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PostPosted: Fri Feb 05, 2021 6:51 pm 
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OK thank you. Now I have a plan


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PostPosted: Fri Mar 05, 2021 1:42 pm 
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Hello, an update:

The engine is back from the machine shop. Al ready to assemble. I have couple of questions before I move ahead with the heads:

I checked the original valves and while the intake is carbon steel the exhaust seems to be stainless since they are not magnetic. Were the stock exhaust valves stainless? Everyone agreed that the engine was virgin before disassembly- never apart.

Another question I had was about decking the heads for increased compression. According to my calculations:

Zero deck with the new pistons, .040" head gasket, 76cc combustion chambers and +2cc for the valve relief in the pistons. .020" over cylinders with 3.5" stroke

2.01*2.01*3.143x3.5=44.143(cubic inches)*16.387(CI to CC conversion)=728.29cc per cylinder .We add to that the 76cc combustion chamber volume, 8cc for the head gasket space, 2cc for the piston valve relief total 814.29cc If I divide that by the combustion volume total of 86cc I get 9.46:1 compression ratio. I was told that decking the heads about .050 for 10cc decrease would be about right . That would bring the compression ratio to 10.71:1 I'm worried that it would get me in the pump gas detonation territory. what do you think?


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PostPosted: Thu Mar 11, 2021 6:43 pm 
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Anyone with a tip? I have to decide on decking the heads to proceed. Thank you!


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PostPosted: Mon Mar 15, 2021 10:34 pm 
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I don't think I'd try that much compression. As Falcon67 stated on page 5 - he had to run 92 octane with 50% VP110 with 10.5:1 compression.


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PostPosted: Tue Mar 16, 2021 8:10 am 
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I wouldn't run a street car on the ragged edge of compression, unless it had an ecu to instantly back off timing and knock sensors to know when to do that. Don't deck the heads, keep the 9.46:1, and then know that you can run comfortably on most pump gas. It's less work to build the thing correctly now, then it is to have to mix fuel all the time.

As far as your valves are concerned, I don't really care what the current ones are made of, unless you know who made them and a PN for them. If they're stock, they have 3 groove keepers, or you're unsure about them, replace them. Ferrea 5000 series valves are cheap and good enough for a street engine that I would use them over your current valves without question.


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PostPosted: Tue Mar 16, 2021 8:38 am 
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I agree with all these guys.

It's much better to err on the side of safety with compression. Going from 9.5 to 10.7 may only net you a 3% increase in power. You can make that up somewhere else and not put yourself on the ragged edge of not being able to run your engine safely.

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PostPosted: Tue Mar 16, 2021 9:27 am 
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Agree with above - I would not cut the heads any more than required to get a good seal. If you cut a couple thousandths off and still end up at 75cc, that's a nice 9.5:1. You can easy make close to 400 HP at that CR and still run pump fuel. The pistons being on the deck helps swirl, so after that it's really up to the cam. PS - I think the 2cc listed for the valve relief is a little low, unless that's the mfg published number. I'm thinking more in the 3~5cc range.

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PostPosted: Tue Mar 16, 2021 11:30 pm 
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Thank you, that puts me at ease. The pistons indeed have only one relief and are spec'd as +2cc.
as an example- the previously mentioned "truck performance cam dynamic compression ratio calculation.
I did my initial calculations

This "truck performance" cam

Part Number: 0314 Grind Number: 270-90H Intake Duration (gross): 270 Exhaust Duration (gross): 290 Intake Duration (.050”): 214 Exhaust Duration (.050”): 224 Intake Valve Lift*: .510" Exhaust Valve Lift*: .530" Lobe Separation: 112 Intake Valve Lash: .000" Exhaust Valve Lash: .000" RPM Range: 2200-6400 *Based on 1.73 Rocker Arm Ratio

has IVC @65 so with the stock 76cc combustion chambers the dynamic compression ration comes up to 6.6:1

If I deck the heads .050 to 66cc the static goes up to 10:4:1 and the dynamic for that cam is 7.4:1.

The second cam is more radical with 70 IVC so the dynamic compression ratio is even lower. Am I on the right track here?
I should probably at this point leave the heads alone since they are decked for flatness and seal, get new valves and work with Brent and Falcon on the cam choice. I'm ready!!!


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PostPosted: Wed Mar 17, 2021 4:36 am 
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When you’re ready for a cam, let me know. I can work with everything you have.

Any cam that you see with a part number is a universal cam and is meant to be a one size fits all. Unfortunately it doesn’t work that way.

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PostPosted: Wed Mar 17, 2021 11:44 pm 
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Thank you. Would you match the valve spring rates and the compressed height to the cam or "standard" springs will suffice?


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