incbed

First I want to say I have been searching the web and have called several well known LS1 builders/LS1 parts dealers for the past 5 days with no one being able to answer my question. So I decided to give Ls1tech a shot at my question.

Ok ,,,,,1st I have a 2000 Z28 M6 that is completely stock down to the factory muffler.

I bought a set of 243 heads that I removed from a 2007 Impala SS that had only 10,932 miles on them.
I had my local machine shop guy who is a good friend of mine install new intake valve seats for 2.055 intake valves and he did a light resurfacing on the exhaust seats and milled the head mounting surface .005 to insure straightness along with refaceing the factory exhaust valves.

Also for you LS1 guru's he did not sink the intake valve pocket for better PTV clearance (because I did not want him to) I gave him the 2.055 valves that I am using so that he could have the install hight of 1.8 along with the valve head sticking out of the pocket extremly close to factory specs ( I can't remember the number),but he said that the valve rim thickness was slightly thinner than the factory valves so they didn't stick out quite as much as factory.

He then assembled them for me using Patriot gold spring kit that I bought from TR. He measured the valve spring pressure's on the seat's at around 135 average for intake and exhuast valves with a thin shim under the springs at around 138 average.(reason for the shim is because the exhaust valve sits slightly deeper in the pocket because of the minor valve seat resurface and from refacing the valves)
So with all this being said my heads are good to go.

The problem I am having is no one can tell me what duration cam I can use for safe PTV with stock pistons and my heads with GM MLS .051 head gaskets and 1.7 rockers.
I am looking for PTV clearance of around .080 intake and .100 exhaust give or take alittle.

I have tried to find out what the factory PTV was for a 1997-2000 LS1 with factory cam so that I could do some math to figure it out, but I could not find an answer.

I did read that a 2.055 valve puts the valve .030 closer to the piston if the valve pocket depth hasn't changed compared to a 2.00 valve. So I had my engine guy take one of the intake valves out to measure how accurate that statement was which he could already tell me it was pretty close which it was.

Also I read that the MS4 cam puts the intake valve .060 close to the piston when installed in a factory LS1, according to what someone at TSP said in a past thread.

Ok so based off the MS4 lobe lift of .387 which from stated above puts the intake valve at .060 PTV.

(MATH) based on MS4 with factory LS1 engine.

Lobe lift MS4 .387 = .060 PTV

Difference in intake valve in the seat from 2.00 - 2.055 = .030

So take MS4 lobe lift of .387 - .030 = .357 lobe lift which should = .060 PTV

Then take lobe lift .357 - .005 (head milling) =.352 lobe lift which should =
.060 PTV

So based on this math and using a factory head gasket .051 head gasket on a factory lower end LS1 it would be safe for me to use a cam that has a lobe lift of .352 or less.

I am looking at the V2 which has a intake lobe lift of .35

Also my machine guy know's very little about the LS motors matter of fact if it doesn't have a distributor in it and a carb he knows nothing about,but he is an outstanding machinest. My uncle has been using him for over 20 years and I have been using him for over 10 years.

Alot of you are probly saying you need to measure to be safe , for those of you that are thinking that I agree with you ,but I am doing all the work in my drive with that being said I need to have all my parts in hand before I dissassemble the top end.Alot of you should understand that.

So if any of you LS1 guy's or gals can confirm my math listed above is correct and the V2 is going to work out for me please feel free to let me know if i'm headed in the right direction or not.I do not want to cut eyebrows in my pistons ether.

Also I have purchased LS7 lifters and tray's, LS2 timing chain set, LS6 oil pump,pacesetter LT's and Y,hardend pushrods, and LS6 intake 80mmTB,and of course all needed gaskets.

thanks

matt d.

You need to take a physical p-v measurment not calculate it. Did your machine shop put larger seats in the heads or did they use the factory seats?

incbed

he put larger seats ,because the factory seats were to thin for 2.055

Wicked94Z

iTrader: (26)

PTV is affected by lobe intensity, duration, intake centerline and lobe separation angle. aka the valves being open at TDC during overlap. The piston is chasing the exhaust valve up during the exhaust stroke, and the intake valve is moving downward towards the piston starting X degrees before or after TDC depending on duration and ICL. Whatever cam you end up going with.... you can either flycut or retard the cam a few degrees to gain some intake valve clearance if you run into problems.

bww3588

iTrader: (49)

you really need to physically measure it. lift is not all that determines PTV clearence. duration and lift are what matters. and there is no way to calculate it accuratly unless you know exactly where the valve will be at a given degrees of crank rotation and what that degrees calculates to in piston depth in the hole....its just not viable, when its much easier to throw the head on, torque it down and measure it and pop it off....just dont use your gasket so you dont have to buy a **** ton of gaskets, and use the old bolts to measure....

Wicked94Z

iTrader: (26)

or you can just put the head on without a gasket and add the gasket thickness to your PTV numbers

garygnu

get a custom cam from Patrick-G.

incbed

I am wanting to use the V2 113lsa

incbed

Garygnu do you know how I can get a hold of Patrick-G??

bww3588

iTrader: (49)

PM him....

odarabla

iTrader: (1)

E-mail or PM him as stated above.

studderin

iTrader: (28)

ya dude you have the mock it up and measuer what it is.


get thouse heads in somones hands that knows how to port them. That valve size gives you some room to set the port up to make some power. Good valvejob and sizing go with that.

garygnu

do a search for Patrick G, get them ported if you can afford it then get a cam to work with the improved flow.

Paint_It_Black

iTrader: (1)

You are also basing your calculations off a stock 2.0 diameter valve. Your 2.055 is going to have even less clearance. You can use a little geometry if you know the valve drop length at tdc with a 2.0 valve to measure how much closer you are are various points wit the .055 oversize valve.

incbed

Thanks for all the replies,
I guess I have been letting my ADHD get the best of me the past week from all the excitement of new parts and the thoughts of new 1/4 mile times. Whats so bad is I told my self when I bought the car that all I was going to do was wheels,lower it, and suspension,but then my ADHD kicked into over drive when I came across these heads for cheap.

I will PM Patrick-G

Thanks agian