Hi guys,


After several months of saving, I'm finally ready to order my new AFR heads today.

Looking at the catalog, I see that AFR offers the L98 angle-plug version in 68cc & 74cc versions. I seem to remember that the L98 came with a 68cc chamber (but I'm not real sure if my memory's correct), so if I went with the 74cc, I'd be losing a bit of compression - which could be helpful in a boosted application... (And yes, I know that aluminum's thermal efficiency is a bit below iron's, so I'd be effectively losing a bit of compression by going to aluminum...)

I'm pretty sure that I'll be getting the 68cc heads, but wanted to double-check with some of you guys to see if I could get other thoughts/opinions on the subject. Short-term plans are to keep it normally-aspirated, but it's looking like I might be getting a good chunk of money in the spring, so a centrifugal blower is a definite possibility...

Thanks in advance!

 

get the 68

 

OK, I appreciate the reply - but I'd like to get an idea of the reasoning behind the suggestion too...

Thanks again!

 

how much are these AFR heads?

 

L98 angle plug heads in 68 cc chambers, with the coolant temperature sending unit option. You need to also specify whether or not you want centerbolt or perimeter bolt valve covers. You also want to specify the size of the screw-in rocker studs, be they 3/8 or 7/16. I recommend 7/16 if you dont already have your rocker arms on the shelf. They resist valvetrain flex a lot better than the 3/8 studs.

You can ask for options, too, such as having them angle cut to 64 cc if you want. However, a 68 cc chamber with a flat top piston that sits .005" down the bore in a 383 will make 10.5:1 compression ratio when you use a .041 thick head gasket,

Sound complicated? It can be. However before you decide what chamber size to get, find out what pistons are in your engine first, and how far down the cylinder they are at top dead center. Then choose your intended compression ratio!

Once you know the volume above the piston, and the volume of your chosen head gasket, you'll know how much volume in the cmbustion chamber you'll need to hit your intended compression ratio. You'll first of all find that most un-decked smallblocks have their pistons between .025 and .039 inches DOWN THE BORE at top dead center. You need to know where yours is at before you can accurately determine your compression ratio with a given cylinder head cmbustion chamber volume.

If you intend on supercharging, you need to know straight up ahead of time to make the right choice.

Oh, and the cost, last time I checked, is $1350 or so. I *love* my AFR195's. If you can afford to pay for their competition CNC port job (and additional $600), it's definitely worth it. Probably 30 - 40 HP extra.

 

I'm trying to save up for the competition ported AFR 195s as well, they are killer. However I need 58cc combustion chambers to maintain 10:1. I'm wondering if I should just buy some forged domed pistons or get them milled down to 58cc, but I know the latter would probably involve having to remove some deck height as well.

 

What head gasket are you using ? You might be able to get away with a teflon coated steel gasket, only .016" thick and 6 cc less than the standard composite gasket.

However, check AFR to see the cost of milling the heads. They are quite flexible when it comes to doing stuff like that, you just need to wait a little while longer to get your cylinder heads is all. FWIW, I got the best price on my cylinder heads through Dave Tuschoff (extension 302) at Thunder Racing, a site sponsor, if I recall.

 

Outstanding, thank you - that's the kind of info I was hoping to get. I didn't know about the coolant temperature sending unit option - that'd be kind of irritating to discover when bolting everything back together...

Sure - but doesn't that affect intake manifold fitment a bit, or is it too little to matter...?

Well, AFAIK, the short-block has never been touched, so it should still be set up the way that GM did it. Probably a good idea to double-check when I take the heads off though... (Fortunately, this isn't my daily transportation!)

Yeah, that makes total sense - but let me tell you what I'm thinking, & maybe you can let me know if I'm off base. IIRC, the stock L98 head has a combustion chamber volume of 68cc, so if I go with the 68cc AFR 195 head, then I should retain the same (or nearly the same) compression ratio as stock - correct?

Now I know that there are other factors that come into play as well, such as piston-to-valve clearance, etc., but shouldn't the CR remain roughly the same?

Well, I'll put it this way - I'd LOVE to go forced-induction, but like most everyone else, I've got to pay attention to the budget as well. There's a good chance that I might be able to do that by summertime, but it's a long way from a "sure thing", so I need to be able to accomodate being normally-aspirated as well.

And that sure doesn't make my decision any easier...

I've found 'em just a little bit cheaper... (Also a site sponsor, I believe...)

Ouch - that's a lot of $$$ per HP...

Thanks again for the good info!

 

BTW - what brands do you like for gaskets? I've heard that Cometic is good, but probably overkill for a mild street/strip application...

Thanks!

 

I think if it is milled down to 64cc from 68cc it isn't enough to require altering the intake manifold/block deck yet. Why do you recommend the angle plugs? I was told all they do is cause clearance issues.

 

I'd like to know why as well.

 

OK, here's my understanding:

The "angle-plug" setup is what's found on the stock L98 heads - straight-plugs were used on earlier heads, so if you used angle-plug heads with headers (or whatever) designed for a straight-plug application, yeah, I could see some issues. But for an L98 that came that way, it shouldn't be a big deal...