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Old 06-29-2010, 05:06 PM
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Will I still be able to run 89 octane with smaller cam?

Hello guys I just have a few question and main one is will I be able to still run my engine on 89 octane. Basic info is 350 sbc with world sportsman 2's with 72cc heads and using a felpro 1003 head gasket and my block was decked .010 and according to machine shop my pistons are .010 in the hole.

My pistons are speed pro h345 pistons which have a 1.560 compression height. Current estimated compression is 9:1 and dynamic compression with my old 284/292 222/230 @ 50 112 LSA crane cam is 7.8 on the keith black website. I am going down to a smaller cam for better street manners which specs at 260/270 212/218 @50 with 510/510 lift with a 106/112 LSA and with that cam my dynamic compression goes up to 8.09 on keith blacks website and will that be too much with iron heads?

I have used 87 before and didn't have any problems with pinging or anything but to be safe I always use 89. Doing a dry cold compression test I have 165 psi with old cam. I have yet to have any pinging issues but going a cam size smaller has me just a little wondering about it. I want to keep my current timing of 16 initial (28 with vacuum advance hooked to full manifold) at idle and I have around 34 mechanical all in by 3500 rpm.
Thanks
Eric

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Old 07-01-2010, 07:31 PM
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Well I see a lot of people have read but no responses which is fine. Does anyone on here run cast iron heads with a smaller type cam similar to mine and run fine on 89 octane without any issues is my basic question.

I have read many articles on the subject but don't get no clear cut answer on dynamic compression related to static compression and fuel requirements. I guess altitude and other things come into play as well. I have seen other 350 sbc with iron heads and they had everything bone stock with only 8.5 to 1 and they could not run the same area of timing I have without pinging. O well I guess I will be putting it in soon and will find out then. Thanks guys
Eric
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Old 07-01-2010, 07:39 PM
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What are your carb adjustment specs? Type , Jet, PV, rods..
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Old 07-01-2010, 08:21 PM
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Well my carb is a holley 600 vacuum secondary 1850s model and I have currently 67 jets in the front and 72 in the rear. I have a metering block in the rear and not the metering plate and am running a stock 6.5 power valve. I did at one time have 70 in the front and 76 in rear but it was getting too rich that way so re jetted it to the specs above. Going from a 284/292 222/230 @ 50 cam to a much smaller 260/270 212/218 cam is a little bit of difference. I might not need 16 degrees initial with that cam but should not be too far off from where my timing is currently set.

This is in a 96 chevy s10 with a turbo 350 transmission with a 2000,2200 stall converter with 3.42 gear's in the rear.

Eric
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Old 07-01-2010, 08:23 PM
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Quote:
Originally Posted by eric32
Hello guys I just have a few question and main one is will I be able to still run my engine on 89 octane. Basic info is 350 sbc with world sportsman 2's with 72cc heads and using a felpro 1003 head gasket and my block was decked .010 and according to machine shop my pistons are .010 in the hole.

My pistons are speed pro h345 pistons which have a 1.560 compression height. Current estimated compression is 9:1 and dynamic compression with my old 284/292 222/230 @ 50 112 LSA crane cam is 7.8 on the keith black website. I am going down to a smaller cam for better street manners which specs at 260/270 212/218 @50 with 510/510 lift with a 106/112 LSA and with that cam my dynamic compression goes up to 8.09 on keith blacks website and will that be too much with iron heads?

I have used 87 before and didn't have any problems with pinging or anything but to be safe I always use 89. Doing a dry cold compression test I have 165 psi with old cam. I have yet to have any pinging issues but going a cam size smaller has me just a little wondering about it. I want to keep my current timing of 16 initial (28 with vacuum advance hooked to full manifold) at idle and I have around 34 mechanical all in by 3500 rpm.
Thanks
Eric
If your computations regarding the CR- both static and dynamic- are accurate, you won't have a problem using 87 octane.

