• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Tahoe motor rebuild

6.2 turbo

6.2 turbo

Well-Known Member
Messages
1,475
Reaction score
247
Location
pa
I decided to rebuild a 6.5 929 engine that I already had and swap this into our tahoe. I don't want to spend a whole lot of money on this. So far I took the motor apart and took the block to the machine shop to get it decked,and cam bearings installed. I got some Jasper heads at the junkyard that seem to be crack free. I'm not quit sure how I'm going to build this motor,but I'm thinking of block filler ,and compression ratio either stock or higher,and o ringing the block. The machine shop owner said if I block fill I will need to rebore the cylinders,which leads to new pistons that are not cheap, so I'm not sure yet what I will do. I'm also thinking of using 12.9 grade bolts for the heads and mains,and a home made girdle. This was a na motor out of a van, the bearings were dated 1995, but it had a mechanical db2 pump,and a crankshaft tone ring,but the crank sensor hole is plugged. I had a talk with Bill Heath about compression and I think I will listen to him this time,although I proved to myself I can make power with low compression it is not that practical for a daily driver. Bill said his race truck has 600 hp and 22.5-1 compression :smile5:
 
It does seem hard to believe,but even if its not 600 I'm sure it runs pretty good,the only thing that baffled me was that he don't blow the felpro head gaskets at that power level and 30 some pounds of boost,and high compression also.
 
As far as I now his only secret is his computer program,every thing else he is happy to share,also gathered he builds his motors to extreme perfection. I'm sceptical of increasing compression,but I'm willing to try it anyhow. Does anyone know what is stock squish area ? Since this block is getting decked, its going to take some home work to figure it all out. Bill has the pistons .007 out of the hole,when I checked mine they were out a hair,guessing maybe .003 at the most.
 
if you step up compression you better get some serious heavy duty pistons, rods, and crankshaft. computer programming my ass. he would make some money if he released tuning like that and all you needed was different turbos and water meth which is what he is running.
 
My main concern is the head gaskets,I'm thinking of using copper,then I can use what ever thickness to get the compression to Bills specs, I am definetly a little afraid of this idea,same as block filling,but I'll give it a shot. I'm imagining a motor with good power under the turbo, which will be the biggest that I can afford,and I might use a nv3500 for close ratio gearing to keep it in the power band between shifts, though it might break. My 6.2 lights the turbo at 2000 rpms and the jump from 2nd to 3rd is to large it takes a little to get spooled again,it has very little power under the turbo which I think is from extremly low compression. The machine shop was supposedly going to work at the block today. If this motor turns out to be a powerhouse I might put one in my short bed s10 that I want to drag race, I got it for free.
 
You can make a 6.5 very powerful by improving flow, like making headers or honing the manifolds and heads (expensive), getting higher lift on the valves with a ground cam (not so expensive if doing rebuild). The larger turbo also helps.

I would stick with 20:1 to 21:1 compression ratio and not try to increase it. the tolerances of piston to head are tight and higher is not needed. Effort better spent in the flow deparment.
 
buddy said:
You can make a 6.5 very powerful by improving flow, like making headers or honing the manifolds and heads (expensive), getting higher lift on the valves with a ground cam (not so expensive if doing rebuild). The larger turbo also helps.

I would stick with 20:1 to 21:1 compression ratio and not try to increase it. the tolerances of piston to head are tight and higher is not needed. Effort better spent in the flow deparment.
Click to expand...

That is where i would use my money too. I know a guy that likes to flow heads and I am gonna have him give it a shot as well as bulid a set of headers that flow better possibly. I would most likely order a cam that is proven to work instead of go custom.
 
Yes its about .040 piston to head clearance with stock gaskets. Both valves are fully shut all through TDC, and are recessed slightly, so there is no piston to valve clearance concern unless modifying the cam profile.
 
My 6.2 heads I bowl ported. I want to spend my money for head gaskets and turbo,a cam is a good idea,but a complicated and expensive one,for me it would have to be a custom ground cam ,but then I would also want adjustable rockers which would take a lot of work and more money. My 6.2 makes lots of power with all stock parts except the turbo and ip, it will spin the tires when the turbo lights in 2nd gear,on a rolling start. A while back I was considering lowering the compression by increasing the precup volume,but nobody knows how that would work,at least the squish area would remain tight.
 
When you say squish area, how is it you use that term compared to compression ratio.

You can have a cam ground any way you want for $140 at some places that have done a 6.5 cam before. And you dont need anything wild, just to get a little more lift. When building an engine youre already replacing cam bearings and such that its not really that big of deal. SSD sells a cam to give .02" more lift with everything else stock, but it is expensive, and I dont really like its cam lobe event timing.

MaxPF managed to use 1.7 rockers with stock pistons and cam, so with stock rockers you shouldn't run into a problem running a few more degrees duration to gain .04" lift, which is 10% over stock. Bill Heath runs stock springs up to 5000rpm, so I have to imagine they arent going to fail under a little more tension.

If interested, I also had Rhoads modify a set of lifters to their variable duartion tpye that bleed down at low RPM but reach full duration and lift at 3000rpm. You just mail them a set and $110 and you get them back a week or two later modified.
 
Last edited:
Follow Bill's directions and you should be good to go.....he is more than a 'forum expert'...
 
I can't imagine that a reground cam would not need adjustable rockers,unless it is ground within the lifter preload area you already have. I might look into it some time ,maybe for my 6.2. Too Buddy, the squish area is the distance between the piston and head,but compression ratio will also include the prechamber.
 
Last edited:
Thats what I figured you meant by squish area, but how can you use squish area in a positive or negative manner. Say you have a final compression ratio of 21:1, what would it matter if your piston clearance was .05" or .02".

I hear things like "positive" squish or "tight" when does that really matter? Does it matter if you lower your compression ratio by machining out around the valve seats, or just using a shorter piston that increases piston to head clearance. Either way its all a volume expansion and not a length or area measurement.
 
I'm a little confused here also,but I guess it has something to do with how the recardo bowl swirls the air,and how well it goes in and out of the prechambers. I also wondered if squish area means more than actual compression ratio,or if it don't mater that much. I pretty much decided that compression should be lowered in the prechamber if I want to lower it.
 
The smaller the squish spot would seem to have more violent turbulence throughout the precup I would think?? IT may change the focal point of the explosion?
 
You must log in or register to reply here.
Back
Top