Which combo has higher performance/horsepower?

[dibbons]

My automatic 1965 Barracuda Formula S has been changed from the original 235 HP 273 to the following: .030 over 1980's 318 with stock pistons and stock hydraulic 318 camshaft. However, it now has a complete TTi 2 1/2" exhaust system with the original 1965 273 AFB carburetor on a factory single plane 1966 273 four-barrel intake manifold (and original factory 273 magnum valve covers). I wonder with the extra cubic inches and the four-barrel carb (and dual exhaust) if I come out with more, less, or about the same horsepower now as the original version? Thank you.

 

[Sedanman]

Did you use the 920 closed chamber heads on your 318? They will boost compression a bit.

 

[Treblig]

My automatic 1965 Barracuda Formula S has been changed from the original 235 HP 273 to the following: .030 over 1980's 318 with stock pistons and stock hydraulic 318 camshaft. However, it now has a complete TTi 2 1/2" exhaust system with the original 1965 273 AFB carburetor on a factory single plane 1966 273 four-barrel intake manifold (and original factory 273 magnum valve covers). I wonder with the extra cubic inches and the four-barrel carb (and dual exhaust) if I come out with more, less, or about the same horsepower now as the original version? Thank you.

I thought I had read that the 66 273 intake won't fit an 80s 318?? Well, either way, to answer your question.....The 302 small block casting should have a 69CC chamber at least that what I used on my '69 Barracuda (factory 318). The '69 318 had one of the highest small block compression ratio (9.2:1 I think). Anyway, when I removed the original heads and CCed them they were 69CC. The 302 casting heads did two things, they allowed me to keep my high compression (69 CCs) and they have the larger exhaust ports. With the larger exhaust ports I was able to use the 340 driver's manifold and the 360 magnum passenger's manifold which greatly increased my exhaust flow.
I need to get off my @ss and sell the original high compression heads which are very low mileage and in good shape!!!!

Treblig

 

[Sedanman]

66 was the first year they changed the bolt pattern. The 65 and earlier went straight down instead of the V pattern

 

[dibbons]

I don't know for sure what cylinder heads I'm using, references show 4027163, 4027593 for 1980. I will have to pull a valve cover this week.

 

[Treblig]

I don't know for sure what cylinder heads I'm using, references show 4027163, 4027593 for 1980. I will have to pull a valve cover this week.

Those numbers are the 81-83 low-pref 64.5-71.5CC heads. But there's no way to know the actual CCs unless you check them yourself or someone here (FABO) has a set that they have checked.

treblig

 

[Sedanman]

The 920 heads 66-7 will boost your compression some but don't have hardened seats. They also used them for the commando engines

 

[273]

Cubic inch don't make hp
With stock 318 cam your making less power but the 318 will make a lot more torque. Just up grade the cam and that will wake it up. I'd change the stock 4 bbl intake to something better while your at it.

 

[DesertRat]

 

[Marcohotrod]

the early la 318 was rated at 230 horse. I would say U are about equal

 

[Sedanman]

A 70-1 had 210 and dropped off after that big time

 

[Marcohotrod]

and 1971 and earlier was rated gross, 1972 and later net

 

[dibbons]

Pulled the passenger side valve cover to find the cylinder head is older than the 1980 318 cylnder block, of course these have the smaller 273 valves:
68-71 273/318 Part# 2843674 casting# 2843675 60.0-67.5
72 318 Part# 3671637 casting# 2843675 61.0-67.5