6.2L turbo

[1999gmc]

My son has a 1983 Jimmy with a 6.2L that has been turbo'd since new. Was wondering if we can put 6.5L heads, and keep his injectors and manifold and run either an ATT or one of the HX hybrids? Don't want to run a 6.5L turbo manifold because I'm pretty sure it will hit A/C accumulator or evaporator box. Truck still runs great and has low blow by.

 

[Twisted Steel Performance]

Yes you can use 6.5 heads, the trouble if it's trouble, is you might need to fab a down pipe, not sure the ones made for GMT400's will fit in the jimmy...

 

[Will L.]

Manifolds yes. Injectors i dont think so. 6.2 and 6.5 injectors are different i think- not 100% which were different threads.

Are your heads bad?

If heads are ok but small precus is the issue, You could run 6.2 heads and just out the precups. Sometimes you need them machined and sometimes not.

Also some 6.2 heads have bigger valves than 6.5 and will flow better- one of the reasons some 6.2 got better mpg than 6.5. Chopping 6.2 valves into 6.5 head has been done for several hopped up for mpg and power. Heaths lsr is probably the most well known example.

 

[1999gmc]

Do pre cups make much difference performance wise? I mean would it be worth the work to pull the heads and install different pre cups and ATT or HX turbo vs. this small turbo thats on it? When he gets home I'll have him grab the paperwork for this turbo kit. It's not Banks or ATS. The guy had the original invoice showing the turbo install at the dealership and had the installation book for the turbo kit. We were thinking of pulling the motor to reseal everything and fix the downpipe where it has rubbed through from hitting the frame over the years with a broken engine mount.

 

[Will L.]

Your stock 6.2 precups MIGHT is the best answer. Ive seen 6.2 with hx35 have no issue. I’ve seen slightly larger turbo put out smoke at every stop sign without trying too, but above 15 mph everything is perfect. Depends which turbo and how much fuel. There are some that figure the older precups might be better for power and newer ones are more emissions geared, I don’t think so. In my experience once you get to the big boy turbos like ATT, hx40, etc. -Yes you will want bigger ones to avoid the smoke at take off and better power from a stop.

@WarWagon has his 6.2 smoke it up, I am sure he just hasn’t seen this thread yet and when he does maybe can post links to his story.

You could probably spend 10 hours reading up on precups at this site alone.

If your gonna put on new heads for sure, maybe dream of some fully done p400 heads while available from Chris?

Not sure what the desired outcome or budget is.

If you are not planning on getting inside the engine, put it on and see. You can always keep the fuel turned down until you want to refresh the engine. Then do them at that time.

 

[ak diesel driver]

Unless you have the coarse thread injectors they're somewhat interchangeable. Internally they're pretty much the same. Could have your injectors rebuilt if you keep the 6.2 heads.
IIRC WW came up with some information that the 6.2 precups are slightly different diameter. So I'd want to verify that before shelling out money on precups.
Could have yours machined bigger.

 

[1999gmc]

Unless you have the coarse thread injectors they're somewhat interchangeable. Internally they're pretty much the same. Could have your injectors rebuilt if you keep the 6.2 heads.
IIRC WW came up with some information that the 6.2 precups are slightly different diameter. So I'd want to verify that before shelling out money on precups.
Could have yours machined bigger.

We just did injectors about a year ago and had them set to 2200 psi. So that's why I was thinking of keeping them. They're only a few $100 if we need different ones for 6.5 heads.

 

[Will L.]

You need to check which ones it uses. There were different 6.2 heads/ injectors.

 

[Rockabillyrat]

There are 3 different injectors for the 6.2. 82 had course threads. 83-92 are normal fine thread like the 6.5. There is a long and short version of them though. As long as you have the correct thread pitch they will work on 6.5 heads. But there was a change in the angle of the injectors from the old 6.2 heads to the 6.5. I can't remember what year. So you might run into an issue with your injection lines not fitting. Might be able to tweak them but it's not recommend to bend them. Both long and short 6.2 injectors use the same specs so you could buy new lines for a db2 6.5 and run short injectors with 253 nozzles. That will keep every thing the same as far as the flow rate curve compared to what you have now.

As far as precups go I personally would swap the 6.2 cups into the 6.5 heads. I'm one of those people who believe the larger "turbo" cups and 6.5 injectors are for emmisions control. But there is no proof either way.... Yet. You can dig up my precup thread and make your own opinion on the subject.

 

[Rockabillyrat]

I forgot to mention running 6.2 cups in 6.5 heads requires machine work. So running the n/a 6.5 cups would be easier and cheaper.

 

[WarWagon]

What are your plans for it? Offroad, towing, daily driver? This is the most important question to build the rig for.

What's leaking and how bad? Once you pull the engine and find out it has cracked main webs... Better not to know sometimes. Re-seal and gapless rings to help blow-by... IMO these rigs never stop sweating power err... leaking something even when new. If it quit leaking it means it ran out of oil!

Why the hi-pop on the injectors? You have a IP Pump builder backing this decision up? If you run into white smoke, no hot starts, and general drama starting... Just saying I am literally changing the 2350 pop injectors out of my truck this past weekend after fighting hard starting for 5 years. Generally use the turbo pop pressures unless you have a custom built pump. The turn-key ease of starting like my 1992 project truck with standard turbo pop pressure or 2350 pop's 1/2 to full throttle in reverse with the brakes on watching white smoke fog rolling in till all 8 finally light off. Just saying it didn't work well for me nevermind going through several pumps.

You reach a fuel limit with NA precups AND big turbo's. You won't notice NA precups with a small GM sized turbo because the turbo is the restriction.

84-85 surplus military 6.2 NA's I have run didn't like all the fuel I could throw at it. Had a hard time clearing the smoke at any RPM with 17+ PSI boost off the ATT. Careful tuning got it to 6.2 NA levels.

I am leaving a stop light with AC on, Fan locked up, over 100 degrees of hot dry air outside, with or without a trailer. Blowing smoke till the damn thing starts spinning 2000 RPM where the big turbo lights off. Big turbo's change the RPM range of the engine: once you understand this trade off the better you will enjoy it. 2000 RPM pulling like a freight train till read line rather than fighting a small Asthma Attack small turbo all the way to red line. I have used a BD Spool Valve and finally a Yank Stall converter to "slip" the engine past 2000 RPM from a stop light. On my build you got a second or so after pinning the throttle before the turbo lights and then the rear wheels light.

I generally built it to tow 550 miles a day over grades beyond 7% that go for miles. YMMV

 

[1999gmc]

Just daily driver and on the injectors I was talking to Dennis(slim shady) after I installed my ATT on my 99 and told him we were thinking maybe to run one on the old 6.2L and if he knew if the DB2 could be made to run well with that bigger turbo and he said if I'm doing injectors anyway have them set to 2200. So far the 83 Jimmy starts quicker than my 99. Always has. The starter barely engages and the 6.2 fires up. My 99 will turn over probably 2-3 times before it lights off, hot or cold. And who knows, the company I bought the injectors from may not have set them to that, I never had them checked. Just took their word for it. It will be interesting to see if there are cracks in the block. My son is thinking of just running this one and buying a 6.5 from Teds and have it all ready to just drop in on a weekend.

 

[WarWagon]

If you don't turn the fuel way up it can run well with the ATT. I have run 6.2 pumps turned up to 6.5 stock fuel levels and have very little smoke. That doesn't take full advantage of the big turbo, but, not everyone needs to like I do.

Keep the higher pop pressure of the injectors in mind if it starts to give you trouble. Chain stretch is a real factor on these engines. So you may need to advance timing often with the higher pop injectors. I will let Dennis know the "trouble" higher pops cause long term.

 

[Will L.]

I know when we were swapping new factory injectors for our in house rebuilt and balanced sets, we found about 25% of them were in the 2350 range already. It seems new Bosch are coming pretty well balanced from what I have been hearing. We found even with couple hundred thousand miles on rig the balanced 2350 were starting easier than unbalanced factory sets. 'Coarse we had real diesel fuel back then, which got me to thinking...

And some recent testing I have been doing since hearing of so many people like @ak diesel driver and @WarWagon having way more issues nowdays and with the ehonal/ methonal cut in, it seems we are running thinner viscosity fuel than we used to.