Budget 318 Build

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Shane Clark

Shane Clark

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Massachusetts
I have a 318 that has been sitting around a while and I planned on just freshening it up to put in my 72 valiant. I had an intake and headers from other projects that I planned on using so I pulled the intake, and exhaust manifolds off. I discovered that a few valve seals were junk. I decided to pull the heads off to have a valve job done because i'm not too pleased at what the heads look like. I have a set of 4027596 360 heads that are just collecting dust and I couldn't justify not using them. I did my research and found that this combo would work but I would lose compression. so either way i'm getting a valve job done (if I use the 360 heads I will see how much extra it will cost to get the head decked to increase compression) but I'm just wondering if the increased flow of the 360 heads is worth the loss of compression when combined with headers, intake manifold, and 4bbl carb. I did the math and with the 360 heads I should get about 8.4:1 with 66cc combustion chamber from 9.1:1 with the stock heads with a 60cc combustion chamber. now I did not cc the heads myself im just going off of what the casting numbers say for for all I know they could have more combustion chamber volume. so my options are to 1: stick with stock heads and just get a valve job. or 2: use 360 heads, get a valve job and spend the extra money on shaving down the head. or 3: use the 360 heads and not shave the head to save money. any tips?
 
If your question is "are the 360 heads flow worth the loss in compression?", my answer is yes. I always take flow over compression. I would cut the heads .040, and at the very least a little bit of home bowl porting under the seats and you'll be set
 
318willrun said:
If your question is "are the 360 heads flow worth the loss in compression?", my answer is yes. I always take flow over compression. I would cut the heads .040, and at the very least a little bit of home bowl porting under the seats and you'll be set
Click to expand...
Thanks for the help. I've been reading a bunch on it and everyone seems to have a different opinion on it. my biggest concern is money right now and I really just want the car back on the road and if its worth it to cut the head down i'll spend the money.
 
I would cut the heads just to clean them up. Whether it's .002" or .020". Here's why. It will take about a .070" or so cut to really make a difference (about 1 compression point).

What I would do is put that money into having the heads ported instead. Ported heads, 340 cam, Holley Street Dominator intake, Holley 650 DP, headers and you will have a peppy 318.
 
RustyRatRod said:
I would cut the heads just to clean them up. Whether it's .002" or .020". Here's why. It will take about a .070" or so cut to really make a difference (about 1 compression point).

What I would do is put that money into having the heads ported instead. Ported heads, 340 cam, Holley Street Dominator intake, Holley 650 DP, headers and you will have a peppy 318.
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I will have to see what it would cost, but I don't have a ton of money right now I'm just using left overs laying around the garage for most of it. I have an edelbrock rpm airgap Intake I'm going to use, some brand new hedman headers that never ended up getting used and I have a Holley 650 that I'm gonna rebuild. But should spending the money on having it ported be worth it if I don't step up to the 2.02" valves? The Intake ports are already much much larger on the 360 heads. So I just assumed trying to get higher compression would be the way to go? I'm just spitting out words I really don't know a whole lot but I'm trying to make my money go as far as possible you know. I wanna spend it where it counts. But thank you for the response!
 
Shane Clark said:
I will have to see what it would cost, but I don't have a ton of money right now I'm just using left overs laying around the garage for most of it. I have an edelbrock rpm airgap Intake I'm going to use, some brand new hedman headers that never ended up getting used and I have a Holley 650 that I'm gonna rebuild. But should spending the money on having it ported be worth it if I don't step up to the 2.02" valves? The Intake ports are already much much larger on the 360 heads. So I just assumed trying to get higher compression would be the way to go? I'm just spitting out words I really don't know a whole lot but I'm trying to make my money go as far as possible you know. I wanna spend it where it counts. But thank you for the response!
Click to expand...
Here is an example of homeporting videos I did...

 
Shane Clark said:
Thanks for the help. I've been reading a bunch on it and everyone seems to have a different opinion on it. my biggest concern is money right now and I really just want the car back on the road and if its worth it to cut the head down i'll spend the money.
Click to expand...

Opinion? How about facts?!?!
It has been proven here with Dyno results posted by a member on both big block and small block engines. The member has no dog in any fight nor is he here to make money from the internet on his postings. His biz is solid. So he is most believable.

Search posts by member IQ52.

If you just want to get it running, use them! And use a thin head gasket to retain as much compression as you can.
IIRC, Mr. Gasket has a .028 thick gasket.
 
Have you cc'd the 360 heads to know the true volume? If you're in the market eventually to replace the pistons, you can use a taller piston or domed to increase your compression as an alternative to excessive decking of the heads to reach your target static compression ratio
 
People will argue the cr thing to death.
Yes it's important but you can accomplish a lot running low cr. Especially if you put it into perspective.

The main problem running low cr is lowers the amount of cam duration, which isn't the biggest problem for a street engine since too much make for an unfriendly street engine anyways.

