I need some pics and ideas on how to increase my CCs on my CCs ! I would like to push them out to 78 to 80 cc and open the tuning window with less efficient cambers. That will get me about 9.5 to 1 on my stock LS3 short block. I'm also gonna open my ring gaps out to .026 top /.028 2nd.
Show me your softened chambers !!

 

Doubt you'll get that much out of an OEM head. Just soften the chamber and run a thicker HG. Call up cometic. They will make you one whatever thickness you need to hit your desired compression level. I've run 3mm thick head gaskets on 30+lbs of boost with no sealing issues.

 

Yeah, no. Because introducing lower quality quench and a lazy flame front is a good idea, right?

 

You don't introduce lower quality quench, you remove it all together. We all know low compression and slow burn CC's aren't efficient NA. Add a crap ton of boost to the mix and there is nothing lazy about the burn rate.

 

I must have missed where this was a topfuel engine? Or a Buick turbo 3.8 for that matter. There is no good reason to dump the characteristics and engineering of a good street engine for short-lived thrills of the occassional WOT blast. The better you build an engine N/A, the better it is under boost.

Buying a set of heads with properlly designed large volume chambers would make more sense. Hogging out the combustion chambers and stacking headgaskets is a lazy band-aid approach in my opinion.

 

I disagree. There are a TON of pent roof and hemi CC designs out there these days. It's not reserved for top fuel.

"short lived thrills and the occasional WOT blast" Is kinda the whole purpose of most turbo builds, no? In my opinion that's what it's all about! If I wanted a nice efficient NA setup I'd buy a Civic.

There are also many different reasons to alter GM's design when you bolt on a power adder and double/triple the intended power output. If you are octane limited, dropping the compression will allow you to make a TON more power without detonation. Softened CC will also help with detonation. There is nothing "better" about a higher compression engine with fast burn head design. Esp. when we are talking forced induction. Boost is more efficient at making power than compression. If you're searching for the highest overall power output with the least amount of cyl pressure, low compression and high boost is the way to do it.

No one said anything about "stacking head gaskets", and there is nothing "band-aid" about it. You obviously know very little about this subject and have no experience running thick aftermarket head gaskets to lower compression. You should go research it a bit if you are going to make suggestions.

 

So.....Forcefed, you don't think there is enough material to clean out at 78cc ? That's only about 6 1/2 CCs of volume. Ive been looking at the water jacket locations and material thickness around the combustion chambers and it looks like a fair amount of material to work with. I'm gonna give it a go and see where it comes out. I have 150 bucks in these heads and they came with a brand new set of 160.00 PAC springs, so I'm in the heads right for a little experimenting, LOL . I already have a set of LS9 gaskets coming , so I will work the CCs as best I can and live where it comes out. No doubt I will be better off than the 10.7 I had with the LS3 heads. To be honest , as far as danger from the turbo, I'm more concerned with the ring gaps on this "600 mile" short block.

 

You really like to flex your e-***** around here don't you (I love LS1tech.com it is like the Yellowbullet of slow cars)? Your responses to anything you don't vehemently agree with inherently have a childish tone.

Just to be clear: You are a full supporter of the OP take a set of box-stock heads, tracing the bore of an LS9 headgasket on the deck surface, and laying back the combustion chambers to drop compression regardless of the final shape and running extra thick custom made headgaskets vs. using properly designed large(r) chambered heads and/or the appropriate pistons to achieve the desired drop in compression?

Simply put: Just because it is done, doesn't make it right.

And it is okay to have a difference of opinion without going on the attack.

 

Not sure how you can discern my tone on a typed message... Or where you think I "attacked" you in the above posts? I think you're way overly defensive... Go back and read your replies and tell me who's acting like the know-it-all internet hero. Pretty clear to me...

Just to be clear: This is what I suggested.

Simply put: I suggested a perfectly good option that doesn't involve buying aftermarket heads/pistons/etc... So what's your problem?

