Thanks in advance to those who already have a hybrid build and take a few minutes to help with these questions.
I have the oportunity to purchase a 97' 2500 suburban with a fresh 6.2 bottom end with new 6.5 heads and the remainder of the original 6.5 setup on top of it. It has about 5k miles on this setup and he has other trucks he drives so it needs to go...
The seller threw about 5000 dollars at this build but doesnt know a whole lot about it other than it runs good and gets good mileage.
The truck has a small lift with 35" tires and 3.73 gears and a rebuilt 4l80 a few years ago.

Concerns are will I have any cold start problems with 6.5 chambers on a 6.2 bottom end?
What mpg could I expect from this setup riding on 35" all terains?
Egt would be an obvious concern and while it would mostly be a driver over a towing truck if the turbo was in proper shape would I routinely be seeing 1100 deg exhaust temps with a stock pump and tune while towing something like a tandem axle travel trailer?

I guess the main concern is 35's with 3.73's and 6.5 pre cups will equal hot engine with poor mpg and towing capacity.
Let me know if my thinking is off base or correct on any of these points.
Thanks,
Mike

 

Backdrop: 1993 Chevy 3500 CCLB Dually. 6300 lbs with me in it. About 12 seconds 0:60 time when I had fuel turned up on the 6.5T IP. (I have since swapped that for a 6.5NA IP for comparative purposes. And yes, it's slower.)

When I built my hybrid (, the thought of calling them hybrids), I used 86 Military 6.2 bottom end, bored 0.020" over, new stock crank and balancer, stock rods. I used a set of 93 6.5TD heads with turbo precups, intake and exhaust manifolds, and turbo with downpipe. I port matched and polished the heads, intake, exhaust, and turbo exhaust inlet. I made a turbomaster (set it to 12 psi) for the GM8 turbo, which has a Porsche K27 compressor (supposed to push 13% more air than the stock compressor.)


Now to your questions:
Cold Start
Since I made my own manual glowplug circuit (complete from glowplugs to relay to manual switch in dash), I cannot tell you if you will have cold start issues with the factory setup. On any given day with the temps above freezing, I cycle the GPs for about 6-8 seconds and it starts right up, no problems at all. On days when the temp is between 10-32F, I cycle the glows for 8-10 seconds and it starts right up but marginally rougher than normal. When the temp is below about 10F, I cycle the glows 8-10 seconds, start up and then afterglow. Afterglow is the term used when the PCM cycles the glowplugs right after startup. If your factory glowplug circuit works as intended, it should work just fine.

Economy
I don't have 35" tires or a Suburban, but a full length Sub and my truck (also with 3.73) probably weigh about the same.

When I had the 6.5T IP (turned up 1/4 turn), I would average 17-18 MPG, loaded or not. I have not checked my fuel economy since I swapped IPs, but I suspect that it's slightly lower, maybe around 14-15.

EGTs
I have yet to buy an EGT monitor, but I have hauled heavy loads and haven't had any teperature related catastrophic failures. If you leave the stock pump alone, I don't believe that your EGT can get that high, especially routinely.

The 6.2 is gonna show less power/performance than a 6.5, all else being equal. If I had to build another 6.2/6.5, I'd take a different approach starting with a 6.5 bottom end. They always say: "There's no replacement for displacement" and when youre talking about all other parts being equal, heads, intake, turbo, vehicle..., the 6.5 bottom end built with a good block would be best.