6.2 NA Performance

[Chevypoor]

Now that the weather is getting cooler we are getting ready to pull a 93 6.2 vin J diesel and install it into the wifes truck. We are leaning towards leaving it NA although she loves the feel and sound of my truck on the boost

We have a set of hummer headers and we were planning on running straight back from each header with 2.5" pipe to dual 4" stacks with flappers. No mufflers, cats, or a crossover pipe. Is this sufficient pipe size for a NA motor?

I was wondering if we should run a set of military pre cups for more power. I have heard the military NA 6.2's were rated alot higher than the domestic motors. Did they just change the pre cups and turn the fuel up?

Anybody here had any experience with the Heath NA diesel cam?

And finally I am assuming we should turn the pump up. How much... or will we have to tune and drive to find the best combo?

 

[just a number]

2.5" pipe will be fine. the highest rating was a 165hp and that was a j code setup(no egr). I'm not sure about the precup differences, but the fuel can be turned up at 1/8-1/4 max without any major issues. a little smoke on hard acceleration is OK but big black clouds is just wasted fuel/money. gauges are your best friend for tuning. Keep the EGT's bellow the 1100F mark or bad things happen. odd spike your OK just don't keep it there.

As for keeping it NA you'll see alot better mileage just don't be in a big hurry. you can always turbo it later. and yes the turbo does wake it up quit a bit.

 

[WarWagon]

The military precups are bigger than the civilian precups. They are IMO also dirtier and smoke like a freight train as they are emission exempt. You trade MPG for power. The bigger the precup hole the more fuel you can run. Smaller precups turn more fuel into black smoke. Smaller precups give you better MPG.

You said you wanted power. You are going the wrong way with NA even thinking "power". NA 6.2's simply don't get out of their own damn way. Have you ever driven one? Think of the Eisenhower pass in Colorado with a 1988 6.2 Suburban. Black smoke, full RPM, AC kicked out from WOT, and going slow. The mudflaps melted to the dual exhaust. The turbo is such a night and day difference to power, but, at the cost of ~1/4 of the MPG.

A stock 1993 6.5 with a TM and 1/4 turn of the fuel screw is peppy around town with no trailer.

Our 1998 6.2 NA 4x4 would get 18 MPG on old diesel. The 1995 has seen 16 MPG with the ATT, kitty, and ULSD diesel. It is a real pleasure to drive when the turbo lights off...

:mad2: What happens exactly over 1100 EGT? IMO it is a myth as my 1986 6.2 Military precup take out longblock dropped in the 1995 suburban will take 1550 EGT sustained with no issues. I get tired of the myth of high EGT's doing anything alone - it doesn't. So quit scaring people or giving them unnecessary worries. High EGT may be bad for economy, but, that's about it.

 

[Chevypoor]

I guess I should have been more specific. The vehicle that this motor is going into is my wife's rig which is not a daily, does not tow, and speed is not really to important when running 37" Super Swampers... even the mild 350 in there before was pokey. I estimate the power of the 350 to be about 240hp and around 360ftlbs. We were hoping to get the power up to maybe 200hp and about 300-350 of torque on the 6.2. She is looking for presence... a little smoke is a bonus

 

[Chevypoor]

I also forgot to add she does do some local parades with it and car shows/ cruise ins. It does idle alot which is part of her reason for going with a diesel.... they can idle forever and crawl around at low speeds better than a carbed gas motor.

 

[ak diesel driver]

to achieve that you'll want to turbo it.

 

[turbovanman]

200 will be a stretch with an n/a diesel.

Do the basics, when I got my van, I didn't touch the pump and did hummer headers, 3" single exhaust all mandrel bent with a 2.5" crossover, turbo lower intake, K@N filter in the stock housing and a cold air feed, made a massive different and MPG didn't change, next was installing a 4544 pump and woo hoo she could move, MPG dropped one. Then came the turbo setup, city MPG stayed the same, hills and towing went from 11/12 to 16 mpg.

 

[turbovanman]

:mad2: What happens exactly over 1100 EGT? IMO it is a myth as my 1986 6.2 Military precup take out longblock dropped in the 1995 suburban will take 1550 EGT sustained with no issues. I get tired of the myth of high EGT's doing anything alone - it doesn't. So quit scaring people or giving them unnecessary worries. High EGT may be bad for economy, but, that's about it.

Thanks, I needed another quote, I think too many get hung up on this, my EGT gauge broke awhile ago and I know I am running way more than 1200 as I am hitting 20 psi at WOT going up stupid steep hills, foot to the floor and black smoke out the rear, :rof:

Gotta get it fixed so I can see how high she's getting.

 

[WarWagon]

For 200 HP and the torque of the diesel the small GM turbo would do the job. The diesel torque will be night and day over the 350 gas in 4 low.

