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Tahoe motor rebuild

Using tables I made for calculating CR and TDC temp and pressure for given boost pressure, CR and IAT, it would appear that at 50psi of boost you have about 40,000 inch pounds (3300ftlbs) of torque/force up on the head for each cylinder when it hits TDC. Granted some of that likely goes up through the valve seats and around the rings, but youre still going to have ridiculous force on the heads, and it will increase momentarily when combustion actually happens. That was assuming a 16:1 CR with 6.2 pistons shaved .09". So I think you would want a few more head bolts to bring your clamping force/area up before running 50psi boost. How many head bolts or size of the heads on the bolts are there per cylinder on a Dmax or other heads in comparison? A more reasonable 30psi of boost would still result in like 25000 in-lbs of force on each cylinder head. Then add the force from one of the other cylinders on that side of the engine being at like half compression and there is more force on the head.
 
I'm hoping that 17 bolts is enough,and the gasket was the main problem,might try 30psi boost at first . I definetly got carried away with boost pressure on the 6.2 ,but it seemed to need it along with extreme fuel to make power. I blame that on the low compression,and also a H1C that was pushed past the choking point.
 
Something tells me that you may actually get higher horsepower at higher RPMs with less boost from a turbo that will only produce 30psi. Or by putting a wastegate at 30psi on yours.
 
I would like to check drive pressure also. Someone told be me low compression won't make turbo lag ,but I'm not so sure.
 
That's what I'm hoping for. At the very least it will have more power under the turbo. This will make the lag less noticeable.
 
If turbo lag is a significant concern of yours, you could get a Delta 206 camshaft. It opens the exhaust valve a bit earlier for faster spooling.
 
Maybe a cam for the next motor. If I change to many things I won't know what to blame when it doesn't run right. I might start with a stock pump and injectors,and possibly turbo just for that reason. So far the only modifications are compression and higher valve spring pressure,and considering adjusting valves looser,with shims under the rocker shaft.
 
I was reading about an article in Jun 2010 DieselPower about Heath's racer, using a 22.5:1 static CR and 30psi of boost. It points out it never goes over 1000 miles between tear downs and inspection. It also points out he uses a lot of water injection and has EGTs over 1400F on his runs. The article claims Heath uses a modified camshaft for better power at higher RPM.

For anyone that wants their engine to run for more than 1000 miles I wouldnt increase CR. I dont think it needs to be lowered much, but some would be prudent on something wanting to make lots of power for a long time.
 
My 6.2 had egt's as high as 1600 degrees . Low compression didn't help there. Actually I think egt's may be lower with high compression,due to better efficiency.
 
lower compression with adequate oxygen will burn the fuel and can achieve lower EGTs. He was also using over a gallon of water for half a gallon of fuel. So he would have been way up there too without that.
 
I'm hoping to not need water injection,but it might come to that.
 
I'm having trouble adjusting the valves,kinda weird that I never heard of any one doing this. I don't see why it would be less important on a 6.5 than a 350 chevy. I don't know what stock preload is but mine was over .100 thou. I now have them adjusted at .035 to .025 thou ,on bank 1 . I did this with shims under the rocker shafts and grinding the valves that were to long . Also in the process cracked two pedestals. :eek: I'm about ready to make my own rocker setup with studs and big block roller rockers .
 
By adjusting the valves are you trying to get the clearance correct between seated valve and the rocker? Or getting the springs set to a certain pressure with shims?

Or you are talking about the lash on the rocker and pushrods, in which case most people probably do not worry about it too much on the hydraulic roller lifter that will compensate some.

I hadnt realized it before but the DMax uses 6 head bolts per cylinder, so 24 bolts per head, so it can hold more cylinder pressure from higher boost and heat without blowing head gaskets, that and it uses 17.8:1 CR.
 
I'm setting the amount of lifter preload , push rod is compressing the lifter .025-.035 ,when its on the bottom of the lobe. Stock was over.100,but my block is decked.010, plus the valve height's are not even. I checked into adjustable push rods from Smith's ,but they have.049 wall thickness ,and he didn't want to recemend them for a performance engine.
 
turbonator said:
The 6 bolts per cylinder needs only 18 bolts, the 6.2/6.5L has 5 per, with 17 bolts..... the inner two cylinders share bolts.

jim.
Click to expand...

That does make more sense, that 6 per cylinder has a much more logical balanced layout than the 5 per cylinder design. Next there should be the 21 bolt 6 per cylinder design with thicker cylinder walls so they can make even more boost.
 
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