360 heads on 318 ??

[Dodgy Dick]

What are the Pro's and Con's in fitting 360 heads to a a 318 ?
I assume there would be better breathing at the expense of a lowered compression ratio??
TKS, R

 

[PurpleBeeper]

What are the Pro's and Con's in fitting 360 heads to a a 318 ?
I assume there would be better breathing at the expense of a lowered compression ratio??
TKS, R

You are correct. I've run 360 heads on a LA 318 many years ago because I was worried about port mis-match & wanted to run a 4 bbl. carburetor. I haven't run small blocks in MANY years, but I've heard a few things about this here & there...this is all "hear-say"
1. I shouldn't have worried so much about the intake/head port mis-match.
2. Some police LA 318's had factory 4 bbl. & some aftermarket 318 4bbl. intakes are available too.
3. I think the modern "hot ticket" is to run magnum 318 (5.2L) heads

 

[Davea Lux]

You are correct. I've run 360 heads on a LA 318 many years ago because I was worried about port mis-match & wanted to run a 4 bbl. carburetor. I haven't run small blocks in MANY years, but I've heard a few things about this here & there...this is all "hear-say"
1. I shouldn't have worried so much about the intake/head port mis-match.
2. Some police LA 318's had factory 4 bbl. & some aftermarket 318 4bbl. intakes are available too.
3. I think the modern "hot ticket" is to run magnum 318 (5.2L) heads

My recollection is that the factory 4BBL that they put on some of the Dippy police cruisers were 360 heads, manifolds and carbs. They did not run very well with this setup. Carb was oversized for the 318 with low compression ratio and throttle response was poor with lots of farting back thru the carb.

Dave

 

[C Body Bob]

I’ve built a few 360 headed 318’s. They run better. If you like power. I always used aftermarket intakes. I built one for a friend & used a Stock 4bbl intake that he provided. It had more down low but died at 60-70 mph. And I have for sale a Factory iron 78-80 318 4 bbl intake.

 

[CBODY67]

I presume y'all are using 360 heads with the stock valve sizes? From what the old DC Race Manual mentioned, before 360s came out, but 340s had the 2.02 intakes, you could use the 340 heads IF you clearanced the top of the cylinder bores to clear the bigger intake valves of the 340.

Bigger ports don't always work better on smaller displacement motors, unless they are really undersized to start with. Port velocity suffers with the larger ports, especially at lower rpm levels, typically.

The QJets on many mid-80s GM engines would not flow buy 650cfm, as the secondary air valve was mechanically restricted from opening all of the way at WOT. Earlier ones were good for 750cfm. Even on the TQuads, having the secondary air valve spring adjusted correctly was important.

LA Magnum heads are the best for performance. Intake ports are a little better, but the exhaust side is a good bit better than the earlier LA heads, as I recall.

The M-cars had issues with their exhaust system configuration. It was good until it got to the single muffler and single tail pipe, I suspect.

It's just really easy to over-carb, over-cam, and over-port a smaller cid engine, no matter what.

CBODY67

 

[70bigblockdodge]

Bigger ports on a small displacement/short stroke, increased combustion chamber volume/decreased compression ratio all points to lower cylinder pressure. Which should add up to crap bottom end grunt, will be okay if using a RV/lawnmower cam but then what have you gained.
You would be better off with a good 340-360 intake manifold, do a little grinding to reduce the port mismatch somewhat, a good 3 or 5 angle valve job and a 340/E58 type cam.
Of course trying to flow more air in a engine with exhaust manifold corking up the outlet is a lesson in futility.
I'm out.

 

[CBODY67]

Bigger ports on a small displacement/short stroke, increased combustion chamber volume/decreased compression ratio all points to lower cylinder pressure. Which should add up to crap bottom end grunt, will be okay if using a RV/lawnmower cam but then what have you gained.
You would be better off with a good 340-360 intake manifold, do a little grinding to reduce the port mismatch somewhat, a good 3 or 5 angle valve job and a 340/E58 type cam.
Of course trying to flow more air in a engine with exhaust manifold corking up the outlet is a lesson in futility.
I'm out.

And add a little looser converter, for good measure, to go with the cam.

 

[70bigblockdodge]

And add a little looser converter, for good measure, to go with the cam.

Would not hurt but a stock 340 cam with 318 heads it could probably make do.

 

[Dana]

That combo needs a stiff rear gear in a c-body.

 

[Dodgy Dick]

To help me do my homework what is individual CC of 318 and 340 and 360 LA engine heads,
Thanks in advance,R

 

[Davea Lux]

To help me do my homework what is individual CC of 318 and 340 and 360 LA engine heads,
Thanks in advance,R

The stock 318 heads should be about 60cc. The 360 heads are in the 70-72cc range. This works out to a compression drop from from 8.5-1 to about 7.2-1. Severe planing of the heads to compensate for the larger combustion chamber is not usually a good idea as this further amplifies problems with the port mis-match. Severe planing will also require the use of adjustable rockers to keep the lifters centered. Piston tops on a stock 318 are usually going to be '060-.080 below deck height, so the installation of domed pistons can bring the compression ratios back up. There is a fair amount of production variance in the block deck height, so some careful measurements should be done to to verify the actual deck to piston height. You can avoid having to modify the lower end by using the 318 magnum head which retains the 60cc chamber size with the larger valves. I would recommend using an after market intake and exhaust manifolds to get the most bang for the buck along with a mild cam (340-360 HP unit is pretty good). Also suggest going to a quicker advance curve on the distributor. (Be sure to check the casting number on the heads to verify chamber size)

Dave

 

[LocuMob]

I'll direct you to your previous thread!

Combustion chamber CC's Chart ??

This picture was provided by @Dana and is on par with what I found over on FABO.

FABO charts, no 360 info.

 

[Dodgy Dick]

G'Day (Scott ?) LokuMob, Thanks for jogging my memory or whats left of it and old timers disease. I'll print it all off and research over a cold beer!
However finding alternative Mopar heads in Oz is difficult because of their scarceness so I think I will have to go for after market Aluminium heads which are readily available, but the problem of the chamber size will probably still be a hiccup!
R

 

[Davea Lux]

G'Day (Scott ?) LokuMob, Thanks for jogging my memory or whats left of it and old timers disease. I'll print it all off and research over a cold beer!
However finding alternative Mopar heads in Oz is difficult because of their scarceness so I think I will have to go for after market Aluminium heads which are readily available, but the problem of the chamber size will probably still be a hiccup!
R

Edelbrock makes a small chamber (62cc) aluminum head for the 318-340-360. It is designed to be used with the Edelbrock performer intake. Edelbrock #60779, 2.02 intake, 1.60 exhaust.

This version is for flat tappet camshaft.

Dave