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Head and carb question.
https://slantsix.org/forum/viewtopic.php?t=33322		 Page 1 of 1
Author:  Mike_64_Valiant [ Wed Jan 14, 2009 8:49 pm ]
Post subject:  Head and carb question.
Ok I have the parts sitting for a head build. I really want to use my holley 390 carb. I am planing to shave the head, gasket match, minor port and polish and then the oversized valves. The bottom end only has 40K miles and the stock cam. But new timing set. If I built the head can I get away with using my 4bbl with the stock bottom end and cam? The other question how much is a safe amount to shave with out having to pull my current head and measuring the piston/block.
Author:  THOR [ Wed Jan 14, 2009 9:14 pm ]
Post subject: 
The 390 would be a bit much carb strictly numbers speaking. If the 390 has vacuum secondaries then you can set them specifically to open at a certain vacuum, in which case you would be running mostly on the primaries, which would yield some pretty good results.

225 cu. in * max RPM / 3456 (magic number) * VE (volumetric efficiency)

So assume you want to spin 5500 RPM max, and with the head work you get a VE of 80% (65-75% for a stock engine in most cases).

That gets you 225 * 5500 / 3456 * .8 = 286.45 intake cfm

Strictly numbers speaking "Theoretically" you would need say a 300 cfm carb to be good to go. However, as many others can attest, the slant responds well to more carb. Get that carb tuned just right, and I'd say you would be fine!

Safe shave is typically achieved at .1" off the head, although there have been alot of people who have shaved .120"+ and been fine.

:mrgreen:

~THOR~
Author:  Joshie225 [ Wed Jan 14, 2009 9:18 pm ]
Post subject: 
My Holley 390 works fine with stock short block, ported and milled big valve head, and 2 1/4" exhaust. Ran 16.86 at Woodburn. Previous best without a big tail wind was 19.42.
Author:  THOR [ Wed Jan 14, 2009 9:20 pm ]
Post subject: 
Quote:
My Holley 390 works fine with stock short block, ported and milled big valve head, and 2 1/4" exhaust. Ran 16.86 at Woodburn. Previous best without a big tail wind was 19.42.
Those were some good runs you got with that old 3 on the tree!

~THOR~
Author:  Joshie225 [ Wed Jan 14, 2009 10:17 pm ]
Post subject: 
We're getting off track here, but... Imagine the car with more cam, more compression and a 4-speed. :D I'm thinking the Oregon Cam Grinding #346 which is 234/228, but only 262/252 advertised, 106° lobe centers and ground 4° advanced. It's either that or get off the fence and go turbo. I want the car in the mid to low 14s, but faster is OK.
Author:  THOR [ Thu Jan 15, 2009 12:07 am ]
Post subject: 
Getting back on track then *salute*.. go ahead with the 390. I think you will find it more than suitable once you have it tuned. Your car should get a move on pretty good with those modifications.

What size/type of exhaust will you be running. A single 2.25" is great, or have you gone with headers/Dutras? Doing all that nice stuff without upgrading the exhaust is going to make the car a bit of a dog compared to what it could be if it could exhale better! :shock:

~THOR~
Author:  Mike_64_Valiant [ Thu Jan 15, 2009 5:31 am ]
Post subject: 
As for now if I did this I would still have to use the stock exhaust manifold because I still have the 3speed on the column and I can find any thing that will snake its way around all the linkage and still stay between the fenders of the early Abody. I will upgrade the exhaust piping to 2.25 as soon as its moving on its own power and then retune it all.
Author:  THOR [ Thu Jan 15, 2009 8:49 am ]
Post subject: 
Well, it sounds like you've got it made... go for it!

~THOR~
Author:  Mike_64_Valiant [ Thu Jan 15, 2009 7:26 pm ]
Post subject: 
Ok so I took the head to the machine shop today. I asked to get the head milled .100 and then pocket port, gasket match, and then prep and install the oversized valaves. I was shocked when I heared the price but after figuring how many hours it would take and then multiply it by shop time and it all adds up. He quoted me $1000. I am trying to get everything figured out so I need pictures of some of your linkage setups on the Holley 390cfms. I also need to know if I do have that head cut .100 what will the approxament compression ratio be and would that make it too much for boost like 2 years down the road?
Author:  THOR [ Thu Jan 15, 2009 11:32 pm ]
Post subject: 
It's going to depend on combustion chamber size. Have the machine shop measure the combustion chamber in cc's. Then take a steel ruler, depth gauge, dial indicator, or other straight edge measuring device, and measure how far down the hole the pistons are at TDC. Then, read the specification for what the total thickness of the head gasket should be when it is compressed.

When you have all that, we can figure out an approximate static comp ratio. You will most likely end up in the 8.9-9.1 compression ratio range, depending on what the chamber size was on the head before machining.

You can figure a good estimate of 9.0:1

Another way to tell, is get a barometer, and note atmospheric pressure. Then grab a compression tester once the head is reinstalled, and do a compression check on all the cylinders. Divide PSI for each cylinder displayed on the gauge by atmospheric pressure to get the compression ratio for each individual cylinder at that altitude. Normally, you would divide by 14.7 since that is atmospheric pressure at sea level, and if you don't have a barometer, use the 14.7 as a divider to get you ballparked.

I don't know much about turbo stuff, but from what I do know, 9.0:1 would probably be a bit high to get much boost (15-20 PSI) without blowing the bottom end out of the car. Stock ratio of 8.4:1 (with wear that number drops slightly) is usually good for decent boost (20 PSI or less). I am sure that there are others who have specifics, and who have run fairly high amounts of boost with a 9.0:1 ratio.

Gotta keep in mind though, if you drop the comp ratio later on to make up for turbo, you want to leave high enough a ratio to get the car off the line, so the turbo can kick in once you are turning some R's.

Like I said, not all too sure on the turbo stuff, and if I am wrong, I know someone will let us know the right info! :mrgreen:

~THOR~
Author:  rock [ Fri Jan 16, 2009 5:11 am ]
Post subject:  Mike, send me your regular email and I will send pics of lin
Mike,

Send me your regular email address to rock at intrex dot net and I will send pics of the Holley linkage I made up.
rock
'64d100
Author:  nqkjw [ Sun Jan 18, 2009 4:53 am ]
Post subject: 
This is what i made up for my 600vac - should be the same for your 390

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