Taking off my AFRs
Thread Starter
Intermediate
Joined: May 2008
Posts: 46
Likes: 0
Taking off my AFRs
I've got a rebuilt 350 bored .30 over with stock type FT pistons. In my eagerness to do something to this motor to satisfy my hunger for speed I removed the stock cylinder heads and cam and replaced them with a set of 195 cc AFR eliminators with 75 cc combustion chambers and a comp cams XE268H cam shaft. I have been running this combo for about a year now but feel like I am putting these cylinder heads to waste on an otherwise rather stock SB. So, I've been thinking about killing two birds with one stone by removing the AFRs, setting them aside for a future, well planned engine build, and in the mean time putting some 65cc cast iron or, say Patriot aluminum heads on to raise the compression a bit. I feel like the increased flow I gained from putting the AFRs on was cancelled out due to the low compression of the motor (too high combustion chamber volume). Sharing your thoughts on the matter will probably be helpful. Thanks. 
Thread Starter
Intermediate
Joined: May 2008
Posts: 46
Likes: 0
But to answer your question, I'm not looking to spend another 1400 bones on a very nice set of 180s. If I do buy 180s, I'm looking for something under a grand. I realize aluminum heads allow you to run a slightly higher compression but I'm not sure that would be an issue if I run no less than 65ccs and do not swap pistons. Looking for a little more tech talk if you will, to fill in the empty holes of knowledge here..
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
compression although often overlooked IS the foundation for performance......everything else follows, camshaft, fuel system, timing curve, etc......
Last edited by midyearvette; Jun 24, 2009 at 09:20 PM.
CF Community Team
Joined: Oct 2007
Posts: 1,134
Likes: 605
From: NorCal San Jose
How about a modest head milling? Get the chamber down to 68cc or something. Milling is cheap and you probably wouldn't need to mill your intake for such a small cut.
What gasket size do you have in there now? That might be another option - you can get gaskets down into the .027" compressed height range for not a lot of cash.
Jim
What gasket size do you have in there now? That might be another option - you can get gaskets down into the .027" compressed height range for not a lot of cash.
Jim
Safety Car
Joined: Aug 2006
Posts: 4,102
Likes: 1
From: Forsyth Illinois
Luke......I have some nice Brodix IK 180s that I had new valves,springs,retainers,etc. installed,and needing a bigger head.I have a chance to get a rotating assembly w/popups,and w/my 64 cc heads,and zero deck......I am going to be sitting right under 13 to 1.Or...I would probably sell them right out.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Racer
Joined: Dec 2008
Posts: 300
Likes: 0
From: Toms River NJ
if its a patch fix you're looking for on the 355, how about a set of vortec heads? theyre all pretty cheap, and flow well. SDPC has some high lift versions too. you could prob get a used set on craigslist for next to nothing. of course, they are iron and some of the manifold bolts are at a dif angle (new manifold or retap the heads), so pros and cons.
Pro
Joined: Apr 2005
Posts: 591
Likes: 7
From: Batavia IL
I disagree....Heads are the main key to making power, says the guy with a 9.8 compression big block with full cnc ported AFR heads that is in the 9's on motor.
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
thats your opinion and that's ok however your engine is built around your compression ratio..also were talkin normally aspirated....power adders may tweak the formula somewhat but it is still based on cr and cylinder pressure based on camshaft etc.....i think you were missing my point...good luck
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Piston change is relatively inexpensive fix but only if you're doing the work. Speedpro hyper dome/popup H618CP30 (+3.5cc dv) or H617CP30 (+11.8cc dv) could put you near 9.6:1 or 10.6:1, respectively. And you'd retain the heads' potential for possible stroker. Check w/ CF member dmaaero ... IIRC, he's pleased w/ H618.
Last edited by jackson; Jun 25, 2009 at 08:27 AM.
Melting Slicks
Joined: Jun 2002
Posts: 2,844
Likes: 99
From: Orrtanna Pa.
If I were you, I'd take a peek at some solid FT circle track cams. Ground on 106 LC and with the right duration it will effectively raise the compression through valve timing, and then your heads will come alive. A cam is only $200 or so, and the heads better than $1400. Why waste the good stuff sitting on a shelf in the garage.
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
I've got a rebuilt 350 bored .30 over with stock type FT pistons. In my eagerness to do something to this motor to satisfy my hunger for speed I removed the stock cylinder heads and cam and replaced them with a set of 195 cc AFR eliminators with 75 cc combustion chambers and a comp cams XE268H cam shaft. I have been running this combo for about a year now but feel like I am putting these cylinder heads to waste on an otherwise rather stock SB. So, I've been thinking about killing two birds with one stone by removing the AFRs, setting them aside for a future, well planned engine build, and in the mean time putting some 65cc cast iron or, say Patriot aluminum heads on to raise the compression a bit. I feel like the increased flow I gained from putting the AFRs on was cancelled out due to the low compression of the motor (too high combustion chamber volume). Sharing your thoughts on the matter will probably be helpful. Thanks.
