Stock Hellcat Exhaust Manifolds VS. Kooks Longtubes - Any Power Gains?

[ostmike]

Unscientific testing on the same car, same dyno, same tune.

 

[Jack_Toepfer]

If 150* to 170*ECTs are worth 40 wheel… how bad is it at 200*?

 

[ostmike]

If 150* to 170*ECTs are worth 40 wheel… how bad is it at 200*?

I have to be honest and say something doesn't seem right here. This is why we repeated the hit (did two total hits) at 150 degrees just to confirm. I think the test would have been more informational if I would have done a second hit at 170+ degrees and if the same WHP was obtained as the previous 170 degree hit I could stand by the results and answer your question with more confidence.
What I can answer with confidence is the power gain with the headers in before/after tests at 150 degrees.
To avoid confusion we probably should have left the 170 degree hit out of the video but left it in so everyone could see what we saw and come to their own conclusions.

 

[Jack_Toepfer]

I have to be honest and say something doesn't seem right here. This is why we repeated the hit (did two total hits) at 150 degrees just to confirm. I think the test would have been more informational if I would have done a second hit at 170+ degrees and if the same WHP was obtained as the previous 170 degree hit I could stand by the results and answer your question with more confidence.
What I can answer with confidence is the power gain with the headers in before/after tests at 150 degrees.
To avoid confusion we probably should have left the 170 degree hit out of the video but left it in so everyone could see what we saw and come to their own conclusions.

I appreciate that you left it in!

I think it shows that you were willing to make 0 HP if you had to, but that you didn't overlook the variables at play between the before/after runs, and then you ran it again at 150*. It was the right thing to do.

 

[Speedy!]

Were cats used on both? I see them on the factory exhaust when dropped, but wasn't sure if they were retained with the headers.

 

[covidcommander]

I have to be honest and say something doesn't seem right here. This is why we repeated the hit (did two total hits) at 150 degrees just to confirm. I think the test would have been more informational if I would have done a second hit at 170+ degrees and if the same WHP was obtained as the previous 170 degree hit I could stand by the results and answer your question with more confidence.
What I can answer with confidence is the power gain with the headers in before/after tests at 150 degrees.
To avoid confusion we probably should have left the 170 degree hit out of the video but left it in so everyone could see what we saw and come to their own conclusions.

Can you repeat the test at 170 and 200 and see how it effects the hp?

Also heard if the trans is cold it won't run at full power

 

[Unholy707]

Can I ask you a question @ostmike? How close was the passenger side header to the rib on the shock tower? I installed the same headers and I have about 1/8th of an inch clearance. I cut some out of the rear rib because it was actually making contact. I also have your 1/4” spacers to drop the subframe down. I feel like if I didn’t have the subframe dropped the clearance would have been worse

 

[Linda's Hell Cat]

Can you repeat the test at 170 and 200 and see how it effects the hp?

Also heard if the trans is cold it won't run at full power

About the Trans, that is correct.
I personally when dragracing like my Trans Temp at 170 degrees. Some will start lower, but a good friend of mine said the 170 temp is also a safer start temp for the Trans.

 

[EricG]

About the Trans, that is correct.
I personally when dragracing like my Trans Temp at 170 degrees. Some will start lower, but a good friend of mine said the 170 temp is also a safer start temp for the Trans.

I thought you just want the trans fluid temp to 120, takes it a while to hit 170 if you are starting off cold.

 

[Linda's Hell Cat]

I thought you just want the trans fluid temp to 120, takes it a while to hit 170 if you are starting off cold.

130 would be the least temp to start off with, but I have a friend that told me 170 is best for the Trans itself.
You definitely will see a difference in your ET if you just start off with a cold temp. When I didn't know about Trans temp, I would say it takes me 3 times down the track and I would have a better ET each time.
Now I make sure my Hellcat is heated and ready to go.
I don't want to change this thread about the Trans instead of what the post is about.

 

[ostmike]

Can you repeat the test at 170 and 200 and see how it effects the hp?

Also heard if the trans is cold it won't run at full power

Unfortunately that ship has sailed and the car has been further modified as you will see in upcoming videos.
Trans temp is not really relavant in these application as long as the tune is properly modified to NOT limit torque during low temp situations. I would not run a trans with 40 degree trans fluid temps. However, it is not unusual for us to go to the line with trans fluid temp at 100 degrees and after the burnout the temps are 120. For all of these tests the trans fluid was between 108 and 118 degrees Fahrenheit.

Can I ask you a question @ostmike? How close was the passenger side header to the rib on the shock tower? I installed the same headers and I have about 1/8th of an inch clearance. I cut some out of the rear rib because it was actually making contact. I also have your 1/4” spacers to drop the subframe down. I feel like if I didn’t have the subframe dropped the clearance would have been worse

I am going to let Micah address this question and our experience with these installations. You are correct in stating that this tube is tight and in some cases is touching and is audible. Micah will explain what he does to resolve.

About the Trans, that is correct.
I personally when dragracing like my Trans Temp at 170 degrees. Some will start lower, but a good friend of mine said the 170 temp is also a safer start temp for the Trans.

It is possible that warmer temps would be better for the trans but cooler temps (within reason) are not going to impact performance if the tune is setup properly. Additionally trans temp is extremely difficult to manipulate in these applications and I suspect a very wide range of fluid temps are acceptable.

I thought you just want the trans fluid temp to 120, takes it a while to hit 170 if you are starting off cold.

See above and you are correct.

For reference, on our track car we have an external transmission cooler that we hook up as soon as we return to the pits. We aim for ambient air temps for the fluid temps (generally 80 degrees) when we go to the line for our next pass.
It may be apples to oranges but thought it might be informative.

 

[Unholy707]

Awesome! Yeah, I’ve been trying to find info on what people do. I think most just don’t notice. Appreciate the insight