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Old 03-09-2013, 02:32 PM
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Is my set up going to be ok

Hi there, new to this forum. I have an 85 350 4 bolt with tbi 193 heads-65cc. 345np .030 pistons, knock off duel plane intake,long tube headers and 600 edlebrok carb I have a brand new summit 1102 cam and lifters to put in it and am wondering if it will knock with my calculated 10.38:1 compression ration on 93 octane and low timing. I have zero money for new parts but I do have the stock cam also. Any help is ver appreciated. It's is going into a mud/trail truck 67 fullsize blazer frame with 94 s-10 2 door blazer body 4.10 gears 3/4 ton axles, 38'' tires
Any help is much appreciated. Heads are also stock

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Old 03-09-2013, 07:01 PM
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Anyone? The cam is a summit 1102
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Old 03-09-2013, 08:04 PM
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What you mean is "is it going to have detonation/pre ignition." AKA spark knock. I think you will be just fine with that combo. I would try to keep your total timing around 34 or so. The 1102 cam is a nice upgrade from stock, but will still allow you to keep your stock converter, good vacuum, etc. It may like less or more timing. If it is detonating at 34 back it down to 32, and if it likes 34 try 36.
Chevyguy13
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Old 03-09-2013, 08:13 PM
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While searching this setup I found a a post saying this cam with more then 9:1 does not have enough duration to bleed off cylinder pressure for the upped compression. Just wondering if this is something I have to worry about. Thanks for your reply.

Last edited by Motosledneck 12; 03-09-2013 at 08:20 PM.
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Old 03-09-2013, 08:34 PM
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This cam has 204 intake 214 exhaust duration @.050 lift. You are correct, it not very much duration, and will not bleed off very much compression. Your stock cam is going to be even less duration.. I think you will be just fine with what you have, with good gas and correct timing. If you had a little extra $ to spend you could get a little bigger cam, with a little more duration and lift to move your power band from 1200-4800RPMs to something like 1500-5800RPMs. If you cant buy any more parts, you will be fine, IMO. I ran a comp 268h in a 350 with 64cc heads and -5cc flat tops for years back in high school. It was just fine, as long as I didnt get carried away with igniton timing. Back in the day muscle cars came with cams very similar, maybe a hair bigger with even more compression than that. IE the 327 350hp in the 60's.

Chevyguy13
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Old 03-09-2013, 08:43 PM
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Awesome! Thanks for the input
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Old 03-09-2013, 08:56 PM
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It should have good torque with that cam and the gears you have. I think you will be happy. Like I say, you are just going to have to see how much timing it likes. Id try 32 total and drive it under load and see if you hear any detonation, as well as read your spark plugs. If 32 is ok keep easing it up until you find "too much" and back up a few degrees. The more timing you give it, the more power it will have, but too much will destroy a piston. Just keep it safe with good gas too.

Chevyguy13
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Old 03-10-2013, 01:46 AM
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Quote:
Originally Posted by Motosledneck 12 View Post
While searching this setup I found a a post saying this cam with more then 9:1 does not have enough duration to bleed off cylinder pressure for the upped compression. Just wondering if this is something I have to worry about. Thanks for your reply.
IMO you don't have enough cam timing to support your static compression ratio, if you have a true 10.38:1

Check out the attachment below..





Duke
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Old 03-10-2013, 08:30 AM
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I think you will have closer to 9.75 cr if the block has -0.020" deck height, which is typical. 10.2 cr with a zero deck.

Still way too high cr for that cam and the load you are going to put on the engine (big heavy truck).

Plus 193 heads are terrible. You would be better off with a set of 882's, 76cc heads.

with 9.75 I would use a cam in the range of 218-224 degrees at 0.050". Like a compcam 268H or 270H.

If you reduce timing it may work, but mpg and power will be reduced. And may make it run hot.
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Old 03-10-2013, 10:26 AM
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Deck hight .040. bore 4.030. Stock stroke 3.48. Pistons are flat top with 4 valve reliefs, dome volume -5. Compressed gasket thickness .039 It actually comes out to 10.5:1. I do have the stock 882 heads but they don't have the bolt holes in them to drive all my acc pulleys that came off of a tbi. And the tbi has much bigger intake valves. So if I could get the comp cam your talking about or one like it I would be in the safe zone? Or would I need to bigger yet? But I need the smaller lift for the stock springs
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Old 03-10-2013, 11:21 AM
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Sorry punched some numbers wiring calculating it came out to 10.38:1
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Old 03-10-2013, 12:07 PM
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Motosledneck 12, I believe your CR will be more in the range of 9.5-1. I am running a 69 3/4t chev 2x with a grandma 4psd, 4.10 dana rear. Have a .010 350 with flattops and 2 eyebrows valve cutouts. A 650 holley, 2 plane performer intake, set of those 190cc, 64cc Proform aluminum heads, Howards cam with 213* @.050 .430 lift. Put some long slot 1.6 stamped rockers on for a lift of .458 Have a Proform HEI with 12* initial and a total of 36* @ 2800rpm. Engine idles @ 650rpm with manifold vacuum at 15.5 inches. With the vac adv. to manif. vac. it runs at 53* total@ 3000rpm. I get no ping and run 87oct. pump gas. Engine is a little lazy below 1100rpm. If I up the intial to around 18* it pulls great off idle with no ping but my total goes to 60*. I am going to find a better adj. vac. can ( this can doesn't adj. it out properly) to bring the total down with vac adv. to 48* and set the initial to 16*. Obviously I have a little more tuning and adj. to timing management to do but the combo works very well. Also I feel a slight off idle, tip in, lean condition. I will be addressing this after I adj. the timing curve to what I need.

Your combo I believe will work fine....your just lacking in the heads flow. You will be fine, just watch your timing. Initial, mech. and total with vac. and make sure you don't run lean anywhere in the range you operate the engine.
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Old 03-10-2013, 01:38 PM
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Using Pat Kelly's calculator and the folowing variables:
4.030" bore
3.48" stroke
65.0cc chamber
0.039" gasket
4.030" gasket bore?(minimum)
0.040" deck
5.0cc valve reliefs
I come up with a 9.40:1 static compression ratio, and a 0.079" squish/quench. Both are too high for pump gas IMHO.
ssmonty
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Old 03-10-2013, 02:56 PM
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Is there anything I could do like maybe get a thicker head gasket maybe?
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Old 03-10-2013, 03:56 PM
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You would need a thinner head gasket to bring your quench down, ideally to somewhere in the area of .040 to .050 in your case. However, you said the block is decked at .040. That seems kind of high to me. Most stock blocks are .020 to .025, unless the engine has been rebuilt and the pistons are sitting lower.
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