SeanR

I am hoping the ST will give me some more - must get that puppy back from Sterling 8>)
Roger

I am on Seans Computer

LI Steve

Wow - what a difference from my stock 86 Auto (which only put down 250hp/252 TQ)! That is awesome, and a great gain from the X-Pipe.

I always thought that HP and TQ were to be equal at 5252 RPM - It looks like on your dyno chart that they intersect at 4500 RPM. Is that possible???

Tom. M

Only when the scales on each of the axes are the same...

LI Steve

Ahhh yea - I see.

Been a long week...

Thanks.

928ntslow

Stock cams, Dave Lomis pipe based off of Louies design, but improved by Dave, no cats, just a swap done in a very short period of time depending on if you have a lift or not. With lift bars, the car was on the road in about an hour.

I know when when we ran the first session, Louie commented on the nice power the car was putting out. Of course I do maintain the car well, but I really can't speak for the internals as I have not done anything to them. Yes, maybe GT cams in the future, but we had to start somewhere to know what we were dealing with. I don't know what the difference would/should be as to compared to a Dynojet. All I know is Louie pretty much developed his monster on this dyno and Ken (Porken) worked on his 86.5 modifications on the same unit. There have been many cars in the PacNW on these rollers, so they would be able to verify if they had experienced more power than any other test equipment. I hadn't heard otherwise, so I expect the numbers are pretty close to accurate. It surely runs like a "summabitch". Maybe I am one of the lucky GTS owners out there with a well sorted car. I see no reason why these cars cannot achieve these numbers in stock formation.

PorKen

Verified with a 32V'r.

Tom. M

If you ax me... it is obvious the scale of the ax on the left is shorter

Louie928

I have always wondered about the "accuracy" of my dyno as compared to others. Sometimes, it appears to give high power numbers, but sometimes not. It depends on the car more than anything else. I've checked both my GT and S4 on other dynos and the results are comparable to mine. Some S4s will show around 270hp and others with some mods will show up to 300hp. Pretty standard I think. One variable I've found is the rear tires. I notice different power readings when I change tires. My GT gave the highest hp when I was tuning it with Hoosier "slick" track tires. I've never been able to achieve those numbers with other tires. Dunlop SP8000 tires cost 25 - 30 hp (5%) compared to the Hoosiers. Fortunately, they didn't last very long and the Goodyears I have now give better power, but not as good as the Hoosier slicks. I don't think there is any tire slip on the rollers. They are heavily knurled with the knurl grooves machined in, not pressed. I've tried it with the dyno straps very tight and moderately tight and not noticed any difference. Tire pressure makes a difference though. Pressure below 35 psi will cost a few hp as well as getting the tire hotter. The car has to be aligned on the rollers. If it is on crooked, that will cost. Run the car on the rollers with the rear straps slightly loose and front wheel chocked. The rear will move over to aligh with the front. Then tighten the rear straps. Drive the car on the dyno for a few minutes to warm up the dyno bearings, the engine as well as the tranny and diff and tires. My dyno temp/humidity/pressure sensor is a small module and I put it next to the intake air inlet. I figure that should better reflect engine atmospheric conditions than having the sensors mounted in a box on the wall where there is no direct relation to the air the engine is using. I check the actual air inlet temperature with another instrument to be sure the temp readings the dyno is using for correction are correct. I put a shield over the gap at the top of the radiator to keep hot air from blowing up and into the air inlets. An external squirrel cage blower forces air in the front air intake and out through the radiator. Normally the electric cooling fans don't come on. The electric fans will add a variable that can cost 5hp. I have another fan which blows air over the top of the engine. All this is to insure as much as possible that external variables affecting engine output are minimized. Which gear you use makes a difference too. On 5 spd 928s with 2.73 final drive, 4th gear will show less power below about 4500 rpm, but more above 4500 rpm than 5th. I think that is because there is more loss in the transmission in 4th than in 5th. As the tire speed (loss) is higher in 5th, then above 4500 rpm tire loss overcomes the more efficient 5th gear to show lower overall output than 4th. Auto trans cars and those with 2.20 final drive don't use top gear.

Setting the probable differences in dyno machines aside, the outcome is dependent on many factors beyond the machines. Trying for exact direct comparisons is really comparing apples to Amsoil.

Keith's runs were done in 5th gear and the compensation was to SAE specs on the charts. No smoothing on the curves. The shop temp was 90+F, humidity 20% and elevation 1350' ASL.

928ntslow

Thanks for the confirmation Louie. I think if anyone knew whether there was a difference in test equipment, it'd be you.

Louie928

Did you want to mention the nitropropane, xylene, and Rislone mix in the fuel?

ew928

So the squirminess of the tire carcass and tread blocks will affect peak HP and Torque readings on a dyno.
Interesting.
Energy loss to heating up the tire unit.

Putting shield on top of the radiator to shield intake from radiator heat is a cool idea, Dr. Louis.

drnick

nice to see these numbers from a GTS and to hear about whats involved with obtaining a reliable and repeatable result from a dyno machine. who was it that said there are lies, damn lies and dyographs?! im not surprised to see this result as although the rwhp differs significantly from mine the trend is the same.

hacker-pschorr

Louie brings out an excellent point, absolute numbers are never as important as the before / after comparison (from the dame dyno).
No matter how you slice it or calculate it, this is a solid 17.7rwhp / 21lb-ft torque gain with a simple bolt on.



I really like the dyno's where it's 30 degrees outside, blowing over the front of the car. WIth the temp/humidity/pressure sensor behind the dyno computer where it's nice and warm.

AO

+928

It's all about the before - after, not the absolute number... but it's nice to be able to say, "See that! 331RWHP! That's 376 crank HP! "

928ntslow

As I had tried to emphasize, that was the only real number we had to work with and it was the first run!

The whole reason for this test was to see what an X-pipe would do for a stock GTS. I was actually expecting higher numbers, but not complaining.

When I get back over there, we will try again and then I will come back and dredge up this thread.