[Will]

Gach,

Appreciate your response. A cam recommendation based on the information I have at hand is all I was after. When people started telling me it wouldn't work I got real concerned and wanted to know why. Even after I posted the port volume people were still going on and on about poor velocity because no one believes it. I guess that kind of thing just makes me a little defensive.

Skepticism is healthy. Probably more skeptics have lived to ripe old ages than naive and overly-trustful types. Still, I have the evidence in my tired hands and if you want to know who did the work, all anyone has to do is e-mail me.

I've been taken for a ride once on engine work, it aint gonna happen again. I continue to do my homework. I can't afford to do this again for another couple years.

Go ahead and believe I've been duped if it makes you feel better. There's nothing I can do about that, but it does makes me feel all fuzzy inside to know you care.

[David Holmberg]

Will, Congrats on the new heads. My thoughts are to let the gentleman who did the porting on them pick the cam. Who else will know the ports and how efficient they are than him. Triggerman is correct on the RPM intake, He worked with me for hours on my TA and found that it could be done. E-mail him, his collection of intake spec's are second to none. Good Luck, David

[Skip Fix]

Will I have raced a 400 in a 78 TA for a number of years. Running 12 teens with a/c.
There a several compromises besides cam choice that affect things too. Want to run fast open headers or through mufflers? A 400 WILL need more converter and gear than a 455(2800 RPM torque peak 455 VS 4200 torque peak on a 400 same heads, cam, intake and headers). 3.73s a must and at least a 3000 stall(there are tight ones).

A bigger cam and more overlap also affect a 400 more than a 455 on idle quality. Older cam designs like the HO and other designs have more seat or total duration when compared to quicker ramp designs like Ultradyne and Comp Xtreme lobes when you look at duration at 0.050 and 0.200 to compare. The lobe sep ground into the cam can change the amount of overlap even when using the same lobes. You can get more duration at 0.050 and “under the curve” by using higher ratio rockers and still have the same seat duration. So look at that too. For every 0.1 ratio you add 2 degrees at 0.050.

So first decision open headers or mufflers. Open you can use tighter(108) lobe sep or mufflers a 110-114(most of the fast Buick guys use a 115). Then looking at the entire exhaust flow from intake to exhaust ratio to primary tube size for the headers.
For a 400 a small tube will keep up the velocity 1 ¾ will be about right 1 7/8 can get you in the 10s. The ratio on the head helps make the decision if you use a single pattern or a dual pattern cam. Round port heads or really ported D ports may like a single pattern better. My RAIV liked a backward dual pattern(292/286 total duration) because it had over 80% exhaust flow. That combined with a 2” header really caused some reversion.

I ran a Ultradyne hydraulic 304-312(247/255) and a 112 lobe sepwith A/C. An Idle solenoid on the carb like the factory system help bump up the idle with A/C. The 288/296 Ultradyne is a standard for a lot of street strip Pontiacs. Mine with a 108 lobe sep pulled 13” of vacuum when tested by NMCA. Moderately lumpy idle but not too bad.

Intake choice makes a BIG difference on bottom end on a 400. While running a 255/258 @0.050 solid power brakes worked fine with the dual plane HO intake. Switched to a Torker and no bottom end. The dyno showed the same only 1 hp difference between the HO , Torker , and Torker II but the torque peak was a lot higher in the single planes.Not a good idea in a heavy car.


My guess an Ultradyne 288/296(231/239@0.050) on a 112-114 lobe sep installed at about 106 intake centerline with some 1.65 rockers and standard lifters, dual plane intake , 3000 stall and 3.73s. Same duration at 0.050 as a RAIV but a BUNCH less seat duration. A slight smaller Comp X treme Energy would also be a good choice.

[Half-Inch Stud]

Skip,

Nice, informative reply. Probably right about the Torker on a 400, But I would insist the Torker restores bottom-end on a grossed-out 455, with a Q-Jet running late Secondary baseplate opening.

I only knew about the low-lift flow being pretty good - because I was told so, yet was told the high lift was poor. I thought the Exhaust flow was poor, by the numbers, yet the 80% to 89% In/Ex ratio suggest I'm doing something. My other 48 heads are hogged-out more, idle better, and presently running on the street.

Will, Are the crossovers blocked? That will make your motor idle.

[Will]

Thanks for the good info Skip! I do want to be able to run full exhaust. The wider lobe separation makes sense. For every degree you spread the lobes out you reduce overlap by two degrees. Going from a 110 to 114 lobe sep. takes out 8 degrees of overlap, everything else being the same.

I have talked with the head porter about cam recommendations, he said pretty much what Skip said but also knows I want to experiment a little. The previous engine ran well with the Comp XE274 cam which was 230/236 @.050" but I didn't like the way it idled. There may have been other things going on with that combo that caused the bad idle though as I never got much chance to really tune it. Looking at the valves and chambers from that engine, one side of the engine was running richer than the other, which makes me even more suspicious of the carb I was using. In any case, I might just go with that cam again but have it ground on a 112 or 114 lobe separation to help with the full exhaust and low-end torque & idle characteristics. The very first cam I ran in that engine was 232/232 @ .050" with 1.7 ratio rockers and it idled really well pulling almost 14" vacuum at 800 RPM, which I attribute to it's 112 lobe separation.

The exhaust crossovers are filled.

Thanks everyone!

[Lee]

FWIW, I filled my exhaust crossovers and really don't think it did a damned thing for me, other than helping to keep the intake a bit cooler. Idle is about the same, and the exhaust note is not really any different.

[Half-Inch Stud]

Lee, Will, too bad you filled the Crossovers and got notin. Suggest you peek under the carb about a month from now to see how clean the runners are. You'll feel much better about the filled crossovers, knowing that 4now-on reversion can be traced to the cam effect only.

I've got the "best" [ it's ideal ] Streeeet/Strip cam choice : 234/244, 112 LS, with 325/340 lobe lift to get 480/510 valve lift. Flat-HYD, usually provided by Wolverine.

...thought of this all by myself, after reading some similar post by Floyd Hand.
How can you go wrong with this!!

[Will]

Hey, I never said I got nuttin! However, I'll never really know whether filling the crossovers will help the idle or not as the new engine will be completely different from the old. Other than the fact they're both the same displacement and will use the same distributor and other engine driven accessories, nothing else will be the same.

I've thought about that cam. One thing though, Jim's engine has nearly 70 cubes on me, which will almost assure it will idle rougher and produce less low-end torque for me than another cam I've been thinking of would. Then again, I may just try it since my engine will be setup to run 6500 RPM no problemo. Just don't know how smart that approach is with 3.23 gears and only a 3000 stall.

We'll all know how things work out next spring. Until then, it's all best-guesswork!