Geneqco

+1

Although I think I'd be a bit more concerned about potential problems excess back pressure may create.

I think the thing to remember is that the dyno with the .82 was done when there were other issues associated with wastegate control and that other changes have also been made since then. You may find there is actually very little downside to the .82 compared to the .63

Paulyy

by figures should only loose 200-300 rpm from the lag. i dont think it's much of a big deal as you'll be way past that rpm point driving around the track.


Any torque graphs?

333pg333

I think the .63 will suit us more for this particular track next weekend. After that we can revert to the .82 and see what the smaller Xover and 'gate gets us. I'd like to stop spending money on this motor and just circulate for a few events this year. The headlift is a further concern. With these very hard and thick studs we don't want to have to torque them down so much as to pull them out of the block. That's a bit of a worry.

blown 944

Did you use time certs?

BTW, I'm running a 2.5 crossover. Sorry, havn't been very active and read this much.

333pg333

I don't think this block has been 'Certed Sid. We did have to do this on one or two of the M8 girdle bolts though. Interesting that you're running 2.5" have you measured b/pressure?
With last nights setup we saw max of 40psi b/pressure on a 26psi pull. According to another well seasoned tuner we know, this is about right. He says in general that track cars should run 2:1 b/pressure to boost and drag cars about 1.5 times.

blown 944

I measured it with the T4, .48 ar housing and it was about 1.5:1 iirc. I now have the larger .58 along with the ptrim wheel, so it's quite a bit lower I'm sure. It's been a few years since I had the smaller wheel/hotside combo.

Thom

Sounds like you are not looking at the right chart.
If you get a difference of 1500rpm in spool but get only 7hp more with the bigger housing, then either the larger housing is barely less restrictive thank the smaller one, or there is a significant leak pre turbine, and a difference of around 1 psi either way is not going to make a big difference up top considering the global shape of the curves, which imo balance out the maths pretty well.

That doesn't make sense to me either, so that's why I carefully mentioned "in this application".

Like Rod I would have suggested to go back to the 0.82 housing now that the boost issue seems to be fixed, but since we now know that the back pressure is well within reasonable levels, the head lift may be caused by the tune...?

333pg333

Here's a quick log file they sent.

I wouldn't think it's the tune Thom otherwise he'd be hearing a ton of noise, no?

Thom

Sorry I meant that perhaps the tune is too aggressive for the hardware to handle, even if there does not seem to be any knock.

Duke

Ouch 50 psi coolant pressure
You can really see how it follows boost.

Geneqco

A couple of thoughts:

1. Why is the throttle position oscillating so radically during the final 8 seconds of the run? Could this indicate some form of reversion resultant from switching to the smaller hotside (hence higher back pressure) whilst using a big cam?

2. Duke noted the high coolant pressure at 50 psi... why is this and why is it oscillating by around 20 psi approximately 5 times per second - does this indicate boiling (what coolant is being used)? And/or is this evidence of head lift but if so, why the oscillation?

Geneqco

Hmm... I was looking at the comparative chart, ie the first chart in post #87 - which one were you looking at? I looked at this one because this was the one posted as a true comparison and suspect it ended at a particular point once it was ascertained there was an issue holding boost whereas the subsequent chart looks to have had some fine tuning improvements once that problem was resolved and hence is not a fair comparison.

Where are you seeing a difference in spool of 1500 rpm... looks more like 800 - 1000 rpm to me depending upon where you look and I think the thing you have to remember is that other changes were also made, not just the hotside + the boost issues.

Up to 7,000 rpm, the .63 tapers off where boost is held fairly constant whereas the .82 looks to hold fairly constant with boost tapering off hence the potential difference looks to be much higher than the peak to peak of 7 HP.

Thom

Not sure I see where you are trying to get to, as I think I have made my point pretty well. Would be interesting to try the 0.82 housing for the sake of science, but it looks like the problem is now elsewhere as the head is lifting.
I have noted down that Patrick mentioned the turbo was quite laggy on his 3l already, confirmed on other dyno charts posted on here for 2 others 3l 8v, and from there on I find no real interest splitting air any further than we already have as far as the turbo configuration is concerned.

Duke

I agree. Too many variables have changed between the dyno runs to know exactly the difference between the two housings.

This is interesting and goes against my own perception of my engine. I have never felt my GTX3582R with the largest 1.06 housing to be laggy and the pro driver that has driven my car also referred to the engine as "almost no lag". Turbo lag is subjective but still I find it a bit odd that it would be laggy on Patricks old 3.1l engine. Maybe it would be much better now with the smaller crossover.

But it should also be remembered that turbo lag is not just about when it spools but the transient response from 10% throttle with manifold vacuum to full throttle and full boost.

Late spool doesn't need to be an issue at the race track as long as you have the right gearing. But often you balance the car on the limit of traction working the throttle and here is where the larger capacity engine will have a much quicker response time. Even if the two engines on the dyno both have full boost above say 4000 rpm doesn't mean they are equally responsive at 4000 rpm when going from vacuum to boost.
Here you simply cannot beat the extra exhaust gases from the larger engine.

Thom

My thoughts exactly.
With a head/cam(s) combo to suit a large 3l+ engine revving to 8k rpm, you have demonstrated what is needed to push the GTX3582R compressor to its sweet spot - and arguably perhaps even further.

Patrick's latest top end with a slightly shorter intake seating on a 3L block would make a killer engine, but this is digressing a bit.