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Discussion Starter #1
well I have been all over the web with all different cr calculators and I get anwsers from 10.5:1 to 11.5:1 so I thought I would come to you guys. I have been running the thing on nothing but 93oct, but for some reason I think Im running at alot higher compression then speed pro told me I am.
bore is 4.060
the heads are 461's not sure if there 64cc or 62cc
the piston is .025 in the hole
the gasket is a felpro .039
the piston dome is -5cc
the cam im useing now is .480 lift with a .230dur at .050
I just got a new cam .518in .536exh lift .244in .252exh dur @.050 LSA106
 

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hmmm, you kinda left out the stroke, is this a 350 or a 383?

350 / 64cc = 9.9:1
350 / 76cc = 8.8:1
388 / 64cc = 10.6:1
388 / 76cc = 9.4:1

to figure DCR, I need advertised duration, intake centerline, and lobe displacement angle (106?)
 

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Discussion Starter #3
sorry stroke 3.75
adv dur.280in .288exh
intake 102*ATDC
exhaust 110*BTDC
 

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ok, she's a 388 then.

At 64cc, 10.6:1 static comp, 8.438 DCR

At 76cc, 9.39:1 static, 7.4:1 DCR

Question is, which chamber do you have, 64 or 76? As you can see, it's a huge difference. Like Paul said, that really isn't "the cam" for a 9.4:1 motor... it's gonna be a lil soggy.

8.4:1 dcr is pushing the limit, but should be OK with a careful tune.

Question: how could you be "certain" on your deck ht but not know which size chamber you have? It's real obvious to look at, and to know your deck ht, you musta measured it with the heads off, and therefore you musta seen em...

If I run the #'s at .030 quench (either decked or thinner gasket or combination of both) I can get the static to 10:1 with 76cc, and the dcr to 8.0:1, very good pump gas numbers.
 

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Discussion Starter #7
I built the motor from the bottom end up I know for a fact there eather 64cc or 62cc I have heard from different people what these old 461's double humps came in, just not a 100% sure weather there 64 or 62. The advertised cr in the catalog for these pistons were 10.5:1, and with all this talk about how piston companys are sometimes wrong in their compression ratio charts I just wanted to make sure I wasnt pushing my luck.
 

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ok, sorry... I saw 64 - 76 rather than what was actually there (64 - 62).
You're up there for pump gas, but it should be a sweet combo. Tune it careful, make sure you use the right heat range plugs (check em after it's run a bit) and you should be ok.
 

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Discussion Starter #9 (Edited)
thanks jim for your help, that is one reason im going to try and run the largest cam I can without the worry of piston to valve clearance to try to relieve some cylinder pressure to keep good for pump gas. im kind of leery about bumping the timing up any more then 30* total because I don’t want a detonation problem(and because I don’t trust a 5$ mr gasket timing pointer)
is there anyway to check the accuracy of these pointers, also can you suggest a plug for me I have been running delco r44's?
 

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Wow. Thats almost my exact combo except i have 462's and 4.030 bore. Tell me how she runs i think im right around 10.7 to 1. This cam shouldnt have any lower than 10.5 with the right tuning you should be fine a guy i know had an almost identical step up same cam and everything in his truck ran 12.2-4 in his 4500 pound truck at the drag of course it was set up for it.

Let me know though when you fire yours up because im getting my car back next week then assembly starts to get her ready to run.
 

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Discussion Starter #11
radcannon the car has been runing for a few months now the only difference is that it has a small performer intake, small 650dp carb, and a small .480 lift cam. its soon going to see a 800cfm carb, victor jr intake, and the solid lifter cam with the specs listed above. its in a 83 camaro that will more then likely see more strip time then street. with the current small intake, cam, and carb, I cant help kicking the back end out every time I try to foot brake launch it at 3000rpm
im hoping for a mid 11sec pass in it with the new intake, cam, and carb.
 

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Checking your timing pointer is pretty easy. You'll need a psiton stop, they make ones that screw into the spark plug hole.

Rotate the engine with a wrench until it hits the stop. Put a line on the balancer that aligns with zero on the pointer.

Turn the engine the other way until it hits the stop, make another line.

The "real line" on the balancer should be exactly halfway between the 2 new ones. ( a fabric sewing tape measure works good, you could also cut a peice of string to the length from one new line to the real one, then use it to measure from the real line to the other new one, should be same.

I use a cheap summit degreed balancer and an adjustable pointer, set very carefully to exactly indicate TDC.

a 44 is always a good place to start with a small block. Do a high rpm run and shut it down, check a few plugs. You'll see a "heat line" on the side electrode, The heat line should be at the bend. If it's closer to the threads, use a colder plug.

Now i just need to remember if a 43 is colder or a 45 is?

Also get a good magnifying glass and check the center insulator for silver dots. If you see any, she is pinging.
 
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