 

[Chevypoor]

We have discussed a turbo as a future option. We are thinking that initially we will get the truck running and the all the bugs sorted as a NA rig and then if the performance is not were she would like it add a turbo. Since I am giving serious consideration to an A-Team trubo for my truck there may a good used GM-4 and turbomaster laying around the garage.

War Wagon, should I go with the military pre cups since I know from reading about your 6.2 that the NA cups held you back. Or should I use the pre-cups from my VIN S 6.5 since I am considering a re ring/ turbo upgrade.

200 will be a stretch with an n/a diesel.

Turbovanman I to thought 200 was a stretch but I seem to remember/ reading seeing that as a spec on the military 6.2's. I was thinking 180 or so would be more realistic.

She was getting 8mpg! Anything is an improvement there....

I agree about the EGT myth... although I did have gauges with only the exhaust and downpipe done. It would hit 1000 easy with no load. Now with the rest of the mods I have to work to see 900... towing. Now for you heavy haulers around here I usually only pull around 4500 lbs... I am sure if I was pulling a bigger load they would be higher, but boy did the tune and turbomaster make a huge difference.

The Heath cam is pricey but he claims 20 hp on the cam on his website.

 

[WarWagon]

Low RPM off road rock crawling you want the turbo to come on immediately. The ATT and Hx40II need around 2000 RPM to light. Even at 1500 RPM it is too high of an RPM off road. Even with the large tires I don't see the small truck being enough of a load to keep a larger turbo lit long. This is the one case I would recommend a small turbo lake the factory turbo. Maybe even a low ratio transfer case. You can best answer this by knowing what engine rpm you usually ran with the 350. Was it over 1500 most of the time? Over 2000 RPM?

Best times I had with the 6.2 NA Suburban was off road or dragging others with gas engines around the parking lot with the hitches chained together. I know... :redneck:

I am not a fan of smoke as it makes people want emissions that is costing the USA big money on shipping now. I make an effort to keep it down myself. Not saying I am successful...

 

[Chevypoor]

It has terrible gearing... 3.08's front and rear. She turns about 1800 at 60 with a 3spd auto. She usually only ran it into the low to mid 2000s at the gear change.

Low power is great off road... my wheeler is a 2.8 v-6 83 s10. Only rated at 110hp. Real slow on pavement but she comes into her own in the dirt.

 

[turbovanman]

For 200 HP and the torque of the diesel the small GM turbo would do the job. The diesel torque will be night and day over the 350 gas in 4 low.

Agreed, I towed 5500 lbs the other day, total combined weight of the my setup was 12,000 lbs, even with 3.08 gears, didn't skip a beat, even beat some Semi's going up a steep hill.

We have discussed a turbo as a future option. We are thinking that initially we will get the truck running and the all the bugs sorted as a NA rig and then if the performance is not were she would like it add a turbo. Since I am giving serious consideration to an A-Team trubo for my truck there may a good used GM-4 and turbomaster laying around the garage.

As suggested, the stock turbo will be better suited, instant off idle boost whereas the turbo's listed are more of a towing turbo and will be awful for idling and rock crawling.

War Wagon, should I go with the military pre cups since I know from reading about your 6.2 that the NA cups held you back. Or should I use the pre-cups from my VIN S 6.5 since I am considering a re ring/ turbo upgrade.

Still learning but based on your intended use, I'd keep with the smaller precups.

Turbovanman I to thought 200 was a stretch but I seem to remember/ reading seeing that as a spec on the military 6.2's. I was thinking 180 or so would be more realistic.

She was getting 8mpg! Anything is an improvement there....

I think 180 is still pushing it for an n/a, I was looking at a HD 6.5 pump rated at 170.

I can't believe how much MPG I picked up towing the the turbo, its unreal.

I agree about the EGT myth... although I did have gauges with only the exhaust and downpipe done. It would hit 1000 easy with no load. Now with the rest of the mods I have to work to see 900... towing. Now for you heavy haulers around here I usually only pull around 4500 lbs... I am sure if I was pulling a bigger load they would be higher, but boy did the tune and turbomaster make a huge difference.

The Heath cam is pricey but he claims 20 hp on the cam on his website.

Be interesting to see the piston tops when you take her apart.

Not sure about cams, I do have a cam grinder and says a small gain can be head but I think there are other area's to improve first.

 

[Chevypoor]

I am thinking I will stay with the current 6.2 NA cups. We are not even planning doing much to the motor other than injectors, glows, and a rebuilt IP. The odo has 245k and the motor has zero blowby and idles very smooth. Appears to be the original motor. Smokes a little on startup but she clears very quickly.

I will probably leave the cam alone as well... I do not think it will necessary to achieve her goals.

Thanks for all the help and I will update our progress in the project thread I started.

 

[turbovanman]

I will probably leave the cam alone as well... I do not think it will necessary to achieve her goals.

.

Good idea, cam's usually move the powerband up.