Towing with 12 cm vs 18 cm

[dpuckett]

I have done a bit of towing with each in my 92. I had the 12 for a bit, then put it on the 93 when its pump died. Then I put the "dead" pump in the 92 after I brought it back to life (guide pin in AFC housing was stuck at far Minimum). while I was at it, I put the 18 cm housing from the 93 on it. When pulling about 8000# with the 12, i would see a peak boost of 22-23 psi, and peak EGT of about 900. THis was at 6500 ft, tweaked pump, and stock injectors, stock H1C, K&N, and no muffler. Cruising flat loaded was about 8-10 psi/ 750-800. With the 18, muffler back on, kink over axle gone, paper filter, and a 40'-7500# GN trailer, flat cruising is about 500-600/ 3-6 psi. Peak boost EGT is 21/ 950. This is also on winter fuel, and summer fuel with the 12. HAvent driven enough with the 18 to get mpg, but I figure it will be 15-16 mpg, vs 13-14 with the 12 cm housing, based on EGT differneces alone. My theory on this is that the 12 cm is good for light towing and empty; good spoolup, lower EGTs. But if you tow more than say 7000#, I think a bigger housing allows better breathing, and reduces drive pressure, and EGTs. BUT..... how do the newer trucks do so well with the 12 cm housing? IS the HX35 that much different from the H1C? I have noted that there is an obvious lag with the 18, but I like the lower EGTs while cruising with 7500 lbs lagging behind. Have any of you noticed any similar trends? I plan to get a PDR HX 35 asap. But I might get an e-brake first.



Daniel



PS- should this go in the towing forum? This IS relevent to first gen trucks, though.

 

[Bob Beauchaine]

I noted similar findings with my 14cm2 wastegated turbo. The other choise is the 16cm2 non wastegated turbo. I have never seem over 1150 pre turbo EGT's at altitudes up to 8500' - even when hauling a$$ and my trailer. I feel comfortable with my 14 and probably would not switch the hot side. The cool side - well thats another story.

Bob

 

[dpuckett]

Oh believe me, when I get the money, I WILL go to a smaller housing. I just thought it kind of odd that the 12 made for higher EGT towing, and apparently less mpg than the stock 18. Maybe the 12 without the gate (or the gate not hooked up) is a little overkill?



Daniel

 

[formula]

Originally posted by dpuckett

But if you tow more than say 7000#, I think a bigger housing allows better breathing, and reduces drive pressure, and EGTs. BUT..... how do the newer trucks do so well with the 12 cm housing? IS the HX35 that much different from the H1C? I have noted that there is an obvious lag with the 18, but I like the lower EGTs while cruising with 7500 lbs lagging behind. Have any of you noticed any similar trends? I plan to get a PDR HX 35 asap. But I might get an e-brake first.

Originally posted by dpuckett

I just thought it kind of odd that the 12 made for higher EGT towing, and apparently less mpg than the stock 18. Maybe the 12 without the gate (or the gate not hooked up) is a little overkill?

You're correct when you mention drive pressure. If you disable the wastegate on the 12cm, things are sure to get very hot in a hurry. The 2nd gens engines have different airflow characterestics and fuel injection system which makes them respond differently to a particular mod than our 1st gen engines.



Here's a bit of a post I made a while ago:



"For the same compressor, increasing the size of the exhaust housing will... ... increase spoolup time, decrease throttle response, make more bottom end and acceleration smoke, require more rpm and load to produce the same boost as a smaller housing, flow more exhaust gas, lower EGT when under load such as towing (better drive pressure), increase EGT under low throttle, operate more efficiently under high loads, allow heavier fueling while keeping EGT under control.



Decreasing the size of the housing will: decrease spoolup time, increase throttle response, reduce low end and acceleration smoke, make more boost at lower rpm, flow less exhaust gas, increase EGT under high load (excessive drive pressure), decrease EGT under light load, operate more efficiently when under lighter loads such as driving around town and cruising down the highway. "



Cheers,

Sean

 

[dpuckett]

Re: Re: Towing with 12 cm vs 18 cm

Originally posted by formula

If you disable the wastegate on the 12cm, things are sure to get very hot in a hurry. .



More like too lazy or uninformed to hook it up (stock has no WG). How would I go about hooking it up? Would it be difficult? I am somewhat mechanically inclined, and can follow directions.



THanks for conferring on my theory.



Daniel

 

[formula]

Do you have an actuator on the wastegate or has it been welded shut? The actuator will look similar to this one (the turbo in the picture is actually an HX40, but that doesn't matter)



#ad




If you have the actuator, you can hook it up as in the picture. The other method is to take boost pressure from the intake manifold to run the actuator. You should also be able to adjust the linkage on the wastegate to allow for more or less travel which will control how much exhaust gas is vented by the wastegate. Another method to control the wastegate actuator is to use a boost elbow or a variable boost controller. This basically provides a small leak that makes the actuator think it's getting less pressure, so the opening of the wastegate will be delayed accordingly.



Cheers,

Sean