How much power can a stock 6.9 block take?

[NapaBavarian]

Down the road this summer I'd like to set a turbo on my 6.9, first chore is to replace the head bolts with ARP studs, I plan to use a Hypermax pulse turbo with an intercooler, I'd like to get reliability but still have plenty of power, but don't need all of the power that this setup can offer, more important that it will run properly at high altitude as well as sealevel, I was wondering if sower compression pistons would be a good idea to aleviate cylinder head pressures a bit.

 

[MIDNIGHT RIDER]

The 6.9 can take all the power that it will produce.

Occassionally, one will burn a hole in a piston when exhaust gasses get too hot.

 

[Agnem]

Lower compression will let you increase your boost a bit, which is the key to more power by being able to burn more fuel. Sounds like a good combination to me.

 

[flatlander]

From all points of view the weak link is the head bolts. Ken from DPS built an idi that put 670 HP on a dyno, but blew the crank out the bottom on his first sled pull. Apparently he figured out how to keep the heads on, though.

So, unless you are planning on spending $15K or more, I'd not worry about the block.

 

[jauguston]

I put a non-pulse Hypermax on my 6.9 last summer. They said to check the torque on the head bolts (were OK). They said the early (83-84) engines were the ones with the weak headgaskets. No need for studs in their opinion. I run up to 13 psi boost and all seems fine - love the power!

Jim

 

[NapaBavarian]

I've looked arround and havn't found anything Anyone know who sells lower compression pistons?

 

[MIDNIGHT RIDER]

Most automotive machine shops can take your pistons and lower the compression ratio.

A lower compression ratio results from removing material from the piston surface, making the compression chamber larger by the amount removed.

High compression pistons have domes or humps that take up room in the compression chamber, raising the compression ratio.

Why would you want to lower compression??

 

[aaklingler]

I'm not sure why he would want to with a non-wastegate hypermax, but I want to so I can stuff 20 pounds of boost in there and not blow the heads off.

 

[Magoo]

I would be leary about milling off the top of a diesel piston even more so for turbo application. I had AMC 401 that the block was milled so the guy could get 13 to 1. To get it down to 8.5 I had to have a special solid copper gasket made. The company makes them for race motors and they were works of art. I was toying with this idea for the 7.3 to lower the comp for higher boost.

 

[NapaBavarian]

I'm with Magoo, I could see milling a very small ammount, but the pistons were designed a certian way, I'd hate to reduce the mass of the piston just to have it melt because it has less material to act as a heat sink

 

[Agnem]

The amount of material you would have to remove to lower the compression ratio is very small. Probably less than .010 Very unlikely to affect the thermal properties of the piston, especially since the piston cooling jets are what keep the piston from melting as it is. If your going to go to that kind of effort, your most certainly going to get them ceramic coated while your at it. I believe Ken will make/sell you these.

 

[towcat]

I would be leary about milling off the top of a diesel piston even more so for turbo application. I had AMC 401 that the block was milled so the guy could get 13 to 1. To get it down to 8.5 I had to have a special solid copper gasket made. The company makes them for race motors and they were works of art. I was toying with this idea for the 7.3 to lower the comp for higher boost.

good idea... but keep in mind you will need adjustable pushrods if you go for a modded headgasket. also, as ken has done on one of his motors, a lowered compression IH IDI is a real bear to start. Dunno why the chebby IDI guys are getting away with 18:1 on their motors but from the wav file of ken's, he will be going through a few starters. oh yea, the chebby IDI piston face is identical to ours but the dish pockets are at 6 o'clock instead of ours at 12 o'clock

 

[aaklingler]

i thought ken's was 16:1???