High compression with aluminum heads and pump gas???????

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duster360

duster360

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Not an exact number yet but compression on my 340 will be around 10.0:1 to 10.2:1 ( depending on head gasket choice, .039" vs .054" ). I am going to be running the edelbrock 63cc chamber heads. Will this be acceptable to run with pump gas. Any issues I need to look for?
 
11.9 to 1 in my Edelbrock headed 416 pump gas 93 no problem..another beautiful thing about using aluminum heads..
 
As far as gasket thickness, have you worked over your piston deck height vs the head to see if the quench gap is around .040"? That is a pretty well established aid to avoiding detonation, and IMHO you would do well to strive for that, regardless of a few tenths difference in SCR. Look at your computed DCR with the chosen cam to see if it is in the 8 to 8.5 range tops. Just don't put in a super-short overlap/duration turbo cam in it and the DCR's ought to end up in that range; there are plenty of DCR calculators out there online.

Personal opinion: My son and I are readying a build with the same AL heads, static CR, and a DCR in the low to mid 8 range, and I am not too worried about it on 93 octane, even with a low duration, torque cam. I ran a similar quench chamber/low duration combo a few decades ago and never had issue on low lead high test. It would occasionally ping and rattle on regular. (Auto trans, stock torque converter). Keep your revs up a bit on the manual trans (i.e., don't lug it), and IMHO, it should be OK.

Just a caution: that is not a guarantee, just an opinion and probability based on generally known engine build info and experiences. That is all anyone can give to you. At some point, you have to draw your own good or bad conclusions, tempered with others' advice and experiences and your own calculations, and go forward with it.
 
There really isn't much of a choice for gaskets... Run the Felpro 1008s.
Static ratio isn't such a big deal as long as you chose the right piston in order to have a tight piston to head clearance to create quench (if it was me I'd be setting it at .030 by decking the block to bring the piston proud of the deck) and the static ratio you want. Run a cam suited to the combination and your fuel type.
 
Long story short, bad machine work on the engine the first time. The pistons were down in the hole on the shallow side of the block .010". Now he block has been square decked and .006" was cut off the shallow side and .022" off the other side. Which will put pistons about .004" in the hole. Need to recheck when I get my engine back to see exactly where it is at.
 
.004 proud is perfect for the 1008s and My 65cc heads.I run 87E10, with a Scr of 10.7 and a Dcr of 8.6. I have run as high as 11.2/9.2sealevel,still on the 87.I have come to believe in the tight quench theory, and am running .034inch. I have run as tight as .024 on the KB107s.My TOTAL chamber volume was calculated to be 77.8cc,with the 1008 gaskets.It was measured at 78.0cc fill volume.
Your results may vary.

TripleBlack what would be the ICA on that, or the Dcr, For comparison?
 
duster360 said:
Long story short, bad machine on the engine the first time. The pistons were down in the hole on the shallow side of the block .010". Now he block has been square decked and .006" was cut off the shallow side and .022" off the other side. Which will put pistons about .004" in the hole. Need to recheck when I get my engine back to see exactly where it is at.
Click to expand...
That is an impressive amount of deck mismatch. Sounds like the thinner gaskets is were I would want to go with the pistons .004" in the hole. With the tighter bore clearance on the hypereutectics, it ought to reduce any piston rocking and help the lower clearance. Either way, it sounds like you have a good handle on things.
 
stroked340 said:
11.9 to 1 in my Edelbrock headed 416 pump gas 93 no problem..another beautiful thing about using aluminum heads..
Click to expand...

11-1 on my 360.

Cam size has a roll in this as well. To small of a cam can cause a problem.
With my 11-1-360 I ran a Purple 292/.509 & A Comp 294S, no issues.
4.10/4spd.
 
Here is a link to the pistons I am using. Part #142068. Why does it say 9.8 compression with 65cc head ( mine are 63cc ) and I am calculating 11.54:1 at .004 deck height? Am I doing something wrong?
 
