I have a '92 F-250 with a stock 7.3. I bought the truck with a cavitation damaged block. I had the block sleeved and installed all new pistons and bearings. I've put about 30,000 miles on it since and love the truck, but with 3.55 gears it leaves a lot to be desired when pulling trailers. When I rebuilt the engine the heads were inspected and everything was good, so I just cleaned them up and installed them as-is. Fast forward 30,000 miles later and I've started noticing a woof woof woof sound accompanied by a noticeable pulse I can feel with my hand if I hold it in front of the exhaust pipe on the passenger side (I have a dual exhaust system). This tells me an exhaust valve is either slightly burnt or not seating properly which has me concerned because I've seen and heard of several of these engines breaking the end off of a valve and self destructing. So, I'm leaning toward pulling the heads and fixing it before its too late. That has me wondering about studs and a turbo upgrade while I'm at it.

By itself the truck runs great and gets excellent mileage on the road. But hook a trailer to it and it really struggles to keep up. I'm looking to improve performance and give it a power boost. I know aftermarket turbo kits have been around as long as these engines have and used ones regularly turn up on ebay. Question is, will this give me a noticeable improvement over stock? And which would suit my needs better, a waste gated or non waste gated version?

 

If you're concerned about pulling power, get 4.10's. The turbo won't help enough with the 3.55's to make you happy. If the 4.10's still don't do it for you, then go with the turbo.

 

I disagree, IMO the turbo does more than a gear swap. Gearing is to compensate for a lack of power.

Let me lay it out for ya. A NA IDI is right around 130whp in good tune. A turbo IDI in good tune can lay down anywhere from 185whp-230whp with a turned up stock pump. Beyond that, you can upgrade to a bigger turbo, bigger pump, intercooler etc. A good tuned turbo IDI should have no problem hanging with a 7.3 Powerstroke, a bit better actually

 

Higher gearing doesn't compensate for lack of power, it puts your engine in the torque band and helps you stay there. That would be like saying that, for argument's sake, you have a 350 in front of 2.78 gears, and a 350 in front of 4.56 gears. Which one will pull better? The 4.56 will, because your engine always makes more power at higher RPM's.

And as far as the IDI keeping up with the PSD, that's apples and oranges. You can't say that a modified IDI will keep up with the PSD without mentioning that the PSD has to be an OBS, non-california style, with 90cc injectors. Completely stock. Highly modified IDI vs stock PSD. Kind of an unfair comparison when you look at it that way, isn't it?

 

I would Disagree...

A 93-94IDIT, which is a great comparison, because they are similar enough truck wise, will walk all over an OBS PSD with a simple turn of a screw.

N/A IDI's are dogs, all the gearing in the world isn't going to touch 7psi from a turbo. I would take a 3.55 truck with a turbo for towing any day over a 4.10+ truck that is N/A... There is no comparison.

 

Here's my 2 cents.
you want to address the possible valve problem and are planning to pull the heads. While you are in there, put in a set of head studs. you know the bottom end is good since you already did that part. with everything off and out of the way, put in a turbo and tuned pump while you are there. As for the waste gate, I'm not the one to answer, but I'm sure there are lots of guys who can answer that. pull your trailer, then look at gears if it doesn't pull like you want it to.
You didn't say if you are always pulling or only once in a while. if only once in a while, enjoy the mileage with the gears you have. If you are pulling all the time, hit the wreckers and grad a rear end.

 

Exactly, you gear to put your engine in the power band for the speed you cruise. IE if you drive 55 all the time, go 4.10, if you do freeway hauling id say 3.55s. But going to 4.56s because you want it to pull better is fairly ignorant. IDI has peak torque around 1800-2000 which is where you want to be cruising. 4.56s will tow better because of the higher ratio, aka torque multiplication, the same reason you tow better in 4th than 5th. But if your engine produces sufficient power, you dont need the crutch of shorter gears, and you can set your gearing to compliment the engines power band.

I completely disagree with your second paragraph. A stock turned up pump IDI turbo is fully capable of 200whp which is roughly 250bhp. A genI psd is rated at 215bhp, genII (superduty) 225-250bhp. I see no reason how this is apples to oranges, trucks weigh the same, same gearing options, same size engine, both diesel engines (if the PSD was so easy to turn up i would give it the same advantage, however last i looked programmers are pretty spendy). Due to the ****ty GenI turbo, my 92 eats our 97 stroke loaded, the gen I psd doesnt have the low end my IDI does, 1500-2k, given the spacing of the ZF, even if you redline it in 2nd you still drop to 1500 even with 4.10s, which is where my IDI walks away. By your reasoning, a NA IDI with 4.10s should out tow a 7.3 PSD with 3.55s

 

Yeah, if I do end up pulling the heads I figured on putting studs in anyway. I think I'd replace all the valves, retainers and keepers as well. I'm very nervous letting it go much longer like this because to me its like a ticking time bomb. I've personally seen two different IDIs ingest valves and destroy the block. As far as towing, I'm not pulling a trailer every day with it. It pulls my boat and a 20' gooseneck flatbed trailer but mostly on the weekends. There are lots of hills in this area and its totally gutless with a trailer behind. I've already had to downshift to third and only running about 35 mph by the time I make it to the top of some hills. Even running empty its sluggish on hills, but nothing like when its loaded. I wasn't sure how much of a power increase I could expect, if it would approach a PSD torque and pulling power without more upgrades.

