Whats the highest compresson i can run on pump gas, or with octane booster,
on a 383 chevy=
on a 350 chevy=
Whats the highest compresson i can run on pump gas, or with octane booster,
on a 383 chevy=
on a 350 chevy=
Cast iron heads or aluminum heads?
what type of octane booster are we talking about.... the cheesy of the counter crap that will do nothing, or something real like touluene, doesn't matter what displacement the engine is either, the only things that matter are the metal you use in the motor, and the cam grind
I have no clue, but my guess is 12to1
As Blackroc alluded to, you can run another full point of static compression ratio with aluminum heads over cast iron heads.
The limit on scr will be determined by cylinder pressure (intake closing point on the cam), head material, combustion chamber and piston crown shape and size, total ignition timing and advance curve, spark plug heat range and indexing of the ground strap, thermostat opening point, inlet air temperature, air/fuel ratio, your elevation above sea level (air density), squish (distance from the piston crown to the underside of the cylinder head with the piston at TDC), rear gear (lugging the motor with a tall gear will allow detonation to occur easier than a short gear), whether or not there are any hot spots in the chamber/cylinder and whether or not you're polluting the incoming charge with an EGR or PCV system.
With everything optimized, it's possible to operate at a little over 11:1 with iron heads on premium pump gas with no octane booster.
my response sounded a little less quality as Techs, so i'll just leave his to do the talking :D
cast heads
What's your goal? What do you want the car to do?
It all depends on the cam specs as more duration will bleed off compression due to overlap. You have to figure dynamic compression ratio rather than static compression. DCR of 8:1 is about maximum with iron heads and 8.5:1 with aluminum heads. DCR takes into consideration your cam specs and is a much more reliable guide to building an engine. For a very thorough explanation of DCR, go here: http://www.chevytalk.org/fusionbb/sh...php?tid/92966/.Quote:
Originally Posted by frankgomez65
Another bad thing on high compression besides today's dismal fuel is that high compression makes more heat... On a street car that will be idling around in stop and go traffic high cylinder temps leads to high operating temps and overheated engines which can cause a lot of very expensive damage. Optimizing the compression may be best left to race cars and sticking with compression in the 9 to 9.5 range could be better. I like to spec my engine components for building torque which IMO is a much more beneficial for street use.....
I thought it would be a cake walk to run pump premium 91 octane in my 10.6:1 motor but I've found I can't put in any more timing than 32* spark lead without detonation (lightly peppered plugs)... This is on an aluminum headed, high altitude motor (carefully prepped pistons and chambers, too!) that should tolerate highest compression... it runs just fine but it runs a whole lot better with higher octane and 36-40*
Just a word of caution, you may be able to get away with 11:1 on premium but you'll have to compromise in many ways to get there...
Two cents,
-Chris
9.5:1 on 93 Octane Max
I run 10.6:1 compression in my 383 and have no problems if I run 91/92 octane. In fact, I had to fill it with 89 octane in a pinch two weeks ago, and still no pinging. My DCR is 8.46:1 which is getting close to the 8.5 edge. But with AFR heads, less timing is more, and 32 degrees total made the most hp and torque. I originally wanted to run a CC XE-274 cam but it put the DCR at 8.67. But the Magnum 280 cam put me under 8.5. I am very happy with my engine combination.
I ran 92 octane in a 11.3:1 350 +.030, nasty solid cam, iron heads ported and polished.
I had to index the plugs to get rid of pinging.
IMO a water injector would get you over the hump, and they are not too expensive nor are they a pain to keep up.
Kitz
what is index the plugs mean.
and 32 degrees mean
When you index spark plugs, you use special washers so the open part of the plugs are facing in the same direction to aid in igniting the charge more efficiently. Drag racers do it because they are looking for every possible hp, but it is not necessary on a mild street engine. 32 degrees refers to the total amount of timing advance. If your distributor has 24 degrees advance built into it, then if you use a timing light to set your timing to the 8 degrees BTDC mark on the cam cover, you will have 32 degrees total advance. The new fastburn chamber designs make more power with less timing--GM's ZZ4 crate engines are set to 32 degrees. It is common for the older style chambers to make more power with more advance--say 36 degrees, but it depends a lot on the cam specs.
Frank, indexing the plugs means placing the gap of the plug facing the center of the combustion chamber or towards the exhaust valve, depending on whom you're talking to. It allows optimized flame propogation (the travel of the flame kernel across the chamber after the plug fires) and equalizes the process in all cylinders for increased power and smoothness. It won't make a world-shattering difference, maybe on the order of 1-2%, but every little bit helps.
32 degrees means the total initial and centrifugal ignition timing advance. Maximum cylinder pressure is generated somewhere between 12 and 15 crankshaft degrees after top dead center after the plug has fired off the mixture. It takes time for the flame kernel to cross the chamber and ignite all the fuel/air mixture, so we must fire the plug before the piston gets to top dead center to give the mixture time to burn and produce maximum pressure after top dead center to push the piston down on the power stroke. On a small block chevy, we would normally use around 12 degrees initial timing at the crank and 22 to 24 degrees centrifugal advance in the distributor for a total of 34 to 36 degrees, depending on the combustion chamber design. Some current heads are being produced with extremely efficient chambers and will require less ignition timing advance than some of the older, less efficient designs.
http://www.advanceautoparts.com/engl...0001001sp.asp#
http://www.fordmuscle.com/archives/2000/07/indexplugs/
http://store.summitracing.com/egnsea...g+washers&x=22
SORRY RUMRUMM, I DIDN'T SEE PAGE 2 BEFORE I ANSWERED. :)
WE SAID THE SAME THING THOUGH, AND THAT'S A GOOD THING.
No problem, Richard. Good explanation.
I'd always heard that if you kept it below 9:1 you are fine.
Judging from the previous replies, i think I'm right.
thanks for the help
jmo but this question can't be answered!!!!!! every engine, head, static comp,cam will make it different.. no one can give a 100% answer to this with every little detail of the engine even with that it very hard to know...
You are right about that. What you can safely run for compression is dependent on what you choose for engine components. My 383 has 10.6:1 static compression, and it runs fine on 92 octane. But I built it knowing that with aluminum heads and a CC Magnum 280 cam, I could run under 8.5:1 DCR which is the edge for pump gas. I originally wanted to run a CC XE274, but it made the DCR too high. Because the intake valve on the Magnum 280 closes 3 degrees later (66) than the XE274 (63), the DCR was lower and within pump gas range.
Ive got a 555ci N/A 802hp that I run on 91 pump gas at 10.50-1 compression.