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Old 10-29-2012, 11:15 AM
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Originally Posted by ap72 View Post
Aluminum heads generally mean you need about a point more compression than iron heads. I would go no larger than a 195cc port with that cam, the duration just isn't enough to support a larger cam.
What do you mean by this. I don't quite understand it.

I'm just not sure what size intake runner (cc) I would benefit from with this cam. I don't want to go too big or too small. I think I have the 1" 5/8 primaries on my headers. They are pretty standard headers...

I know I REALLY need a good carb tune but I can't get it any better. I need to get some tuning time on the dyno with someone who knows what they're doing with a carb.

I think with this cam I will continue to make good power through the power band I just am looking at extending the power band higher in the tq and hp. I want to squeeze every last bit of power from this setup. I feel its a great street motor where I can hit the gas and break the rear end loose and just play with.

As soon as I can find one, I am going to swap in a 95" impala SS rear axle so I can get a little better 3.08 gears, limited slip, 8.5" rear end and disc brakes. More bang for my buck and its a direct bolt in to my "G" body.

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Old 10-29-2012, 11:32 AM
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aluminum heads cool better so they will tolerate more compression with other items remaining the same.If you keep that small cam I see no reason to go very big on the intake runners.180s are good enough.it depends what the heads flow,how many cfm the heads flow at what valve lift,then factor in your cam and see what you can make HP wise
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Old 10-29-2012, 11:55 AM
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How would someone go about selecting an intake runner size rather than someone just saying I should be ok with such and such? How would I know what to pick, say a 165cc, 170cc, 180cc, 195cc, 200cc, 210cc, 215cc, 220cc, 235cc etc... The 235cc will flow the most air because it's bigger. Why would 180cc be ok for my setup? Help me understand why. Thanks
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Old 10-29-2012, 12:03 PM
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Originally Posted by Caballerokid View Post
How would someone go about selecting an intake runner size rather than someone just saying I should be ok with such and such? How would I know what to pick, say a 165cc, 170cc, 180cc, 195cc, 200cc, 210cc, 215cc, 220cc, 235cc etc... The 235cc will flow the most air because it's bigger. Why would 180cc be ok for my setup? Help me understand why. Thanks
The volume itself is actually meaningless. What you're concerned with is the minimum and average cross-sectional area. A typical sbc intake runner length is about 5.6" so given the volume you can easily figure the average area.

As a general rule the more rpm you turn the larger of cross-sectional area you'll need. Also increased displacement requires more area. For a street engine you want to go with an adequate volume and no more. Bigger is not better, smaller is not better- just right is better. If you do have to go slightly larger or smaller go a hair larger.
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Old 10-29-2012, 12:52 PM
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Quote:
Originally Posted by Caballerokid View Post
How would someone go about selecting an intake runner size rather than someone just saying I should be ok with such and such? How would I know what to pick, say a 165cc, 170cc, 180cc, 195cc, 200cc, 210cc, 215cc, 220cc, 235cc etc... The 235cc will flow the most air because it's bigger. Why would 180cc be ok for my setup? Help me understand why. Thanks
My ex-wife used to ask me about the size of her *** and I'd always tell her, "It's not the size that matters, it's the shape."

Same with intake and exhaust runners. The tiny little 170cc intake runners in the L31 Vortec 5700 heads will do a better job of filling the cylinder than a lot of aftermarket heads with larger volume runners. A rule of thumb for a small block Chevy street driver is cubic inches times 1/2......283/140, 305/150, 327/160, 355/175, 383/190, 406/200. This assumes STREET use, idle to 5500 rpm's, not racing. The runner must be sized so that the "slug" of air/fuel mixture has sufficient VELOCITY to continue to pack the cylinder even after the piston has reversed course and is headed back to the top of the cylinder on its compression stroke. Remember, compression cannot begin until the intake valve closes and that is quite a number of degrees after bottom dead center with the piston coming up the bore. Of course, you also need VOLUME. If the runners were the size of a drinking straw, you'd get some hellacious velocity, but you wouldn't get much volume because the other factor involved is TIME. Your goal is to fill the cylinder with as much mixture as possible during the time that the intake valve is open.

Most of you fellows who are building street motors will use too much head and too much cam in an effort to make high horsepower. Horsepower is not what moves the car from point A to point B in a street use setting. Torque is what does that. If you really want to build a pleasant driver that will pull like Jack the Bear, bolt a set of L31 heads onto a 383 and enjoy the torque created from 1500 to 5500. Build it 9.5:1 with a matching cam, long-tube, equal-length headers with 1 5/8" primaries, dual-plane high-rise intake manifold such as an Edelbrock RPM #7116 or Professional Products Vortec Crosswind #52028, 650 vacuum-secondaries carb and you'll have a really pleasant, tractable daily driver motor.

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Old 10-29-2012, 04:43 PM
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More TQ than HP???

I have done some checking on this combo. Stock 350 block height is 9.020"-9.025". The rod length, 1/2 of stroke, and piston compression height don't add up to what you say. 5.70"+1.740"+1.560"= 9.0". Pistons are .025" down in the hole. For quench you have .025"+.015"= .040". You have 55" for quench. On the KB compression calculator your combo has 10.10 static compression and the dynamic compression ratio is 9.075. To run on pump gas you would want to have 7.5-8.5 DCR to avoid detonation. Keep an ear out for any pinging or knock. The 882 heads have the small 151cc intake ports is probably why it seems torquey. Here is the intake flow rates .100-70, .200-125, .300-175, .400-204, .500-205, .600-206. The exhaust flows .100-59, .200-109, .300-136, .400-143, .500-144, .600-145. A stock set of Vortec heads have 170cc intake ports and flow .500-239 intake and 160 exh. But like was said you cannot use them because they have 64cc chambers. The good news is I just finished reading an article on a 355 9.1 compression engine with 882 heads that were ported and 2.02 & 1.60 valves were swap in. The cam was a Crane PowerMax .427/.454 lift with 204/216 duration. Hold on to your hat, it produced 367hp & 442 lbs torque. Chevy Small Block Build - Mildly Amusing - Super Chevy Magazine
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Old 10-29-2012, 04:56 PM
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Ya the build is a little goofy. The pistons are .040" in the hole which is how i have .055" quench. That is some great info on those heads! I have the ports opened up pretty good at the mouth but just the way they are cast you can tell they are restrictive. I'm looking at a set of TrickFlow fast as cast 72cc aluminum heads with 180cc runners and 75cc exhaust. Those should really help the flow out along with the 2.02 int valves. I'm going to notch the intake plenum and add an open 1" spacer which should also help. Then see where i go from there. What do you guys think? Thanks!
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Old 10-29-2012, 05:00 PM
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The way i checked the quench was just a quick check since things were already together i used a dial indicator to get dead 0 and then used a straight edge and then roughly measured it.
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Old 10-29-2012, 05:04 PM
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Originally Posted by Caballerokid View Post
The way i checked the quench was just a quick check since things were already together i used a dial indicator to get dead 0 and then used a straight edge and then roughly measured it.
Close enough.
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Old 10-29-2012, 05:22 PM
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Originally Posted by cdminter59 View Post
I have done some checking on this combo. Stock 350 block height is 9.020"-9.025". The rod length, 1/2 of stroke, and piston compression height don't add up to what you say. 5.70"+1.740"+1.560"= 9.0". Pistons are .025" down in the hole. For quench you have .025"+.015"= .040". You have 55" for quench. On the KB compression calculator your combo has 10.10 static compression and the dynamic compression ratio is 9.075. To run on pump gas you would want to have 7.5-8.5 DCR to avoid detonation. Keep an ear out for any pinging or knock. The 882 heads have the small 151cc intake ports is probably why it seems torquey. Here is the intake flow rates .100-70, .200-125, .300-175, .400-204, .500-205, .600-206. The exhaust flows .100-59, .200-109, .300-136, .400-143, .500-144, .600-145. A stock set of Vortec heads have 170cc intake ports and flow .500-239 intake and 160 exh. But like was said you cannot use them because they have 64cc chambers. The good news is I just finished reading an article on a 355 9.1 compression engine with 882 heads that were ported and 2.02 & 1.60 valves were swap in. The cam was a Crane PowerMax .427/.454 lift with 204/216 duration. Hold on to your hat, it produced 367hp & 442 lbs torque. Chevy Small Block Build - Mildly Amusing - Super Chevy Magazine
Thanks for the link CD. SCR is 9.1:1, DCR is 8.265:1. Makes a beautiful little torque motor for the street on cheapo pump gas.
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Old 10-29-2012, 05:26 PM
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More TQ than HP???

