11:1 340 on pump gas?

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swinger340

swinger340

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Is an 11:1 alluminum headed .030 over 340 w a 248/250 duration @ 50 cam to much for pump gas? Highest octane offered at the pump in this neck of the woods is 91 or 93 at few select stations. Can get a deal on some heads but dont want detonation problems. This is just a hot street car. Will very seldom see the track. Had planned on using 1008 .039 thick 4.18 bore gaskets, are any of the thicker gaskets any good? That would help ease my decision on buying heads or not. Would feel more comfortable around 10.8:1.
 
I did it, though, in your area, you may not be able to get a full advance on the distributor.HP will suffer due to this. You might be able to drop compresion a tad with thicker gaskets and run 93 w/full advance.

My Edel. headed .030-360 with Zero deck KB-1072 and that purple cam ran just fine.
Get a comp calc and use 5 cc extra in the head for the valve reliefs on the piston and use a Fel-Pro gasket @ .039 thick by 4.1 bore. Getthe math done on that for exact ratio as I forget and am cooking dinner tonight so... OH sht,,,BRB
 
It's fine. Watch your timing curve and tune up, but it should be fine.
 
rumblefish360 said:
I did it, though, in your area, you may not be able to get a full advance on the distributor. HP will suffer due to this. You might be able to drop compresion a tad with thicker gaskets and run 93 w/full advance.

My Edel. headed .030-360 with Zero deck KB-1072 and that purple cam ran just fine.
Get a comp calc and use 5 cc extra in the head for the valve reliefs on the piston and use a Fel-Pro gasket @ .039 thick by 4.1 bore. Getthe math done on that for exact ratio as I forget and am cooking dinner tonight so... OH sht,,,BRB
Click to expand...

Sorry, I was doing 2 things at once.....

I also ment to say...


IDK about 91 octane for that. I only have 93 or 89. And the Edel. heads rae the standard units, not the 340 units, so it would be 63 cc head chamber.

It ran very good. Mid to Low 12's OOTB, so to speak. 4spd & 4.10's.
 
rumblefish360 said:
I did it, though, in your area, you may not be able to get a full advance on the distributor.HP will suffer due to this. You might be able to drop compresion a tad with thicker gaskets and run 93 w/full advance.

My Edel. headed .030-360 with Zero deck KB-1072 and that purple cam ran just fine.
Get a comp calc and use 5 cc extra in the head for the valve reliefs on the piston and use a Fel-Pro gasket @ .039 thick by 4.1 bore. Getthe math done on that for exact ratio as I forget and am cooking dinner tonight so... OH sht,,,BRB
Click to expand...
So whats for dinner???
 
11:1 CR is not too much for pump gas, it depend your camshat and you should calculate your dynamic CR and cranking pressure. DCR should be around 8-8,5 and it should not cause detonation.Aluminum heads allows that DCR maybe higher, Check your intake valve closing point also. You can calculate your DCR here: http://www.wallaceracing.com/dynamic-cr.php Put your cam specs here, and maybe we can help you, and you don't have to change head gaskets.

I have 390 stroker,11.2 CR. DCR is 8.46:1. Kb flat-top pistons, 0-decked, Mopar aluminum heads with 65cc chambers. I have comp cams hydraulic flat tappet cam 20-228-4. Intake closing point is 69 deg.ABDC. Head gaskets is fel-pro 1008.
I also have hughes 3742 hydraulic cam in stock, but if i use this cam, DCR will be too high, maybe. 10.17:1. And cranking pressure will be over 216 psi, when it should be around 185 psi. Maybe i try this cam, maybe not.Fuel is 93 octane:burnout:
 
dartswinger84 said:
11:1 CR is not too much for pump gas, it depend your camshat and you should calculate your dynamic CR and cranking pressure. DCR should be around 8-8,5 and it should not cause detonation.Aluminum heads allows that DCR maybe higher, Check your intake valve closing point also. You can calculate your DCR here: http://www.wallaceracing.com/dynamic-cr.php Put your cam specs here, and maybe we can help you, and you don't have to change head gaskets.

I have 390 stroker,11.2 CR. DCR is 8.46:1. Kb flat-top pistons, 0-decked, Mopar aluminum heads with 65cc chambers. I have comp cams hydraulic flat tappet cam 20-228-4. Intake closing point is 69 deg.ABDC. Head gaskets is fel-pro 1008.
I also have hughes 3742 hydraulic cam in stock, but if i use this cam, DCR will be too high, maybe. 10.17:1. And cranking pressure will be over 216 psi, when it should be around 185 psi. Maybe i try this cam, maybe not.Fuel is 93 octane:burnout:
Click to expand...
Thanks, been playing w the chart punching in diff cam specs and i see now i will be absolutly fine as long as i use the rite cam.
 