The AFRs are great heads - I'd hate to see you going backwards...
1. Use a thinner head gasket such as Fel Pro's steel shim at ~0.018 thickness instead of a .040 thick gasket. This will raise your CR by 1/2 point from 8.5 to 9.0 - this assumes stock deck height - check your quench height - should be .035 to .040.
2. Mill the heads by .060 to get 65 cc chambers - this will raise the CR by another full point to 10:1.
3. Do the above and add a bigger cam such as the Comp XE-274H.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
I have the AFR 195's with 75CC chambers. Milled them to 70CC's right out of the box to optimise compression for my build. Quench is @ .040. What intake and exhaust do you have? Restriction at either of these will drasticaly reduce power. Tuning is another consideration. Going to stock 65CC iron heads or Patriots is a giant step backward. More compression and less flow will not help your power. Look elsewhere for performance gains, you have the right heads.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
here is a quote from another post. Shows a stock L-82 (your flat top = L82 comp.) Adds intake, Adds headers then compares different heads, including AFR 195:
Intake and headers are a must:
Patriots don't flow as well as vortecs!!! This has been proven in back to back dyno tests on this forum before.
Vortec adds 21HP
Edlebrock adds 33 HP
Brodix IK 180 adds 50 HP
AFR 195 adds 81 HP
Intake and headers are a must:
Patriots don't flow as well as vortecs!!! This has been proven in back to back dyno tests on this forum before.
Vortec adds 21HP
Edlebrock adds 33 HP
Brodix IK 180 adds 50 HP
AFR 195 adds 81 HP
Either of the suggested 64cc non-Vortec heads are a good choice if you can make the budget. Remember that for those heads you still need to invest in head bolts (aluminum heads require bolts with washers, ARP recommended), rockers and a gasket set. Just don't short yourself on budget - getting something twice as good 1/2 way done doesn't really help 
I did some DD work this morning just for fun. Note that DD is a useful tool - but results aren't perfect by any means.
I have an L-82 baseline model that makes 262HP@5000 RPM and 346TQ@3500 RPM at the flywheel. I use a correction factor of 80%HP/75%TQ (DD is torque-optimistic) for drivetrain and accessory losses, which gives 209HP@5000 and 259TQ@3500 - reasonably close to published specs.
So let's make some changes in the model and see what we get. All of these are in flywheel numbers, so apply the above 80%HP/75%TQ correction for reality at the rear wheels.
BASELINE: 262HP@5000, 346TQ@3500
Intake: 287HP@5000, 352TQ@3500
...add headers:
Headers: 319HP@5000, 379TQ@3500
Now let's do a head comparo based on the above updated baseline; flow numbers are from published tests where available.
Vortec: 340HP@5000, 389TQ@3500
E-Street: 352HP@5000, 392TQ@3500
IK180: 369@5000, 394TQ@4000 (<--new peak)
And, just for fun:
AFR 195 Street: 400HP@6000, 400TQ@4000
This exercise tells us a couple of things, but mostly heads = HP when properly matched with all the components as DRIVESHAFT noted. Interestingly, going with a modern cam profile at about the same lift showed a slightly better torque curve, but typically less peak power. As the cams got more radical, the better heads started to shine...but I don't think your goal is big HP numbers but just a stronger driver.
OK, that's my hour today
I did some DD work this morning just for fun. Note that DD is a useful tool - but results aren't perfect by any means.
I have an L-82 baseline model that makes 262HP@5000 RPM and 346TQ@3500 RPM at the flywheel. I use a correction factor of 80%HP/75%TQ (DD is torque-optimistic) for drivetrain and accessory losses, which gives 209HP@5000 and 259TQ@3500 - reasonably close to published specs.
So let's make some changes in the model and see what we get. All of these are in flywheel numbers, so apply the above 80%HP/75%TQ correction for reality at the rear wheels.
BASELINE: 262HP@5000, 346TQ@3500
Intake: 287HP@5000, 352TQ@3500
...add headers:
Headers: 319HP@5000, 379TQ@3500
Now let's do a head comparo based on the above updated baseline; flow numbers are from published tests where available.
Vortec: 340HP@5000, 389TQ@3500
E-Street: 352HP@5000, 392TQ@3500
IK180: 369@5000, 394TQ@4000 (<--new peak)
And, just for fun:
AFR 195 Street: 400HP@6000, 400TQ@4000
This exercise tells us a couple of things, but mostly heads = HP when properly matched with all the components as DRIVESHAFT noted. Interestingly, going with a modern cam profile at about the same lift showed a slightly better torque curve, but typically less peak power. As the cams got more radical, the better heads started to shine...but I don't think your goal is big HP numbers but just a stronger driver.
OK, that's my hour today
Last edited by 63mako; Jun 25, 2009 at 11:31 AM.
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
Last edited by midyearvette; Jun 25, 2009 at 12:01 PM.