Question Reguarding my Recent Dyno

[10secdream]

I dynoed my car a few weeks ago and I am still puzzled why my hp drops off significantly after 6800 rpms. The cams in the car are Jun 272 exhaust and Jun 264 on the intake. Cam marks are pointing straight up and the crank is at zero. I do not have gears but most guys leave them at zero anyways.

I have a couple ideas of what could be the actual issue but I am looking for other suggestions. My first thought was a major boost leak or my tune. Since then I have fixed both and my fuel map still says that power is dropping off. Reason I know this is at 6800rpm I have to take out a portion of fuel to keep my AFR at 11-11.3.

My first idea is that the turbine AR is too small and is thus restricting flow. I guess it could be my exhaust but I am running a 3inch downpipe to the BIC 3 1/2 inch catback.

My other idea is something is not right with the cams but there is not many ways to mess up cams. Even with a tooth being 1 off the car would run like junk.

Any suggestions?
BTW the turbo is an Apexi IHI C7(66mm) and I have no clue how big the exhaust side is. I get 20psi by 4400rpms.
Maybe it is just me but the torque curve is pretty impressive and seems to hold on for a long time.

 

[Turbo Drifter]

What size intercooler and piping do you have? Also try taking off the inlet pipe and filter to the turbo to see if that makes a difference. On my IHI RHC7 it was worth about 20whp lol. If you look on the exhaust housing you should see a size marked on it, mine was a P20 I have also seen a P24 and a P18 all for the IHI C7. Have you tried playing with the timing were the power starts to fall off? it sounds like a flow problem but its worth a shot.

Jeremy

 

[10secdream]

I have an ARC Intercooler with 2.5" outlets in dimensions 18x12x4 with 2.5" piping. The piping is the shortest I could mount it and has minimal bends. I will try just running it with the filter on and go from there.

As for timing it increases as the RPMS go up. Just for reference I think my timing starts at 17 and goes to 19 at my redline in my powerband.

I will check to see what my exhaust housing says but it does read C7 on it. I can't see if there is something under it but there might be.

I agree that it does seem to be a flow problem and I think the issue is with the turbo somewhere.

 

[10secdream]

Any other ideas?

 

[suprahero]

I would think the the AR is too small also, but with a smaller AR it seems you would hit boost a little quicker than what you posted.

 

[10secdream]

Turbo Drifter when did you hit full boost by on your IHI RHC7 setup?

 

[Turbo Drifter]

Turbo Drifter when did you hit full boost by on your IHI RHC7 setup?

I cant remember off the top of my head but I think about 5k. It was quite laggy.

 

[10secdream]

Ok well this is starting to make sense now. I get 20psi by 4400 rpms with cams. So my AR must be smaller than yours. That would explain why my turbo falls on its face by 6800 rpms. Well time will tell when I get a new turbo.

 

[WeDgE]

66mm turbo still shouldn't fall on it's face @ 6800rpms on a 2.5L though...?

Have you played with timing at all?

I vote for increasing IC piping to 3".

 

[10secdream]

66mm turbo still shouldn't fall on it's face @ 6800rpms on a 2.5L though...?

Have you played with timing at all?

I vote for increasing IC piping to 3".

I agree it still shouldn't fall off at 6800rpms. Should I just change out the cold side or the hot side as well? Will it still be a restriction being that the end tanks are only 2.5"?

I can start playing with timing a bit and see what happens.

 

[OneJSupra]

I agree it still shouldn't fall off at 6800rpms. Should I just change out the cold side or the hot side as well? Will it still be a restriction being that the end tanks are only 2.5"?

I can start playing with timing a bit and see what happens.

Lots of performance shops here in Fl use larger intercooler pipes out the cold side. I ran 2.5 hot and 3" cold.

 

[RacerXJ220]

Take a pic of that turbo, let's see it!

You can also try removing your intake to the turbo on the dyno and see if the pipe is a restriction.

The boost doesn't drop does it? Maybe a weak spring?

You should have no problems with 2.5 in/out turbo to TB for that power. You should clear a lot more power with 2.5 inch pipes.

 

[10secdream]

Well the first hit the boost spikes about 2 psi and then it settles and then the manifold starts to creep. So pretty much it goes 24psi at 4500 rpm then 22 psi from 4500-6500 and then from 6800-7500 it creeps to about 25 psi.

 

[10secdream]

Also the turbo is not clocked like that anymore.

I just thought of something and the boost starts to drop off where the turbo starts to creep at 6800. I am willing to bet it might be in my tune then.

 

[foreverpsycotic]

What are you tuning with?
Whats your timing?
AFR?

 

[Tim]

Were the cams shimmed properly when installed, cause the valves might not be closing all the way on the compression stroke. Also it is always a must to degree the cams with adjustable gears when using different cams especially with 272's-

 

[10secdream]

What are you tuning with?
Whats your timing?
AFR?

I am using the Stinger EMS. Timing was around 17 degress at 22 psi. From 6800-7500 my timing was around 16 degrees and boost increased from 22-25. I have since changed my timing and it starts at 17 and ramps to 21 by redline.

AFR was around 11-11.2 at 22psi. My AFR from 6800-7500 was around mid 10's. I am using a fairly large methanol injection nozzle so my AFR is leaner in reality.

I really need to get back on the dyno since I addressed the issues with my tune and now I am just speculating what could be the problem.

 

[10secdream]

Were the cams shimmed properly when installed, cause the valves might not be closing all the way on the compression stroke. Also it is always a must to degree the cams with adjustable gears when using different cams especially with 272's-

I might just double check the shims to make sure they are within spec. I am still on the fence if degreeing is worth the time. I have not seen a lot of information saying that degreeing gives a significant gain. It might be needed in my case since I am running a staggered cam setup?