sadisticsavage

I was just wondering if I swapped some heads from a 71' Olds 455 to a 75' Olds 455 with "J" heads would it make a difference on power output? I heard the "J" heads are a lot more restrictive as far as flow, but I am not sure how true that is. The 75' 455 was rebuilt by Joe Mondello for a motor home and is on sale for $200 on craigslist. The motor has 100,xxx miles on it so the bottom end is still in rather fair condition. The 71' 455 I bought was said to have been in great running condition, but it was advised to have the pistons reringed and bearings re-done mains and rods. So that made me feel a little sketchy of the actual condition. Now myself being a gentleman with no patience I was just going to buy a 455 with a good bottom end so I could get the car going asap. I plan on using the 71' block still but it will be a full rebuilt pistons, rods and cam. But for now if I were to get the car going would just be a new intake and remanned quadrajet carb. Thanks for any info I can get on this, if I need to do some further info giving as far as the 71' 455 I have I will.

tru-blue 442

I think a lot would depend on
the dish of the pistons as far as
making power. The 71 G heads
could be large valve, so that would
be a plus for sure. There are more
guys with far more knowlege than I
who will hopefully chime in to help.
Good luck with it.

sadisticsavage

That's mainly what I was worried about, valve and piston interference. The 75' motor does not belong to me so I won't be able to drive over and rip a head off to see. Hopefully someone would know so I don't end up buying a motor for nothing when I could have the bottom end of mine rebuilt for about the same price. Thanks!

oldstata

There isn't any valve interference between the heads from what I have learned the olds pistons sit down a bit (stock ) and you can deck the block about .025 and mill the heads down as well . The j heads don't flow as well, but I am not sure if the average guy would feel the difference with out other upgrades as well.

sadisticsavage

Oh alrighty... I just figured I'd do it this way to start off as a good base. Eventually I would like to do a mild cam but I just figured I hear so much about the "J" heads really not being that good at all. But I'll take this route as long as they do not cause any problems and see how it goes. Mid summer I will probably do the cam.

oldstata

Did you here the motor run ?

If it's a motor home motor it most likely has a mild cam for towing

I would consider any motor a core unless I heard it run or if they had very well documented paper work that you could call a shop and verify with

joe_padavano

Under about 4000 RPM (and depending on cam, induction, and exhaust), you're unlikely to see a measurable difference, especially considering that a motorhome engine likely has an RV cam in it that peters out at 4000 RPM or so. I'm sure this motor is also an 8:1 CR motor. Swapping the heads will not change the CR.

J-(Chicago)

It's true the J heads are more restrictive. In fact, the bowls are about 1/4" smaller.

You would have to port a decent amount of material out of your J head just to turn it into a stock G head size.

Will you notice the difference in a huge motorhome? I have no idea.
Heck, maybe the j's would be better for mileage. I have no idea.

As far as a G headed 71 motor, and any 73-76 motor.... They are identical as far as bottom end goes. Same everything.
Once you put fel-pro headgaskets on any one of them, they're only 7.8:1 compression.

matt69olds

In Bill Travoto book he says there isn't a big difference in port size and flow ratings with the BBO heads, with the exception of the J heads. He even says to remember J=junk. However, unless the engine has a camshaft that would require better breathing than the J heads provide you probably wont see much of an improvement. If your installing a more aggressive camshaft I would suggest the earlier heads, with thin head gaskets with the heads milled .060. You will need to machine the intake side of the head or the intake itself to get it to fit correctly.

sadisticsavage

Alrighty. Well for now I guess a little experimenting won't be to bad. I will just buy the 75' 455. And yes they do have documented paper work on the rebuild. Thanks for all the info guys. I will just throw the earlier heads on the 455 with the W/Z manifolds and a new intake and carb and let everyone know how it runs.