I've been speaking to a mechanic about swapping out my L81 heads for some AFR190's. As a result I'm now :confused: so here's a few questions:

He has some 3890462 heads lying around. I've looked up the numbers & they are listed as 64cc double humpers. Are these heads any good for performance & just what are double humpers!???

He's told me that increasing my CR would be a bad idea as my fuel consumption would dramatically increase. I've never heard that one before, so have any of you guys that have increased the CR noticed that your frugal SBC has turned into a gas guzzler?

Do ally heads affect the engine sound?!

Are there any advantages in having iron heads rather than ally?

I decided on 68cc AFR190's as they look like they'll give me a nice performance improvement & won't restrict any future upgrades I might want to do. Does that sound sensible for normal street use, or would an iron head be better suited?

TIA
Paul

 

The first thing that woke up my 79 L-82 was going to 186 casting double hump heads with 64 cc chambers. Without any other changes other than increased compression. Both the 186 and my original had 2.02/1.60 inch valves and both were all ported and polished with screw in studs and push rod guides.

I could feel the difference. Increasing compression by 1 point gives you @ 3-4 % more hp and TQ at all rpm. Increased engine efficiency should give you better mileage. but it requires higher octane.

with @10.7:1 compression ratio with iron heads and a Crane power max 272 cam I had to run octane booster with 92-93 octane gas or retard the timing. I eventually went to a larger cam to solve the detonation problems.

I originally built my Crane 272 355 ci motor after an article in Hot Rod mag. Where they got 386 hp with 9.8 c/r and lessor flowing heads than mine. They used the double hump 186 with just bowl blending. We had the same intake, 750 carb, headman 1 5/8th headers, no emissions. On long trips that motor exceeded 20 mpg with 3.55 rear gears. I ran the crap out of that motor for many years and over 50,000 miles before I had the money to move up in power with bigger heads and cam

If you choose aluminum AFR 190 10.7 C/R would be no problem with 91 octane and no octane booster.

 

'462s dont have accessory holes for mounting the (some of)
alternator, AC, smog, etc.

Other than that, they are 64cc and I've always heard they improve mpg
(assuming you don't get too enthusiastic.)

 

The 64 cc 462 is a performance head. But they may not have accessory holes (for alt, AC etc) tapped ... some don't even have bosses that can be drilled-tapped. The 462 will require port work first ... to equal the improved flow found in AFR 190.

Smaller combustion chambers (Fe or Al) result in higher CR ... but I doubt raising CR ALONE will lower fuel mileage. You may spend more money per mile because you may need a more expensive, higher-octane fuel. To prevent detonation/spark rattle, an Increased CR usually requires a higher octane gas (I think y'all have higher octane gas in UK than in USA?). Due to more efficient cooling, Aluminum heads permit higher CR than iron.

If an overheat were to happen, iron heads are more forgiving (less prone to warp/crack).

Higher CR heads make the motor sound more crisp (crisp = power = good) ... but no discernable difference between Al or Fe.

Do your homework before acquiring either ... calculate static CR with your pistons, deck height ... ensure your cam will make the most of higher CR. This is not a recommendation, but some bloke got a TRW L-82 cam (TRW pn CS1095R) while in USA ... maybe you? If so, that cam should be fine with either 64 or 68 cc chambers.

IMO, if I had a choice between AFR 190 or 462 (even if ported) ... I'll take the AFR!

 

Thanks for the replies.
I'm tending to not want to go with the 462 due to the 64cc chamber. I think with stock pistons that would increase the CR to more than I'd want (drilling/taping holes wouldn't be a problem). There would also be the expense of getting the port work done here & it would soon mount up towards the cost of new Al heads. Another thing is that fitting Al heads would reduce front end weight slightly, helping to get more toward a 50/50 weight distribution.

