I just bought a 1990 crew cab dually with a J code 6.2L. I bought it to tow a trailer for work and it does the job nicely. It is a 3 speed automatic and when I get on the highway it pretty much tops out at 60 mph. I guess it could go a bit quicker but the motor seems to be reving pretty quick and I want the old girl to last a few years at least.

When my neigbour looked at the truck he pointed out that the two exhaust pipes seem to be very small for a diesel. They only look like they are about 1 inch! So I was thinking, if I put a better exhaust on the truck, and maybe a better intake, would I get more speed out of it? I think I know the answer, but if I make the engine more powerful, would it turn slower at highway speeds, or is that entirely dependant on gearing?

Thanks

Peter

Entirely dependent on gearing. You've likely got 4.10 gears which are great for towing, but not very good for economy/top speed. Your only real options are a Gear Vendors overdrive unit, changing your axle gears, or putting in a 700-r4 (4 speed trans).

Yes, 1" exhaust is silly. I've got dual 2.5" pipes stock.

Yeah, I kind of glazed over that part -- take a good look at your exhaust, with something to measure. If you have the 2.5" dual exhaust that came stock, that's a total of 40 sq. in. of exhaust cross section. A single 4" exhaust is about 50 square inches, which is what a lot of other diesels run. Now, going to dual 3" or dual 4" will increase power slightly, but without a turbo the exhaust pipes on these 6.2s is really not a bottleneck. If your dual pipes actually are 1", get rid of them! That's a cross section of only 6.3 square inches! Get 3" pipes!

open exhaust and maybe dual ram-air snorkel air filter housing will increase efficiency of engine running and may pick-up some mpg, by reducing power(fuel) used to exhaust engine. if you can find hummer headers cheap, wouldn't hurt either.

to get more speed you can invest in a gearvendors overdrive

guys....if he puts the overdrive in.....he probrably wont be able to pull the trailer anymore....

but with the overdrive he'll be able to kick it in on level spots where he wants more speed then when he climbs a hill it can kick out and then he can climb the hill just fine

id put bigger tires on myself

unless its a 4X4 thats not nessesarily a great plan unless theyre just taller street tires

If you have the 2.5" dual exhaust that came stock, that's a total of 40 sq. in. of exhaust cross section. A single 4" exhaust is about 50 square inches

I think you hit the wrong buttons on your calculator for the area of the pipes.

The formula is: pi x radius x radius = area of the pipe cross section.
pi = 3.14
radius = 1/2 x Diameter


Diameter.....Area...........Duel Area (x2)

2.0 inch..... 3.1 sq. in.... 6.3 sq. in.

2.5 inch .... 4.9 sq. in.... 9.8 sq. in.

3.0 inch .... 7.1 sq.in... 14.2 sq. in

4.0 inch .. 12.6 sq.in.... 25.1 sq.in.

My stock tailpipes each measured 2-1/8 inch ID. For my Banks turbo installation, Banks Engineering recommended a single 3 inch exhaust pipe as adequate. Remember, we are talking slow turning diesel engines that put out half of the exhaust volume that a Gasser puts out turning 4-5000 rpms.

Yup, I was using a 2.5 radius, not diameter. Still correlates the same tho, where dual 2.5s are not far behind a single 4", and more than a single 3".

Also, diesels might be 'slow turning' but they move MUCH more air than a gasser. It's the compression ratio that does it -- our 6.2s are putting out almost 3 times more air than a gasser at the same rpm. When I was in the Navy, our single best way to ventilate the submarine was to run the diesel engine -- it's such a huge air pump it was waay waay beyond either of the electric blowers (which mind you were huge) as far as airflow goes.

Stock dual exhaust isn't 2.5 inches, its 2 inch's with very restrictive mufflers. :(

You have a few options for more power-open up the intake, IE better air cleaner but it will make more noise, turn up the IP, Hummer headers, dual 2.5 inch or single 3/4 inch setup, or best setup is a turbo.

As for the highway, your topped out RPM wise, so you can change to a 5 speed, 700R4, 200R4, Gear vendors or larger tires.

start by identifying your current gear ratio a simple ring and pinion swap is easy and while your there you can service some bearings as well

start by identifying your current gear ratio a simple ring and pinion swap is easy and while your there you can service some bearings as well

Its not simple if you have a 4x4.

whats hard about a 4x4 as long as you match front and rear ratios

whats hard about a 4x4 as long as you match front and rear ratios

Mmmmmmmmm, you need to buy 2 sets of gears, bearings etc and double the labour. Not exactly easy or even cheap.

Have someone press the throttle all the way down and see if the throttle linkage is going all the way over and hitting the stop.

thanks for the responses

It is a 4x4 :(

I just want to do some simple (cheap!) upgrades to give it a bit more horsepower.

As for the throttle going all the way down, I don't know if that is a problem. When I get on the highway, even at 60mph it seems to be reving pretty good. No tach. I don't want to push it as I have heard about the block cracking. My goal is to keep it under 60 to try and extend engine life. Does that make sense?

anything to extend the engine life makes sence unless it means leaving it parked in the shed

as far as speed goes. 4.10s will get you up to speed fastest, but you also run out of gear and have the motor screaming, like you've stated.

my blazer has 3.08s in it and a 700R4 automatic overdrive trans. the 3.08s are more highway gears than anything else. i can't tell exactly when it shifts MPH wise and the damn speedometer cable is melted where it's near the exhuast(truck was run way too hard in it's life).

hum so you think switching to a 700r4 or a 200r4 or a gear vendors od or even a good set of tires is cheaper than swaping two ring and pinions well lets see a complete gear set for a dana or 12 bolt or a gm corp is about 250 out the door around here ill set them up for 150 w new crush sleves so thats bout 800 whats a good set of lets say 35 in tires selling for these days hummm

He said it's a 4x4, so you'd have to get 2x gear sets ($500) and double the labor ($300) which comes a lot closer to a basic 700r4 ($250-600 on craigslist around here) plus install. He also wouldn't lose any towing ability, he's just gaining an overdrive gear to keep the engine turning slower on the freeway.

well i dont know what you pay for gears where your at but i happen to run a shop and i know what we charge for a 4x4 with two sets of gears out the door is 800 ball park so if you want to put a craigslist 700r4 go ahead so what about the cost involved with a drive shaft and tv cable possible tranny mount mods and the unknowing condition of the trans ???maybee i dont charge enough to do gear sets no harm no foul :)

ive found most gears, (i beleive superior) for $125 a set, and my guy puts them in for $125

I just bought a completly built stage 2 700r4 for $1000

So you could do gears and tires for about the same price as a trans.

i beleive if he has a th350 tranny you wouldnt need any driveshaft or tcase mods though

So we're back to square one, which is, what's more important to the OP? Economy (lower RPM on the highway) or power (towing or hill-climbing ability)?

Having 3.73's and 31" tires, I cruise just fine on the flatlands. 65 MPH is doable. 70 is doable but noisy. I don't know what towing a trailer would be like, but I suspect it would be a long, slow process to get to freeway speed.

And with the heavy truck you could go with taller gears like 3.42's but then you stress out the trans and drivetrain more with each standing start. A TH400 doesn't have a super-low first gear like the 700R4. It also doesn't do too well at part-pedal downshifts.

On the plus side, this rig's TH400 went 220,000 miles before it was rebuilt. Unless you had a 700 built up to handle the heavy load, I for one wouldn't do a tranny swap. I've thought about Gear Vendors, etc. but can't justify that kind of money for what would get a good used mid-90's truck with a 6.5 turbo...

My main concern is to have a vehicle that can handle the towing with no problem and speed is not that important. What I am towing are trailers for location filming for commercials. We have a yard in Toronto and the locations are usually within a 20 miles of the yard. I tow the trailer to the location and sit all day with it then drive it home at night. I am not like a landscaper who will tow maybe 100 miles stop and go each day. I would imagine I have a heavy duty transmission, I will look at the build sheet and try to figure it out

I guess what I need to do is make the engine breath a bit better. thanks for the suggestions. If someone can point me to a thread about intakes or reccommend some good products that would be great. Changing the heads is a bit beyond me right now as I am very busy and I have never done anything like that. I might give it a try thought, I like learning how to work on my truck.

Thanks

you should try making a simple cold air intake for it like this one, or similar to it:http://www.dieselplace.com/forum/showthread.php?t=36285

and getting some less restrictive mufflers and some bigger pipes under there would help with the sound and power and the engine should run a little bit cooler

I guess what I need to do is make the engine breath a bit better. thanks for the suggestions. If someone can point me to a thread about intakes or reccommend some good products that would be great. Changing the heads is a bit beyond me right now as I am very busy and I have never done anything like that. I might give it a try thought, I like learning how to work on my truck.

Thanks


Exhaust-

http://www.dieselplace.com/forum/showthread.php?t=147364&highlight=hummer

Exhaust-

http://www.dieselplace.com/forum/showthread.php?t=147364&highlight=hummer

whered you pick up those hummer headers at and for how much?

Thanks for all the advice so far.

I measured my exhuast pipe and I do have 2" dual exhausts. That doesn't seem too bad. It also seems I have a turbo 400 automatic according to my build sheet.

whered you pick up those hummer headers at and for how much?

Check Ebay or here or the other diesel forum. I paid like $60 for them, :cool:

ok sweet if i dont get a turbo soon ill look into some of them

the hummer headers are on ebay for $40 plus shipping last i checked. I plan on getting a set eventually myself.

I"m still in a a toss up of keeping the blazer N/A or going turbo. Helps to get it on the road first. :o:

the hummer headers are on ebay for $40 plus shipping last i checked. I plan on getting a set eventually myself.

I"m still in a a toss up of keeping the blazer N/A or going turbo. Helps to get it on the road first. :o:

$40 is an even better deal, :cool:

I am still going to use them in my turbo setup, should help spool quite a bit and keep the backpressure manageable, :D