Beefing Up a 1969 318

[Eric Griffith]

I have a set of 4027596 360 heads,1.88 intake/1.60 exhaust valves.
My Motor is a 69 model engine.
I have aqquired a stock 69 340 intake manifold,and some Factory headers (Cast),correct for a 1970 340 Cuda.
I have heard I will lose compression,not sure if this applies to the 69,and also wanted Info on Cam specs,etc.
Not looking to make it a Race Cuda,but would like some input as to how to make is better than it was.
I plan to use a Holley 650 Spreadbore.
Need info also about Valve springs....Some Have Damper springs,some do not.
Are those Necessary??
Additional Info: &27 Auto,273 Rear end Gears. 83/4

Any help is appreciated.
Thanks,Eric

 

[moper]

I think, given what you have for the "package", that adding the 340/360 heads is a mistake. Add the HP manifolds and the 4bbl intake and carb. I would replace the camshaft with something like the stock 340 cam or the Comp XE262, and the valve springs with Comp 901-16s. The bigger port heads will lose compresion, but more importantly the larger ports won't help in the rpm ranges the gears keep the engine in.

I'll add - if you had some deeper rear end gearing - say 3.55 or numerically higher, the larger port heads might give a bonus. But as it sits I'd leave the 318 heads on it.

 

[Litchkar]

I agree with Moper, the 360 cu in heads have a much larger combustion chamber, closer to 70cc's compared to a 318 which is around 58-62 cc . This will cost you compression ratio in a motor that is not a high compression ratio to begin with. That alone will off set any gains by the performance parts you plan to add. The higher flow heads will not help that much.

 

[Eric Griffith]

I agree with Moper, the 360 cu in heads have a much larger combustion chamber, closer to 70cc's compared to a 318 which is around 58-62 cc . This will cost you compression ratio in a motor that is not a high compression ratio to begin with. That alone will off set any gains by the performance parts you plan to add. The higher flow heads will not help that much.

I am now Planning to Shave the Heads, and get adjustable Rocker assemblies.
If I kept the 69 Heads, the Valve seats are not hardend for Unleaded fuel, and would not last long.
It is true though, that Chrysler Valve seats are harder than most others anyway, But I want larger valves/ ports, for my other accessories.

 

[moparleo]

Is it budgetary reasons that you are not wanting to use a 360 ? They are inexpensive, have unleaded heads ( valve seats, valves) and all of your parts are compatible without modifications. You would have a better performing engine for less money in the end. Lower rear gears will wake it up the most.

 

[moper]

Milling to the extent you need to in order to get any feelable gain will cause other issues - mainly pushrods will need to be measured for and ordered, and the intake may need to be milled to match the heads. Once you get past .030" of so you have to machine the head's intake manifold side too. But you can't go too far there either, so big milling means cutting the intake to fit only those heads too. I don't knwo what your plans are but be aware of the intake fitting and pushrods too.
On the seats - the '69 heads made it this far, right? They haven't had lead on them in 30 years and yet - they've lasted. Heavy valve springs and steady lean cruise may exasperate the situation but not in every case. So again - seats might be important, but maybe not right now. If the seats are bad, the rings are shot, and chances are the bearings are worn too. Get the picture?
Lastly - the bigger ports do not help unless and until the rest of the car is matched. Big ports on a 318 will like deeper rear gears as Leo noted.
So with my issues with it aired out - have at it.