[455Grandville]

Originally Posted by 79Poncho

Hello all,

I'm in the planning phase of my 455 build and I'd like to see what people's thoughts are on the value of porting work for my build.

I've got a '74 4-bolt main 455, std bore.

I'm planning to run forged pistons (Sealed Power L-2359NF - Speed-Pro Forged Pistons) with stock rods on a stock crank

I'm considering the SD performance hydraulic roller "Stump Puller" grind

I have a set of 6x-8 heads that came off a 400 that I wiped the crank on. They've been milled to reach 93cc chambers and have 2.11 and 1.77 valves. I think it's about 9.57:1 compression.

I've thought about porting these heads at home using Jim Hand's book, but am hesitating to get started due to repeatability concerns from port to port. I'm considering if it's worth to do the work myself, pay to ship the heads to SD Performance for CNC work, or just bolt them on as-is and see how it runs.

I'm not looking for anything crazy, any form of 455 is a bump up from the Oldsmobile 350 small block I'm running now.

Thoughts? I'd really like to hear from guys building and running mild 455 combos to see what the impact of 20-40 cfm really is.

Thanks,
Geoff

I built mine in 2001 and had a place shot peen the rods and I resized them with ARPs. Today that might cost you close to new aftermarket rods, so like another poster said I’d go that route.

I started with a like new 1975 200 horse smogger with around 26,000 orig miles and yanked it because of an oil leak the car had due such limited use. It ran great, but it lacked power.

I rebuilt a 1970 455 short block w/.030” forged trw pistons & balanced it & used a torque plate.
I went with the larger chamber 6X heads, I Milled em, and pocket ported em, did some bowl blending, a 3 angle valve job with new stainless valves. I believe the compression came to 9.4 to 1. The porting and bowl blending I did just what I was taught with Ford FEs and applied it on the 6xs.
Added a 1971 non egr intake as I was told they were superior to later egr manifolds, comp cams 255 Dual Energy cam, roller tip rocker arms, and added Ram Air Restoration exhaust manifolds.

Really, nothing special and I’m not sure how many cfms I gained but the end result was night and day. For a tall feared land yacht it moves pretty quick.

[HoneyHush]

I say get Pete McCarthy’s video on porting Pontiac d ports. It’s old but very well detailed and explains how to make and use a shaping valve. Take your time and it’s not that big of a deal. They are just 6x heads after all and not Ram air ll’s or Something. Start with a dremel to get the feel of using the grinder in there. Then get a bigger one that has speed control. You’ll have that great feeling of doing it yourself and learning something.

[steve25]

The very great thing about the 5 series heads and the 6 series heads ( other then the big 124 cc chamber of the 6H heads and some 5 series heads ) is that the change in the runner shape ( more rectangular) that the factory made of some reason that late in the game help to make for a head that is easier to port and not F up in many ways!

Note that I am talking about the runner hear and not the critical valve bowl and short turn!

Other then the 670 head casting a given amount of proper valve bowl rework and resizing in these castings will produce a bigger high flow gain then in any other D port head other then the late 62/63 421 SD 980 casting!

To all of you home porters allow me to repeat myself for your knowledge gain.
In terms of iron heads once Pontiac started to have to make the combustion chambers deeper to attain the needed compression this change also brought with it shallower valve bowls.

This fact means that good or bad flow changes take place faster with valve bowl reworking then in the high comp heads of 1970 and early, so you had better know what your doing with the guidance of someone who knows what to do and then also take it slow!

It's easy to loose air flow and some home porters have been lucky in that during there rebuild they went up big time in cid and with a increase in the amount of minimum port area these folks also got a gain in upper rpm HP over stock, but it was only due to luck!

Luck in the fact that the added cid of there motor and in turn gain in low speed port velocity covered up for the incorrect valve bowl porting work that lost them cfm and the velocity that the stock port had!