Not hijack the thread but I don't want to clutter up the main page with almost the same thread. Calculating my CR it looks like the engine I'm building is going to be running about 11.3 : 1 static and 8.99 : 1 dynamic, is that going to be too high to run a high octane pump gas? I'll be running a comp 274 solid cam.
 
Fo - I use 8.75:1 dynamic as a top limit with a closed chamber, alumnium head, and tight quench. You may be able to get along with higher, but with pump fuel being what it is, that's the high limit for me.
 
W my 11.1:1 340 and the cam i intended on using anyways comp. XE282S the intake closes @ 67 deg. ABCD witch would make my dynamic compression 8.60:1 Sounds like this will be a fine combo on pump gas to me. Im going for it. Will keep you guys posted on how it runs on 93 octane
 
I was going to say with alloy heads and that much overlap on the cam you should be fine.
 
my boss had 12.5:1 on our crap 91 on the street and 110 @ the track in his AWB plymouth...

the trick is to get the thermal coatings on the piston tops, chambers, valve faces and exhaust ports...

this will keep more heat out of the combustion chamber and send it thru the exhaust...

also have to dial back the timing for pump...

as for the meth or water injection the boost guys seem to be having great luck with it so i see no reason why it wouldn't work... just need to have the correct "curve" for injecting it...
 
You can do it just fine. There's a guy over on The Hamb that has an early Hemi running 13.5:1 on pump premium with no spark knock. I think he has 34 degrees in it.
 
QUESTION:

In figuring dynamic c/r are you supposed to use the intake closing degree @ 50* or Gross....??????

I'm guessing @ 50* (was told Wallace uses the @ 50* IVC)

Our 408 spec's are:

Bore: 4.030
Stroke: 4.00
Rods: 6.123
Static CR: 11.00
IVC @ 50*: 50*
Altitude: 15'

Using the cam IVC @ 50* specs gives us a dynamic CR of 9.70 with J-Heads :shock:

Dynamic cranking pressure calculates to: 203.63 which is what our compression tests run.....200-205 :shock:

Looks like some race fuel will be needed :banghead:

Are these calculations correct....??????

Rickster
 
rickstershemi said:
QUESTION:

In figuring dynamic c/r are you supposed to use the intake closing degree @ 50* or Gross....??????

I'm guessing @ 50* (was told Wallace uses the @ 50* IVC)

Our 408 spec's are:

Bore: 4.030
Stroke: 4.00
Rods: 6.123
Static CR: 11.00
IVC @ 50*: 50*
Altitude: 15'

Using the cam IVC @ 50* specs gives us a dynamic CR of 9.70 with J-Heads :shock:

Dynamic cranking pressure calculates to: 203.63 which is what our compression tests run.....200-205 :shock:

Looks like some race fuel will be needed :banghead:

Are these calculations correct....??????

Rickster
Click to expand...

Don't know , but I get 195-200 on my compression tests and car pings on 94 octane .
 
The calculations use the intake closing event at .050". My impression is this removes any of the cam grinders' tricks to control valve bounce on the closing ramp, which would make duration calculations kind of weird as you get closer to the base circle.
Wallace does not ask to change that figure. The KB-Silvolite site has you add 15° to that figure. IMO, the KB version is closer to reality only because they assign a given figure of 15° and calculates instead of ignoring the duration of the closing ramp, which is still duration and therefore not a sealed cylinder. Because of the later (and IMO more true) closing event, the KB numbers are usually a little lower.
Something neither of these calculators take into affect is the cylinder pressure will go up as rpm rises. SO while the compression ratio is never changing, the amount of material being squeezed goes up, which means more pressure, and means more tendency to detonate. Which is why some great running pump gas engines show signs of detonation even tho you never hear it. It's happening at WOT at higher rpms.. Where it's just as destructive.

All that being said, I'd expect that 9.7:1 dynamic to only drop a small amount. Less than .5 point. So yes, race gas will more than likely be needed.
 
Thanks for the clarification....and KB computed out to 8.8 dynamic and 11 static which was a pleasant surprise.....the proof will be in the pudding :glasses7:

I'ts a very light car and the 4-spd and 4.10's should also help :burnout:

Rickster
 
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