 

Hey fellas, can I butt in here somewhere? To Motorhead mike, I realize this isn't the "most professional " way to go about lowering compression, but its a he!! of a lot cheaper than new heads or a reworked shortblock. Its a toy, plain and simple. I can put an efficient NA combo together without too much issue. Don't let my user name fool ya, I'm an old fart and have been building hotrods for over 30 yrs, but all NA stuff. All I asked for in this thread was some pics of work that others have done, so I could get a little ahead of the curve on this experiment. Ive done a fair amount of port work over the years, just never any CC reshaping, thus the reason for this thread.
To forcefed, my thoughts at this point are to push the edge of the quench shelf back, while trying to keep close to the same approach to the valves. Looking at the water jacket location, I think I can pick up a bit of volume without getting too thin. Loosing that material , unshrouding the valves, and smoothing the rest of the chamber should make it worth while.
PICS ANYONE ?

 

I threw up the same pics in your last thread. But this is a basic "smooth job" on a CC. Without a CNC machine I wouldn't try and grind a ton. Just smooth it over, ditch the quench with a thick HG and press on...

 

I wish I could tell definitively just how the old quench area is shaped in that pic. It looks like a Hemi chamber that is rounded pretty evenly. What kind of head is that anyway?

 

if your octane limited why not just put a meth kit in the car and turn the power up instead of trying to grind up some heads for such little gain? dropping comp wont get you a TON of power but able to make a little more.. id put meth in it and that can make great power

 

It’s an SBC head. Wish I had a better angle of it, the picture is deceiving. The flat area on the lower portion of the CC was not knocked back any, it’s just been smoothed a bit wher eit enters the bowl and is no longer as reflective as the CC next to it. The hump by the plug has been taken down, and all sharp edges smoothed/removed. That’s about it and as far as I’d go in the “softening” process. Doubt you’d be removing that much material. Can always slap the burette on afterwards to confirm and try to get them all the same.

Should read up on min/max quench area and detonation. There is a go/no-go range. Around .050-.080 depending on the CC. If you don’t go big (basically removing the quench pad) there a chance you will make the motor more prone to detonation instead of less. A .100 gasket alone should put you close to 9.5:1. Then factor in your CC softening… I think you’d be semi pump gas friendly at those levels depending on the amount of boost you want to run. A thicker HG doesn’t cost more and would allow more boost and a wider tuning window. A .125 should drop the compression down closer to 9:1 and wouldn’t cost any more.

For every full point of compression you only gain about 4% NA HP. So if an LS3 is rated at crank 430hp NA at 10.7:1 dropping compression down to 8.7:1 would cost you roughly 35 NA HP. Yet you’d have the ability to run 20+lbs of boost on pump gas. Each additional pound of boost (assuming you have an efficient turbo system) is worth roughly 6% more power I’d trade off 30 NA HP to pick up 400++HP in boost any day.

Point is… Dropping a little compression so you can run lower octane fuel isn’t going to hurt a thing. Most water/meth kits don’t inject near the volume necessary to allow a 10.7:1 motor to run what I’d consider a healthy amount of boost. A 9:1 (or lower) would be much more forgiving on pump gas.

 

I would run them untouched with a much thicker headgasket, but that's just me.

 

Already running a small meth kit for insurance, but my end goal is a more forgiving tuning window, and to go ahead and tune for more boost with this setup from the get-go.

 

OK, I ordered some Cometic .098 gaskets today. I will just clean up the CCs on the 317s and spend my time doing a little port work in the runners while I wait for the gaskets to be made and get here. Wallace calculator says I will be at 9.17 comp with that setup.

 

Heads are now ported ! That was fun. Aluminum is so much more enjoyable than iron for porting. Much easier to screw the pooch with a slip up too, LOL ! I didn't find any air or water, so I'm satisfied.
I measured the CCs, intake runners and exhaust runner to see my net changes. Combustion chambers measure in at 72.5 cc. The intake runners at 220 cc. The exhaust at 80 cc. So an increase of 1.2 cc CC volume, 10 cc intake volume, and 5 cc exhaust volume. My Cometic head gaskets will be here late next week, so I'm hoping to have everything buttoned back up be the end of next weekend.