</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by cablebandit:
<strong>My normal spool time starts at 2800 and I have 13psi by 3300. Now the changes I have made.....advanced 01 zo6 cam 6 degrees. Added 3" downpipe and 2.5" crossover pipe. My boost starts at 2800 still but doesnt reach full 13 psi till like 4200. A big noticeable difference. I expected the bigger downpipe to lower spool time so I am thinking the 6 degrees advance on the z06 cam is the problem. Any idea why that would be?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Turbos like to see velocity on the turbine wheel. But they hate exhaust backpressure after the turbine wheel. So, opening up the exhaust with a 3" downpipe was a great idea. But maintaining a small cross-section on the cross-over, was the way to go. Think of it this way, it follows the same rules as a good street port on a head... You're after smooth, mandrel-bent curves for a good exhaust velocity. Smaller is better on the cross-over as long as it meets the need of the turbo size. OK?

As far as the cam goes, I am admittedly not well versed in the FI results, but my guess would be that bringing the peak VE (which occurs around peak torque) down should bring the peak efficient exhaust gas velocity down with it. That, it seems to me, would be good to get the spool RPM down, based on the yammering I wrote above.

So I think the cam advance was a good step. I think it was the cross-over mod that killed the improvement. Put the original cross-over back on, and see what happens. REMEMBER, only one change at a time! And let us know. I need a score, I'm depressed about waiting for the LS1Motorsports Stage II... <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />

And then again, I'm an idiot, so go figure.

SC

<small>[ August 25, 2002, 01:13 PM: Message edited by: SS00Blue ]</small>

 

hMM...OK I think I will wrap the crossover to keep some of the heat in it for velocity. It is definitely faster once the turbo spools up tho. I am now maxing out the maf where I never did that before. Advancing the cam gave the car a better sound and a little N/A back on the bottom end. It's only a couple of hours to zero the cam so I may try that after i see the result of the crossover being wrapped. I need to look at the a/f again now.....it could be pretty rich down low and that would affect spool time as well.

 

Wrapping the cross-over is cool... but it doesn't cut down on the cross-section. Remember that the size of the tunnel counts... I mean that air slows in larger confines. Wrapping isn't a bad answer, but velocity is best suited to smaller cross-sections.

SC

 

sunce spool rpm has changed, I'm gonna lean it out some under 4000 and add some timing back. I'll report back. if this doesnt work, I have access to a BB t-70.....i think I can live with this spool time if the upper hp is there....need to go to a dyno

 

hey cable some guy on bfbody want to talk to you I was going to tell you when you got in he listed his #.

 

Well forget all that....I fixed a leak I had between the manifold and turbine housing and now its back to normal. I am very pleased with the car at this point. It is running very well on pump gas. I need to get to a dyno and wideband again. My hp curve has changed and now I need to work on a new timing curve as well. There is one more small leak i will fix in the morning. Afterwards, I need to still wrap the crossover.
Thanx for the help guys.....I severly underestimated the effect of an exhaust leak pre-turbo.

 

The stock cam for a turbo is better. The only way to go with a new cam if you have a turbo is a custom grind turbo cam. CAll up any cam company, they will be more than happy to help.

 

My normal spool time starts at 2800 and I have 13psi by 3300. Now the changes I have made.....advanced 01 zo6 cam 6 degrees. Added 3" downpipe and 2.5" crossover pipe. My boost starts at 2800 still but doesnt reach full 13 psi till like 4200. A big noticeable difference. I expected the bigger downpipe to lower spool time so I am thinking the 6 degrees advance on the z06 cam is the problem. Any idea why that would be?

 

If you are looking at cams take a look at cam motion or turbo people. Only thing with turbo people is you will not get a cam card.

Steven

 

Man those little things can kill you, like leaks, glad to see it was somthing "simple"

How did you route your 2.5 crossover? did you go around the front of your engine or did you try somthing diferent. im still gonna go right around the tranny with mine.

if i could just get it done.
im now waiting on my heads to come back, getting valve job and springs installed. <img border="0" alt="[boring]" title="" src="graemlins/gr_zzz.gif" />

 

The guy went under the tranny with the crossover. We moved the wastegate to the passenger side on the crossover. Ideally it needs to be on the manifold to relieve pressure from both sides but it was working like this before so I figured what the hell. I almost had the wastegate dump to atmosphere but the welder was concerned with a fire while using the 2 step.
He didnt have a mandrel bend machine so the crossover is a lot of cut and splice like the downpipe. Once it is wrapped, it will look mandrel bent <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> I am playing around with 12 psi right now on pump gas and no knock. Once I'm confident everything is ok, I'll see what the limits are. Be warned...dropping the compression and a bigger cam is gonna be damn noticeable on your bottom end.....keep that in mind. I almost wish i had kept the stock cam or went to the smaller 01-02 ls1 cam

 

i wonder what the 224-114 cam will be like.
if it is real bad im thinking of going with 3.73 gears. I think my CR is a little higher its real close to 9.0:1

And get those pics sent id like to see them.
sounds like you got your exhaust working out.
i like the idea of the mac heads, its a shorty that bolts up like stock right? I think ill get that as soon as the funds allow.

I tell you you've had your engine in and out twice before ive got mine in. im slow.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by zturbo:
<strong>If you are looking at cams take a look at cam motion or turbo people. Only thing with turbo people is you will not get a cam card.

Steven</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I just called up Duttweiler himself....why not call the guy who started it all <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

BUT

The Spetters (Turbo People) do amazing things....

 

Yeah the Mac is a mid length header. I wish i had wrapped it or coated it as is puts off a lot of heat. it's easy to take in and out from the top so I may wrap it soon. I understand now that we NEED that heat to keep exhaust velocity up with bigger pipes. I did wrap the turbo manifold as best I could and it did help cut down underhood heat. You can get the header from Mac for 220.00 shipped......not cheap but I figured what the hell. I need all I can get. Trying to catch ny bud 2bseen....his hp/tq is flat as a board!!