2004 Cobra

My bone stock dyno numbers were 362 rwhp and 358 rwtq. The only other modification has been an SLP Cat Back. I've got just over 16K miles on it now and am still using the original air filter. My numbers today were 413 rwhp and 390 rwtq. That is a net gain of 51 rwhp!!! I have never heard of anyone gaining that much with no other mods. I'm so surprised that I want to have it dyno'd somewhere else, but there are a few guys who dyno'd today and got the same numbers from the last time they dyno'd and they haven't made any changes.

Anyone see that type of gain? Thanks Mustang Tuning for selling me this Cat Back!!!

 

no way, couldnt be. that much of gain is inaccurate. Scan your dyno and post it on here so that we can see and might see why it is off. what weight did you use?

 

your first dyno numbers seem awfuly low i bet something was wrong witht he first one.

 

Something is not right. I think the firt one is low. car should have dynoed around 385 stock I believe. The SLP Catback has shown very nice gains on the cobras. 20 rwhp I think is realistic.

 

My response was exactly the same as yours. Infact, I came right out and told them that there was something wrong with the dyno. 362 rwhp bone stock is not an off number. If you go to svtperformance.com and follow some of the numbers posted there, it is definately in the ballpark.

Few things to consider here. best 1/4 time stock was 13.2 and with the SLP I've run a 12.7. I thought that was a heck of a jump. I'm going to have the car dyno'd again somewhere else to verify this 400+ number. Because like all of you, I can't see a catback giving me 50 rwhp. BUT, the only thing allowing me to think the dyno was correct for both runs is that we had a club member who dyno'd his car the same days I did both of mine. He hasn't done anything to the car since the last dyno and his numbers were the same.

So if the dyno is off, then there should have been some change in this other guys numbers.

Here is a picture I took of the graph because I knew this post was going to cause debate and probably some to call me a liar. I have no connection with SLP other than I bought one of their products. I installed the exhaust myself so the dyno garage stands nothing to gain by increasing the numbers. Bottom line is that I'm as miffed by this as everyone on this one.

 

Was the car dyno'd at the same place with the same dyno ?? Ive heard Mustang Dyno usually show about 20 less rwhp than a DynoJet...

Oopps... u post the graph when I was typing... a half second gains is also a ;ittle hard to believe from just a catback, but if so thats great for you !!!

 

Same place. Same dyno. Same car. Different exhaust.

 

Here is a vid from my first dyno (362/358) and yesterday (first run 413/390, second run is 411/392).

I wouldn't have believed it except everyones numbers appeared to be good on both days we dyno'd. If there is a problem with the dyno, then it looks like it is only happening to my car.

Please right click on the link and save the file.

musthaveperformance.com/videos/51hpGain.wmv

 

The 1/4 mile time i bet money is from you learning how to drive the car better (no offense ment) that car stock will go mid 12's.

 

not with stock rubber ive seen plenty of stock cobras stay up around 12.9 and 13.1. everytime they launch the rear breaks loose on em. stupid irs

 

Freind of mines went 12.4@114.5 with only a flowcrapper catback and airfilter. stock everything else and at Orlando Speedworld where they dont spray VHT on test and tune nights.

 

I don't think I'm qualified to say I'm a great driver, but I'm not terrible. The fact I weigh just over 300lbs tells me that there are few tenths that might have come off if I was down to fighting weight. Yes, the IRS does present lots of issues when launching. I had a very tough time just getting a 2.0 60' because the car really wants to break loose out of the whole. So I'm sure with a bit more practice, I could get my numbers down a bit more.

When all is said and done, no matter what the numbers are, I'm very happy with the car and the power. I'm still looking to dyno the car again at a different location to verify the numbers.

 

Good God almighty your speedo climbs like my Tach does...hate you 04 cobra owners...all of yas.

 

Don't hate. Just trade your GT in like I did. I had the same car and decided to get a SC'r with a warranty. This month the car payment won't be so distasteful with that dyno result.

 

How long ago did you dyno it before?

Break in can have a huge impact on numbers.

 

Official word from SLP is that they have never seen the results on any car they have tested as I have. They are offering to look at the dyno sheets to figure out what may be the cause, but they feel 15rwhp is where I should have been.

I'll keep everyone posted as I get the info. Here is the info I have right now.

