[wilkija]

Hello Everyone,

I recently went to a dyno after my mods and was extremely disappointed in the numbers. what came up was 373 HP and 382 torque. now for stock this is not bad but I would say I'm mildly modded. I am wanting to know if anyone has any ideas of what could be going on or has had the same issue. I already changed the O2 sensors out with no success. below is a list of mods and car, Johan tuned the car and I attached a picture of the dyno pull. thanks in advance

2007 charger srt8 6.1 in Texas

SRT MAX PLUS CAM
cold air intake
transformer shift kit
long tube headers
no cats with 3 inch straight pipe
180 thermostat
oil catch can
wideband O2 sensor

 

[Ddaddy]

I'd love to review it, but your pic is too small...

 

[wilkija]

I added the PDF of it let me know if this helps

 

[krautmaster]

If you did not have it on the SAME dyno before you did the mods, then the readings you have are fine...every dyno reads differently. You could take it to a different place tomorrow and it could show 50 more horsepower...or 50 less.

The dyno is only useful to make comparisons, and to do that you need a baseline.

 

[wilkija]

Your right! its just weird it was that low. And I did screw up and not dyno it stock. I just haven't seen any dyno numbers like this from anywhere on the net unless the cars are stock. I am going to try and take it to the track this week and see what it runs. I figured if I get anywhere under 12.7 its good depending on the 60 ft.

 

[tacamo01]

Dyno's do vary even the dynojets. If it is not properly calibrated and cleaned I have seen Dynojets that are lower in readings than the Mustang dynos.

With that said, see what your track times are. If they are not good or as you expected, then look at your exhaust set up. 3 inch piping is not recommended for that type cam. What type of Longtubes are on the car? You may have slowed the velocity down with that setup and may need to go back to a 2 3/4 inch exhaust. Your power below 4000 rpms looks normal for your setup. It is not climbing after 4000 rpms like you would see with that Cam and Longtubes. (From the dyno's I have seen)

 

[wilkija]

the long tubes are 1.8 inch primaries going into 3 inch collector. then out to 3 inch exhaust with magnaflow crossover resonator then just straight out the back. do you think maybe putting some mufflers back on would help? or reducing the pipe all the way back. Also didn't the car come with 3 inch exhaust stock? that is what the size of the stock collector was. with no reducer.

 

[wilkija]

Also here is a log of my last pull that I did for Johan. Maybe you can see something. I think it looks good except for my wide band readings and the small stall at the beginning

 

[tacamo01]

Are the primaries 1 7/8 going into the 3 inch collector or 1 3/4? There is a thread, I will have to see if I can find it on another Lx forum that discusses the importance of using the 1 3/4 inch and no larger than 2 3/4 piping out back. I do not believe that just putting the muffers back on will increase the velocity out which is what you want for the LT's. I am pretty sure that the 2012 +SRT's come with 2 3/4 inch piping from the cats back. Not sure about the 6.1L Srt's.

Could you post the data log in .log form? My dataviewer from Diablo will not read your attachment.

 

[tacamo01]

Another possibility that just came to mind is the gas. I remember last year when I was tuning for the longtubes I got a bad tank of gas just before the dyno session. I dyno'd around 25 rwhp lower than before and my AFR was all over the place. This time of the year is when the refineries are gearing up for the summer blend.

 

[wilkija]

Could you post the data log in .log form? My dataviewer from Diablo will not read your attachment.[/QUOT


the file is a ZIP you need to save it to your desktop and then unzip it then you can see the log. this forum does not let me post a .log file. I have been using shell gas for a while just because it is close, I usually like chevron. I wanna say the primary is 1 and 3/4. I'm pretty sure they came with 3 inch.

 

[tacamo01]

Could you post the data log in .log form? My dataviewer from Diablo will not read your attachment.[/QUOT


the file is a ZIP you need to save it to your desktop and then unzip it then you can see the log. this forum does not let me post a .log file. I have been using shell gas for a while just because it is close, I usually like chevron. I wanna say the primary is 1 and 3/4. I'm pretty sure they came with 3 inch.