For a street 318 with iron heads you don't want to go with much more than 9:1 anyways and every point is worth about 5% hp which equals out 10-20 hp. So half a point is 5-10hp.

Ultimately cylinder heads decides you engine hp potential.
So a stock 318 head with 9:1 and a comp xe268h cam could hit 1 hp per cid.

But with more head you could reach the same hp with less cam. So say comp xe262h with 8.5:1 and 360 could hit the same or go xe268h and 9:1 to build more hp.

And if you were to run something like a xe285h you could go 10:1.

But really most street friendly cammed engines are gonna fall in the 8.5:1 - 9.5:1 range so it's pretty much a moot point unless your trying to run a 285 cam on a 8:1 cr engine.

Yes you could port the 318 and keep the cr but I'd still go 360 since porting them will give you even more power or same power with less cam.
 
Shane Clark said:
I will have to see what it would cost, but I don't have a ton of money right now I'm just using left overs laying around the garage for most of it. I have an edelbrock rpm airgap Intake I'm going to use, some brand new hedman headers that never ended up getting used and I have a Holley 650 that I'm gonna rebuild. But should spending the money on having it ported be worth it if I don't step up to the 2.02" valves? The Intake ports are already much much larger on the 360 heads. So I just assumed trying to get higher compression would be the way to go? I'm just spitting out words I really don't know a whole lot but I'm trying to make my money go as far as possible you know. I wanna spend it where it counts. But thank you for the response!
Click to expand...

IMO air flow will trump compression in your situation. It's your build. Do it the way you want to. It will be fine.
 
So what is the planned use for this car? Hauling logs to the sawmill? Pure drag race?

Be aware that the chamber volumes that you list are NHRA minimum volumes... i.e., that is the chamber to which you can shave the heads to and still be legal for NHRA competition in certain classes.

Real volumes are gonna be up around 68 cc for the 318 heads and 72-73 cc for the 360 heads. So your compression ratio computations are overly high and may be misleading you. And, know that the standard Felpro head gaskets are thicker than stock OEM's so that is a CR loss too; that is why RF360 made mention of thin head gaskets, like the Mr Gasket 1121G at .028" thick.

CR is important for low RPM torque so if you cruise or run the roads, that is good for low RPM driveability. If you are purely at the strip and will change torque converters, then it matters a lot less. Head breathing makes flow at mid and high RPM's and thus HP; very important for the strip, not so much for hauling groceries. But head flow makes the engine ready to do more things so is always good.

So there is always the trade-off; low RPM and torque and 'tooling-around' driveability, versus high RPM and peak HP. Where you shift the torque curve depends on how you use this engine. If 'twer me, I'd use the larger heads but mill as much as I could afford, to get CR up and try to get the best of both worlds. But budgets are quite understandable, and so the next best IMHO is use the big heads and keep the cam down in the 256-262 advertised duration range to not effect low RPM torque any more than you have to.... if this is daily street driver.

BTW, you might be well served to learn about something called DCR (dynamic compression ratio). That is what you really end up working with and combines the effects of cam and static CR on low RPM torque (like you have been computing). It also is a predictor of when to worry more about detonation if the CR gets pushed up; but that is not going to be the problem here; too low of a DCR is the concern.
 
nm9stheham said:
BTW, you might be well served to learn about something called DCR (dynamic compression ratio). That is what you really end up working with and combines the effects of cam and static CR on low RPM torque (like you have been computing). It also is a predictor of when to worry more about detonation if the CR gets pushed up; but that is not going to be the problem here; too low of a DCR is the concern.
Click to expand...
This ^^^^ is important.
Learned this the hard way.
 
273 said:
People will argue the cr thing to death.
Yes it's important but you can accomplish a lot running low cr. Especially if you put it into perspective.

The main problem running low cr is lowers the amount of cam duration, which isn't the biggest problem for a street engine since too much make for an unfriendly street engine anyways.

For a street 318 with iron heads you don't want to go with much more than 9:1 anyways and every point is worth about 5% hp which equals out 10-20 hp. So half a point is 5-10hp.

Ultimately cylinder heads decides you engine hp potential.
So a stock 318 head with 9:1 and a comp xe268h cam could hit 1 hp per cid.

But with more head you could reach the same hp with less cam. So say comp xe262h with 8.5:1 and 360 could hit the same or go xe268h and 9:1 to build more hp.

And if you were to run something like a xe285h you could go 10:1.

But really most street friendly cammed engines are gonna fall in the 8.5:1 - 9.5:1 range so it's pretty much a moot point unless your trying to run a 285 cam on a 8:1 cr engine.

Yes you could port the 318 and keep the cr but I'd still go 360 since porting them will give you even more power or same power with less cam.
Click to expand...
Thank you so much for this this helped a lot and I've brought my heads to the machine shop, getting a valve job and their shaving 0.030" off the head. I'll cc the heads before I put them on to get an idea and I can't afford a cam right now so I'm staying with the stock one but at some point I think I will put a cam in it. Thanks again!
 
nm9stheham said:
So what is the planned use for this car? Hauling logs to the sawmill? Pure drag race?

