Low Turbo Boost

[jaluhn]

Looking for ideas here, I'm trying to figure out why my truck isn't making the boost I feel it should. The truck is a 85 F250 6.9 diesel. The turbo system I've got is a home built setup using a Banks Sidewinder waste gated turbo. I'm getting about 5 psi at 2000 rpm increasing to about 9 at 2800 rpm, but full throttle and 1150-1200* EGT. Multiple other people I've talked to with the same turbo (apt a real Banks system, not my hodgepodge thing) have said they can easily make 10psi at 200 rpm and over 15 at 3000 if desired.

The turbo spins freely and seems to make boost well initiailly but then acts like it's choking. at 2000 rpm it'll easily hit 4 psi within 5-8 sec of opening the throttle but then seems to bog down after that and doesn't want to make much more. Same thing at 2800 rpm except it gets up to 6-7 and then bogs.

I've got the wastegate set so start opening at about 12 psi, this has been verified with a hand pump. I have also completely disconnected the actuator and tried that, no change.

The engine is in good shape, good compression, no issues. The turbo system I've got is a home built setup using a Banks Sidewinder waste gated turbo. The uppipe uses the stock manifolds and part of the y-pipe and then runs up the driver's side of the firewall modeled on the older banks non waste gate turbo system. The tubing is 2 1/2" and I recall. The down pipe is 3" expanding to a 3 1/2 straight pipe exhaust system.

The turbo itself appears to be the correct banks unit, but I got it off ebay as a partially assembled unit (complete turbo but missing heat shield and wastegate actuator) and it turns out that the wastegate port was drilled too large in the housing preventing it from sealing as manufactured. I was able to machine an insert seat and press fit in in, however I wonder if there might not have been other things wrong.

Any thoughts on what would cause this? I've had this behavior since the system was built, so it's not new. I'm sure my fabbed up pipes are not as free flowing as the banks system but i can't see them causing that much difference. To me it just seems like the turbo is mismatched somehow or there's something weird going on.

Thanks,
~John

[Beat95YJ]

Pics please.

[jaluhn]

Here's what I have at the moment. This is obviously missing the downpipe and the intake piping but you can get the idea.

[Beat95YJ]

What do you have from the turbo back?

[jumbo2]

Sounds like lack of fuel , low egt and bogging

[jumbo2]

What's you fuel system ?

[jaluhn]

3" 90* bend coming out of the turbo and dropping down the passenger side of the bellhousing and then transitioning to 3 1/2" all the way back to the rear axle. No muffler.

I think the next thing I want to do is put a backpressure gauge on it and see what the preturbo pressure is actually doing.

[jaluhn]

The fuel system is the stock DB2 pump turned up about 2 flats. I get pretty decent black smoke under load, and I think 1200* pre turbo is about as high as I'd want to go. The fuel system and egts are in line with what similar trucks are running and getting the 10-15 psi boost.

[dieselboy740]

I have a complete '94 7.3idit that makes 15 psi that I'll sell you for dirt cheap. With all wiring and zf5 etc. Boost doesn't mean chit. Anyways it made over 200/400 at the rear wheels on the dyno. Locally too.

Btw you need more fuel. My friend with the banks on his 7.3 maxed out pump can't hit 10psi. While my factory (ats) would walk away from his auto with my manual.

Edit: that "kludge" pipe will play hell on your clutch slave cylinder.

[jaluhn]

Sent you a PM.

I am pretty convinced it's not lack of fuel since I'm getting decent EGTs and some black smoke. It's acts to me more like a air side issue.

I know the pipe location isn't great for the clutch slave, but I've got everything well insulated down there and a aluminum cylinder instead of the plastic one.

I plan to eventually put a real turbo system on, the kludge was because I din't have the money to go dropping thousands into a manufactured setup and it's actually worked quite well.

[jpfrk2001]

You could go to a smaller up-pipe to the turbine. 2 1/2" up pipe seems large to me. Step it down to 2 1/4"

[TrailTamer XJ]

I'm not sure if this matter or not but to me it looks like you have too much distance from the exhaust manifold to the turbo.

[jpfrk2001]

Originally Posted by TrailTamer XJ

I'm not sure if this matter or not but to me it looks like you have too much distance from the exhaust manifold to the turbo.

Thats why I say a smaller up pipe. Smaller pipe = faster exhaust gas flow into the turbine. Then it leads faster spool up times. Definatly check to make sure your wastegate is staying closed under boost conditions.

[reklund5]

Let's see the plumbing from the turbo to the intake of the engine. Intercooled?

