[dogwalkin]

Afternoon folks
I've got a 50 pontiac with a 350 pontiac and 700r4 that's my daily driver. The engine has some issues and I've got a 68 400 I'm freshening up with new rings gaskets and bearings.
It has the stand "254" cam i think was just the 2bbl cam. Should I just leave it or I have a brand new summit 2800 cam i could install. I know it's never gonna be great on mpg but it is my daily most of the time. Thanks for your help

[Stan Weiss]

Have you check volumes, and what will your CR be?

Stan

[dogwalkin]

I haven't checked the volumn but they are 1968 "15" heads.

[steve25]

If it’s got the 254 cam then it was a 265 hp motor .

The heads are 88 to 90 CCs which would have made for an actual 7.8 to 8 to 1 compression.

Have the heads ever been rebuilt?

If your not looking to mill the heads then I would go no larger the something like the factory 066 cam , and even then that would be dependent on what rear gears your car has.

[dogwalkin]

Steve. Maybe I need to cc those heads. Wallace racing website show them at 10.5 cr. I can leave the factory cam in. I'm not trying to build nothing to wild just a daily driver and reliable

[Skippy597]

Honestly if not chasing performance I would leave the factory cam in and avoid the worries of a cam going flat.

[Formulas]

I would look at the 254 cam with a critical eye then go from there, not to hard to pull the valley cover pull the lifters up and look at the foot and lobe, if you replace the summit 2800 would be fine

[Goatracer1]

With the problem today's cams and lifters are having with wear I would not change the cam if it is in good condition. Why go looking for problems?

[Formulas]

You have to look at the old cam to even tell if its in decent shape ... you know precisely nothing until you look

I have yet to pull an original Pontiac build apart that had a cam i would run again and the worse was a 254 cam with 3 nearly flat lobes ..

[dogwalkin]

I'm gonna pull it all down and inspect everything. Just trying to make sure what the best direction is gonna be.

[Squidward]

I think a 2800 cam would work great on a daily driver. I ran a 2800 cam in a 350, and was pleased. Fun yet manageable, with specs that allow stock valvetrain components and durability.

[steve25]

When I run these numbers for your stock 400,
Cylinder volume = 819.136 CCs

Chamber 87 CCs

Head gasket 9.4 CCs

Deck clearance ( .023") = 3768 CCs

Valve notch volume = 6.4 CCs

The result is a 8.9 to 1 compression.
As far as stock stated compressions go before 1971 they where all at least 1/2 a compression point higher then you find published.

I have a set of 15s I use as development / Mule heads and somewhere I have written down what they CC'ed at and I will try to dig that up so maybe I can save you from CCing yours, , but for now and until you CC yours I would use the 8.9 to 1 number when looking at Cam picks.

Also like I asked previously, what rear gears does the vehicle have ?

[dogwalkin]

The car has 3.73 gears and a 700r4.

[400 Lemans]

1968, 15 heads are 75cc. 1970, 15 heads from a 455 are 87cc. So yeah you have about 10 to 1 compression. Change the cam for sure.

[steve25]

If they are 75 CCs then you have 9.92 to 1.

[Stan Weiss]

Bore = 4.12 Stroke = 3.75 Swept / Cylinder Volume = 819.2505
Combustion Chamber Volume = 75.0 Piston Dome (+) / Dish (-) Volume = -6.4
Deck Clearance Below (+) / Above (-) = 0.023 Deck Clearance cc = 5.024737 <<<<
Compressed Head Gasket Thickness = 0.043027 Head Gasket Bore Size = 4.12
Head Gasket cc = 9.4 Top Ring Land cc = 0.0
Using Calculated Base Compression Ratio of 9.5494:1

Bore = 4.12 Stroke = 3.75 Swept / Cylinder Volume = 819.2505
Combustion Chamber Volume = 75.0 Piston Dome (+) / Dish (-) Volume = -6.4
Deck Clearance Below (+) / Above (-) = 0.00475 Deck Clearance cc = 1.037717 <<<<<
Compressed Head Gasket Thickness = 0.043027 Head Gasket Bore Size = 4.12
Head Gasket cc = 9.4 Top Ring Land cc = 0.0
Using Calculated Base Compression Ratio of 9.9206:1

Stan

[dogwalkin]

I'm wondering if that's to much compression for a pump gas daily driver?? I have a really good pair of 6x4 heads. What's yalls opinion of those on that 400. Gonna have an aluminum intake and factory manifolds.

[Formulas]

#15 heads are not 75cc ... stay away from online charts that have nearly every head from 1967 to 1970 at 72-75ccs

If a head was destin for a 2bbl it is going to have approx 10cc more chamber per a given CUIN. Than a 4bbl head.

Check your heads and you will know

[Tandyman]

MY Pontiac service manual's engine chart and lists a 290HP 400 offered in Full size Pontiacs. It lists it came with a 2 bbl carb , a 254 cam and 10.5 compression.
Glenn

[dogwalkin]

I'm gonna cc those heads this weekend and I'll report back. Curious what anyone's thoughts on the 6x4 heads are??