Warhead

BACK TO THE SUBJECT....I have run both engines in the same car, and this is my experience. This is by no means scientific, and I no longer have the time slips for a more direct comparison of both of these combinations. Basically a high 11 second car.

The 455 launches harder. Not a whole bunch harder, just a little. Be ready to shift because you WILL SOON be out of useable RPM. With my real good set of heads (275 cfm on the intakes), 5500 was it. It made less power above that rpm, and ONLY RAN SLOWER.

The 425 we ran launched hard for what it was, just not quite as hard as the 455, but would keep making power longer. Best shift point was 6200 rpm. The car did run faster with this engine, even though it was saddled with lesser heads. Less parts breakage, and quicker times meant more fun.

That was our experience. Love it or leave it.
Hope this helps Bullet1
Jim

captjim

So the 425 launched less hard (better for a consistent R/T) revved higher, and was quicker. In your opinion, having raced both, do you feel the the 425 revved more quickly?

Warhead

I would not say it revved more quickly...almost identical when you were tuning/idleing around, or out of gear.
They both have 77-78 pound crankshafts, and heavy assed P/R assemblies.
When it got down to business, it seemed to have more AT the business end, so to speak, when you got some rpm in it.
The car kept pulling hard for a longer time with the 425, as opposed to the 455 ritual of launch and shift immediately.
I think the 425 Horse powered better.
They still seemed to rev at about the same rate, as I recall.
I imagine if I had kept the 455 in there longer I would have sorted it out, and ran just as fast, if not faster, but not due to spinning it any higher. I know I would have to re-gear the car for the lower crankshaft speeds.
It definitely was not as much fun as the 425 was to me.
Just my experience, as I recall.
I may have to pull the 425 out of mothballs.
Jim

captjim

Thanks for the info!!

88 coupe

Following Warheads lead:

Same car with nothing changed except the shortblock.

455 = Under 8.5:1 CR and a larger cam = 11.95 at 116 MPH on a good day.
425 = Over 8.5:1 CR and a smaller cam = 11.95 at 114 MPH on a good day.

Read into it, whatever you wish.

Norm