Can I make this work on pump gas?

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Freezerman

Freezerman

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This is the 318 I asked about the scratches in the cylinder. It has the p4120281 11.5 pistons in it. It had x heads on it, it has been run, I don't know how well it worked. I cc ed the heads at 68 cc. As best I can tell the pistons are zero deck. When I put it .5 in the hole it calculates to -12 cc for the piston.

That calculates to11.3 with a .040 gasket. There is a Crane 272 cam in it now which specs at 33° ABDC. That shows as 10.45 dynamic CR.:banghead:

Am I wrong (I hope). :prayer:

Can i make this thing run on 91 or even 93? Should I sell the heads and put the money into something else?

I just don't want to spend more time and money on something that just isn't worth the trouble. Thanks
 
Your compression figure is probably close.
 
I run 11.25 on 93. Put a straight edge over the cyl and bring to TDC then check with feeler gauge to see where piston is at this is critical to find the true CR
 
EL5DEMON340 said:
I run 11.25 on 93.
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Not with a crane 272 you don't... :) 216 at .050, not a chance. Cylinder pressure will be above 200psi is my guess

With about 10* or less total timing you might get it to run on pump gas.
 
This piston is domed with valve relief so I checked the flat part to make sure it was zero deck, then dropped it .5 in the hole to be able to cc the dome.

I am more than willing to change the cam and/or head gasket to make this work. I just need to know what I should change it to.

I have a 318 in the car now but would like to know if I can run This one and get some more performance.
 
crackedback said:
Not with a crane 272 you don't... :) 216 at .050, not a chance. Cylinder pressure will be above 200psi is my guess

With about 10* or less total timing you might get it to run on pump gas.
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...and run like total crap.
 
IMO, I think you would be better off lowering the static compression ratio. Maybe even another cam, too. Usually putting 360 heads on a 318 is a bad thing, but it might be the thing to do in your case if you could find some that spec out around 75cc or more. IMO you should lower the SCR about 1 full point if this is a street car. JMO, I am sure others will argue.
 
Not sure if this is an option in your area but if you re-jet it you can consider running it on E85 as well. I understand as long as you don't let it sit for long periods the requirement to run stainless steel for your fuel system is just a myth. I am doing this with an old project I have that I built 12.5:1 (young, stupid and HP hungry) and currently needs race fuel.
 
I am stuck in the same situation, I have a fresh 360 mag, with eddy heads.
I have 11.37 static, dynamic 10.71, cranking compressioin 216.

Just buy new pistons, and pay to re-balance...
You will be much happer.
Or mill the tops off the pistons?
 
RustyRatRod, I do value your opinion and enjoy your posts.

Some options, sell the x heads and use some 308s maybe? Would a thicker head gasket help enough? Sell the whole thing and try something different?

michformulaS the E85 is interesting idea. We have it all over the place here for $2.50 a gal
 
sireland67, what are you going to do? I don't think I want to start milling the pistons.
 
I ran the numbers too, if your measurements for volume are correct and assuming zero deck with 12cc domes and 68cc chambers, yeah, 11.2:1. I'm in agreement with Rob, if you could relieve the chambers to 75cc or so, then it would still be 10:1 with that and the same .040" gaskets...I'd be sorely tempted to run a .528" solid MP cam, or something similar with that much compression. :)

I honestly have no idea how the fuel blends are in your area, so really only you can answer how it would run on premium pump gas, or E85 for that matter...but I'm inclined to believe it would detonate pretty easy on premium E10 pump...
 
EL5DEMON340 said:
No my cam is bigger 244@ .050.. but my psi is 205. 30 total timing and runs fantastic with the a bad a** sounding hi compression pop out the tips!!
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I wasn't talkin about yours. I was talkin about the example Rob gave. 10* initial or less. THAT would run like crap.
 
Put a .080-.090 head gasket on it.

You aren't going to be building a quench engine, so get the head away from the piston.

Lots of ways to get compression down. Big chamber, thick gaskets...
 
Freezerman said:
This piston is domed with valve relief so I checked the flat part to make sure it was zero deck, then dropped it .5 in the hole to be able to cc the dome.

I am more than willing to change the cam and/or head gasket to make this work. I just need to know what I should change it to.

I have a 318 in the car now but would like to know if I can run This one and get some more performance.
Click to expand...

i really hope you mean at least .005 or .050, not half an inch
 
With that camshaft it really needs to be no more than about 9.5:1 static.

Yes, cometic or SCE 17050 fel pro is about the thickest cheap gasket at .049.
 
I can get 93 octane at some stations, but I can get 91 everywhere.
Would this work better with 308 heads?
 
805moparkid said:
i really hope you mean at least .005 or .050, not half an inch
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No, I meant .5. According to Sheppards book, you drop the piston down .5" and then fill the chamber and subtract the difference from 99.9 cc to get the dome volume
 
I was wondering about Cometic gaskets at .060. I would be happy to throw a different cam in it if you guys can tell me one that would be good.
 
If this engine is going in a light car with a 3.91 or so gear and a good converter in the 3,400 + range I would try it as is with just a bigger cam a solid in the 244 to 250 @.050 range or a hydrolic cam in the same range. No heat crossover, keep the fuel cool with a electric pump and the big plus would be a ram air setup. Remember to use a spark plug about 2 to 3 steps colder than a stock 70/71 340.
 
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