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What's wrong with my dyno numbers?

  • Wrong grade tune

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  • No performance exhaust + larger tires = 30 less hp

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Discussion Starter #1
So at our GA Chapter Dyno day, I was hoping (and expecting) to get around the 190-200 mark with intake, tune, and gutted cat. Instead, I got 170ish. Needless to say, I was very disappointed. The part that really confused me was that J-Bo pulled around 206 with nearly the same mods... Here's the rundown:

J-Bo (xtreme)
3.5L Auto transmission
gutted cat
premium tune
K&N FIPK
GM Performance Parts exhaust
206.8 WHP -- 206.9 FP

Me (z85)
3.5L Auto transmission
gutted cat
premium tune
K&N FIPK
170.4 WHP -- 193.2 FP

Now, since J-Bo is running smaller tires (i think they're 245's...) and has an exhaust (I'm running 30" tires btw), does that make a 30 hp difference???

So there are 3 scenarios that could have made this big of a gap (vote it the poll)

1) I originally asked for the mid-grade tune, then made a note on the order form to do premium instead. Accidentally gave me the wrong tune? Not blaming PCMforless here, just speculating

2) No performance exhaust + larger tires = 30 less hp

3) I didn't hit the gas hard enough when I got to 3rd. (it was my first time doing the dyno)

So my next plan of action is to drive up to Dalton and do another dyno run, except get J-Bo to do one of the runs.

Whaddya think people?
 

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Tires can make a huge difference. I'm currently running a 33" tire which is about 8-10% larger than the stock 31" tires. This means that my power output will read 8-10% LOWER than a truck with exactly the same mods running a 31".

Factor in the weight difference ( stock generals are about 36lbs and the BFGs I have are around 54lbs. ) and you get even more of a difference.


All possible reasons.
 

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Xtremes have more power than all others...thats why they call them Xtreme


















Just Joking, I would say it would be a combination of the tires and the exhaust.
 

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I've been looking for the article, but I cant find it...tire size will not effect dyno numbers THAT much; unless your stock tire size was a 155-80-13 and you went to 22's. Some engines react differently to mods, even if it is the same type of motor. I've seen it before. It could be the tune. The only way to know would be for yall to swap ecu's and try it again.
 

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Im gonna have to go with #2. If you look at your torque from your run, its up at 193.2 FP. Factor in the weight of the larger tires, the size, and the lack of a performance exhaust, you're looking at a decent decrease in HP. I think all it needs is a good exhaust system and you maybe looking at gaining at least 10 horses back.



FYI... You can't lift it 6 feet and outrun a Lambo at the same time. Just ain't gonna happen. :lol:
 

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You have an automatic...that is easily chewing up 5-8% of your power compared to a manual.
 

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It's the same for corvette also, they all vary in power.

My stock 06 346a6 vette numbers where 346hp and 348ft lbs, after doing AR headers and tune, i was 376hp and 375ft lbs, another guys vette same year and same trans was about 30hp lower with the same mods.
 

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Your rear gearset is a big determination of how much power gets to the pavement, if his is a 4.10 and yours the 3.73 he will definatly put down better numbers.

I was wondering have they made a set of headers for the colorado I5 yet? Figure a cold air, and an exhaust with headers and keeping the stock cat in place would get you a decent 20 - 30 hp gain with the right tune at the wheels.

Also being a smaller engine not a V8 you wont get the bigger power gains as you would with a I5 or I4. Well not without some sort of forced induction.
 

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The rear gears are taken out of the equation.....
 

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tire size + diff tune + exhaust

put on his rear tires when you go back :D
 

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OffroadJunkie84 said:
Your rear gearset is a big determination of how much power gets to the pavement, if his is a 4.10 and yours the 3.73 he will definatly put down better numbers.
actually a car/truck with 4.10 gears would dyno less hp than the exact same car with 3.42 gears.
 

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Dyno racing is a tough sport. How do you even know there is anything "wrong"? The dyno should be used as a tool for determining the effectiveness of mods relative to yourself. Don't get caught up on the actual number.

-Geoff
 

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SomeGeoffGuy said:
Dyno racing is a tough sport. How do you even know there is anything "wrong"? The dyno should be used as a tool for determining the effectiveness of mods relative to yourself. Don't get caught up on the actual number.

-Geoff
Ding ding ding! Winnar winnar winnar!

The first question that should have been asked in this thread is this: what type of dyno was used for both trucks?

Different types of dyno's give different readings. They also have differen't outputs for the type of correction factor which will change #'s as well. Since we don't have a baseline for either truck there's really no way to know if you're lower/higher than you should be.
 

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brakenit said:
The first question that should have been asked in this thread is this: what type of dyno was used for both trucks?
they had a dyno day, both trucks were dynoed at the same place and same day.
 

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twopoint8 said:
brakenit said:
The first question that should have been asked in this thread is this: what type of dyno was used for both trucks?
they had a dyno day, both trucks were dynoed at the same place and same day.
Ahh, ok. Somehow that managed to slip through the crack between my ears. :lol:
 

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twopoint8 said:
they had a dyno day, both trucks were dynoed at the same place and same day.
Did they line them up and see who was actually faster on the street? That would be good info too.

-Geoff
 

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grandmastrblastr said:
3) I didn't hit the gas hard enough when I got to 3rd. (it was my first time doing the dyno)
After reading your post again I realized I missed this as well. What do you mean? Did you not have it at full throttle for the entire time they were recording?
 

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brakenit said:
grandmastrblastr said:
3) I didn't hit the gas hard enough when I got to 3rd. (it was my first time doing the dyno)
After reading your post again I realized I missed this as well. What do you mean? Did you not have it at full throttle for the entire time they were recording?
That could be it.. :lol:
 
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