300 build: 240 head cr and pinging ?'s

[fomocoguy]

Awesome. Here you go:
9.9:1 cr
6.21" rod length
3.98" stroke

Intake valve closes at 61* ABDC with .004 lift (advertised specs). If you go by .050 lift it's 29* ABDC.

Cam is currently advanced 5*

I think that's all you need, right?

Just in case- 65cc head, 24cc piston area @ tdc, .021 head gasket, 4.030 bore

[woods]

I'm getting 8.06. Some condsider that on the high side for pump gas. I however do not. I can tell you that if you ever plan on running a turbo on it, it will be too high to operate like it should.
That straight six with that quench and compression will get you some pretty decent power and MPG to boot.

[fomocoguy]

Well, I think I may go ahead and change the cam timing back to 0* to help it a bit. As far as a turbo goes, if I ever go that route I think I'll probably go through the spare 300 block I have and put forged pistons in it.

Thanks for all the help! Now I just have to get the head gasket straightened out...

[woods]

I was going to suggest moving your cam straight up, but looks like you have a handle on the situation.

[fomocoguy]

The fella from gasket works USA has been talking with me about the copper gasket. He says .022 is pretty thin, but for a motor with a max rpm of 4500 it should be fine. Cost is about $150. I'm still going to contact Cometic and see if they can best him, but at least I've got the copper one to fall back on.

Any suggestions on any other custom head gasket makers? I could probably get some .022 copper stock from work. My tin snips are still pretty sharp....

[woods]

I tried that before, it worked once, so from then on I thought it should work, but not much luck after the first one. I would buy it. I'm not sure what he ment by thin and low RPM. Some really high rpm engines use very thin gaskets, but whatever, not really the point here.

[averagef250]

How many pistons did you measure? Good idea to measure all of them from the deck as they can easily vary .01" or so from differences in rods/pistons and crank. I just wouldn't expect to here "my pistons are .034 in the whole at TDC" if all the pistons were measured, I'd expect something like "they range from .031- .036 from the deck", often there's a pattern to how far they're out and the angle the block is decked at can be used to compensate a little if you don't want to redo everything in the rotating assembly.

for a daily driver type build I'd try to stick to an off the shelf head gasket, something easily available and proven. Also, copper gaskets are made from special annealed "dead soft material" the stuff is amazingly pliable. But at .022 thick I'd be real worried about flatness/water leaks given a little time. It's not easy for most any automotive machine shop to get a long ass head or deck flat to within a few thou over it's length. They may say they can, but odds are against them even haven't the tools to measure something like that. Just be careful using custom parts like a wierd headgasket in your build.

FWIW, I ran 11.5CR in a small block on 92 octane for a lot of miles with the pistons even with the deck (don't recall the actual clearance distance, but it was less than recommended) Anyway, it ran hard, made good power, but did have evidence of pinging in the rod bearings when it was eventually tore down. I think that was right on the cusp of the limit of cr/octane for that motor.

[fomocoguy]

Thanks for the input Dustin. If I could find an .022 off the shelf gasket I'd be all over it, but to get my quench down in the .040- .050 range it's going to have to be that thin and there really are no other choices. I'm thinking as long as the block and head are good and straight and I use the gasket dressing they sell and the aviation permatex around the water passages I should be good to go. I've got a top notch machine shop here that I will have do the head. Also I still haven't talked to Cometic yet and those aren't copper, so we'll see what they have to offer.

As far as my .025 piston to deck clearance, your right that I only checked the front piston. I was thinking along the lines that the block was cut and they should all be good, but I'll go through and check them all just to be sure. I need to pull the timing cover back off and move the cam back to straight up timing anyways. Thanks!

[fomocoguy]

Well Dustin, thank you for reminding me to check all the pistons. I went down and checked the last cylinder and low and behold it's got .020 piston to deck clearance. At first I thought "OK, it must drop .005 front to back..." I went ahead and checked the rest and was a bit startled by what I found. Front to back the clearances go like this:
.025, .022, .014, .025, .020, .020
The block is flat, so either I've got issues with the crank grind or it's the cast replacement type pistons I bought. I'm leaning toward the pistons, as the one that measures .014 actually goes to .016 on the opposite side of the piston.

SO, this changes things a little bit. I believe .040 is about as tight as I want to be on quench, right? So .014 plus a .026 gasket would put me there on the tightest cylinder. This will put the two .025 cylinders at .051 quench. Will this still be sufficient for the "anti knock" effect provided by the right quench? Could I go a little tighter than .040 on the .014 cylinder?

[fomocoguy]

Well a little reading and I find a lot of guys saying they have .035 or so and are running 6500 rpms. I'm thinking my 4500 rpm six should be fine with .036 on the tight cylinder, putting the "loose" cylinders at .047 still.

[woods]

You have to be a bit more careful with close deck height when using aluminum rods, very high rpm, a crank that can flex, etc. You will be okay with it on the tight side in your low rpm six.

[fomocoguy]

OK, well EPIC FAILURE today. I wrestled the crank gear off and set everything back to straight up timing in prep for the 240 head. I then proceeded to work on the head, with the object being to smooth the chambers and do a little smoothing of the short side radius and clean up the ports a bit. BUT FIRST, I noticed one of the screw in studs was loose. I grabbed the impact and ran her on in. That's when I learned a valuable lesson on how brittle cast iron can be. I manages to put a nice sized crack in the mounting pad for the rocker stud. I thought "maybe I can just use some thread lock on it". So I cleaned it out and low and behold it goes straight into the water passage in the head! So my awesome head deal is now a boat anchor.

SO, back to the 300 head. I went ahead and cc'd it and she's got 76cc chambers, so my static cr will be 9.0:1. I think it's a sign from the universe that 10:1 was just too much compression for my big heavy truck. I still plan on using the copper .020 gasket to get my quench down, so it should be a cool running pre-detonation free inline 6 powerhouse that will take all the advance I can throw at it. We shall see.

[silverbullet07]

subd for updates.
i would also want to run a turbo on my 300. what are yalls suggestions for it? i am currently carbd i wana switch to EFI for MPG purposes. AND if i have to in order to turbo it. will i have to do an efi conversion?

[silverbullet07]

with all this modifying will you need a different fuel pump? do the EFi engines have an external electric one or is it in the gas tank?

[woods]

I can walk you through all the steps of a turbo install and what you need to do. But I don't want to cloud up fomo's thread too much. If you want to start another thread or PM me, I would be happy to help out.