badgta

iTrader: (4)

i'm sorry if i didn't post this in the right place, i really didn't know if here or the power adder board would be the right one..

my question is, really it's a debate i cannot figure out, is if i decided to put a supercharger on my carbed 383 that has 10.2:1 compression, would i really have to run more than 93 octane?

the reson i ask is factory lt1's and ls1's have over 10.2:1 compressions but yet have kits that bolt right on and run on pump gas...... and there camshaft is a factory type where mine would bleed off more cylinder pressures...... i was wanting to buy a vortech blow through type when the time comes, but i cannot afford 104 octane, so it would have to run on 93...... i can by an intercooler...... it has afr 190's with a comp xr282hr cam with a 112* lsa.... the carb is a 750 demon with vac secondaries....

any ideas?

dj haf

it depends on a few things...

are you going to use an intercooler or water/alc injection or anything of the sort?

and how much boost do you plan on using? low boost with an intercooler should be fine, but if you'd like to reach somewhere between 12 lbs or higher, you're going to need to lower your CR to make it run good on pump gas (as well as retard timing), or start fillin' her up with race fuel. personally... this is what i would do. put some low CR pistions and retard your timing so you can run more boost. retarding your timing a few degrees to raise your boost is still going to give you more power than if you were to keep your timing where it was without raising the boost.

IROCZ1989

iTrader: (1)

A roudabout figure for reliability and streetability is 8.5 -9.1 .You can get by with either. Usually like the befor ementioned post said intercooling is a factor. If you are running 9lbs say. and you are sure this is all you want to run you can most likley get by with 9.1, I wouldnt go any higher. Ive read you make more power with less compression and more boost VS more compression less boost. You can get a procharger with an intercooler for your carb setup, but I would change the cam, 112 is not ideal for blowers. Some will argue you can run more boost than 9lbs on 9.1, and I agree but you will be threading a thin line between detonation and motor damage. I feel 9lbs would be totally reliable and all you would have to worry about is putting gas in the tank. For your application I would lean more towards a 250 holly, or 173. Easier to install and tune than the blowthrough and makes alot more torque down low. But with the roots setup I recommend to go even lower than 8.5, making 8.5 thr latter and depending on boost down to 8.0 to 1.

dj haf

this should answer all your questions

flrtin1

This link has a table of Static vs. Effective Compression at different Compression and boost levels
http://www.holley.com/HiOctn/TechSer...fo/SCTech.html

dj haf

the chart on that page is for non-intercooled superchargers... if you look at the picture i posted, and put it next to the chart on holley's site, you'll see that the effective cr matches the line for the for the roots-type blower cr

flrtin1

lol, I got tied up after I read that post and didn't see you put the chart up

dj haf

it's all good