I'll post the dyno later tonight. Installed some high flow cats today.

I went from 352 rwhp / 352 Torque to 352 rwp and 342 Torque. Lol, wth?

Did I just have a bad dyno or should high flow cats have this kind of affect on my car?

Anyone with FI loose HP or Torque after the install?

 

if you didn't have any cats before... but from the tone, i assume you had stock cats on.... then this would not be a good outcome.

m

 

Which high flow cat did you install?

 

Had stock cats before.

One thing I did notice is my origional 352 pull was done when the car was being tuned. We did 10+ pulls and it kept getting higher and higher numbers, even after the tuner had finished adjusting the car.

This time we did 3 pulls.......first pull: 340 rwhp, second pull: 342 rwhp, Third pull: 352 rwhp.

Hmmmm.

Even though I doubt anything is wrong with the car, I'll take it back next week for one more dyno just to make sure.


I was really expecting 10+ hp and torque.

 

your car was getting warm and loosened up internally thats why you keep seeing higher numbers the more dyno runs you do. Everything is gettin nice and lose, nothing wrong with it thats just why higher numbers the more you do. Do 68 dynos and on the 69th one you'll have 387rwhp "LICKED" foresure.........LOL, J/K......

 

Ok, I just scheduled 2 days on the dyno next week. I'll hit 387 for sure now!

 

Yeah...I think you had a weird dyno run. High-Flow cats reduce back pressure, which is always a good thing with a turbo. I dynoed my car with RT cats and stock exhuast and the TRQ was only 316. When I switched to the Evo2 exhuast, I hit about 335TRQ. Almost a 20lb gain! I also gained HP and TRQ across the entire curve.

 

I'll take the Crawfords if they don't help ya

 

Ive seen this happen a few times with people on the dyno, their numbers keep going up. I think it might be the stock ECU learning and adjusting itself for the available levels of air etc.

 

The ECU doesn't 'learn' during WOT, ie open-loop, operation. It operates based off preprogrammed values stored in the factory maps. Those values don't change.

As said above, as your tranny fluid, engine oil, bearings, clearances, etc. get warmed up, they lose friction/loosen up allowing better numbers. Also, the tires heating up/gaining pressure reduces rolling resistance between the tire and the drum allowing better numbers.

So, when you dyno, you need to keep making pulls UNTIL you either A)get two or three consistent pulls or B)power begins to drop due to heat-soak or whatever. Then just use the best run as your AFTER run. Otherwise, it's going to be too inconsistent to make any definite conclusions, since like in this case, you don't know whether you peaked or not yet.

 

So you can gain as much as 12hp or possibly more due to the reduction of friction in the drive train etc when everything gets warmed up? How cold was his car? Surely he drove it to the dyno and it would have been some what warmed up.

Wouldnt the warmed up tires have more friction increasing resistance between the tire and the drum? Wouldnt that cancel out any increase in pressure you would get from warmer tyres?

 

Yes, depending on the viscosity of the oil and how much it thins out in high shear, high RPM situations. Less viscosity, means less friction. Try throwing a 20W-50 in your car next oil change, I bet you'll notice. That's also a reason why they say certain dyno variations are negligible, because it's hard to know whether the mod added power or it's simply a variation in tire pressure, oil temp, gear lube temp, etc..

Driving to the dyno and then waiting for them to strap it down allows it to cool down. Oil temp needs to be up to normal operating temp, which takes longer then water temp, which could take a few dyno pulls. 2-3 is definitely possible.

Warm the tires, air inside expands, less tire/contact patch touches drum, so you have less rolling resistance. You're not heating tires up enough to get sticky, if that's what you're thinking.