To 12 or not to 12?

[Mgrant]

Living here in Idaho and pulling these heavy loads, I've been considering installing a 12cm housing on my truck for some time and I'm hoping all the 12cm 1st Gen owners can offer some thought. I currently have the 16cm housing, but to me it doesn't seem to be enough low end boost to shift up through the Getrag without getting things warm, especially starting a heavy load of a steep grade. After making a gear change, smoke will roll and my post pyro will often take a quick spike to 1000* at 10-12 psi until I gain the magical RPM where temps will drop back down to 850-900 or so and boost climbs to 15-20. I know the math puts it at 1100 or so pre turbo, but that EGT will so quickly that it makes me wonder if doing the math is accurate at that RPM. I've tightened the starwheel to the point where I think I'm starting to cut into the top end and I don't want to tighten it any more. I'm wondering if the 12cm will give enough low end air to keep things cool until RPM rises and not have to tighten the AFC to the point where it cuts into my top end power.



BUT, what's holding me back from going to the 12cm is that the wastegate only dumps one side of the divided exhaust manifold, leaving the front exhaust port to do all the driving with heat and pressure and the rear port being relieved of it's pressure. This is my theory why the 2nd Gen brothers and cracking their manifolds when they bombs away. Can anyone give any differing EGT numbers between the front and rear port with a 12cm wastegated housing? I have been considering getting my HX35 Piersified and keep the 16cm housing, but will it be enough? What I really need is a split gearbox or a Roadranger, but that can be tough installing one infront of the married np205. I'd love to hear any ideas, thoughts, or suggestions anyone has.



Mike

 

[JFitzgerald]

First let me say I'm no expert, but will offer you what I've learned/read/seen.



The 12 cm housing is not the best choice for heavy towing. I was leaning that way before I bought my 16, but everyone said the 12 is more suited for no load or light loads. You'd get a quicker launch, but likely see higher EGT's. Maybe since you have an HX35 instead of the H1C, this doesn't apply? I have no experience there.



Have you advanced your pump timing? That made the biggest difference in heavy towing EGT's for me. It went from having the power, but having to back off, to now being able to use it, which puts a on my face in the hills. Also, if you haven't already, consider raising your governor setting to about 3000. This helped me get my load moving faster, especially with the shift from 2nd to 3rd. This allows you to shift at a higher rpm, and keep the turbo spooled after shifting, intead of getting all smoke and no boost for a few seconds.



Hope this helps.



Fitz

 

[Mgrant]

Hi Fitz,

My pump timing is set at 1. 4, since that is what Piers recommends. I've considered bumping the high RPM up, but I also considered that a Cummins has a lot of internal mass to be rotating at 3 grand. I know that most haven't had any trouble at all, but I don't trust my luck. You know, that brings me to a good point. Have you noticed that the T444E in the binder trucks seem to last 500K or more, but the Powerstrokes rarely go past 200K? Well, I found out that Navistar rev limits the T444E at 2500 while Ford run theirs to 3400 or more, so they can advertise the big horsepower by reving it up. With the rev limited at 3400, people will stab the throttle and drive it until it shells. Just an observation, but it is something to think about.



Mike

 

[Paychk]

I noticed in your sig that you have a glass pack, is the rest of your system stock? If so what would a good 4" system do? That kink is a killer as it goes over the rear axle.

 

[Mgrant]

Actually, it's a stainless muffler that's built and looks like a glasspack and it's a true 3 inch all the way through, then it goes out a mandrel bent pipe over the axle and out. It's quiet under light throttle, bellers when pulling hard, and lots of turbo whistle as an added plus The only time I see the EGT spike is when i change gears under heavy load up steep hills. It has plenty of power and will accelerate into the realm of lower EGTs, but it makes me nervous when it's going through the low end pull. My pump is 1 1/2 on the power screw, smoke screw all the way out, starwheel up 2 1/2 turns and diaphram at stock or straight up. I'm just wondering if the 12cm is the way to go or go for the PDR-35 with the 16cm instead. Some people say the 12cm is great for EGTs and other say it's not, so I wonder if the discrepancy is which port their pyros are mounted in relation to the wastegate dump. What we need is a dual port wastegate setup, HHhhhmmm, good idea to give to Piers!!

 

[formula]

FWIW, I was running a wastegated 14cm housing and switched to the 18. 5 because the 14 was too hot on the top end. Yeah, the 14 spools better, but the 18. 5 gives much better mid and top end power and keeps egts down when your foot gets heavy (to a point, that is) If you're bogging down on upshifts, you need to wind it up more before you shift.



