[RicksGTO]

I love the HO motor and think it's underrated by most people, especially outside the Pontiac world, but I don't think many people here would wish anything less than the best for the SD numbers. Let the numbers be what they may! Are you tweeking the cams in a similar way to the versions of the 068 in your HO builds, and will you be using the 041 cam or the 744 profile? My guess is if you stick with the 744, the HO will win again by a small margin, if you use the 041 then I think the SD will come out on top this time. Either way, this will be very interesting! Thanks for the great posts and keep the updates coming!

[Mark Weymouth]

We will be using a 744 profile as that is what the rules require.

The 041 cam within the confines of our rules and max compression for an SD would actually hurt it. That has been one of the current problems with the SD's. To much .050 duration for the compression.

Pontiac needed a cam half way between the 068 and 744 in duration for the HO and SD. That would have been perfect in conjunction with their compression ratio's.

Mark

[giles]

Originally Posted by Mark Weymouth

We will be using a 744 profile as that is what the rules require.

The 041 cam within the confines of our rules and max compression for an SD would actually hurt it. That has been one of the current problems with the SD's. To much .050 duration for the compression.

Pontiac needed a cam half way between the 068 and 744 in duration for the HO and SD. That would have been perfect in conjunction with their compression ratio's.

Mark

Mark, if you don't have to live within the confines of "rules" what would you estimate the minimum acceptable CR for a relatively stock HO or SD with a 744 cam to be? 9, 9.5, 10?

[Mark Weymouth]

Within the confines of the rules Paul's SD can make it to 9.5:1 and that seems to be area on the computer where the 744 cam starts to work well. If you want to stick with a pump gas motor and have that cam work the 9.5-10:1 range seems to be a honest location to start from what we have seen.

Wolverine and Melling have been our best picks for over the counter items. I have Mellings in several cars.

One the RA IV's we have dyno'd everyones RA IV option and they spec out on paper the same usually but not in the motor. So far the Melling has been the best option there.

Mark

[Jim Rotella]

Hi Mark,

I've been really enjoying all of your expert input to this 455 HO thread. It's not often that we get to see a builder's comparison of these two great engines in in pure stock form. I've got one question. Within the confines of the rules, if a 9.5:1 compression limit is in effect for both engines, I would think that the SD 455 with the stock 744 cam would benefit quite a bit more from a compression boost of over a full point than the 455 HO with the stock 068 cam. What's your thoughts on this? Thanks again for keeping us up to speed on your progress.

Jim