really loads up the drivetrain. As you know, tire spin is really easy on a drivetrain, but obviously something to be avoided when racing.

On the other hand, a centrifugal's power delivery will be easier on the drivetrain since there's nowhere the large amount of torque down low, and it's power is spread more evenly across the top. However, it remains to be seen if that theory holds up on the track. This year I will be at the track doing as many DE's as I can at Road America, and we'll see what happens. I know DE's are not the same as racing, but at the very least, they offer a much more hardware-intensive environment than anything one can do on the street, legally.

Another issue to be aware of at boost higher than 8psi is head gaskets. All of our Wisconsin cars at 11+ psi have blown out the crappy original factory installed one, and we are now all running 'top-secret' ones the 951 and Import guys use in their mega-boosted engines. For whatever reasons, the factory original 928 head gasket does not age well and deteriorates.

 

Thanks for the information,especialy about the head gaskets.I am pretty sure that the head gaskets were already changed out on my car once upon a time before I owned it.I was not planning on exceeding 8 psi as I will be using pump gas only unless I race it which wont be more than 1 time a month. I am looking for "soft hp"from a centrifical blower because I dont want to consistently throw parts at it like the ss. Have you had drivetrain issues with your setup? You are running a roots blower Correct?

 

'Soft hp', you know, not a bad way to put it.

Negative on the roots as I'm running a Vortech SuperQuiet at it's max of 50k RPM. This spring I'll be running a T-Trim and more boost.

Here are some pics of the setup: https://rennlist.com/forums/showthre...g&pagenumber=2

As a matter of fact, that thread was started by 'Gretch' who is supercharging his GT with the same kit I'm running.

I haven't had any drivetrain problems related to the supercharger itself. I had to replace the clutch after I installed the Louis Ott X-Pipe as it provided enough extra torque to push the original 53k mile clutch over the edge. After I resurfaced the flywheel (..it had circular ridges like a Ruffles potato chip) and popped in a new disc and pilot bearing, I have had no slippage problems whatsoever on the street.

We'll see what happens out on the track though.