My 318 Build with questions

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prostreeter9

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Hey guys:

What I have is a 318 bored 40 over running stock height pistons. I'm putting a Comps cam XE256 in it with a double roller cam set. For heads I have a set of 714's that I had .010 shaved off the surface, the valve increase to 1.88 intakes and 1.6 exhaust and he cleaned up under the bowl and the ports have been enlarged to match the intake which is a Edelbrock performer. I also have a set of TTI headers that will be going on once the cam is broken in. On me the header are on I will be getting the duels with an H or X pipe.

So here are some questions I have. What do you guys think my compression ratio will be with this combo? Thoughts on use a 262 cam over the 256? What do you think this combo will produce in horsepower?

This is my first build and just want to make sure I'm consider everything before I spend money on the wrong thing.

Just for info this is going in a 64 valiant with a 904 push button, right now it has a 7-1/4" with I believe 2:73 gears. Looking for a 8-1/4" 3:23

Thanks for any wisdom
Jon
 
I like it ! IF your going with a little looser stall converter than the factory one, then I might go with the 262 cam of the two you've listed. But I like it as you have it listed
 
I like it too. And if you do the looser TC like will-run sorta hinted at, then I would try the 2.7s . But make sure it is SureGripped, cuz it will last a lot longer.
Don't let anyone talk you out of big pipes.
I ran a teener for 4 winters (mid Sept to late May)with dual 3 inch pipes, all the way to the back bumper. Best LC factory longblock I ever ran. I think that engine saw those pipes as straight atmosphere, maybe better than. Ok maybe not, but you get the idea. At least run some big pipes to the mufflers; I guaranty you won't be sorry.
 
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Hey guys:

Maybe some one can tell me the best way to figure out what my compression ration will be? I still have the heads off and plan on resealing the lower end before putting it back together. I would like to be in the 9:1 range. With hope that the combo gets in the 300 HP range.
 
prostreeter9 said:
Hey guys:

Maybe some one can tell me the best way to figure out what my compression ration will be? I still have the heads off and plan on resealing the lower end before putting it back together. I would like to be in the 9:1 range. With hope that the combo gets in the 300 HP range.
Click to expand...

Here ya go: How to Check Compression

This is your best bet if you want to know what your actual static compression ratio is. Dynamic compression ratio is also important but you'll need to figure static first. It is hard to give a good answer to your question without being able to measure the parts you have, so you need to do it yourself for the most accurate results.
 
Trying to work on the CR number for you but there are a number of 'standard' 318 pistons with different compression heights. Do you pistons have 4 valve reliefs on them or are the flat tops? Better yet, do you have a piston part number?

And we'll have to venture a guess on the combustion chamber volume unless you have measured it; I'm guessing 60 cc's.
 
nm9stheham said:
Trying to work on the CR number for you but there are a number of 'standard' 318 pistons with different compression heights. Do you pistons have 4 valve reliefs on them or are the flat tops? Better yet, do you have a piston part number?

And we'll have to venture a guess on the combustion chamber volume unless you have measured it; I'm guessing 60 cc's.
Click to expand...


Sorry I don't have any of the pistons out and not sure I'm taken them out unless something looks bad when I get the pan off to inspect the bearings. I do however know that the pistons do have four reliefs cut in the top. Also they do not come all the way flush with the deck when rotating the motor over.

Jon
 
Four valve reliefs should be a late 60's 318. These motors had " 9.2:1" compression but I think in reality they were a bit lower. the later, lower compression, 318's had no valve reliefs. I've never popped open a late 318, but my '68 had four valve reliefs.
 
4 bbl headers and comp's XE262H cam supposed to make 282hp @5000 on a stock 318 longblock. With head work probably hit your goal of 300 hp. Some will disagree cause of the build comes from a magazine.
Either way should be a fun car :)
 
OK, well with the 4 valve reliefs the pistons could be either .080" or .100" below deck at TDC. If the OP could measure this carefully, he'll have better info.