 

your riding a common 10 speed bicycle.you come to a steep hill.you change the gears to make peddling easier.but notice you have to peddle faster to maintain the same speed? notice how much less strain there is on your leg muscles though.

the same is the case when you select a lower gear in your diff.the engine works easier but the revs are higher.because we need to select just one gear set in our trucks,we have to select one that is the best compromise.

with a small 4 cyl gas engine and enough gearing,you could do the same work a diesel pickup could do.it would do it slowly and of course be impractical.
main point is,gearing is very important and does provide a more capable truck that can undoubtedly out tow a truck setup the same with higher gearing.


now put an athlete/body builder on the same bicycle,you'll notice now (like having a larger engine - turbocharged vs n/a) he probably wont select a lower gearing like a normal person without daily riding/training would select.
there are limits though and as the rider tiers,he may select a lower gear for easier peddling.to a degree an engine/trans will work and last longer with less strain on it too.

it's all about finding the happy medium of both.gearing and engine power.it's about ones budget,desire,time and ability,when it comes to powering up the old idi.it also depends on how the truck is used too.

for one person it's well worthwhile to pull the engine and add 50 hp or more.
whereas the other person may not use the truck much,or drive in slow speed limited rural roads and have a much tighter budget (as in simply can't afford to overhaul and build up an engine.especially if it's all running fine) so adding in a set of 4.56 gearing for just a day or twos work and a few hundred bucks could be a more practical option.

for chip truck i did;
3.55 to 3.84 gearing (by way of shorter tires.)
turbo.
intercooler.
i don't use all the power it has very often.i could have stuck as n/a for my 90% 45 mph driving lmao.........but it sure is a more enjoyable truck now!
plus all the downshifting into 2nd and high revving when hauling and hill climbing as n/a.....can't say i miss that.

i don't know yet how the turbo + 5.13's will be,but i bet i'll be thankful come load up time when i hit the hills.i bet she would have really slowed and crawled...........but hey.hauling so much as once,what's the rush? seriously.when i take this truck rather than chip out,i'll be hauling two loads in one.i couldn't have just planned on enjoying the scenery?
power is like a drug.careful.

 

I've got 4.10 gearing and an GV Overdrive unit. In 5th + GVOD it's approximately equivalent to 5th with 3.55 gearing.
With my turbo, I can haul quite well, at highway speeds. The turbo really kicks in around 2000RPM, and for me peaks at 2500 or so. This means that in top gear, you start getting into your real power around 70MPH.
Downshift to 5th(4th or so in your case), and you can get that power much easier.

I would install a turbo, myself. The power is *so* worth it, especially if you can find a used kit for under $1k.
You've got 5 speeds on your transmission, use them. The turbo will give you a wider power band(instead of 1600-2k, you now have 1600-2500, with an exponential curve giving you higher power).
It's super awesome.

 

No. Take 4.1 times .78. You get 3.2. When the gear vendors is engaged, you have the equivalent to 3.20:1 gears. That should be a good setup for mileage.

 

Read again, he has a ZF-5, so in 5th + OD he is at a final drive ratio of 2.46 which is just a shade taller than 5th with 3.55's (2.73 final drive ratio) but a close comparison...

 

I thought there would be some difference, but didn't know the numbers. Thanks.

For comparison:
4.10+zf5+GVOD = ~1600RPM @ 60MPH with my 235-85R16's
3.55s+zf5 = ~1775RPM @ 1600MPH with the same tires.

I'm thinking that the 3.55s + zf5 + turbo would actually be perfect for towing at highway speeds, as it's slightly lower geared than my rig.
I'm also thinking that it's 'good enough' for highway use, and my spare truck is going to get a set of 3.55s(because I can't find another GVOD cheap) this coming year.

 

Here is the rpm math assuming stock tires are used... I know I've posted these a few times but the OP might be interested in gearing and the resulting rpm's...





Personally I think turbo IDI and 3.55's is a sweet combination for these trucks unless you need to get monster loads rolling from a dead stop, and you do it all the time. Cab noise, engine life, and mpg's are much happier at lower revs if you do much highway driving.