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I always ask when these types of builds pop up: Why didn't you move to a roller camshaft? I'm sure given the custom route you had to go that the price would be close to the same.
Oddball engine project; which oil to use?
- Thread starter A_Harman
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9 to 1 compression with that hot cam is not optimal.
Your intake is closing late, and your compression is going to be lower than stock.
10.5 to one or a bit more should be great for street use and fuels.
If you don't do this, you are throwing away a lot of power for no good reason. Might as well go to a less aggressive cam.
Your intake is closing late, and your compression is going to be lower than stock.
10.5 to one or a bit more should be great for street use and fuels.
If you don't do this, you are throwing away a lot of power for no good reason. Might as well go to a less aggressive cam.
There were a few reasons for that.
1. I figured out that I could get my targeted valve lift within a streetable duration number using the large-diameter flat tappet that came in the engine.
2. The OE lifter is a hollow-body chilled iron unit that is actually lighter than a roller lifter.
3. The design of the lifter bore area in the engine block and heads made it impossible to use the link-bar lifters that are available at a reasonable price.
4. The .990 lifter bore diameter either required sleeving down to use off-the-shelf .842 keyed lifters, or procuring ultra-expensive Top Fuel lifters in a custom diameter from Jesel.
Overall, the flat tappet decision was made for cost-effectiveness.
1. I figured out that I could get my targeted valve lift within a streetable duration number using the large-diameter flat tappet that came in the engine.
2. The OE lifter is a hollow-body chilled iron unit that is actually lighter than a roller lifter.
3. The design of the lifter bore area in the engine block and heads made it impossible to use the link-bar lifters that are available at a reasonable price.
4. The .990 lifter bore diameter either required sleeving down to use off-the-shelf .842 keyed lifters, or procuring ultra-expensive Top Fuel lifters in a custom diameter from Jesel.
Overall, the flat tappet decision was made for cost-effectiveness.
Originally Posted By: mechtech2
9 to 1 compression with that hot cam is not optimal.
Your intake is closing late, and your compression is going to be lower than stock.
10.5 to one or a bit more should be great for street use and fuels.
If you don't do this, you are throwing away a lot of power for no good reason. Might as well go to a less aggressive cam.
You're thinking from the standpoint of engines that have 4" bores, not 5.185" bores. I was tempted to go the 10+ CR route, but keeping in mind that detonation resistance decreases with flame travel length, and that the engine has iron heads with archaic combustion chamber designs, I went safe on the compression ratio. The stock engine had 7.5:1, so I have made a substantial step up.
I guess it all depends on where I'm posting; the board members on the GMC Truck website think I'm crazy for going as high as 9:1.
9 to 1 compression with that hot cam is not optimal.
Your intake is closing late, and your compression is going to be lower than stock.
10.5 to one or a bit more should be great for street use and fuels.
If you don't do this, you are throwing away a lot of power for no good reason. Might as well go to a less aggressive cam.
You're thinking from the standpoint of engines that have 4" bores, not 5.185" bores. I was tempted to go the 10+ CR route, but keeping in mind that detonation resistance decreases with flame travel length, and that the engine has iron heads with archaic combustion chamber designs, I went safe on the compression ratio. The stock engine had 7.5:1, so I have made a substantial step up.
I guess it all depends on where I'm posting; the board members on the GMC Truck website think I'm crazy for going as high as 9:1.
Yeah, it is a heavy duty TRUCK engine, after all!
What a monster. I sure hope I get to see it at a show somewhere.
What a monster. I sure hope I get to see it at a show somewhere.
I noted the very large piston area, for sure. And those iron heads hold heat - you gotta watch that ignition advance!
I still maintain that a real hot cam is not best for that total package.
At least bias it with one that has shorter duration, and higher lift [than the full race type].
I still maintain that a real hot cam is not best for that total package.
At least bias it with one that has shorter duration, and higher lift [than the full race type].
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