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Old 04-22-2013, 07:09 AM
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big block chevy and pump gas commpression

Hello.. I'm almost in the market for new heads for my long awaited 496 build , well it's a 489
back in the day when I was young and single I bought heads to make my chevelle fly at the track with 345cc ports.. that everyone in their brother is say'n is way to big for the use the engine will see now..
more a street car with track time.. than a ballsout redheaded stepchild..
any ways , a guy is surpost to come look at my heads(fingers crossed) and this will allow me to get heads more inline with the engines use now..
my dome pistons (18cc) if I read correctly will give me a 10.2 to 1 compression in a perfect world.. in a 118 chambered head..
the heads I'm looking at (brodix) come in 119 and 115cc chambers
with either 294/305/312 intake port cc
what compression is about it on street pump gas..(at the moment it's 94 at sunoco, 93 everywhere else)
here is the cam that I own . it's a solid roller, may change it to a hyd roller if I can swap one for one.. unless my fears of the solid roller failure in a cam like this(mild for a solid roller) won't be an issue


was looking at heads and man o man is there a ton of choices now..

the vehicle is 3900 lb and at the moment(subject to change) would be th4003500stall(would like to run my 2004r3000stall we'll see about building it to live) a 4:11 rear with 26-28" tall tires..
think fun,wild hair street vehicle, that will at times,more offen than not be driven like it was stolen..
oh and it may see the holley hp efi at some point if I can save enough pennies..
and will get hit with happy gas at the track if it ever hooks(pick up)
but thats down the road a bit,if ever.. traction issues with a bbc in a p/u will be hard to overcome

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Old 04-22-2013, 07:59 AM
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look at the AFR 300 cc oval port heads
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Old 04-22-2013, 08:11 PM
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I really like putting combos together on the DynoSim, particularly with AFR heads. They use real-world parameters for their flow numbers and I use them AS-PUBLISHED. Some other head manufacturers fudge on the numbers by using larger pipes, so I factor the flow a little to make it real. AFR uses a 4.280" pipe to flow these BBC heads, so I use their flow as published. RHS, for instance, uses a 4.200" pipe to flow SBC heads. Now, you tell me, when's the last time you saw a production SBC block with a 4.200" bore?

Being a contrarian though, I decided to use the tiniest little heads that Air Flow Research makes for this street motor Sim.
The short block is 4.280" by 4.250" with 6.385" rods and 1.270" 18cc pistons, for a stack of 9.780". We will cut the deck 0.010" to arrive at a piston deck height of 0.010". When used with a Fel-Pro 1027 gasket, the squish will be 0.049".
AFR 265's get the nod, part number 3620-1. 2.19"/1.88" valves with 112cc CNC chambers. These little jewels will generate 10.44:1 static compression ratio with the dimensions listed above and should operate smoothly on pump gas with enough camshaft.
Cam will be Comp solid roller, part number 11-772-8, as seen on the cam card in this thread. It will be installed retarded 4 degrees on these 0.050" tappet lift numbers.....
IO (14) BTDC
IC (54) ABDC
EO (57) BBDC
EC (17) ATDC
Intake centerline 110
Exhaust centerline 110
Lobe separation angle 110
Overlap 31 degrees
We'll use an Edelbrock #7164 RPM Q-Jet intake manifold mounting a Cliff Ruggles-prepared 800 CFM Rochester Quadrajet. Fuel pressure at the carb inlet will be dialed in at 5 psi. Large fuel line will be used to facilitate VOLUME, not pressure.

RPM....HP....TQ
1500....113....395
2000....173....454
2500....221....463
3000....277....484
3500....357....536
4000....441....580
4500....517....604
5000....591....611
5500....621....593
6000....640....561
6500....633....512
7000....601....451

Peak volumetric efficiency 99.3% @5500 rpm's
Peak BMEP 188.3 lbs @5000 rpm's
Dynamic compression ratio is 8.113:1. This motor will easily run on pump gas.
The motor will make another 18 hp and another 15 ft/lbs of torque with a 1050 carb, but driveability and mileage would suffer greatly in my opinion.

Last edited by techinspector1; 04-22-2013 at 08:30 PM.
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Old 04-22-2013, 09:30 PM
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wow,that would be a fun engine.The oval port heads rule for this type of use.
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Old 04-23-2013, 05:16 AM
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Quote:
Originally Posted by techinspector1 View Post
I really like putting combos together on the DynoSim, particularly with AFR heads. They use real-world parameters for their flow numbers and I use them AS-PUBLISHED. Some other head manufacturers fudge on the numbers by using larger pipes, so I factor the flow a little to make it real. AFR uses a 4.280" pipe to flow these BBC heads, so I use their flow as published. RHS, for instance, uses a 4.200" pipe to flow SBC heads. Now, you tell me, when's the last time you saw a production SBC block with a 4.200" bore?

Being a contrarian though, I decided to use the tiniest little heads that Air Flow Research makes for this street motor Sim.
The short block is 4.280" by 4.250" with 6.385" rods and 1.270" 18cc pistons, for a stack of 9.780". We will cut the deck 0.010" to arrive at a piston deck height of 0.010". When used with a Fel-Pro 1027 gasket, the squish will be 0.049".
AFR 265's get the nod, part number 3620-1. 2.19"/1.88" valves with 112cc CNC chambers. These little jewels will generate 10.44:1 static compression ratio with the dimensions listed above and should operate smoothly on pump gas with enough camshaft.
Cam will be Comp solid roller, part number 11-772-8, as seen on the cam card in this thread. It will be installed retarded 4 degrees on these 0.050" tappet lift numbers.....
IO (14) BTDC
IC (54) ABDC
EO (57) BBDC
EC (17) ATDC
Intake centerline 110
Exhaust centerline 110
Lobe separation angle 110
Overlap 31 degrees
We'll use an Edelbrock #7164 RPM Q-Jet intake manifold mounting a Cliff Ruggles-prepared 800 CFM Rochester Quadrajet. Fuel pressure at the carb inlet will be dialed in at 5 psi. Large fuel line will be used to facilitate VOLUME, not pressure.

