Exhaust housing question

[Farmboy]

I am trying to understand the exhaust housing on our turbos. The way I am reading and thinking is say a 16 cm housing will have less volume but a higher velocity of air flow than like a 21 cm housing. Is this right? So I guess what I am asking is... is it better to have more air flow or higher velocity of air going into the turbo. Which one gives you faster spool. I am just trying to wrap my head around this.

Thanks for the help.

[peobryant]

With your Non Intercooled '90, you should have the "baby" H1C with the 18.5cm housing. Going to a 16cm will give you a little faster spool up, but it really isn't worth the money.

I hear the 5spd guys really like a 12cm housing, if you have minor mods. It will spool up almost instantly, but be restrictive and raise EGT's, if you are more than lightly bombed.

Personally, I wouldn't go smaller than a 16cm housing on an H1C.

[Ramrod90]

The non-IC trucks have the baby H1C with the 14 cm housing. The IC trucks had the 18.5 cm exhaust housing.

[Ramrod90]

You really have to balance out those two aspects when buying a turbo. too big of a housing will have high volume and low velocity which translates to slow spool and lower egt because the air can escape easily. Too small of a turbo and you will have high velocity and low volume because the exhaust will bottleneck behind the wheel and not be able to escape till the turbo is fully spooled.

Confused yet?

On the other hand...... if you have too big of a housing you will still have higher-than-normal egt's on the low end because the turbo will not spool so you will not be getting a sufficient air charge into the engine
If you have too small of a turbo, you will have higher-than-normal egt's on the top end because the turbo will be out of its effective range and get too hot.

There you go. Have fun and feel free to ask questions/correct me.

[Ramrod90]

One more thing to add to the mix.

An automatic is usually happier with a larger exhaust housing (16 cm) because it only has to spool once due to the quick loaded shifts, whereas a manual is better with a smaller housing (14 cm) because it has to spool it after every shift. Turbo's spool better when the engine is under a load so when an auto shifts, it never takes the load off the engine and a manual will unload the engine every time you hit the clutch. git it???

[wjones]

if you really want to make things complicated throw wastegates in there. you can get a 12cm with a wastegate and get the best of both; quick spool then when it becomes a restriction it will open the wastegate to let the gas bypass the turbo.

also my 91's 'baby' h1c was an 18cm and my 92 had a 21cm.. i wouldn't waste my money on a housing for a 2cm gain.

[Farmboy]

Thanks for all the replies. I was just trying to get my head around it, not looking to change my housing. I have the houseing that I want. Thanks though.

It is just the way I figured it using basic phisics. You all did not confuse me at all. Thanks.

[Ace]

My 12cm never made more than 30psi with the wastegate bolted shut and the fuel screw maxed. Don't even worry about it with stock injectors.

[dpuckett]

But, with a piston lift pump, stock injectors, and the fuel screw with 2 threads from the collar, I can hit 30psi pretty easily, and that's with a 16cm housing.

FWIW- I turned the pump back to where it was when I first bought the truck, and when I got on the street and shifted, the RPM hung there at whatever 20mph is in 2nd. I pulled over and backed it out 1 turn. I definitley have some wear in the pump......

Daniel

[Richie O]

The non-IC trucks have the baby H1C with the 14 cm housing. The IC trucks had the 18.5 cm exhaust housing.

The non i/c had the 18.5 also. The i/c trucks had both the 21 then they switched back to 18.5 after low power and lag complaints.

[Ramrod90]

I've always understood that the non ic trucks only came with a 14 cm on them... That's what mine has, sorry for the misinformation.

[peobryant]

I've always understood that the non ic trucks only came with a 14 cm on them... That's what mine has, sorry for the misinformation.

The previous owner must have swapped housings then. 18.5cm was on all Non I/C trucks (stock) and they gave us '91.5 and '92 guys the 21cm housing.

They wised up for '93 though, and went back to the 18.5cm housing.

[ontos]

Just to ad to the info mix ,the stock turbo on my 89 5.9 had a 50mm compressor wheel. I didn't change the exhaust housing but I did move up to a 58mm compressor wheel. Seemed to be an improvement and simple to do.
Not sure how it effects spool up if at all but it should be moving more air.

[Ramrod90]

So if I get the GDS upgrade, do I have to rebalance my turbo since I am swapping wheels? or is it just bol on and go.

[Richie O]

I just put mine on and ran it. No balence. I had my front tires balenced,,, does that count?