Engine/Transmission (1994 - 1998) Too Much Turbo ?

[Josparkz]

After hearing about bigger turbos for years, I finally got down to it.

I took my turbo to the shop for a bigger compressor and an exhaust housing. They were out of the exhaust housing, so I got it fitted to a compressor w/60 mm wheel. Figured it should help lower the egt.

While I had it off, I drilled and tapped the manifold and put another thermocouple in there, to supplement the one in the elbow.

So, I drive it around for a couple of days, heat it up and cool it off, .

Sounds good, seems like it is a bit peppier.

Today was field test day. I noticed when the pyro was hooked to the elbow that it was getting up to the 1000* mark when I punched it and it got up to about 60 mph. 0 to 60 in a little over 12 seconds, not too bad for a 9500* vehicle.

I hooked the pyro up to the manifold thermocouple and took it out. Whoa. In the 0-60 run it was getting up to 1400*. Not good.

Going from 60 or so and flooring it, it was right up there by 80, although it I kept it about 1000* @15 lbs boost or so it would continue to accelerate. With the other pinwheel, I could floor it and it wouldn't get to the 1000* (post turbo) mark till about 113.



So what have I done? I have added more volume, but a little less boost(28 lbs. instead of 32). Am I burning the fuel that much more rapidly that the egt is rising considerably faster? As in, maybe I was overfueling before and just was getting enough air for complete combustion and was wasting fuel?

I would have thought I would have lowered my egt, instead it seems to be higher, and it definitely gets higher a lot quicker.



Anyway, it seems that the amount of time I can run it at wot is greatly reduced. I guess I'll just put a 2"X4" under the pedal till we get this one figured out.



Any thoughts on this?

Thanks

 

[Forrest Nearing]

28lbs of boost is less oxygen than 32lbs of boost, and 32lbs of boost isn't out of range for an HX35...



sounds like you might benefit from a smaller turbine housing.



Forrest

 

[Josparkz]

I just doesn't figure that this would appears to be raising egt's instead of lowering them.

 

[Forrest Nearing]

well, if the boost level stays the same, a larger compressor will generally be more efficient, and a larger turbine side, will reduce drive pressure... both will lower EGT's a little.



BUT, the key ingredient is oxygen...



all things being equal, the lower your boost at a given fueling level, the higher your EGT's.

 

[bmoeller]

If you had kept the same exhaust housing, it should lower the EGTs, assuming it won't cause unnecessary restriction.



The problem is, it takes more fuel to spin it faster with a bigger exhaust housing. Think of it this way. If you have a blow gun on your air hose, and have the rubber tip with the small hole, it feels like alot of air out of that small hole. Now unscrew the tip off so it is the 3/8" hole on the end. Doesn't feel like as much air, even though it should be. Get the idea? Kinda the same principle. Makes it harder to spin the wheel with the larger exh. housing area. Clear as mud huh?

 

[Forrest Nearing]

also realize that you haven't added more volume...



you've still got the same volumetric efficiency... same cylinder head, same cam, etc.



the larger turbine side can help slightly, but I seriously doubt these camshafts have much overlap at all.



so the CFM doesn't really change... MASS changes depending on pressure, but volume doesn't. you're moving essentially the same CFM at a lower pressure... IE, less oxygen. and, therefore higher EGT's



Forrest

 

[Josparkz]

Option 5 would be to turn up the boost. I can put my adjustable boost elbow in and turn it up a bit.

 

[nfox]

Turbo

So is your exhaust housing the stock 12cm?

 

[Josparkz]

Originally posted by nfox

So is your exhaust housing the stock 12cm?

yes

 

[nfox]

Turbo?

Does the truck seem to smoke more now that the boost is lower than before?

 

[Josparkz]

Originally posted by nfox

Does the truck seem to smoke more now that the boost is lower than before?

No

 

[Cooker]

I am a little confused as to what EGT's you are actually comparing. It seems you moved your probe pre-turbo now. For a true comparison I would move it back post turbo and see how it responds post turbo with the new turbo as compared to before.



Pre-turbo temps will always respond faster during acceleration, and 95% of the time will be higher than post turbo temps. So if you are comparing your pre-turbo temps now to post turbo temps before you are not really comparing apples to apples. JMHO

 

[Josparkz]

Originally posted by Cooker

I It seems you moved your probe pre-turbo now. For a true comparison I would move it back post turbo and see how it responds post turbo with the new turbo as compared to before.



So if you are comparing your pre-turbo temps now to post turbo temps before you are not really comparing apples to apples. JMHO

No. I added another probe, so I have one pre and one post turbo. I did the first test runs post turbo for comparison.

I then switched to the other probe to see what it was doing.

 

[Josparkz]

Calling All Turbo Gurus

With all the turbo swapping, research and analysis that's gone on in this group over the years, has nobody had a similar situation ?

Or are you just not admitting it ?

 

[1dslram]

What you did is increase the drive pressure and thus increased EGT's and lowered boost. That is why you need to add a 14cm wastegated housing or a 16cm non wastegated housing. You will then achieve what you are after. The 14cm wastegated is my #1 choice because it will spool faster than a 16 and is wastegated to reduce backpressure. The problem is the 14 wastegated housing is about 3 times the price of a 16 non wastegated, that is why most people go with the 16cm housing.

Bruce

 

[Josparkz]

I clamped off the wastegate hose. Had the boost back up to about 32 lbs. This helped quite a bit, kept the egt's just below 1300* at wot.

I'm going to put my adjustable boost fitting back in and play with that a little.

 

[Forrest Nearing]

just keep the wastegate blocked off.

 

[Josparkz]

Originally posted by Forrest Nearing

just keep the wastegate blocked off.

I think with the smaller(12 cm) housing , the wastegate is a good safety measure. I am wondering if one would be neccesary on a 14?

Anyone running a non/wg 14?

 

[Cooker]

Originally posted by Josparkz

I think with the smaller(12 cm) housing , the wastegate is a good safety measure. I am wondering if one would be neccesary on a 14?

Anyone running a non/wg 14?

It depends on your level of fueling. If you are hitting 32psi with the wastegate blocked on your 12 housing, you could get by with the non-WG 14 housing no problem. That is if you do not plan on adding more fuel

 

[SEmerson]

I ran 45 psi with my gate blocked off for over a year. 32 is nothing for that turbo.