CamTom12

iTrader: (1)

I was just wondering for the heads I'm trying to plan, up to what compression ratio can 93 octane handle well?

MUSTANGEATER

iTrader: (10)

It really depends on the total combo most people will say 11.XX is the limit. That's untrue you could get away with more compression than that on 93 octane.

CamTom12

iTrader: (1)

ok, well let's use this as a combo:
C1 cam (222 / .566) (maybe a C2 later down the road, 224 / .581)
5.3 stg 2.5 heads (trying to find out how much I can mill)
1-3/4 headers (might bump to stepped later)
& full bolt-ons

What kind of CR could I run safely on 93 octane?

Are there any reliable alternatives to driving out to the airport or dragway everytime I need to fill up if I need higher octane fuel?

PREDATOR-Z

1- You can only mill so much for PVC reasons.
2- 11.2> 11.5:1 CR usually gives best results in LS1/LS6
3- Stock unmilled 5.3's are allready 61 cc which would give you close to 11:1 depending on which gasket you use.
4- By milling heads you run into a load of valvetrain geometry headaches, so my advice is keep it simple, don't mill. That also gives you more room for a bigger cam without flycutting.

CamTom12

iTrader: (1)

I know it's safe to mill 5.3 heads to .030, and I wouldn't go any farther than that.

I was curious about whether 93 octane would ping like 87 with 11.5:1 (just for example). I'm just trying to figure out how much compression 93 octane can handle.

Good info on the milling though, it's all true

jrp

iTrader: (16)

think DCR, with the proper cam to bleed of cyl pressure you can run 12.0 CR on 93. since you dont like the type to take every little step i'd keep it @ 11.1 SCR compression and leave it at that.

CamTom12

iTrader: (1)

hmmm... interesting thoughts on dynamic ratio. That hadn't actually crossed my mind. I'd like to have some latitude with my cams because this thing is a sickness that's only cured by changing stuff ( = spending more money...). I want to be able to run a variety of options, so SCR is certainly what I'm looking at. if 11.1:1 is 93 octane's highest safe CR, I'll just stick with that.

This site's so full of good info...

jrp

iTrader: (16)

thats not the highest but its easiest route to go if you dont want to delve into the more intricate parts of a setup.

FWIW my SCR is 12.04 and DCR will check in the 8.8 - 9.1 range. i'll find out through tuning how much timing i'll be able to run on 91, a 50/50 mix w/ 100 octain will be added if alot of timing has to be pullled. i've done everything on my part to lower detonation potential: .035 quench, polished combustion chambers, colder plugs, 160 T-stat, ect.

CamTom12

iTrader: (1)

OK, I think I'll shoot for around 11.5:1, then. I want a fair CR but I need the ability to run 93. I'm sure I'll be able to do it with this SCR and a variety of cams. Thanks for the input!

FWIW I'm going to do my own HP Tuners tuning with some pointers from a few tuner friends so hopefully I can get a dead-on tune with a good cam.

I'm pretty sure even the C2 224 won't have PtoV issues, but don't doubt that I'll double-check with PRC and/or MTI and do a cam check before I fire it up (besides, that C2 would be at least 2-3 yrs. down the road. Working on a small budget...)

SSean

Its all about your DCR. I have a 12:1 static compression ratio, but my DCR is around 8.7-8.9, and dont have any problems with 93 octane