As I mentioned in another post I'm ordering a pair of AFR 195's for my stock 350 L98 bottom end (short block).....now the only detail I'm stuck on is the combustion chamber size to get. The heads are available in 74 or 68cc sizes....but those sizes will give too low a ratio for my engine. I'm installing a SLP 51010 cam with the following specs:
Valve Lift Duration Duration@.050
in: .502" 280º 224º
ex: .510" 288º 230º
Centerline - 112º
Lobe Separation - 112º

along with Comp Cams Pro Magnum 1.6RR's. I've discussed this with Tim (Traxion) a little while back and he was awesome enough to give me some excellent insight. He shed light on alot of things I needed to watch out for...he's great! Tim suggested to get the heads angle milled down to around 58cc's I believe in order to get the ratio around 10:25:1 with the stock pistons. He said that I'd have to watch out for piston to valve clearance though. He mentioned the stock L98 CR rating is actually lower than advertised due to the blocks not being zero decked so that's why he recommended the 58CC chambers.

In a couple years I plan on building an all forged 383 short block and then throwing the AFR's and Miniram II on that so I've gotta watch out for piston to valve clearance there as well and select the right pistons. I don't want to mill the heads too far now for the stock block and then regret it later when I build the 383 bottom end....

Please help me out guys...I want to do this right the first time...any suggestions at all would be great!

Thanks,
- Joel

 

Joel,

Given the fact that you would like to reuse the heads at a later date on the 383 then you might want to go with 60cc chambers. I have a feeling that with the 383 you would want to use a bigger cam (specially with a MiniRam). The higher lift of the bigger cam is really gonna give you some tight P-to-V numbers with 58cc chambers.

Right now I am pushing 0.550" lift on both intake and exhaust and have the following clearances ...

1) Lowest intake reading was 0.125".
2) Lowest exhaust was 0.144".

With a decked block my clearances would be 0.095 / 0.114. With flattop pistons it would be even closer.

Definitely don't get less than 60cc if you are going to use these heads on a 383 with a 0.550" or greater camshaft. In fact, if you get 60cc chambers then you will have to make sure to run pistons with valve reliefs in order to have respectable P-to-V numbers with a cam in the 0.550 range.

... and thanks for the props

Tim

 

I had more than .125 and .125 on both intake and exhaust on my
AFR 190's with 63 cc chambers. I have the dished SRP pistons with .604 and .608 lift, though.

 

Hey Tim...you're awesome man! You really helped me out alot!

89GTA: Thanks for the reply too....

So I'm stuck between 63cc's, 62, 61, or 60cc's....that is the last thing I really need to decide before I send my money in. Tim's got 60cc's...89GTA's got 63cc's....either way I'm spending the $250 to get them angle milled so I can't make up my mind at all on this I'm running 1.6RR's and at some point in the future the bottom end will be stroked as well.

Any suggestions guys? Pleeeeaaasseee!!!????

Thanks,
- Joel

 

Joel, I'm just finishing up a new 383. For what its worth, my afr 190s are 58cc, deck is right at 0 . Pistons are kb #102 with 18cc dish. With the .039 gasket I'm right at 10.4 to 1. With a .560 lift my mock up with clay showed plenty of room. I noticed your in palos hills, I'm over in burbank. Good luck

Gary

 

i'd run the smallest chambers i could and dished pistons with a zero deck. i've never seen or had valve to piston clearance problems without a head gasket till around .65 lift. better to measure it with an indicator and soft springs than clay.

 

... and there ya have it. I was looking at the combo from a flattop or valve-relief position. But, if you go dished ... you could get away with small chambers. I'd still go 60cc to be on the safe side and then try to choose a piston that will yield the P-to-V that you need.

Tim

 

Hey Gary...if you wouldn't mind I'd love to come over and take a look at that 383!

So let's say I go with the 60cc chambers, would I have any problems down the line after zero decking and rebuilding to a 383 in terms of finding pistons that would give me the CR of around 10:4:1 or 10:5:1?

Any best estimates of the CR I'd be yielding after throwing 60cc heads on my stock L98 bottom end that's not zero decked?

Also do I need to get the heads corrected for the 72º Angle Intake Bolts (a no charge option from AFR) if I am using my Miniram II?

Thanks,
- Joel

 

Joel, As a start, I'd suggest checking out Keith Blacks web site. It shows all the pistons and gives all the specs on them. It also has a easy to use calculator for checking your compression with all the variables. As far as finding pistons for your set up, no problem at all. Depending what your buget is for it, you can check into a set of JB's or any others out there. Personally, I ordered my afr's with the standard intake bolt angle. With the superram I had to elongate the four center bolt holes in the base, but it's easy to do and can still use the heads later on for a standard manifold. I've never used a mini-ram before, but I'm guessing their drilled for the standard angle. Give them a call to find out for sure. If you'd like to stop by drop me a e-mail.

Gary

 

For what it's worth, this was my experince. I've done exactly what you are thinking about doing with the chamber size.

When I bought the heads, AFR talked me into 58cc's because as you already know the reasons why. These were for my 350.

When the motor went after running my supercharger, I wanted to build at least a 383. Ever try to buy pistons for a 383 with 58cc volume chambers? Let's put it this way, it is rather difficult. If you plan on building a 383 later, it is something to think about. Difficult to find "streetable" compression ratios in "budget" pistons for the 383 with those size chambers.

Not saying they aren't out there, just takes some looking. And with the way projects go, I don't create any "obstacles" that I can prevent. I would stay with the 64cc head because there are an abudance of readily available pistons in streetable compression ratios for a 383.

Just my $.02, take it for what it's worth.