The motor: LS vtec, built not sleeved, stock head and intake manifold
The turbo system : Rev Hard manifold, T3/04e brand new turbo 54 trim .63 a/r, open downpipe 2.5 inch, Hondata tuned by me, personally.
The problem: Car loses boost (correspondingly, hp and tq) beyond 6500rpm.
Things it's not: the turbo, the manifold, the wastegate, exhaust leak, boost leak of any sort, tuning, cam timing, ignition related components, boost control components, valve train and motor has perfect compression/leak down.<u>It is all there, checked and double checked</u>

Basically, we have what amounts to a Rev Hard turbo kit for a GSR, turbo correctly sized, and everything is in perfect working order. Beyond 6500rpm, boost begins to drop, and torque falls off quickly. It will lose 2psi each and every time, no matter what you do.

My theory: Charge pipe is too small. It measures 2.25 inch from i/c to t/b. This would explain the good midrange and fast spool, but as the motor needs more air up top, the size of the pipe chokes it off. The loss in power becomes more exagerated as boost is increased. Keep in mind, every B series turbo kit I've seen comes with a 2.5 inch charge pipe, even every AEM or similar intake is 2.5 inches or larger, hell for that matter the OEM pipe is 2.5 inch in diameter. Others are not so sure, but this car has ALWAYS had this problem, and we have changed, checked, swapped, measured or otherwise verified that every other possible part that could do this is working properly. The only thing that seperates this car from every other one I've ever done is the size of the charge pipe. Your thoughts?

 

dude, i've been wondering about that for a long time...what size pipe do b series kits normally have from the turbo to ic? 2 or 2.25?

 

Sharp bends, charge pipe diameter, and intake temps. Those are the things that are probably to blame here. Also could be a very small leak that opens up when the boost gets higher and hotter. Mmm very interesting problem I've never seen that one before with everything else checking out ok, but that's what I can think of currently.

 

the system has been pressure tested to hold 20 psi, it does not leak. Cool downs had no effect on it, and the piping is designed properly outside of the size of the charge pipe. Every B series kit I've seen has a 2.5 inch charge pipe, hell the OEM intake pipe is 2.5

 

top

 

Your initial theory should prolly be investigated. I mean depending on the pipe materials thinkness, the I.D. of your charge piping is prolly some where in the size of 2". And like stated before bending the pipe will change it's I.D. also, so at some places you could be choking down to smaller than 2" inside.....

 

You say its not the turbo, but I think it is. Its a 54 for christ sake! Put a 50 or a 57 trim on there. The 54 trim is the lowest flowing of the the 50,54, 57, and 60.. Look at the map and that trim makes no sense to me.

art

 

could be a longshot but have you tried checking for vacuum leaks?

 

Disconnect any lines to the wastegate (force WG to not open).

Connect boost gauge to the compressor housing BEFORE the piping.

This will confirm or deny your theory.

 

no way its the charge piping, thats deifnatley not possible. The laskeys went 9.40s on 2.25. When 2.25 reaches choke flow youll be around 80 lb/min of air. thatsl ike 750 hp.

id say go back, and check for cracks in the manifold, maybe the flange on the manifold is not perfectly flat, maybe cam timing is off, maybe the turbine has a crack (rare but ive seen it)

Also is the turbo brand new? Take the housing off and look at the wheel, sometimes a bad turbo has too much play in the shaft so the turbine wheel grinds itself down on the housing.

edit just reread things its not, nevermind that. its not the piping tho, add that to the things its not.

one more idea, maybe a bad valve spring ?


[Modified by FFgeoff, 2:09 PM 1/29/2003]

 

Sorry for the OT, but is the 54 trim really that bad? I'm still running that DRAG III 54 trim on my built 2L LS. Should I be worrying about it not flowing at higher RPMs?

 

It maybe the charge pipe, but what air filter are you using? My friend has a 92 turbo rx7 with a t3/60-1; he dyno'd 330whp at 5500rpm's but his power dropped sharply after that. It was his air filter that restricted flow; he changed it to a larger and better one and it fixed he problem.

 

I seriously doubt it is the charge piping. Many cars are running 9-10 second times pushing 5-650whp on 2.25" piping from the intercooler to throttle body.

Probably the turbo. Swap it out and see what happens.

 

I read what everyone said I must have missed the sizing of your turbo. Get that thing out of there. You're hitting it's peak way too early to make good top-end power.

 

I don't think it's the turbo sizing or the intercooler piping. Has to be something else. Something weird.

 

yep, no way is it the size of the turbo. its not gonna "loose boost"

how do the bearings inside the turbo feel?

if it were an exhaust leak your boost wouldnt be falling off, it would be overboosting but feeling flat.


[Modified by FFgeoff, 5:23 PM 1/29/2003]

 

put a drag manifold on it, then it will spike and solve ur problem

 

how do u know its not the wastegate? did u take it off and apart and inspect it? or swap it? its a long shot but so is everything else u r going to try. sounds wierd but id look at the wastegate.

 

dude its just the flux capacitor, swap a new one in and your golden. Although something wierd happens when you hit 88 mph so dont go that fast.

 

On a serious note have you thought maybe its either the spring in the wastegate or malfuncitioning boost controller?

Maybe a bug in whatever computer you're using.


[Modified by foozball-26, 6:48 PM 1/29/2003]

 

Just get a VNT and that will take care of your turbo and wastegate.

 

amen to that

 

As flow rate increases, so will the differential pressure (pressure loss) across any restriction.

So providing your turbo/WG/ BC ect.. is all functioning normal, then you are losing pressure between the turbo outlet and the TB. Check the turbo inlet also, any probs there will affect the turbos ability to pull air in... I know it sounds dumb, but..

As Dustin suggested, measuring the pressure at the turbo outlet - how much less is it than the TB? This # will tell you where your pressure drop is (if its in the intake plumbing)

 

This is a very good idea and I think i will try this.

It's not the turbo size - I've dyno'd at least 40+ turbo VTEC's using this exact same turbo, and it does not exhibit this behavior. It is a brand new turbo, used for 600 miles before being beaten on, and also on another car, it performed flawlessly. It's not the wastegate, we swapped on a known good one, same result. It performs this way regardless of b/c on or disconnected. All vaccum lines checked, and replaced. Boost gauge also checked. The valve train is all brand new, the motor is in time. Perfect leak down and compression numbers. I'm telling you guys, this is a damn head scratcher!

The air filter was a good suggestion, however, we removed it on the dyno, no power gain anywhere.

I need to post the dyno chart. The torque is right for the boost level, but say at 8psi, it makes 174 in torque, but only 212hp. That's not right. I've done GSR's at that same boost level that make roughly the same torque, but 250whp, it's like clockwork, can do it all day.

Exactly, which is why at wastegate pressure it only loses just a little boost, hardly a pound, but at 12psi it drops to almost 9! Hence why I think it is the charge piping, it is rather hokie looking. At this point, its either that or the intercooler, which is a Rev Hard unit, and I doubt it's that. We're going to build a new charge pipe hopefully this weekend and throw it on the dyno. Worst case is I'm proven wrong, which wouldn't be the first time, and it'll look a lot nicer. Best case is it's fixed

 

If you check the charge piping, and it's not that, could it possibly be somthing wrong with the intercooler?