[jpfrk2001]

Originally Posted by reklund5

Let's see the plumbing from the turbo to the intake of the engine. Intercooled?

Possible leak on the pressure side?

[reklund5]

Originally Posted by jpfrk2001

Possible leak on the pressure side?

That's what I'm driving at. Getting the intake hat to seal on these can be troublesome. Some guys attempt to seal it with RTV- which just isn't right. I have a 1/4" thick Viton o-ring in mine to seal it.

Ryan

[guidolyons]

Originally Posted by reklund5

Let's see the plumbing from the turbo to the intake of the engine. Intercooled?

Originally Posted by jpfrk2001

You could go to a smaller up-pipe to the turbine. 2 1/2" up pipe seems large to me. Step it down to 2 1/4"

Agreed, I think you can clean up your plumbing, and that will help. jpfrk2001 knows a thing or two about turbos.


I wonder if you can use early PSD manifolds to mount the turbo? I know the IDI 7.3 and the PSD are not identical, but the exhaust manifolds look similar.

This is the 96 PSD in my Scout (94.5-97 PSD were not intercooled). I did a custom downpipe to cross over to the driver's side since I'm running Chevy D60. Some U-bends from Summit made it pretty easy.

[Turbos10]

Do you have black smoke off idle or under boost?

I dont think the piping on the hot side is your issue. It is a little long, but that should only cause a little lag if anything at all. I'd also check for boost leaks. That is a biggy.

[jam0o0]

you are doing this with a trailer or some other load on the truck right? not just the truck on flat ground? mine wont make shit for boost unless i have more than 3k lbs behind it.

you said the waste gate was set for 12 psi. but i bet you tested that without the drive side pressure on the waste gate. get some good wire and wire the waste gate shut. then find a loaded trailer and let us know what it does.

if you have a china made ebay turbo it will not be as efficient as a real garret turbo. and the turbo's on most of the kits available for these trucks are really too small. combine that with a shit ebay turbo with questionable internal sizes and you get no boost.

side note: i had the same problem. my stock turbo made 3-5 psi. i noticed the wheel had some play. when i sent it to get rebuilt it turned out someone had put the wrong cold side wheel in it when it got rebuilt the last time. so unless you have disassembled the entire thing don't count on it being right.

[[486]]

Originally Posted by jam0o0

and the turbo's on most of the kits available for these trucks are really too small.

Could you give an idea on a size that is good? All I've heard is "the stock turbo from a 12V cummins" which I have observed as a holset H1C, but nobody refers to them as anythiong close to that, it's all hx35 and such.

tl;dr, I'm asking for a link explaining turbo sizing.

[HahnsB2]

I agree on the hot side not really being an issue, maybe a bit more lag but should not affect actual boost numbers. I'm thinking a boost leak. And yes, drive pressure will help open the gate earlier than just air pressure in the diaphragm during a bench test.

CTDs have used a few turbos. First was the H1C, there were a couple versions in the 1st gen, I think they started out as a 46-48mm compressor and worked their way up to around 54mm and with an anti-surge compressor housing. Also there's different turbine housings depending on what tranny. Then in 94 there was the WH1C (W stands for wastegated) which had a 56mm compressor, then in 95 the HX35 started, just think of the HX as the newer version of the H1C. And among the the HX35 there were a couple different compressors (56mm and 58mm I believe) but all had 12cm wastegated housings, and then there was the HY35 which had a tiny 9cm turbine housing.

[jpfrk2001]

Originally Posted by [486]

Could you give an idea on a size that is good? All I've heard is "the stock turbo from a 12V cummins" which I have observed as a holset H1C, but nobody refers to them as anythiong close to that, it's all hx35 and such.

tl;dr, I'm asking for a link explaining turbo sizing.

Oh boy.. Here we go:
http://www.pirate4x4.com/forum/showt...205&highlight=

[motoracer]

Try popping off the down pipe and brake stand it. Like a boosted launch. See what it builds. I have seen those with a clogged cat and it just wouldn't make power. Pulled the downpipe loose so it could breathe out and the turbo started making a lot more boost when brake standing.

[[486]]

Originally Posted by jpfrk2001

Oh boy.. Here we go:
http://www.pirate4x4.com/forum/showt...205&highlight=

Breaking out the ti84

EDIT: Now I've got 3 pages of calculations and can sorta read compressor maps. Thanks, man!

EDIT2: And I'm back to a junkyard HX35 [H1C's map didn't match up too well], but at least I sorta have some understanding of what's going on.