gimmeluvin

iTrader: (10)

Well this weekend I had my car retuned. I originally had a pt88 on this setup that made 690rwhp at 12 psi. I recently downgraded to a 76gts for quicker spool. It made 645rwhp at 12psi. That was pretty much all we could get out of it. It would not make more than 12psi past 4500 rpm. When we went up to 15psi it would make a much more aggressive ramp but starting bleeding off to to 12psi past 4500 rpm. My first thought was that the turbo seems to be maxed out. But this turbo is rated higher than 750hp even on a 347... My wastegate has a 7.5lb spring in in controlled by a greddy electronic boost controller. We tried bypassing it with a manual boost controller and it did the same thing. So im starting to think that that higher back pressure at higher rpms is opening the wastegate due to the 7.5 spring. Anyone have any ideas?!?!?! here are some of the dyno sheets...

gimmeluvin

iTrader: (10)

Both dyno sheets we were at 15psi... You can see on the second sheet how the boost falls off..

RealQuick

iTrader: (14)

Turbo isn't maxxed out.

What size wastegate you have?

gimmeluvin

iTrader: (10)

Turbosmart hypergate, I think its a 44mm.

NicD

iTrader: (7)

Yeah I've got a 76gts on my 347 and I've pushed 20 psi before but only run it at 18... I have a feeling it wouldn't be making much more power at 20 anyways. Regardless you have a wastegate spring issue, run a stiffer spring. Also, what size is your downpipe/exhaust? Sounds like it's got a fair amount of hotside backpressure.

gimmeluvin

iTrader: (10)

Yea im hoping its as simple as the WG Spring... Exhaust housing is 96ar. 4inch downpipe ending by the back of the tranny.

123quattro

You certainly won't have backpressure issues with that exhaust.

KILLER-LS1

iTrader: (18)

wastegate springs are rated at 1:1 backpressure ratio. If you have 2:1 backpressure, you need apx double the spring, or you need a good boost controller that can hold it shut. You will need to increase the duty cycle on your boost controller.

willizm

iTrader: (10)

Sounds like it might not be a backpressure issue. What size turbine wheel do you have? I have a tc78 with a 68mm turbine wheel that is my bottleneck on the exhaust side and that is with a 96ar and 3" dp. The springs are typically good for twice the pressure of the spring rating, however that is easier said than actually accomplished as the controller solinoid is working it's *** off to get it there. I would suggest going with a 10lb spring and see if you can push 15psi.

KILLER-LS1

iTrader: (18)

also, the turbosmart eboost 2 controller has compensation for boost dropoff. for example you can increase boost by xx% between 4500 and 7000 rpm to fix the drop.

gimmeluvin

iTrader: (10)

It has the standard 75mm turbine. Yea im going to try the 10lb spring. Just not sure when im going to be able have it tuned again. So im kind of stuck driving it like this... still a blast to drive tho!

gimmeluvin

iTrader: (10)

Thanks for all the feedback guys!!

68lsxc10

iTrader: (1)

Is there a big difference in spool time between the two? I have someone trying to sell me a pt88, and I am thinking that it would have too much lag for my setup.

gimmeluvin

iTrader: (10)

the 76gts definitely spools faster and sooner on a 347. pt88 would be fine with a stalled auto. My car is a t56 so the lag was annoying. I have a dyno graph showing boost and hp with the pt88 somewhere. I look for it tonight and post it.

Slow94Formula

iTrader: (18)

Good to hear it's spooling faster. Hopefully you get the issues worked out soon and can push it a little harder! Did you leave the turbo red? lol

gimmeluvin

iTrader: (10)

Thanks man! yea its still red.. I also have a polished cover too, i might run that one. But it doesn't really matter to me. you've seen under my hood, its not the cleanest setup!

Ryans99ls1

iTrader: (16)

that looks exactly like what my boost is doing. Ive got a manual controller on it but all turning it up does, is increase the boost spike and it eventually settles back to 9lbs. ive got a JGS 50mm right on the merge. Does having the (manual) boost controller farther away from the WG make it harder to control the boost ?

Nitroused383

iTrader: (10)

With a manual boost controller I thought you could only double what the spring pressure is in the waste gate? 7.5lb spring x 2 = 15 lbs so it sounds about right. Put a stiffer wastegate spring in.

Ryans99ls1

iTrader: (16)

idk about the OP, but my wastegate spring is a 9lb spring.. i can turn it up but it always settles back to 9lbs

simplysix

iTrader: (1)

Glad to see you went to DTM. thats who I had to mine. Brian knows his stuff