Fireball

iTrader: (21)

Say someone were to build a 12:1 compression 346 motor....what would have to be done in order to get it to run decently on

1) Pump gas (timing/fuel map changes??)
2) 104 unleaded at the track?

this is just something I've been toying with in my mind <img src="gr_grin.gif" border="0">

Fireball

iTrader: (21)

Also...how much would need to be milled off a 5.3L head to get up to 12:1?

Jim98TA

I personally would stick with a bit lower compression. Upping compression does not provide a HUGE increase in power. I think it is only like 5% for every FULL point (IE 10.1 - 11.1) increase. I could be off on that, but its not like you will pick up 50 more horsepower or anything.

Also, the higher compression makes things much more picky. You would have to reduce your timing for big part throttle loads, and in the heat, your engine may be very sensitive to octane, etc. Although with your insane gear ratio, your engine probably isn't under much of a load most of the time. At the track you could get away with putting race gas and full timing with no detonation worries, but you probably won't be able to do it on pump gas on the street.

So really I guess it may come down to whether you want an all out car at the track, and sacrifice a bit on street/pump gas. Or settle for a compression that will allow you to get maximum power on pump gas and useable on the street...

Ragtop 99

iTrader: (7)

[quote]Originally posted by Fireball:
<strong>Also...how much would need to be milled off a 5.3L head to get up to 12:1?</strong><hr></blockquote>

Seems like that will depend on the size valves you run. Increasing the valve size will likely increase the chamber size to unshroud them.

Jim98TA

Just as a reference, I get a lot of my experience about this from my Monte. It has cast iron heads, and 10.7:1 compression. In cool weather it can run an alright amount of timing. However during the summer (pretty much anything over 70) everything becomes a crap shoot. Ideally I am always putting in 94 octane and 104 octane booster. Even with this, most of the time I can't run as much timing as I would at the track. So when it is warm out, it makes for a slightly sluggish performer on the street. Gets kinda old after a while...

Fireball

iTrader: (21)

luckily...I know plenty of people running 11+:1 no problems...but I'm wondering about raising the ante up to 12 <img src="gr_tounge.gif" border="0">

Skelton

You most likely can get away with 11.0-11.3 without worries but 12.0-1 would be pushing it on pump gas. I would run 11.2-1 and not worry about the 16 or so hp difference. Anyway thats what I'm doing. That way I can utilize full timing and add a little sunoco 110 unleaded if it pings a little in the summer heat. With 12-1, I would guess I would need around 98-100 octane to not detonate on 85+ degree days. Good luck!
P.S. 4.71 gears are SICK!

Terry Burger

iTrader: (4)

I think going from 11:1 -> 12:1 would be worth only 5-8rwhp midrange in most cases (no real peak gain, unless you have a huge cam). In California we only have 91 octane pump gas so I just run 24-25 degrees of timing with my 11.3:1 heads. Works ok for me. <img src="gr_images/icons/wink.gif" border="0">

Fireball

iTrader: (21)

I'm gonna be stepping up the cam quite a bit at the same time...

230ish duration

JasonShort

iTrader: (242)

I dont think that going 12:1 is a good idea if the car spends the majority of time on the street.....even if you pull enough timing to run on pump gas.

There are power percentage figures by altering compression (IE 5% power increase for raising compression one full point), but at a certian point that percentage of increase diminishes some. Say someone went from 10:1 to 11:1 and picked up 5% hp. The next guy could take his race car and go from 13:1 to 14:1 and only pick up 2-3% more power. Obviously there are alot of dynamic variables that can have an effect (positive or negative) on power when compression changes are made....especially when comparing static compression ratios.

I agree with Terry in that you would probably see less than 10rwhp.

11.3:1 is a good for an LS1 car that sees the majority of its time on the street.

I run 12:1 compression on my solid roller LT1. I was debating going with 12.7:1+ in my new motor, but that extra 8-12rwhp was not worth the money I would have to spend in upgrading other areas (Evans coolant, BeCool rad, etc..) and pulling the timing for street use...not to mention if I even got a bad tank of gas.

