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Old 02-03-2011, 07:10 PM
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Vortecs,10:1CR,and 89 pump gas

Is anyone successfully running flat top pistons,good quench,Vortec heads,355 cubes,87-89 pump gas,and a 218-220ish duration at .050 cam with 108 LCA?

Without having to retard the timing?

Would like to run flat tops for the better compression but may have to go with a 12cc D dish for 9.4:1

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Old 02-04-2011, 05:57 AM
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The impossible dream perhaps?

I am running a very similar combo but am down in the 9.25:1 area with a 214/224 cam on a 112 LC, no quench to speak of. I have to run 91 octane. My initial timing is around 12 degrees, 10 if I want it not to ping, and my vac adv is limited to 10 degrees. I'm also running 2 steps colder plugs gapped to .045.

My engine was built with 10cc flat top pistons with a .020 taller pin height, putting them .020 deeper in the hole - wasn't my choice but it's done - quench distance is around .065 right now. Average measured deck height is .0276 and I'm running a .040-ish gasket with 64cc vortec 906 heads.

I am contemplating a head gasket swap to get me down to .040 quench which will also bump my static CR to 9.8 - not sure if this is going to help or hurt and may prove to be a lot of effort wasted if it doesn't net me any benefit from improving the quench.

From my experience tuning my build, you need to control your timing and temperature to keep it from pinging, and from what I have surmised, the only way to run lower octane fuel will be with EFI and electronic ignition/timing control. I can't put more than 32 degrees of timing into it without detonation on 91 octane at 9.25:1, and that's in normal driving conditions in So Cal, perhaps you could get away with what you are looking for in a much colder climate...

Hope this helps
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Old 02-04-2011, 09:17 AM
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There might be something that needs a bit more tuning...

I'm running 906 heads with a 190 stat in my boat with a 196/206 cam, 9.55:1, and I run 87 octane all day with heavy loads. Of course, I don't have a vacuum advance, but its set up for 12 initial and 34-35 total. Never a single ping.

I find that with my vortec builds I can get away with almost one full point of compression with the same cam on low octane, and just over one full point with more cam (more duration AND overlap).

For instance - on a mild-cammed 8.5:1 350 (76cc heads) I was able to swap to vortecs (about 9.25:1) and keep the 87 octane.
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Old 02-05-2011, 07:05 AM
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The are most likely many guys running a flat top 355 with 64cc heads on the street with 87 octane but there overall setup may be allowing this, gears, cam and vehicle weight etc will factor in.

There seems to be a consensus that -12 or -18cc d dish pistons are the ones of choice for a 64cc headed street type motor with approx 9.5 final SCR. Keeping a good quench in the range of 0.035-0.045 with these set ups is also a common practice.

Your question leads me to believe that you may be in the same boat as I was last spring when I put together my 383 with -18cc hypers to keep things around that 9.5:1 with my vortec heads. At the time the machinist/builder who put together the short block asked me a very important question. He wanted to know what the motor will be installed in and what are the intentions for the truck in my case.

What it boiled down to was that going to dish pistons is the way to go for my daily driver and occasional tow rig. Thing is after all that I wished I would have went flat top and a bigger cam since I put limited mileage on the truck this summer anyhow. I could have lived with paying for premium and building the rest of the truck to suit since I put in a new 700R4 and a posi with new gears. Thats when I would could have moved into a higher stall, bigger cam and 4:11 gears.

IMO Making the move to flat tops has allot to do with the rest of the setup and what you will be using the mill for.

TJ
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Old 02-05-2011, 09:05 AM
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Similar situation Custom10, my builder asked me a few questions and put 10cc pistons in knowing I would run 64cc vortecs, cam was my choice.

I opted for 3.42 gears as my original trans was a T350 w stock converter, but I sprung for a 700R4 last christmas with a 2300 rpm converter and have never been happier - I just wish I had 3.73 or 4.11s out back.

I think I can tune the ping out of my setup, and the few extra pennies at the pump to run premium has not been a huge issue - just not sure if going to 9.8:1 SC is going to be a good thing or not to get to an .040 quench
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Old 02-05-2011, 09:08 AM
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kb makes a piston that is a dish piston with a d shape cup. The design of the piston puts the dish on one side of the piston so you still get the flat top burn benefit, in a perfect world the fuel should be burnt before it leaves the flat part of the d shaped cup piston
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