second_2_none

iTrader: (6)

I have an 05 LQ4 I'm going to be putting in my camaro and feeding it a healthy shot of nitous and a high lift cam. Since LQ4 motors have dished pistons and heads with big combustion chambers I am trying to make some of that compression back up. I was going to run a really thin head gasket with some 243's but I was told I wouldnt have enough quinch (not sure what that is). So I started thinking about running some 5.3 heads because of the smaller chambers but I'm not sure if that will kill my cam selection and be forced to run a small lift cam to prevent ptv contact. Which heads do you guys think would be the better choice?

baronsmith98

iTrader: (2)

I would run the 243. Quench is the distance from your piston at top dead center to the bottom of your heads. So if your piston comes out of your cylinder .005 at TDC and you run a .050 head gasket your quench is .045.

second_2_none

iTrader: (6)

Oh ok got it. I seen in another thread that you shouldnt run anything less than a .040 head gasket, does that sound about right to you guys? I was going to run a .020 gasket and mill the heads a little, glad I didnt buy anything just yet. I'm probably going to buy everything today if I find somebody selling the heads or tomorrow from a vendor.

onefast84

I got the 243s with stock gaskets unmilled. I figured that nitrous likes low compression anyways. Havent had it to the track yet, but this thing effn screams! My vote is 243s. you will also loose flow with a set of stock 5.3 heads. The new 5.3s run 243s now too.

second_2_none

iTrader: (6)

Yeah the stock 5.3 heads have smaller runners and valves. The ones I was looking at are after market.
http://www.tickperformance.com/prc-2...-ported-heads/
I really want to get the most compression I can without killing my cam choices and leaving the bottom end stock. I'll be happy with anything over 10.1:1. I had a mustang with a forged 393 that had 13.5:1 compression and it loved nitrous!

onefast84

The ported 243s flow a little better than those, and will get you around 10.3:1 I believe. But those heads will probly work great, Too. I would call martin at tick and talk with him. I havent dealt with him, but he has a reputation of awesome customer service, and I bet he can spec you out a cam too. I am Planning on a custom grind from tick myself in the future. As my current cam is a fuel injection cam.

second_2_none

iTrader: (6)

Yeah I was going to call him and a couple others tomorro. I was just going to run an off the shelf cam for now and do a custom cam when I actually build the motor, but I may have to have custom spec to keep the valves from hitting my pistons depending on which heads and gaskets I choose. Seems everyone is leaning towards the 243's so I'll probably buy those, now I just have to figure out which thickness to go with for a head gasket.

64post

iTrader: (5)

He could run a .040 thick MLS head gasket and have the pistons .003-.005 out of the hole at TDC, you can get away with .035 piston to head clearance. Quench is distance and volume, or lack of it.

second_2_none

iTrader: (6)

So I could safely run unmilled 243's with a .040 head gasket and a higher lift cam? What about with stage 3 243's with larger valves or with the heads in the link?
http://www.texas-speed.com/p-3515-pr...ral-heads.aspx

RezinTexas

I just tore down a stock LQ4 and the pistons were about 0.010" out of the hole at TDC. Assuming yours is the same (you should measure it to be sure), I would not run anything thinner than a 0.045" head gasket.

second_2_none

iTrader: (6)

So a .045 head gasket, even with 62cc combustion chamber heads?

RezinTexas

0.045 - 0.010 = 0.035 = generally accepted minimum quench. the volume of the combustion chamber does not effect the quench. Use the cc volume to calculate DCR and SCR.

second_2_none

iTrader: (6)

Ok I'll buy the .045 thick head gaskets tomorrow. But would a 62cc chamber bring the valves closer to the pistons and limit my cam choices compared to a 64cc chamber? The stage 2.5 243 heads are the same price as the 225 as cast heads, but the 225's have a little smaller chamber.

RezinTexas

theoretically yes, however I am not a good person to ask will X cam work with X head milling. I'm sure some of the sponsors on here will be able to answer that one for you.

All I can say is be sure to measure your PTV clearance before running your new engine. I prefer the checker springs and dial indicator method.

Good luck, post pics of the progress

64post

iTrader: (5)

The more quench you can build into it the less prone to detonation it will be. I am running .040 Cometic head gaskets with pistons out of the hole by.003" .612 lift without issues.

second_2_none

iTrader: (6)

Ok yeah I'm going to order the new .040 gaskets today and call about the prc 225 as cast heads and try to find a good matching cam.

RezinTexas

keep in mind that peak lift of the cam has virtually nothing to do with PTV clearance. PTV issues happen when the piston approaches TDC, when the lift is low and the valves are near closing.

second_2_none

iTrader: (6)

Damn, not to come off stupid but I thought it was from the lift of the cam. Thanks man! I see I'm getting over my head now so I'll call Martin and a couple other shops to make sure I don't destroy my new motor.

baronsmith98

iTrader: (2)

Duration has more to do with ptv clearance. Do as rezintexas said and get test springs and check your clearance with a dial indicator. I like to check mine at 15, 10, 5, and 0 degrees before and after TDC. Not checking your clearance will make you have a tight ******* when you go to start it up haha

Sales@Tick

iTrader: (3)

RezinTexas as always, great information! We also prefer checking springs and a dial indicator to show how much distance we have by pushing the valve into the piston while checking the dial indicator for clearance. Do this at least 20 degrees BTDC to 20 degrees ATDC or until your clearance begins to increase again. Also as Rezin Texas mentioned maximum valve lift has nothing to do with P to V as the piston is at BDC when the valve is at max lift. P to V issues occur when the piston is ATDC during overlap when the exhaust valve is closing and the intake valve is opening. Valve lift ATDC is what matters in terms of P to V and the more aggressive the lobe(meaning the faster it opens between .006" and .050" will really determine how much P to V is available considering free valve drop stays at a constant).

Second to none, like I told you today on the phone, you can run a 5.3 head on your motor and still have the exact same P to V as you did with your 317 heads since the valve size of the 5.3 heads is smaller and GM cast the chambers @61cc's. That along with having more valve drop on the 5.3 heads is why you can still retain factory P to V clearance. This is also why you can take a 64.7cc 243 head and place it on a LS1 motor that came with a 67.7cc head and still have the same P to V clearance as they both have the same valve drop.