compression vs deck height

[gtxrt]

440 engine, 217-221 cam with 90 octane gas. what's the best way to go. felpro-8519 head gasket with 9.57 comp and 57 thou quench. or felpro 1009 9.6 comp with same 57 quench. or cometic gasket with 9.80 compression and 48 thousand quench. don't want that dreaded ping. thanks.

 

[R413]

440 engine, 217-221 cam with 90 octane gas. what's the best way to go. felpro-8519 head gasket with 9.57 comp and 57 thou quench. or felpro 1009 9.6 comp with same 57 quench. or cometic gasket with 9.80 compression and 48 thousand quench. don't want that dreaded ping. thanks.

You forgot some important pieces of the puzzle. What is your altitude? Are you using ethanol gas or ethanol free gas? What cylinder heads?
aluminum or iron?
Closed chamber?
Open chamber?
9.57 or 9.8 compression on 90 octane? Sounds like wishful thinking.

 

[gtxrt]

You forgot some important pieces of the puzzle. What is your altitude? Are you using ethanol gas or ethanol free gas? What cylinder heads?
aluminum or iron?
Closed chamber?
Open chamber?
9.57 or 9.8 compression on 90 octane? Sounds like wishful thinking.

closed chamber iron 915 heads. 700 ft above, and non ethanol gas. i can get 93 10% ethanol but really don't want to run that. i have the 8519 gaskets on the shelf.

 

[68Dart470]

Felpro 17059 maybe

 

[gtxrt]

the last 440 i built like this one but had 9.9-9.95 compression with a recurved distributor not doing to recurve this one. had to run only 33*- 34* total timing.

 

[BSB67]

Cam specs please

 

[Nate S]

I have a 413, 975 heads, 214/225 @.050 cam, with timing at proper 37-38 all in and vacuum advance for part throttle. At 9.25:1 I find that 89 octane, 10% ethanol pings at mid throttle to full on some days but not the cooler ones. With 93 octane, 10% ethanol it really doesn’t ping under any conditions. Altitude is 300-1000 ft. Mixture is good, maybe a tad rich if anything, plugs look like the book. Hope this helps.

 

[1968rt]

Im running 915 heads with an .020 steel shim gasket., .040 quench 10.3 compression, no problems. 8519 are like .039? Get closer to .040
.059 quench is borderline, wont help much.

 

[gtxrt]

Im running 915 heads with an .020 steel shim gasket., .040 quench 10.3 compression, no problems. 8519 are like .039? Get closer to .040
.059 quench is borderline, wont help much.

what gas are you running ?

 

[gtxrt]

Cam specs please

217-221@50. 110 lsa with 106 centerline but i can move the centerline

 

[1968rt]

Running 93 octane. I have it advanced 32. So far no pinging. If I go higher I will add booster. Im running the Mopar .528 284 with manifolds.

 

[gtxrt]

what would be a better change of not pinging. 9.6 with 57 quench with head gasket or 9.8 with 48 thousand quench with head gasket ?

 

[Nate S]

48 isn’t much quench. I’d take the lower compression.

 

[gtxrt]

48 isn’t much quench. I’d take the lower compression.

sorry, not piston's in the hole but 18 thousand in hole with 30 thousand head gasket

 

[Nate S]

sorry, not piston's in the hole but 18 thousand in hole with 30 thousand head gasket

You’re not going to make or break anything horsepower wise with .2 points of compression. You will however give up some power if you need to back off the timing 4? degrees to make it stop knocking.

 

[1968rt]

.038-.043 is good. https://www.motortrend.com/how-to/ideal-quench-height/

 

[beanhead]

With that camshaft and pump gas, I think you're pushing it either way. Will you be in the clear without having to retard ignition or cam timing? Perhaps...but you won't know until you run it.
I agree with Nate, I'll sacrifice a little SCR over timing anyday.

 

[gtxrt]

.038-.043 is good. https://www.motortrend.com/how-to/ideal-quench-height/

that's say am good to 60 thou total quench, so am going with the 9.6 compression.