If their website is wrong and that number is actually +5 the numbers will be a lot closer. It would then calculate out to 10.10 vs. their posted 9.8, which I can live with.
 
duster360 said:
Here is a link to the pistons I am using. Part #142068. Why does it say 9.8 compression with 65cc head ( mine are 63cc ) and I am calculating 11.54:1 at .004 deck height? Am I doing something wrong?
Click to expand...

Uncut 63cc ebrock's measure pretty consistantly at 64cc. I measured mine at that.

I hope everyone quoting their compression ratios have actually meaured their heads.

The cam is a big factor on compression tolarance. So when quoting compression and pump gas (w/octane #) you really need to know the cam you are running.
 
And that takes us back to Dcr's.
With aluminum heads, I can/have run up to 9.2 Dcr on 87E10. That was with 11.2 Static cr.With no timing issues and no detonation.
Guys with Iron heads are reporting success with Dcrs in the range of 8 to 8.6, on 91 to 93.
Your results may vary.

I wonder if I couldnt run 12:1 with a bigger cam, say with an ICA of 75*. That would get me a Dcr of wait-for-it............... 8.6...... Thats do-able on 87E10/aluminum, and 93/on iron. Lets see With an ICA of 75*, what cam would that be? Hmmm. That would be in the neighborhood of 295*adv. A pretty big cam to be sure. Almost not streetable. Almost.

I really think its about time we stopped making blanket statements about Scr and fuel.
Let me rephrase that; I stopped thinking about Scr in every way except as a means of obtaining a Dcr number with a certain cam.Or if your build is stuck with a Scr number, work the calculator in reverse to obtain the ICA for the Dcr/fuel combo that is known to work.
But hey, if someone wants to limit their Scr to 10:1, and run 93............Its totally your choice.
 
duster360 said:
If their website is wrong and that number is actually +5 the numbers will be a lot closer. It would then calculate out to 10.10 vs. their posted 9.8, which I can live with.
Click to expand...
The JE/SRP site lists 'dome volume' and they list -5 cc's for these pistons; the - sign means 5cc's of ADDED combustion chamber volume due to the piston eyebrows. The KB site will list the same number as +5cc's of 'head volume' for the same ADDED combustion chamber volume due to eyebrows. The DCR calculator you use will have to have the right polarity of volume added (eyebrows on flattops) or subtracted (domes). You are probably using a DCR calculator that needs a + number for proper results for eyebrows, and would use a - number for reduced combustion chamber volume for domes. But we don't know what DCR calculator you are using.
 
nm9stheham said:
The JE/SRP site lists 'dome volume' and they list -5 cc's for these pistons; the - sign means 5cc's of ADDED combustion chamber volume due to the piston eyebrows. The KB site will list the same number as +5cc's of 'head volume' for the same ADDED combustion chamber volume due to eyebrows. The DCR calculator you use will have to have the right polarity of volume added (eyebrows on flattops) or subtracted (domes). You are probably using a DCR calculator that needs a + number for proper results for eyebrows, and would use a - number for reduced combustion chamber volume for domes. But we don't know what DCR calculator you are using.
Click to expand...

Exactly. I called JE pistons and told them my issue and they said the same thing. Depended on which calculator you use as to whether you put in a + or -. Problem solved. They even calculated it for me just to be sure.
 
"But hey, if someone wants to limit their Scr to 10:1, and run 93............Its totally their choice." I didnt wanna say Bs. I wonder if hes been reading along.

When you guys post your Scr and successfully used octane, it would sure be nice if you also posted your ICAs or Dcrs, for comparison, and alum. vs iron heads.It would help to build a data base for parts selection for guys that are perpetually asking those question on new builds.
Something like this;
367cid/alum/11.2Scr/8.3Dcr/71*ICA/87E10/.023Quench/full timing up to 36*/750altitude.or
367cid/alum/10.7S/8.7D/62*ICA/87E10/.034Q/36*T@750ft. or
367al/10.7/8.5/65*/87E10/.034Q/36T@750
These are the combos i have run.
 
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