Turbo survey

[R.E. Miller]

I'll second that.....

I like the bottom end power gain over the high RPM loss. At 75 MPH you can feel the loss, but If you could get the engine back to it's happy RPM range, i. e. gear change/O. D. , you would never look back. I am currently trying to decide how to get lower RPM's at 65+MPH, and that change with the 12cm^2 housing would make my truck perfect Oo.

Russell

 

[RDBuck]

12turbo penalty at 75mph

RE Miller- what are the rear-end ratios for your trucks? I'm going to install a 12c turbo in my 92 with a 5sp and 3. 5 rear. Will I suffer a noticeable loss at 65-75 cruising? I'm willing to sacrifice this if I have to as the majority of my use is around town and short distances of 20 miles or less. The low end improvement would-in my case-be worth the upper end loss.

 

[bflood]

12turbo penalty at 75mph

I lowered my ratio to the road by 8-10% by switching to 235/85/R16, load range E, tires (from 215/75/16). they (Firestones)have a 32" diameter versus about a 29" (or so) diameter on the original tires. I don't expect any problem with the spacing between the dual wheels and I've read of others doing the same thing. Although I'm not dealing with a 12cm2 situation, I have a 4. 11 rear and was looking for lower cruising RPM's. It worked nicely!



I went to the tire manufacturers websites to find the tires with the highest profiles. There are other ways to do this but this way didn't involve the cost of new wheels.



This would also help with the 12cm2 concern depending on your rearend ratio. Oo.

 

[Matt S]

The only thing I notice at highway speeds of at or above the stated 'power loss' is a higher boost reading on the gauge. I don't see this as a problem. At those speeds you should be empty anyway and not need the extra 5 horses at 2600 RPM. I'll look up my dyno sheets and try to figure out what the RPM's are this weekend and post them again.

 

[cerberusiam]

Have any of you that have the 12 and 14 turbos tracked EGT's on towing? It is pretty obvious the smaller housings make more HP faster in the lower rpm's but what happens to EGT's when you drop a load on them? I gather that is a glaring problem on the 2nd gens when towing. Since mine does double duty commuting and towing and I intend to push the HP as much as possible I am a little nervous about dropping under a 16. I would sacrifice the lower end if it meant keeping the rig driveable at highway speeds with a load. Any information? Opinions? Experiences?

 

[R.E. Miller]

Q&A attempt, please go easy on me.

RDBuck,

Both of my trucks run the 235/85/16 tires and both have the 3. 55 gears. Now this won't make any sense, but this is the truth in my little truck world. My 1-ton dump has not trouble rolling along at 70+ MPH once you get there, and that is with the 16cm^2 and a pinch more of fuel. Remember, the gear ratios are suppose to be the same. My club cab has always seemed to be wound up at 70, although it will do 80, it is ugly, and I refrain from that activity I cannot explain this, my gear ratios should be the same, otherwise I do not think that 70 would be feasable with the 4. 11's. My point, you can notice a slight difference at the RPM limit for our engines... it feels to me like you would expect... the feeling of restriction. BUT, the extra power that you now have to propel you to the same speeds outweighs that 5-10hp loss IMHO



Towing,

I just towed a small load yesterday, about 3K of junk. My egt's would not exceed 1000*+/- 50* even while I was getting into it good . My engine would pull under load between 20-23 psi with the above egt #'s. This is not what I expected at all out of the smaller housing. But for the record... with the 21cm^2 housing, I was able to pull only 17psi max and the EGT would soar to 1200 without too much right foot action. Differences that I attribute to this are, new 3" downpipe for slightly more surface area for cooling, and the ability to produce higher boost #'s with the same amount of fueling which to a certian degree will allow cooler operation If this is not right, some one please give me an internet dunce cap, but these are my honest tinkering observations, I hope they help you guys out



Russell

 

[bflood]

Just for reference

Some of this thread has included tires/ratios. Its related so why not.



My recent data (w/ 4. 11 rear, 16cm2 hsg):



Tires - Top Spd - Mileage(NLoad,local)



215/16R LR"D" 77mph 17-18mpg (Yes, 4. 11 will reach 70+)

235/16R LR"E" 85mph 17-18mpg Oo.



I have not towed w/ heavy load since the tire change. We'll see, might have to drop a gear on big hills?

 

[R.E. Miller]

Gulp...

bflood,

Thanks for pointing that out, may be my truck isn't telling the truth :-{} I guess I need to pop the cover and count teeth because your figures seem to indicate that my pick-up has the 4. 11's.



Russell

 

[RDBuck]

rear gear ratioi

R. E. Miller- If your truck is running anywhere near "normal" and has 3. 5 rear gears you should be able to run in the low and mid 90's(mph) wide open. My truck will hit 92-95 with no problem and actually runs very quietly at these speeds. It is just too illegal to do this very often but it is capable.

 

[R.E. Miller]

Fart

I told bflood that I am going to jack this thing up tomorrow and do the old chalk and driveshaft count. I would actually be happy to find that my truck has 4. 11's, because the 3. 55's will be on the way if that is the case.



Next question, this might clear-up everything. If your truck was ordered with 3. 55's, but the limited-banana peel option was chosen too, does this mean that the ratio automatically is 4. 11?



Thanks,

Russell

 

[RDBuck]

3.5 w limited slip

My truck has the limited-slip rear and the 3. 5 ratio. Frankly I have not been impressed with the limited-slip plus it eventually needs to be rebuilt and can cause total rear-end wear out---in my experience.

 

[R.E. Miller]

FWIW, and whoever cares

My truck has 3. 50 gears, jacked it up, and counted the turns. I can't figure why it doesn't just haul like my other trucks. Oh well.



Russell