[Suns_PSD]

Basically I took the time to hook up a gauge to my exhaust manifold yesterday to measure exhaust backpressure (my early '99 did NOT come w/ the stock sensor).

Here is what I got (averages after several runs):

Boost/ Back Pressure

5# / 7#
10#/ 10#
15#/ 13#
20#/ 21#
25#/ 26#
30#/ 30#
35#/ 42#
40#/ 50#

That's as high as my boost goes right now w/ my current set up. The spool up is not acceptable at this time although it has gotten lots better as the new GT42R (T6 frame) has loosened up.

I know I am going to tighten the turbine housing up but I'm not sure how much of a difference each size makes and I'm not sure what is really a reasonable Drive Pressure #. Daily driveability/ response is much more important to me than top end hp and I only tow lightly and spend most days stuck in slow traffic anyways.

Any recommendations guys?

Thanks.

 

[gregrob]

Suns, have you guys tweaked with the tuning at all?

Maybe have Jody send you some tunes with less tip in, if it's fogging traffic out?

Live tuning would help too.

 

[Charles]

Or if it's not in there now, maybe.....just maaaaybe, put the damn cam that came in the truck back in it.

Sorry, but it has to be said.

Daily driveability/ response is much more important to me than top end hp

Not one thing about that statement says aftermarket camshaft and large frame single charger. If driveability/response is really what you want, you sure fooled us with the higher rpm VE cam, and the large frame turbo.

Not bustin your balls, just trying to kind of slap some sense into why you're truck is doing exactly what you have set it up to do. Maybe your ID needs to stop building a bonneville speed trial truck so that you can daily drive it

Good Luck with it, maybe the smaller A/R will get you closer to what you want.

 

[Suns_PSD]

Programming is by DI and it does not fog out the road at all. It's very clean and drivable with no haze, lite haze, and medium haze programs. The medium haze one hits 40 psi of boost. David has gotten it to spool up much quicker and be much cleaner than the two other vendors programming I have tried. (the other vendors programming was not optimized for these nozzles however)

The truck has a 100% stock cam in it and has for about 1 year. Turns out the cam was never my problem however as the truck was still running very poorly once we put the stock cam back in w/ the same injectors as the injectors were the problem all along.

My GT42R on a T6 foot has an identical center section as the T4 foot GT42R according to Chris @ RCT. So performance is the same but AR sizes do not directly correspond complicating the issue a bit. My 1.0 EH seems to run pretty similiar to the 1.39s on the T4 frames from what I have gathered.

Anyone have any insight on Turbine sizing? For instance, what % increase in BP is common when dropping 1 housing size and what is the max that one would want for a street truck?

Thanks.

 

[PowerstrokeJunkie]

Can't help you on the turbine housing info, but those backpressure numbers in relation to boost are REALLY good. 1:1 is ideal and you've hit that a few times with those numbers.

 

[HotRodTractor]

If response and driveability are your concerns why did you go to a T-6 foot?

What is your turbine wheel size?

When I was running my TN I had a turbine wheel that was much smaller than the turbo I have now. Response was NOW! It was great for driving but absolutely sucked at the track. That turbo was set up to run the street and was great at that. But since I was after more HP for pulling I upped the size of the turbine wheel and left the housing similar with the new charger. I will also admit that the compressor wheel got a little larger at the same time, but the charger is now doing what I want it to do. Setting up a turbo involves compressor wheel size, turbine wheel size, exhaust AR, etc....

Jason

 

[mech2161]

Are the numbers listed at wide open throttle? My II K31 never meets 1:1 until 45lbs of boost. It's always more boost than drive pressure until I run out of fuel then it will equalize.

 

[Charles]

I plan to swap from the 1.39 housing on the GT47 to a 1.23 housing when I do the tranny swap. With the TC locked it should be comparable even after the swap, so after that I could give you some better insight on the A/R swapping and expected results.

I will say that on the 38R going from 1.0 to 1.15 freed up the top end about 10 or so hp. But being compared to a gated 1.0 and a non-gated 1.15 I have to hold my tongue about the bottom end changes.....because the 1.15 made more boost sooner than the 1.0. It was actually more responsive.

On a side note, a larger turbine A/R sounds meaner too IMO, lol.

Did you do anything crazy with the compression or the "squish" volume at TDC with like thicker gaskets or something? Why does this engine just flat out REFUSE to be crisp and snappy? Maybe you have built an engine that just doesn't want to come alive until about 90lbs of boost or something. Did you surface the pistons/run thicker gaskets or something? Why does it not seem to want to burn fuel? Or am I reading this wrong?

Good Luck.

Oh, and good to hear the OEM cam is in place. That's always a good starting point.

