Turbo2L

Does anyone know how much you can reduce the combustion chamber size on LS7 heads before you need to have them angle milled? I need to knock about 8cc out of the chambers to achieve the compression ratio I'm looking for.

Michael_D

I would hold at .040

You can (should) also run a .040 gasket.

Josh B.

On my TFS castings, Tony Mamo took the heads down .054" to achieve 62cc. Then another .012" to achieve 60cc. Used with .040" HGs I got to 13:1 on my stock bottom end, piston was .005" out of the hole.

I wish I could give you some insight as to how much a stock casting LS7 head can go down. I know TFS casts a thicker deck. My stock casting LS7s were milled by WCCH, removing .030" down to 65cc.

If you want 8cc out, I'm betting you will need something like a .054" mill, if the casting will take it.

Turbo2L

I appereciate the replies.

I plan to run the 0.040 gaskets. I'll call TSP today and get the deck thickness for their PRC castings.

Josh, did you have to angle mill or were you able to flat mill and retain the intake/header geometry?

Josh B.

It was achieved with flat milling. Intake manifold fitment is fine. I haven't checked the exhaust fitment but I'm confident it will check out fine.

Michael_D

I'm more concerned about PTVC than deck thickness. OE piston reliefs are not that generous. Also intake fitment. DO you know the valve events? I'm assuming OE pistons?

Josh B.

Regardless of cam events or piston selection, PTV verification with clay is a basic engine building principle. Both methods are good to use and both have their benefits, dial indicator and clay. I assume that your question related to deck thickness.

At any rate, I had ample PTVC on my engine build, but I digress. So much depends on valve timing that the only way to know for sure is to measure which I am sure you already know. This goes without saying.

Tony Mamo discussing PTVC on LS1TECH:

While clay sounds "caveman" compared to a dial indicator, its actually just as effective and can offer some insight that a dial indicator does not.....specifically how much radial clearance you have around the valve.

You may have a country mile in depth but without also using clay to check, may not realize the valve was a blond hair away from one or both sides of the valve relief in the piston which could cause mechanical interference under operating conditions when pistons and valves are slightly moving and flexing, especially at higher RPM (ever see a valve dance and move around when viewing a video made on the Spintron....you would be afraid to get on your car if you did....LOL)

I like clay for backing up the data my dial indicator provides me with and I really like clay for seeing exactly where the valve lands in the pocket. Both are key pieces of information necessary when building any motor, but especially a high performance engine.

However (big "however" here guys), the key to using either method, which gets missed by so many rookie engine builders (and not so rookie engine builders as well), is you must use a solid lifter or a welded hydraulic (so it acts solid) when your testing piston to valve and when your degreeing the cam as well for that matter. I have a set of Crane solid roller lifters that I use specifically for all my engine mock up. I cant tell you how many people drop the ball on this using the hydraulic lifters that either came with the engine or they planned on using. The plunger collapses a bit under the load of the test spring and .068 P to V is really .018 or worse and they find out after the fact when they have tagged and bent a few valves or potentially scrapped their engine with an even uglier outcome.

Sorry to go off a bit in a slightly different direction with this reply but is all related to the same procedure and its good advice that I'm sure potentially might save some of you reading this alot of financial hardship down the road.

Michael_D

I always use clay. Stupid to not. Need to check both axial and radial distances. Clay is the only way to do that.

phipp85

What's the deal with a 40 thou gasket over OE thickness? Is that just for additional compression or some other reason? I'm about to order some head gaskets.....

Dan_the_C5_Man

Quench.. Improves detonation resistance, "free" power. I thought about it when I did mine, but I went with .020 mill, knew I was keeping the stock cam, was paranoid about having to pull timing - in hindsight, I should have done it.

I used Cometic's on the old motor, they never leaked.

phipp85

I see. I guess I'll order up the $100 a piece gaskets then lol.

spra4u

When I sent my heads to Texas Speed. I had them mill my LS7 OEM castings .050. I believe they said my compression would be 12:1 using OEM head gaskets.

Josh B.

Cometics are great. They aren't quite $100/ea, they can be found for $82/ea. Very cheap horsepower, quality isn't cheap.

https://thmotorsports.com/i-462064.a...G64hoCWOHw_wcB

Michael_D

Dan covered why. You can actually get away with more SCR with a tight quench / squish because the chamber is more resistant to detonation with wedge chambers. That's why I target .035 - .040 for steel rods. A touch more for Aluminum rods. I'd check your piston height first, before buying gaskets. And if you are using forged pistons that have cold rock, lean towards the higher side.

I also don't focus on DCR. I stick with SCR. SCR is fixed, whereas dynamic can vary. I don't like being "locked" into any one particular camshaft profile. Most of my race builds that see the engine dyno will have several camshafts stabbed before I'm done. Computer based simulators are not a smart as their proponents like to make them out to be.

Josh B.

Who would you source if you have to resort to angle milling? Any particular shop in mind?

Turbo2L

WCCH would probably be my first choice as they've done several sets for forum vendors. It looks like I will be good to go with flat milling though.

American Heritage

We rework quite a few sets every month for Forum vendors and even GM dealerships.
We can flat mill.
We can angle mill.

We offer top tier work at a very competitive price point.

We have many many many satisfied LS7 head customers all over the united states and Canada (We even have very satisfied LS7 head customers in other country's such as UAE and Germany, ect...).

http://www.americanheritageperformance.com/
310-326-2399
or
HP@americanheritageperformance.com

Turbo2L

Definitely a great option as well. You guys seem to be building a solid reputation with quality offerings.

phipp85

Thanks for the link

Thanks, I'll check them. I believe they are about .005" out of the hole but I'm just going off memory of last time I had the heads off. I'm currently pondering the option of throwing in a set of the drop in Mahle forged pistons and having the rods checked while I have it half way apart. Not sure I want to do that yet though.