Fitting new LA X/Indy heads to my 340

Jon Connolly · Post by **Jon Connolly** » Mon Mar 02, 15 5:54 pm

Hi Miles

That block wasn`t decked when I built it so may be worth getting a dial guage and a machined piece of steel and see what you`ve actually got ??

MilesnMiles · Post by **MilesnMiles** » Mon Mar 02, 15 6:19 pm

Hi Jon, thanks for chipping in. I remember you saying it wasn't decked, but there isn't much below the deck to the piston although there will be a slight drop I'm sure.
Not sure where I can find a dial gauge down here in surf city. Given your experience with these motors do you think I am likely to run into clearance issues with what you know so far?
Cam, even if it's getting full lift is only .48 I believe.

Jon Connolly · Post by **Jon Connolly** » Mon Mar 02, 15 6:24 pm

MilesnMiles wrote:Hi Jon, thanks for chipping in. I remember you saying it wasn't decked, but there isn't much below the deck to the piston although there will be a slight drop I'm sure.
Not sure where I can find a dial gauge down here in surf city. Given your experience with these motors do you think I am likely to run into clearance issues with what you know so far?
Cam, even if it's getting full lift is only .48 I believe.

You`ll get one at any engineers suppliers ( or try our member on here Chronos Engineering ).

Clearance will be fine.

Take your time selecting head gasket ... loads of choice 0.027 - 0.120 ( probably more ? )

Jon Connolly · Post by **Jon Connolly** » Mon Mar 02, 15 6:30 pm

http://chronos.ltd.uk/acatalog/Engineer ... s_228.html

Newport100 on here ... Mark

Dave-R · Post by **Dave-R** » Mon Mar 02, 15 7:25 pm

MilesnMiles wrote:I can't get a feeler guage under there. It certainly is pretty close to being decked. As for .20 thou, no way.
If I cleaned what little coke there is on the piston top I may just be able to get a sliver under but not as it stands.

That is perfect in my book. Valve clearance will not be an issue. 39 thou gasket will give you perfect quench.

The only worry is what static compression ratio will be. Or, to be more precise, what the cylinder pressure will be with a mild cam.

Static compression ratios are 10.5:1 MAX for iron heads and 11.5:1 MAX for alloy heads. But with a mild cam you will need less than that to keep the cylinder pressure down.

Les Szabo · Post by **Les Szabo** » Mon Mar 02, 15 7:58 pm

Miles wherever your pistons are, at 0, -.005, or -.0010 thats where they are, your not going to deck the block?. What you need to do is CC your old heads, find out what they are, that will give you a better idea on how much a CR increase you will get, as you'll know the difference in the 2, for now, checking your PTD properly is fine if you want to set your motor up for a perfect as you can quench or you wanna do a proper CR calc, but you'll need piston relief CC, gasket volume, and PTD volume to do that.

Bolt a head on with an old .039 h-gasket, do your check with the valvetrain your gonna use, and if your .090" inlet, and .100" exh, you can safely go to a thinner head gasket for even more CR and better quench? you should have no probs with that mild cam and be in excess of those figures.

Les

MilesnMiles · Post by **MilesnMiles** » Mon Mar 02, 15 8:07 pm

Thanks all for again for tutoring me and that link Jon.
In essence it all boils down to what head gasket I use as everything else in the relationship is a fixed entity.
IMM recommended and supplied the .39 gasket, but equally did not know the full details of what the pistons were at the time and assumed - .20
Even tracking down the exact details of the piston is tricky but what I've found suggest -5cc for valve relief.
I'll cc the old heads as that is straightforward and could be instructive.

Les Szabo · Post by **Les Szabo** » Mon Mar 02, 15 8:13 pm

Suggested cylinder pressure for the cam you have now is 165psi...but that is easy to check once its all finished, depends how good a seal you got etc. Just get your PTV done and off you go, there's a lot of info to take in but I'm sure it will be well worth it all in the end for the extra performance.

Les

Dave999 · Post by **Dave999** » Tue Mar 03, 15 8:51 am

with new info. DCR 8.1

and to quote Mr kelleys article

It appears that most gas engines make the best power with a DCR between 7.5 and 8.5 on 91 or better octane.

i.e 95RON UK fuel

based on nout much but what ive read and my own use of this tool with my own engine.

i don't think you will be pinging your way to the scrap heap if all data is good and you don't have glowing spark plugs or raggy bits in your combustion chamber.

i used this cos i didn't feel confident working with cylinder pressures and a load of other variables that change with RPM i understand the concept of pressure obviously but i wanted to use something based on what i could measure with the limited tools i had, i felt my risk then was just "did the bloke who wrote the programme write it correctly"

needless to say what i worked out matched more or less exactly the advice i got here, and was slightly tamer than the advice i got on the aussie message boards, they seemed intent on me building a 7000 rpm screamer, obvioulsy none of this means my motor is any good, but it didn't ping and i went faster than i had before.

Dave

MilesnMiles · Post by **MilesnMiles** » Tue Mar 03, 15 9:01 am

Thanks for the vote of confidence , Dave.
The actual cam spec detail is here

http://www.compcams.com/Company/CC/cam- ... d=627&sb=2

I tried to use the programme you linked in but it won't work on mobile devices or at least, not on my ageing ipad!

Dave999 · Post by **Dave999** » Tue Mar 03, 15 9:14 am

that puts it up to 8.8

i think you might need super unleaded

or you could retard the cam slightly if it pings under load

Dave

Dave999 · Post by **Dave999** » Tue Mar 03, 15 10:20 am

MilesnMiles wrote:Thanks for the vote of confidence , Dave.
The actual cam spec detail is here

http://www.compcams.com/Company/CC/cam- ... d=627&sb=2

I tried to use the programme you linked in but it won't work on mobile devices or at least, not on my ageing ipad!

no windows only

written in the days before Mr Jobs thought a phone was more useful as a camera walkman and PC

Dave

MilesnMiles · Post by **MilesnMiles** » Tue Apr 21, 15 9:18 pm

Ok after a couple of weeks off surfing and going to portugal I got stuck back into the car. First test drive tonight and not really able to get on it due to heavy traffic on such a nice evening, but the car feels stronger, really starts to howl once the revs come up. The guys that built the heads told me that it all comes together at 3,000 rpm and a couple of quick blasts proved the point.
Got to fix some exhaust leaks and adjust the trans shifter, but happily no pinking under load so the compression calculations have worked out nicely.

Pete · Post by **Pete** » Tue Apr 21, 15 11:53 pm

3000 rpm??

That's a fast idle

Glad its working out for you, Miles...

MilesnMiles · Post by **MilesnMiles** » Wed Apr 22, 15 6:09 am

Cheers Pete, lovely sunny evening on the coast road made 3000 risky!