 

[hotwheels]

It all really depends on what you are looking for. Ideally from what I've always been told you want to stay below 1.2:1 at your max point. However depending on what you want it to do that can be compramized as well. If you really don't care about the top end and just want response you can sacrafice some of that top end by putting a smaller housing on which will bring the drive pressure up but will make it spool faster. It won't make a big difference to you if the top end is slightly lower because you probably aren't going to be there much.

However if you are all about the top end then put the bigger housing on. Your bottom end will suffer a little and it will be a little more laggy but you probably won't care to much because your WOT max rpm power is where you want it. You just have to compramise between the two.

The other option is the smaller housing with a waste gate which is IMHO the best route for a street driver for sure. You get the quicker repsonse of the smaller housing but the WG relieve the excess drive pressure on the top end. And you can tune your boost to what level you want.

 

[Charles]

Don't forget the super small housing for spool, combined with the super big housing for top end option.........aka Compounds.

 

[Suns_PSD]

The thing I was thinking about increased Drive Pressures is this: If reversion dirtys up the incoming intake air shouldn't the greater boost offset that considerably by pushing back on the exhaust? At least as long as the numbers are close to 1:1. Either way, I need more response from the motor and I will happily give up 50 top end hp (due to excessive Drive Pressures) to get it. I only go full throttle like 10x a day for a few seconds at a time, that's like <.1% of drive time no matter how you look at it!

Charles, I agree about the snappyness missing from this motor. That is a good way to describe it. But it does now burn the fuel. The days of smoking out an 8 lane freeway are gone for me. I suspect my poorly thought out method of lowering the CR is partly to blame for the sluggishness however. Slightly thicker Cometics. They were .009" thicker than stock but we decked the block .004". I figured at one point that my CR should have ended up around 16.3:1 or so. But now I know that lowering the CR is better accomplished by increasing the volume of the bowl area and nothing else. For that matter, for my goals, lowering the CR was probably entirely unneccessary.

Either way, DI has gotten the truck 100x better than it once was and it keeps improving. I suspect in a few more weeks we'll have this thing all straightened out.

 

[Tom S]

The thing I was thinking about increased Drive Pressures is this: If reversion dirtys up the incoming intake air shouldn't the greater boost offset that considerably by pushing back on the exhaust? At least as long as the numbers are close to 1:1. Either way, I need more response from the motor and I will happily give up 50 top end hp (due to excessive Drive Pressures) to get it.

Is that ever gonna happen with a stock cam?

Tom

 

[hotwheels]

Sun I haven't done that math but I don't think an overall of .005" higher heads off the crank center line is going to decrease your compression by that much. How much did they have to take off the heads to get them square to the world and smooth enough for those cometics?

 

[Suns_PSD]

Geoff, I'm not sure what they took off the heads although since they are flat does it matter?

Things are really starting to look up to be honest.

The GT42R has loosened up dramatically in the last 1000 miles of driving and it comes on much sooner than it did when I first got it. Plus, I have a one size smaller turbine housing on the way. Then I will run over to my friend's shop and ceramic coat it before it goes on.

I've discovered that my air filter is still offering significant restriction. It will have two air filter elements on it very soon.

I fixed an oil leak that was severe enough to effect injector firing.

I can really see a light at the end of the tunnel (thanks to DI's suggestions and tuning mostly). It's a long shot to get it all done by this weekend however which was my goal. I'll be there either way.

 

[DarkShadowDiesel]

what kind of intake/filter are you running?

 

[Charles]

I have never found a filter to be restrictive. Course I run the K&N filters that you can see through, lol.

 

[hotwheels]

Sun the amount off the heads really doesn't do much. It will do a little because you are makeing the valve pockets a little shallower but probably not really a noticeable a mount. I was just curios.

do you have a gauge or something showing the restriction caused by the filter?

 

[Suns_PSD]

I have a stock restriction gauge installed into a 5" diameter piece of exhaust tubing that I use as an intake pipe. In fact I tried 2 different restriction gauges.

First my old AFE Stage II airbox would throw my restriction gauge w/ my old setup before I built the motor.

Then I rigged up some huge ass Fleetguard under my hood thinking that would get me lots of quantity and quality. No go, that thing would really slam the restriction gauge.

So then I just bought the largest, poorest efficiency AFE that I could get reasoning that I'd have to accept some dirt to get the required air flow in the space permitted. It's the best in terms of air flow so far but it still puts the restriction gauge down about 1/2 way or so. I'm ordering an additional air filter today and I'm just going to run 2 oddball sized air filters under the hood to gain some surface area.

I tell you guys, when this thing gets spooled it is really go time. The truck really scoots once it has that 1.5 seconds or so to spool and the smoke is not bad either.

 

[Tom S]

Sun, I had this discussion with Massami a while back. You might try moving your gauge to where it is not in the intake pipe where it is perpendicular to the fast moving airflow. Thought was that this might be creating a false high reading.


Tom

 

[Charles]

Or just take the filter completely off on the dyno with it stopped slap up and watch as nothing changes.

That's always been my experience anyway.