mguidry629

iTrader: (6)

I'm in the process of dialing in compression ratio and wanted to get some other opinions. It will be run on 93 octane pump gas, driven on the street/strip a few times a week. 383 w/ 232/242 LE Cam.

I haven't cc'd the heads yet, but assuming 54cc (we can mill it down if needed), .026 gasket, pistons are now .030 in the hole, and +12cc pistons. I'm at 11.1 now and I'm thinking I want to be about 11.75, so I could deck the block down .020 to give me .010 in the hole and mill the heads to where I need to get to. I could easily get to 11.75 without any clearance or quench issues, but 12.0 would be pushing it I think.

What y'all think?

86formula

iTrader: (3)

im at 12.5 and i think Joe is at 12.8, we both run pump gas still with no problems

Larry @ AMS

iTrader: (1)

with the mentioned cam you should be fine in the 11.7 area, but anymore you will need to look at a cam change if you want to run pump gas

I run 12.4:1 with an LE HR 245/253 on a 105.

quik95lt1

iTrader: (7)

its impossible to tell you;re DCR with those cam specs............but besides the point you should be ok in the 12.0 area....

mguidry629

iTrader: (6)

That's a serious cam right there! I didn't know cam size had anything to do with CR? Why is it that you need more cam to go higher CR?

I was thinking 11.5, but I didn't want to put it all together and get it back in the car and wish I would have gone higher, so now I'm thinking 11.7-11.8. It's free horsepower right?

Edit: Cam specs....232/242 @ .050 .578/.576 lift on a 110

gatorhead

iTrader: (4)

Because you don't go buy static compression ratio, you go by dynamic compression ratio and when dealing with a higher dynamic your valve events need to occur at more specific time in order to keep the dynamic ratio down......it is a little more complex than that, that was just a taste

quik95lt1

iTrader: (7)

thats very misleading...........dont get caught up with DCR nubmers......dcr numbers is a calculation that is done to approximate the cylinder pressure in a stationary state........this works great untill the motor actually starts spinning........then cylinder head, cam, intake , exhaust, SCR and most imporntatly the product of all them; Volumetric Efficency will determine the real cylidner pressure at a specific time thusly the static compression ratio is very important......my "DCR" on my motor is down lower than you'd think because of cam specs.......however the car wont even run on anything near 93 octane fuel......even at part throttle with a 14.22:1 SCR.......my DCR is the same as soem cars with smaller cams with 12.5:1 SCR that WILL run on pump gas around town............so again.......DCR is a very misleading number that internet people seem to love to get caught up in.........


i know that may generate some controversy but nbd.....

gatorhead

iTrader: (4)

It's all good I know exactly what you are saying. I was trying to leave it more vague as it can be quite complex, and well to most, confusing. My main point was that too many people get caught up with the static CR, when in fact the bigger demon to contend with is the dynamic CR. They both have to be kept in check (and save for VE) the cam is normally the inn keeper

mguidry629

iTrader: (6)

So, should I try to push it to 12.0? What are the pros and cons?

Low N Slow

iTrader: (4)

I'm bet the guy that designed the cam would have some advise for you.

Puck

iTrader: (17)

I was aiming for 12.5:1 on my build but I could only muster 12:1 with my huge heads.

Like stated though, it has a lot to do with the cam - mine is def on the aggressive side @ 255int with a decent amount of overlap, and will keep my DCR down less then a smaller cam with the same SCR.

Honestly with your engine I wouldn't fret about a tenth here or there - .25 CR will have a very small effect on your peak power.