Sean

 

[Mgrant]

Maybe a 6 speed would be the solution. I just don't like the idea to stretching the rubberband beyond the stock governor setting, sounds like it's really turning hard as it is, but maybe it the Getrag making the noise I guess I'm just used to driving truck with low grunt engines and lots of gears to play with.

 

[BushWakr - RIP]

I sort of go with formula on this one... .



I was running a stock H1-C with a 16cm housing. On a posted 10% grade, in OD I would crest the hill and just be breaking the 1200*F mark (pre-turbo).

I changed to a NW 14cm housing (with a bit of relief porting of the inlets) and on that same hill with exactly the same conditions, I then found I was hitting 1300*F and a bit sooner too.

Now that is cresting the hill top at around 2800 RPM and passing 90 + MPH, but both tests were run empty.



The drop in housing size on an empty truck resulted in a total boost increase of nearly 4 psi and a full 100*F more EGT's.

Now, on the lower end of the power band, it ran a tad cooler, but as I transitioned into the upper midrange and thru to the high end range the benefit of the smaller housing deminished quickly and became a handicap at the WOT end... and that's empty too. .



I am now using a PDR HX35 with that same 14cm NW housing and I now see about 1175*F under identical conditions. The boost comes on MUCH quicker and it is a cleaner/cooler boost. My smoke has decreased markedly across the board.



I strongly suggest you stick with a 16 housing, OR swith to a custom turbo with a wastegated 14cm.



Just my thoughts for what it's worth. I also defer to the guys who tow, since I do not run my truck at full rated weight capacity.



Bob.

 

[J DeMaio]

I towed with mine one time since I changed the housing and was very pleased with it. Just from changing from the 21 to the 12, I gained 10 pounds of boost. It is REAL quick off of the line. When it was running, It would hit 1000* on the pyrometer pre turbo with my injectors and the smoke screw in ~3 turns. When towing it never got hot either, keep in mind I didn't have the fuel turned when i towed but It wouldn't hit 1000* then. Towing stock I had seen 1200*. I'd switch to the 12 if i had to work on another truck, I'm very pleased with how it was running. A reason why I liked that swap so much is because a buddy gave me his housing and I only had to buy $9 in gaskets One other note, you have to cut 1. 5" out of the downpipe right behind the turbo. This can be a pain, I didn't cut my pipe like I should have so I didn't have an exhaust for a while.



John

 

[nascar mark]

You can run a 12cm non wastegated also and not have to cut your downpipe or move you exhaust at all. But I would stick with a 16cm for towing. Its the best all around housing for our (1st gen ) needs. I'm running a 12cm w/g and do see cleaner bottom end but I would not pull heavy with this housing even with dumping alot of boost. Around town the 12 is good.



Find your power/torque band and take your rpm's up above it so that when you shift you drop back just before it to keep your load going.

 

[Midnite]

Originally posted by Mgrant

Maybe a 6 speed would be the solution. I just don't like the idea to stretching the rubberband beyond the stock governor setting, sounds like it's really turning hard as it is, but maybe it the Getrag making the noise I guess I'm just used to driving truck with low grunt engines and lots of gears to play with.

Mike, one thing you might want to do (if you're not already, that is) is to start doing oil analysis. Get a couple of reports to establish a baseline for how your engine is wearing under your current use pattern. Then turn up the high idle stop and start taking advantage of the higher rpms and see if the oil analysis reports show any increase in the rate of wear.



That way you don't have to guess--you'll have hard evidence how turning up the rpms is affecting the engine. For that matter, you can do the same thing with the oil in the Getrag if you wanted.



Mike

 

[Mgrant]

I see some good thoughts and ideas!! That's what I love about TDR, there's always good people willing to help. After doing more reading and searching it's sounding more and more like the 16cm is still the ideal housing and more gears with RPM is the solution to my gear shifting. I was mainly curious on how the 12cm affects EGT at low RPM, but it's doesn't sounds much different than a 16 other than quicker spool. Another thing I might start doing on the really steep and windy roads is to shift the transfer case into low range, bringing all the 5 speed ratios closer together to less RPM drop after a gear change. I think one can go up through the gears, then after the grade levels out, shift the divider into high range and go back to 4th and on to 5th for a total of seven speeds. Man I wish I can stuff an Eaton Fuller in this thing! Then maybe some stacks, air deflector, air horns, chrome saddle tanks... ... .