Just my thoughts

Jason

Jim98TA

I think I would probably stay with the 11.3 or so too. However, the cam may help you quite a bit with the higher compression. I am gonna start on my next project of swapping cam, head work, etc. on my car. The duration on the one I am looking at is 230/238, so it should help bleed off more cylinder pressure then my current one. If you pick your cam carefully, you may be able to bleed off enough pressure to get away with a higher CR. But then you may get into a cam that is a bit to radical, esp with a 346 CI engine.

I would stick with the 11.0-11.3 range, a cam with low 230's duration, good heads, and the LS6 intake. I would think that would give you a good combo, that may spin in the RPM range you want.

Nine Ball

iTrader: (38)

My 382ci is at 11.0:1 cr and runs/races great on pump gas. My next motor is going to be 12.0:1 with a nice cam though.

I remember back in '99 everyone told me that installing a 112 LSA cam in an LS1 was crazy, so sometimes it pays off to be the first "crazy" one, right Mr 4.71?

LOL!

Tony

CHRISPY

You may have to weld the heads as well as notch the pistons for P to V clearance to get 12:1.
I would think the 230/230 cam with about 58x lift and 112LSA would be nice <img src="gr_stretch.gif" border="0">
Cheers,
Chris

Damian

iTrader: (89)

Guy's, how much milling is require on an LS1 head to acheive 11:1? Maybe .030 and a short head gasket? I have asked this question before with no solid answers. Thanx


Josh

XLR8NSS

iTrader: (4)

Here is a nice little compression ratio calculator. <img src="gr_stretch.gif" border="0">

http://www.smokemup.com/utilities/ca...sion_ratio.cfm

Pro Stock John

iTrader: (34)

IMO if you were building a racecar, and never really drove the car on the street, I'd just 12:1 or higher.

I am running 11.3:1 on pump gas with 28 degrees of timing.

I have heard two LS1's now that had high compression and audible pinging. Both cars needed more tuning to address that problem.

I do think that 12:1 is very possible on the street, but in July, how much timing can you run on pump gas? I'm thinking a motor like that might end up only taking like 22-24 degrees of timing.

Paulie

[quote]Originally posted by Pro Stock John:
<strong>I have heard two LS1's now that had high compression and audible pinging. Both cars needed more tuning to address that problem.
</strong><hr></blockquote>

Yes I do. <img src="gr_stretch.gif" border="0"> <img src="gr_stretch.gif" border="0"> I don't ping on 100 though, just 93, usually in 4th, especially 4th with the converter locked.

I have welded heads with notched pistons. Trying to find my CC numbers. I did have some eyebrows on my pistons before heads/cam with my A4 (stock limiter), so things were probably tight to begin with. <img src="gr_eek2.gif" border="0"> <img src="gr_images/icons/wink.gif" border="0">

ArcticFormula

I would kind of go the opposite route if I had the cash, lower compression with forced induction (but I'm biased as I sold an 89 Turbo TA to get my car). I think a supercharger with mild boost on stock compression might be a better route. Or a turbo set up and lower the compression to 8.5 (if that is even an option), haven't researched it, nor will I ever dump that kind of money into my car again, I learned through my TTA. But for some reason extreme high compression seems more dangerous to me than mild boost. But what do I know.

Ragtop 99

iTrader: (7)

[quote]Originally posted by Chris ARE 360:
<strong>You may have to weld the heads as well as notch the pistons for P to V clearance to get 12:1.
I would think the 230/230 cam with about 58x lift and 112LSA would be nice <img src="gr_stretch.gif" border="0">
Cheers,
Chris</strong><hr></blockquote>

com'on chris, this is FIREBALL I look for a little more duration and less LSA <img src="gr_eek2.gif" border="0">

Mike Morgan

I think you will have a hard time getting 12:1 w/ a stock shortblock. Milling the p!ss out of them and doing minimum chamber work to match the bore might get you to 11.8:1

You may be able to running a slightly thinner gasket, but you have to look out for piston to head clearance. Anything less than .035" will get pretty risky. So you might get to 12.0:1 and would have nice quench.

If you have 94 octane pump, then with a MMS229 cam or similar I'd say you'd be fine with some tuning. The combo would work well, because you'd get all the topend of the 229 cam, and get a ton of torque back in the midrange.

Hmm, now that I think about it, maybe I'll do that on my C5 <img src="gr_tounge.gif" border="0">