If you get greedy w/the total timing by bringing it in sooner, or use more total, this will change for the worse. I would be prepared to tune the vacuum advance- either at the vacuum when it begins to advance, the total amount the vacuum advance adds, or both.

The ACCEL #31035 is an adjustable vacuum advance can for GM HEI that allows infinite adjustment to BOTH the amount and rate of advance. Comes w/instructions and tool.

To limit the amount of advance w/an OEM or some adjustable vacuum advance cans like the Crane can, you will need to physically limit the vac can's travel w/a VACUUM ADVANCE LIMITER PLATE- Crane #99619-1, #99619-1 INSTRUCTIONS.
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Old 07-01-2010, 08:35 PM
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Hello cobalt thanks for info. I just got one of the accell units that you just posted but the instructions don't say much or at least maybe I don't understand them.

On my other truck when I adjusted my vacuum advance I just put in the allen wrench and kept checking my timing till I saw to where I had 12 more of degrees at idle on full manifold vacuum. That is what I assumed on how you set them but maybe I am missing something here by the amount of rate that it can be tuned as well. As far as timing goes I don't use more then 34 degrees total mechanical and it's not supposed to start advancing till around 1500 rpm or just a shade higher.

By reeving my engine up to 3500 rpm I get about 34 or close to that but not over. I got a set of mr gasket medium spring's on my hei to give me only 15 degrees added to idle. I don't need to run it at 36 to 38 degrees for every last ounce of power cause am not racing the thing.
I know 16+15 is 31 but timing light says about 33-34 when reeved up to 3500 rpm.

Thanks
Eric
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Old 07-02-2010, 05:12 PM
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Check the actual piston TDC and make sure its correct. Sounds like a timing mark is off or stretched chain.

My 440 in the photos made over 500 hp, but couldn't fit the engine under the hood the way it wanted. Being a driver 3.23 gear were the max. Switching back to stock HP mopar 440 cam, springs, AVS, and Mopar CH4 4bbl intake made it smooth. That was much better choice for a nice driving road car.

Cam went from 230 duration .550" lift 108 center , to 210 duration and .455" lift on a 114 center.

Intresting jetting results . Tuning you usually learn that engines want timing first. Baseline carbs jetting are set pretty well for what you need fuel wise. The relationship between the power valve and secondary vacuum pod is needed to be understood.

Last edited by spinn; 07-02-2010 at 05:35 PM.
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Old 07-02-2010, 05:23 PM
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Well my timing chain is brand new and only a year old with less then 3000 miles on it and also nothing wrong with my timing.

Many of the after market advance spring kits say a certain rpm range with there springs and weights but I did not use the weights that came with my advance curve kit as the ones on my distributor where better made. Anyways I get a couple of degrees of extra advance because of the difference in them.

Timing on those kits can vary which is why I always check mine with my timing light. Marks on my balancer are accurate with my timing tab so nothing wrong there with my timing wise.
Eric
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Old 07-02-2010, 05:31 PM
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I'd try running 89-octane and listen for any pinging...and adjust accordingly. I ran a similar 350 with somewhat similar cam-specs of your "new" cam (but the one I used had less lift). Had +/-155 psi across the board. Didn't ping w/89. But if it pinged a "little" I wouldn't be able to hear it. The header/exhaust noise could cover up minor-pinging sounds. Plus this engine I had was something I ran 15-20 years ago. Fuel was different back then...no ethanol/blended fuel...well...not as much as there is now.
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Old 07-02-2010, 07:13 PM
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Well I figure if it might ping and I don't believe it will but with a slightly smaller cam it might make it the difference but I will just have to adjust it to where it is happy. If I did it should be nothing more then a few degrees.

Heck a couple of times I put 87 just to see how it would run and it did just as good with 89 with no issues but I just like to use 89. Thanks for your experience. I just know you can't run smaller cams with to high of compression or you will have to many issues. I am sure my new cam is not too small its still way more then a stock cam.
Take care guys
Eric
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