Yeah, that's the part I don't understand. A 350 chevy block has a deck height of 9.025. Add 1/2 the crank diameter, the rod length, and piston compression height on your pistons. The total comes to 9.0". How can the pistons be .040 in the hole? The Trick Flow heads have a 72cc chamber, that will put your static compression at 10.571 and the DCR at 9.493. You will have to use 110 octane with a DCR of 9.493.
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Old 10-29-2012, 05:28 PM
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Quote:
Originally Posted by cdminter59 View Post
I have done some checking on this combo. Stock 350 block height is 9.020"-9.025". The rod length, 1/2 of stroke, and piston compression height don't add up to what you say. 5.70"+1.740"+1.560"= 9.0". Pistons are .025" down in the hole. For quench you have .025"+.015"= .040". You have 55" for quench. On the KB compression calculator your combo has 10.10 static compression and the dynamic compression ratio is 9.075. To run on pump gas you would want to have 7.5-8.5 DCR to avoid detonation. Keep an ear out for any pinging or knock. The 882 heads have the small 151cc intake ports is probably why it seems torquey. Here is the intake flow rates .100-70, .200-125, .300-175, .400-204, .500-205, .600-206. The exhaust flows .100-59, .200-109, .300-136, .400-143, .500-144, .600-145. A stock set of Vortec heads have 170cc intake ports and flow .500-239 intake and 160 exh. But like was said you cannot use them because they have 64cc chambers. The good news is I just finished reading an article on a 355 9.1 compression engine with 882 heads that were ported and 2.02 & 1.60 valves were swap in. The cam was a Crane PowerMax .427/.454 lift with 204/216 duration. Hold on to your hat, it produced 367hp & 442 lbs torque. Chevy Small Block Build - Mildly Amusing - Super Chevy Magazine

This isn't that different from what you currently have, BUT it has a better intake, better carb, and is probably painstakingly assembled and tuned, and ran under ideal conditions. As TI has implied though their engine has great midrange power and yours can too (and already does to some extent).

If you want a good street engine concentrate on midrange power (what people often mislabel as torque) not peak power.

BTW can you post your dyno graph, often the graph can show problems that you may not be aware of.
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Old 10-29-2012, 05:31 PM
How fast is fast enough?
 
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Originally Posted by cdminter59 View Post
that will put your static compression at 10.571 and the DCR at 9.493. You will have to use 110 octane with a DCR of 9.493.
Don't tell anyone with a stock lt4 engine that.
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Old 10-29-2012, 05:42 PM
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Originally Posted by Caballerokid View Post
The rpm air gap won't make a difference accept at high end.
Ummmm, not true. The RPM will make more power throughout the range over a standard Performer. In my opinion, all you're doing when you replace a stock cast iron intake manifold with a Performer is reducing the weight on the front end of the car. While that's a good thing, it's a fairly expensive way to reduce weight. Best intake manifold idle to 6000 is an RPM or other dual-plane, high-rise intake manifold.
Gen I SBC with conventional heads (not L31)
Edelbrock 7101
Professional Products 52020 Typhoon
Weiand 8016 (out of production, but can be found used)
Holley 300-36 (out of production, but can be found used)
All these high-rise intake manifolds were patterned after the aluminum Z-28 302 CID intake manifold that was cast by Winters for GM in '68/'69.

Last edited by techinspector1; 10-29-2012 at 05:53 PM.
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Old 10-29-2012, 06:23 PM
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Originally Posted by cdminter59 View Post
Yeah, that's the part I don't understand. A 350 chevy block has a deck height of 9.025. Add 1/2 the crank diameter, the rod length, and piston compression height on your pistons. The total comes to 9.0". How can the pistons be .040 in the hole? The Trick Flow heads have a 72cc chamber, that will put your static compression at 10.571 and the DCR at 9.493. You will have to use 110 octane with a DCR of 9.493.
Rebuilder pistons are 1.540" compression height, not 1.560", so the stack could be 8.980", yielding a piston deck height of 0.045" in a block with a block deck height of 9.025. Actually, it could be done with 400 rods too. Crank radius of 1.740", rod length 5.565", 350 piston with stock 1.560" compression height would make a 8.865" stack. I'm not saying this is likely, I'm just sayin' it's possible. In this short rod scenario, the crown of the piston would be down in the bore 0.160" with a 9.025" block deck height.

I want to re-figure the SCR and DCR, as the numbers don't seem right.
Cylinder 738 cc's
Chamber 72.5 cc's (deduct 3.5 cc piston dome from 76 cc chamber, then figure the piston as a zero value).
Piston 0
Piston Deck Height @0.040" in the hole at TDC 8.5 cc's
Gasket 3.3 cc's
Total 822.3 cc's
less cylinder volume
Total 84.3 cc's
Divide 822.3 by 84.3 and find 9.75:1 SCR
The 274 HO6 stick closes the intake valve at 31 degrees after bottom dead center @0.050" tappet lift and will make 8.764:1 DCR on the KB calculator.

Now, we need to find out from the OP what kind of fuel he runs and we will know that this particular combo will run on "X" fuel at 8.764:1 DCR with a 0.055" squish.

Last edited by techinspector1; 10-29-2012 at 06:33 PM.
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