It unzipped as a .PHP file on my computer. Try sending it to my email address:

[email protected]

 

[tacamo01]

Just found a thread on another forum WRT the 2007 Charger SRT. Hemi31 confirmed (Eric is the mechanic at BNFY that does a lot of Hemi builds)

SRT is 2.5"......R/T is 2.25"...........the SRT cat pipes are 2 3/4"

 

[neuroticdave]

I'm no tuner, but 3" exhaust sounds really big to me. There comes a point where a bigger exhaust begins to LOSE power rather than help gain. I remember I tried a slightly bigger exhaust on the Daytona and I could feel the difference, especially on the low-mid range. The same applies if it's straight pipe because, again, back pressure (among other things).

 

[wilkija]

Ya it sucks 3 inch just seemed standard with V8 muscle cars I guess. maybe adding heads and intake will offset the 3 inch pipes.

 

[tacamo01]

Ya it sucks 3 inch just seemed standard with V8 muscle cars I guess. maybe adding heads and intake will offset the 3 inch pipes.

I have seen the Stage 1 P/P heads and 6.1L Intake from High Horse Performance package pickup 40 rwhp on the SRT's. Great package for added power. But not with the 3 inch piping. Like said, IMO those 3 inch pipes are slowing down the velocity of the exhaust gases. Even if you add the heads and intake you need that velocity to help the cam/heads/intake expel the exhaust and make the engine work the most efficiently as possible.

Let me know when you try that additive in the gas tank and shoot me another 3rd gear WOT.

Here is a table from Hot Rod Magazine on how to pick the optimum pipe size after the Cats. They are just estimates but it gives you an idea about how much is too much.

Pipe Diameter (inches),Total CFM (est.), Max HP Per Pipe, Max HP For A Dual Pipe System

1 1/2: 171 78 155
1 5/8: 203 92 185
1 3/4: 239 108 217
2: 318 144 289
2 1/4: 408 185 371
2 1/2: 509 232 463
2 3/4: 622 283 566
3: 747 339 679

As you see the 2 1/4 piping is estimated to be good for 371 hp. (Charger RT 2011+ 370 factory)
2 3/4 piping good for 566 but the 2 1/2 only for 463 (Charger SRT8 2012+ 470 factory)
2 1/2 piping good for 463 (Charger SRT 6.1L 425 factory)

 

[wilkija]

So I should just get 2 1/2 pipe from the headers back

 

[tacamo01]

So I should just get 2 1/2 pipe from the headers back

Your SRT Cats are 2 3/4 inch I believe.

I just looked at what is available for the 6.1L and most all of the inexpensive catbacks are 3 inch piping. Corsa is 2 3/4 and a few others but very expensive.

Maybe you should shoot Ddaddy a PM and get his opinion on the piping. I have an RT and all the threads I have read say 3 inch is too much but there could be something different about the 6.1L that I am overlooking. Even the Hot rod mag says 3 inches is large but most all the aftermarket systems are indead 3 inches for your SRT8.

 

[wilkija]

I have no cats. so I would just take and buy some 2 3/4 inch pipe and weld it up. I had a magnaflow Cat back system on it before this and it was 3 inch. And my Cats bolted up to that.

 

[tacamo01]

I have no cats. so I would just take and buy some 2 3/4 inch pipe and weld it up. I had a magnaflow Cat back system on it before this and it was 3 inch. And my Cats bolted up to that.

I just did some research on the 2007 SRT8 and it comes with a 2 3/4 inch catback system. That explains why the aftermarket is selling 3 inch. So what I found out earlier on the LX Forum from Hemi31 is incorrect. The Dodge Press release stated 2 3/4 inch catback when the SRT8 first came out.

You could try putting your cats back on with the magnaflow cat back IF you still have them. Get the short term knock out of your logs, check the AFR again and then see what you dyno.

I would also call Stu at Inertia Motorsports and tell him about your dyno results and explain to him the mods and exhaust system you currently have. He is the expert on the cam you have and could better tell you about running with straight 3 inch pipes and no cats. He usually gets into the shop in Texas around 10am EST.