We do have "Super unleaded" fuel here, but a lot of us are finding that it burns very hot (probably not an issue with a water cooled engine, but very dodgy for air cooled ones). I have to buy octane boosters anyway, so if I had to use them in the Vette it wouldn't be much hassle. I'm not sure that we have higher octane fuel here than you guys - maybe the octane rating is measured differently? Our super unleaded is 97 & base unleaded is 95, but I suspect that you might have better fuel even though our numbers are higher.

What I'm worried about is the statement that increasing the CR will drop fuel economy. I've regularly increased the CR in engines & have never notice this happen, but the engines are usually 650cc or 750cc, so fuel economy doesn't really come into it. A 5700cc engine drinking more fuel would be an economic disaster for me :lol:

I like the exhaust note (correction: I love it) of an engine with high CR but what this guy was saying is that the Al heads would make it lose that lovely Chevy growl that Fe heads give & make it sound more like a Range Rover (& I don't want that!!!). Normally I'd ignore that sort of advice & go by my own experiences of fitting high CR Al heads to engines that should have low CR Fe heads, but I have a lot of respect for him, as do a lot of local mechanics (maybe he's just not up to date on the latest SBC aftermarket Al heads & has had bad experiences of Al heads back in the '60's & 70's?). So, now he's planted a seed of doubt in my head I'd though I'd ask you good people if his comments rang any bells? I'm not bothered if the growl under the hood is muted by Al heads as I can't really hear it above the din from the tail-pipes, but I'm very interested in the fuel economy comment.

I was planning to aim for in the region of 9.5:1 to 10:1 CR with some good flowing heads.

The guy that bought the L82 cam in the States was VettePaul. Last week he traded his beautiful '81 in for a black '98 C5, so we probably won't be seeing him on the forum anymore :( I've heard a rumour that he was so underwhelmed with the performance "improvement" after rebuilding the entire engine & fitting the cam along with some different heads, that he went looking for more power in the form of a C5! The Cheat :jester

Thanks for the help - any other comments?
:cheers:

 

Increasing the compression ratio will give an increase in power and torque, I will require less throttle to accelerate and use less fuel. There is a good expaination of effective and mechancal compression ratio and its affects in the book on modifying and building small block heads by David Vizard.

 

Hey Paul;

>Al heads would reduce front end weight slightly, helping to get more toward a 50/50 weight distribution

Careful - the 81 is something like 49.1/50.9 - .9% is about 29 pounds.
Don't take off too much - especially on the wrong side.
I don't know which is heavier the front or the rear.

 

Hi Paul :)

I recently swapped my 186 heads for Edelbrock performer rpm heads and noticed a big difference in performance (this went hand in hand with a load of other mods, see sig)One of the most noticeable differences was in the sound, it now has a bit of a snarl to it (which i think sounds way better than it did) I didnt notice any change in fuel consumption.
I carefully checked the deck height and chose a gasket that gave me a cr of about 9.5:1 with 64cc chambers i have no problem with pinging and run it on regular unleaded. I think i was probably a bit conservative with the c.r and reckon 10:1 would probably be ok with these heads and cam.
From what i have read the AFR's would be a good choice and i would have had them if i could have afforded them.
Hope this helps.

David
:seeya

 

350camaro:
That's the theory I've always worked to. If there's more power available then theoretically I'd need less throttle than before for the same acceleration (in practice I just use the same throttle as before & enjoy myself :D ). As the guy got me worried about fuel consumption I'd thought I'd better post & get some opinions from people that have actually done it. Thanks for the reply.
adam:
Yeek! I'd seen figures that showed a few % between front & rear weight. Obviously the composite rear spring, etc, etc has had an effect on weight, but I didn't know it was that much. Thanks for the warning :)
David:
Hi, thanks for the info (esp. about running OK on our unleaded). I'll probably end up with Edelbrock heads as they are readily available here, but if you look at the price of AFR's in the US & then convert that to £'s it comes out at £50 less than Edelbrock heads in a local shop!!! I'll ignore mateys advice & carry on saving the pennies :)
:cheers: