300 build: 240 head cr and pinging ?'s

[fomocoguy]

Here's a question for you engine builders we've got around here. So today I went and picked up a head off craigslist that has been rebuilt and had screw in rocker studs installed for my 300 inliner build. The thing is as soon as I saw it I knew it was a 240 head by the kidney shaped combustion chamber. Since it came with a header and was only $100 I ran away with it, but now I need to make sure it will work ok without causing too much spark knock. I figured with the 300 head I was going to be pushing 9.0:1. The 240 head brings things up another half a point, so I'll be at 9.5:1. The motor has a Crane 901 torque cam, Clifford intake, and efi split manifolds. I wouldn't be too concerned, but when I installed the cam I used an adjustable timing set and set the cam at 5* advance. I read over at fordsix that this would bring the torque curve down and give her a little more low end grunt, but I'm afraid that at 9.5:1 it will be too much dynamic compression and bring on the spark knock. I could always take it back apart and set it to 0*, or even 5* retarded. Any thoughts? Anyone think that having the dizzy recurved would make it work with 9.5:1 and 5* cam advance?

[fomocoguy]

I hear crickets...

[Canuck]

Yeah, not a lot of interest in the 300's here it would seem. Fordsix is a better spot for that it would seem but I can't get them to ok my registration so.....

I'm not experienced in this but I think you'll be ok with today's gas at 9.5:1

I'm looking at doing something very similar with my 300 rebuild but I'll likely stay stock on the cam and I have an EFI head that apparently has the same volume as the 240 head (and I got it for FREE) so I'm trying to figure out if there's any way to make that work !

Sorry I can't be more helpful with your specific issue but keep posting how you progress, I for one am VERY interested in how you make out.

[fomocoguy]

Well, I've got a build thread from the beginning that has everything up until this point here if you are interested: http://www.fordification.com/forum/view ... =3&t=46269
I plan to blow the dust off it very soon with the addition of this new head as long as I can get to a point where I feel confident that I won't have spark knock issues.

[nevrenufhp]

I dont see it as a problem. I would certainly run 9.5 on mine. My 2 cents: run the cam at 0*, and recurve the dizzy to get less total timing. The rest will be fine & dandee.

[fomocoguy]

Thanks for the ecouragement! I think what I'm going to do is buckle down and do the work to get an exact number for where I am at with the cr and the dynamic cr. I'm going to cc everything again (I did it about 8 months ago but can't remember the numbers ) and run the numbers off my cam card with advance factored in and see where I'm at. If it's too much I'll change the adjustment. I was reading that on 91 octane the dynamic cr should be 8.25 or less, so I'm shooting for 8 so I can run regular. We shall see...

[woods]

Sorry I did not answer earlier. I have been pretty darn busy lately. 9.5 will be fine as long as you keep a tight quench area. That and aren't you running a different cam? Camshafts can have a huge effect on compression and how much and engine can take.

[fomocoguy]

How tight of a quench area are we talkin? I know my compressed gasket thickness is .039 and my pistons are .033 below zero deck after doing a little research. .072 ain't real tight is it...
I can say that with the pistons I'm using and the 240 head there will be more quench area than a normal 300.

[woods]

Well, 9.5 is not super high by any means, but I always try to keep it between 0.040 and 0.045.
This is really an apples to oranges comparison but just to use as an example...I run nearly 11 to 1 in the 428 in my truck and use pump gas, with no pinging. If things are properly set up, a guy can run a lot more compression than the usual status quo. Combustion chamber design, quench, cam, proper ignition set up, etc, they all play into it very heavily.

[fomocoguy]

Well I just did some measuring and it looks like my pistons are actually .025 below deck, so the quench is .064. As soon as I can find a graduated cylinder to measure cc's I'm going to cc the head and piston to get a concrete compression number to work off of.

Thanks woods!

[fomocoguy]

Haven't done any measurements yet, but I did find a company that makes custom copper head gaskets out of .022" material, which would put me right at .047". Any thoughts on copper head gaskets at approx. 9.5:1 ?

EDIT- Just found a company called Cometic that claims they can make gaskets in any thickness too...

[woods]

Copper is just fine as long as both the deck and head are good and flat. Also, you should use aviation permatex around the water jackets.

[fomocoguy]

Well the deck was cut but on this new head I can't tell if it was cleaned up or just hit with a scotchbrite. If I go the copper route I will take it and have it checked and cut if needed. We'll see how much this gasket is gonna cost and go from there I suppose. The company sells a spray on gasket prep that I would go ahead and use that's upposed to fill in any tiny imperfections.

Where can a person purchase aviation permatex?

EDIT Nevermind! http://www.google.com/products/catalog? ... CD0Q8wIwAg#

[fomocoguy]

Ok, so I have some good numbers to work with now. After cc-ing my head and a piston at tdc (so as to take into account the distance to deck and space above the rings) I came up with a 65cc chamber and 24cc piston area. With my bore at 4.030 and .021 copper head gasket thickness it comes out to a static cr of 9.9:1. With this setup my quench would be at .047.

At first I thought this was pretty high until I ran the numbers with my cam for the dynamic cr. Even with my 5* advanced timing set the dynamic cr comes out to 8.15:1. I think with a .047 quench and 8.15:1 dynamic cr I should be in good shape. Penny for your thoughts....


Oh yeah, woods if you happen to have a link to an accurate cr and dynamic cr calculator I would be greatful! After about 10 different ones I think I have the static nailed down, but the dynamic seems to be a bit all over the place depending on the calculator.

[woods]

Give me your cam specs and I'll just do the math. The online stuff for dynamic calculators jump around.