Case 1 assuming:
- 8 cc total valve reliefs
- Standard Felpro gaskets
- 60 cc chambers
and -.100" deck height
CR is 7.7:1

Case 2 assuming
- 6 cc total valve reliefs
- Standard Felpro gaskets
- 58 cc chambers
and -.080" deck height
CR is 8.25:1

I am being pretty conservative above in estimating the chamber sizes (I think). It would help to do some more measurements (like cc'ing the heads and a precise the piston deck height measurement to see if it is .080" or .100") and perhaps plan on some more head shaving if you want to be up nearer to 9:1, and maybe some Felpro 1008 gaskets or even thinner ones. But at least the 256 cam will work well with no fear of too much compression ratio and consequent detonation. And with the low rear gears, more torque with less duration will be better IMHO. I might really consider some sort of stump-puller torque cam.... what do you plan to use this for? Pure street and cruising? Drag racing? The application will steer you a lot on what to do.

You are working to make the breathing better.... that will extend the RPM range of a milder cam. That is all real good. (I am channeling some 318willrun today....LOL) If you get the chance to extend the collectors, I'd do it for street use.
 
Sounds like you will need the 65-67 273 heads or the 302 swirl port heads to get the compression goal if staying with LA configuration. Or are the 714s low enough volume?
 
I'm gonna suggest cutting the heads another .020, for a total cut of .030, thin MP head gaskets, you might make 9 to 1 compression.
 
JBurch said:
I'm gonna suggest cutting the heads another .020, for a total cut of .030, thin MP head gaskets, you might make 9 to 1 compression.
Click to expand...
Yes, if he cuts the chambers down to around 56 cc and uses a .028" thick head gasket, and the pistons are down .080" in the hole with 6 cc valve reliefs, then it'll be around 8.8.

DCR would then be around 7.6 for the 256 cam installed as ground, which should work well with pump gas.

BTW OP, you can work all this out yourself. I use the Pat Kelly calculator, available as a download program online. I don't mind, but it is not any particular magic, just knowing how to derive or find the numbers to put in the 3 tabs.
- The 3rd tab is for CR (SCR and DCR), which can be run on its own for SCR.
- The 2nd tab is for intake closing angle per the chosen cam.
- It's output is used in the 1st tab to compute effective compression stroke length for the DCR option in tab 3.
 
Hey guys:

First off thanks for all the info. Looks like I have some more work in front of me to get this figured out. This car is a street car just for driving around town having fun.

nm9 can you tell me what you meant by extend the collectors? Will shaving another .020 cause any intake fitting issues. What about a different piston? What is SCR and DCR?
 
Hey guys:

I finally got the motor out and was able to get some better measurements. It looks the heads measure out at 63 cc and i have 16 cc in the chamber above the pistons. So with this info can the compression be figured?

Jon
 
Using the above I got a rough crunch of 8.64 to 1............If you dropped chamber volume to 56cc you could end up around 9.3 to 1 for a compression ratio
 
I am coming up with around 8.3:1 with Felpro 1008 head gaskets (.039" thick). The 16 cc number looks a mite low.... which would make the CR compute out a bit higher than reality. Do your pistons have valve reliefs or as they flat on the tops? Are these the stock pistons that were in there? If flat tops, the 16 cc number makes more sense.

BTW, I never answered the extended collectors question. You just weld another 6" or 8" or 10" onto the existing collectors at the existing collector diameter. That is done to extend the headers' effective RPM lower and give some more low end torque. I did it once upon a time and it did indeed help the low end. The engine had large breathing heads, intake and headers, but was cammed for low RPM, so I cannot say if that combo made the collector extensions have more effect.... or not.

And SCR is the static compression ratio.... the classic CR number like we are kicking around here. DCR is dynamic compression ratio and takes into account the fact the intake valve closes part way up on the compression stroke and so the effective stoke is shortened; that lowers what you could call the 'effective' CR, or what the engine really sees in terms of operating CR. It is derived from SCR and the cam timing, and has a very real effect on actual torque; for example, all else being equal, longer duration cams lower DCR and thus cause the classic drop in low RPM torque with a big cam. DCR is also computed to see if a SCR and cam combination pushes too close to the point where detonation can easily occur.
 
Stop worrying about compression. You don't have to have 9:1 to run good. Build it. It will be a good performer.
 
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