Thread: 7.4 to 8.1 conversion

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I am considering replacing my throttle body 7.4 with a 8.1 short block. Need mope power for towing.

Has anyone done this there looks to be a few more things to consider than a simple bolt on the heads and go.

The head bolts are a different size, probably have to drill out the block to bigger size for 7.4 head holes.

Using nv4500 manual trans, which flywheel works?

The holes are a different size? Everything is pretty much identical between the 454 and 496. The 496 just has a stroker crank. Both are external balance and I don't think the balance changed, so the flywheels are probably the same. If not, just buy the flywheel from a newer truck that came with the 496. I see no reason for it not to work. The injection setup should be able to compensate. The new motor just going to pull a little more air at WOT.

I looked closely at using the top end too but the heads have no water crossover ports, it is done thru an added tube attached to the front of the heads. That would be in the way of mounting a/c, p.s. and alternator. To this point there is no throttle body manifold made for those heads.
The front pully/ balancer is one piece but measures out the same for drive belts.
I was suprised to find the firing order different. this is what makes me wonder about the balance.

You're getting a short block. Aren't you just going to reuse the heads you have on your 454? If so, you won't have to worry about any compatability issues with components that bolt to the top end of the motor.

I have the entire engine, it just looks like more trouble than it's worth to use more than the bottom end.

What I need is towing power, the 8.1 should give me abot 60 ft. lbs and 75 hp,, most of it around 2500 rpm, this engine came out of a motorhome and has 2300 miles on it.

There are 2 more head bolts in a 8.1 head than a 7.4 and one other is slightly in the wrong position,
What has been done to compensate for that? The 2 extras look like they could be done without but the slight relocation of the 3rd one is what concerns me.

If you want some REAL towing power, look into either a supercharger or a turbo....

This conversion will get me nearly 100 hp and 100 ft lbs, I don't need any more than that nor do I want the problems that come with superchargers and aftermarket turbos. The two extra holes are in places where they don't do much unless you are using aluminum heads and the one that is slightly mis placed could be located correctly. I was hoping to find out if someone had done this before and if there were any other resulting problems