RPM....HP....TQ
1500....113....395
2000....173....454
2500....221....463
3000....277....484
3500....357....536
4000....441....580
4500....517....604
5000....591....611
5500....621....593
6000....640....561
6500....633....512
7000....601....451

Peak volumetric efficiency 99.3% @5500 rpm's
Peak BMEP 188.3 lbs @5000 rpm's
Dynamic compression ratio is 8.113:1. This motor will easily run on pump gas.
The motor will make another 18 hp and another 15 ft/lbs of torque with a 1050 carb, but driveability and mileage would suffer greatly in my opinion.
one question,, if my 18cc domepistons give 10.2 to 1 with a 118 chamber
how is a 112 chamber only 10.44 to 1.. what am i missing??

and thanks for running that..
if you could, could you flash a rec port through just for giggles(well and that I have a single plane intake for when and if I efi)
thanks again..
my dyno sim, only works with windows 95..
it should be noted that these engine has a cloyds "hex a just" timing set and a 3 piece timing cover to make fine tuning the cam to the engines "wants"
next best thing to a jesel belt system,
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Old 04-23-2013, 06:10 AM
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not married to the intake I have.. so ovals are ok..
how are afr heads I've always run brodix and dart
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Old 04-23-2013, 06:36 AM
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tech if you could. could you run the afr 300 ovals and 290 ovals..

whan and if you get the time..
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Old 04-23-2013, 06:58 AM
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Quote:
Originally Posted by gearheadslife View Post
tech if you could. could you run the afr 300 ovals and 290 ovals..

whan and if you get the time..
scratch that.. just saw the price of the 290 and 300.

maybe run the brodix rr bb 0 through the sim..
tho .these would need milling to get the compression up .. but have bigger valves..
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Old 04-23-2013, 07:03 AM
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the afr's have raised exhast ports just like my darts did afr list that as not a fitment issue.. I'd think raising the port 3/8" would play havic with headers
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Old 04-23-2013, 07:43 AM
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the edelbrooks ovals are 290 cc with either 110 or 100 cc chambers.
with a 18cc dome,
there must be a formula to get static compression with chamber size..

I know with 118 chambera I'm at 10.2 in a perfect world..

and tech. what made you pick "that" afr head and not the other two ovals??
the g.m. ovals are like 312-317cc ports..
these afr "265"s arn't those close to peanut port size?? (try'd looking up the intake port size on p/p heads and came up empty)

what would the afr2100 305 with 115 chamber being to the air dyno.


again thanks for the help

Last edited by gearheadslife; 04-23-2013 at 07:54 AM.
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Old 04-23-2013, 06:44 PM
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any other ideas,(sorry) just try'n to keep my mind off the marathon..
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Old 04-23-2013, 08:30 PM
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Quote:
Originally Posted by gearheadslife View Post
one question,, if my 18cc domepistons give 10.2 to 1 with a 118 chamber
how is a 112 chamber only 10.44 to 1.. what am i missing??
I don't know. I'll run through it again for you to be sure.
I figured the short block at 4.280" x 4.250".
(.7854) x 4.28 x 4.28 x 4.25 x 16.387 = 1001.99 cc's
chambers = 112
Pistons = 18cc dome, so we will deduct the dome from the chambers, so that the piston is zero and the chambers are 94 cc's. Just visualize slicing the dome off with a sharp knife and glueing it into the combustion chamber. That makes the piston flat at zero and the chamber at 94.
The piston deck height is 0.010", so it figures like this....
(.7854) x 4.28 x 4.28 x 0.010 x 16.387 = 2.35 cc's
The 1027 gasket is 9.7 cc's
1001.99 + 94 + 2.35 + 9.7 = 1108.04
Deduct 1001.99 from 1108.04 and find 106.05
Divide 1108.04 by 106.05 and find 10.448:1 SCR

Maybe you figured it wrong to begin with. Or maybe my math is wrong.

"and tech. what made you pick "that" afr head and not the other two ovals??"
Street motor. Needs torque, not hp, although those tiny little heads ended up making a ton of hp too. Bigger heads will make more hp, but that's not what you need on the street. If you want a race motor, then let's stop fartin' around and build a 632 and make 900 hp.

Last edited by techinspector1; 04-23-2013 at 08:45 PM.
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Old 04-23-2013, 08:46 PM
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thanks again..
with a package like this, that only see fair weather, would an air gap be with it. or just "hay look an air gap"

Last edited by gearheadslife; 04-23-2013 at 08:51 PM.
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Old 04-23-2013, 08:59 PM
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thanks again..
with a package like this, that only see fair weather, would an air gap be with it. or just "hay look an air gap"
I personally don't put much stock in air gap intakes. I think it's a load of crap and hype from the manufacturers. My thinkin' is that the fuel and air will atomize a little better with a little heat in the manifold and that should make the motor more street-friendly. Of course, I could be completely wrong because I have no scientific facts to hang my hat on.
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Old 04-23-2013, 09:07 PM
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I don't know what your budget is but it seems that with an intake and carb and Efi swap you're getting ready to drop some serious money. If it were mi e I'd use what you currently have and go to a good Efi system first. No it is not optimal but I don't know how much having optimal versus still pretty damn good is worth to you. Your heads are big but they can work just fine on a street engine, not optimal but still just fine.

None of the suggestions have been bad ideas but they're not cheap either.
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