Be aware that the chamber volumes that you list are NHRA minimum volumes... i.e., that is the chamber to which you can shave the heads to and still be legal for NHRA competition in certain classes.

Real volumes are gonna be up around 68 cc for the 318 heads and 72-73 cc for the 360 heads. So your compression ratio computations are overly high and may be misleading you. And, know that the standard Felpro head gaskets are thicker than stock OEM's so that is a CR loss too; that is why RF360 made mention of thin head gaskets, like the Mr Gasket 1121G at .028" thick.

CR is important for low RPM torque so if you cruise or run the roads, that is good for low RPM driveability. If you are purely at the strip and will change torque converters, then it matters a lot less. Head breathing makes flow at mid and high RPM's and thus HP; very important for the strip, not so much for hauling groceries. But head flow makes the engine ready to do more things so is always good.

So there is always the trade-off; low RPM and torque and 'tooling-around' driveability, versus high RPM and peak HP. Where you shift the torque curve depends on how you use this engine. If 'twer me, I'd use the larger heads but mill as much as I could afford, to get CR up and try to get the best of both worlds. But budgets are quite understandable, and so the next best IMHO is use the big heads and keep the cam down in the 256-262 advertised duration range to not effect low RPM torque any more than you have to.... if this is daily street driver.

BTW, you might be well served to learn about something called DCR (dynamic compression ratio). That is what you really end up working with and combines the effects of cam and static CR on low RPM torque (like you have been computing). It also is a predictor of when to worry more about detonation if the CR gets pushed up; but that is not going to be the problem here; too low of a DCR is the concern.
Click to expand...
Thanks for the response! But yes I think I'll spend my money on the 360 heads and go from there. I'm just looking for a mild street car but I wouldn't want to wast money on the stock heads only to throw them away when I go to add performance later on. But thanks for the advice, appreciated!
 
Thanks for the replies, everyone helped a lot. I went with the 360 heads and had them decked 0.030". We'll see how it goes when I get them back from the machine shop. Thanks everyone!
 
The smaller stock cam will keep the DCR up and help you. The big problem is when someone goes with big head chambers on a starts-with-low-compression 318 and puts in a big cam, and 'blaaaaaaah' off of the line.

I'll tell the "jokes-on-me" story again: Way long ago, I put a 300 duration cam in a 4 cylinder race engine with 7.6 stock CR; DCR was in the LOW 5 range! If you wanted to get on it, it had to be revved to 3800 RPM to get any torque! It was a race engine and could rev to 8k all day long, so it sorta worked with that narrow 2:1 RPM torque band, but it would have a better race car with a smaller cam, and more DCR.

Looking back over your thread, with no new cam, I suspect the headers are gonna be you biggest improvement. The heads will not give you much more with the stock cam, but you'll be ready later.
 
Basic 4 barrel and headers perked up my stock cam 318. Then changed to oem 340 valve springs which helped it rev a little higher. On the whole the best improvement came with ignition timing and carb tuning. It just changed everything for the better, from starting to throttle response and off idle torque for cruising.
 
I went this route and I don't remember my 596's having 2.02's stock? Maybe 1.88's?
On our 596's I went .040 or .050? Can't remember, but I would have went more more in hindsight - FOOD FOR THOUGHT ?
I'd call them today and ask for more- don't be scared! LOL
If the cam that our 318 cam with didn't have a 450 lift we would have bought a cheap Summit cam and lifters (like a hundred bucks or so?) Out of everything discussed I believe that would help most. My-2.
 
In our case are 596 heads had better valve guides and we're a lot tighter than the 318 heads. I was able to just get some lapping compound and clean them up and get them to seal. more food for thought....
 
j par said:
In our case are 596 heads had better valve guides and we're a lot tighter than the 318 heads. I was able to just get some lapping compound and clean them up and get them to seal. more food for thought....
Click to expand...
how's it been running anyways? Haven't heard/seen anything from you in a bit...... :realcrazy:
 
yellow rose said:
Vacation? Really? Snowmobile season is coming up. I thought that was your vacation? Must be nice living in paradise?
Click to expand...
UH-oh... this I gotta hear about. Been thinking about applying to the lottery for the Yellowstone non-guided snowmobile permits for this winter. Now back to your regularly scheduled program....
 
Shane; If you install a set of KB 167 (IIRC) pistons at zero deck height, assumed 6cc valve relief, .038 X 4.1 head gasket & 72cc - 360 heads, you will have a 8.5-1 ratio,
You would need to bring the cc down to 63cc's and should be a 9.5-1 ratio.

9cc's to be removed from the chamber.

You have stock pistons?
How far down the hole are they?
 
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