2004 Cobra

Stock Dyno: 10582 miles, 362 rwhp 358 rwtq, 13.2 @ 107 1/4 mile, 70 degrees

SLP Catback: 16200 miles, 412 rwhp 390 rwtq, 12.7 @ 113 1/4 mile, 55 degrees

Both dyno's were taken at the same shop on the same dyno by the same person. No other mod's have been made.

 

the dyno is just weird, but like i siad i bet most (not all of it, as the catback did help some) of the 1/4 difference is from you learing to drive the car better. also the weather had a large inpact on your 1/4 mile as blown cars love cold air even more so than n/a ones like mine. good tie either way. whats your 60"s like?

 

the 70 degree and 55 degree temps are the difference supercharged motors love cold air its like having an intercooler and you cant compare numbers from a different dyno they all very chasi dynoes are good for tuning and checking gains from mods

 

But does the weather really matter? I mean, isn't there a correction that is made to take into account temp and humidity?

 

yes their is but a supercharged ( or turbo car ) are affected by tempeture more than a naturaly aspirated motor cold air usualy means that there is low humidity as well so you get a colder denser charge this is perfect for any car. but when you compress the air it heats up so on a cold day your compressing the colder denser air so you have less heat and even more air compressed so you have the same boost preasure or lower with a larger volume of air The corection factor would be based on n/a motors. becuase you can have supercharged and turbo setups of diferent varieties ie intercooler non intercooler ive seen stock grandprix gtps run 14.5 in cold air vrs 14.9-15.00 thats almost 5 tenths my n/a car only picks up 2-3 tenths when its cold out Its a bigger benifit for forced induction cars to run in the cold and nitrouse cars like it when its hot

 

I'll buy that. Sounds logical and makes sense. But I think there is a lot to say in this picture as well. I babied this car for the first 1000 miles. I didn't once get into the boost until after an oil change and 1000 miles on the car. I made 8 passes at the track to get some times. After only 12000 miles on the car, this is what the mufflers looked like when I took them off. That isn't mystichrome paint, but were the hot spots in the stock mufflers.

 

the more power you make the more heat you make i have a trans am (like the bandits but gold) and i warmed the engine up to change oil and when removing the drain pulg i hit the exausth no headers and i touched for less than a second ive got a scare from the 3rd degree burn i recived and all it did was sit and idle

 

I've worked in a paper mill once. They have pipes there that need to cool for 2 days before you can work on them. Well, after the two day cool down I went to working on one and my forarm brushed against a bolt and I instantly had a blister the size of a nickle. Hot things can do that.

But the point here is that if the mufflers on a stock car with only 12K miles on it look like that, then they had to be a huge bottle neck and may have freed up more than the usual 20 rwhp.

 

For those who are interested in SLP's response:

"After further review and also speaking with our engineers here is what I come up with regarding your SLP Loud Mouth exhaust and the Big horsepower gains you encountered.

The temperature difference is almost 25 degrees ambient temp. This causes an even greater (about double) temperature difference after the supercharger compresses the air.

Yes the dyno corrects for the ambient temperature but only the ambient temperature. When dealing with a supercharged engine there are actually 2 different atmospheres. One being the ambient atmosphere, and the other being the compressed "supercharged" atmosphere.

A difference of 25 degrees ambient is about a 50 degree difference after the air is compressed by the supercharger, and can not be corrected by the SAE correction factor. This is the reason you have such a large power gain between the two days!

You can quantify this further by running at the track with your current set up in the middle of the summer then in the fall and the car will be completely different.

If you want to find out the true gain of the cat-back on your vehicle you will need to do same day testing. A pull with the cat back, swap the system, then a pull with the stock setup. Then you know the true numbers
I hope all this makes sense and is helpful.

Sincerely,
Kevin "

 

I also want to add something about SLP.

As a Mustang owner I think we can pit ourselves against other performance cars and the rivalry can go far beyond that of who drives what. SLP has been the main aftermarket provider for GM machines and I think many of us saw SLP get into the mustang market only for the need to stay in business after GM axed the SS and TA. I for one will have nothing but good things to say about SLP. Their product performs as it should, looks great, sounds great (just my opinion), and the quality appears to be there. Since my dyno, I've sent several emails to them and they have taken it upon themselves to look into this and try to help me make sense of it all. I for one appreciate someone who'll give me some time out of their day to help me out. I hope every damn thing they make for GM breaks because what they did for me works just fine!