#7416, BBC forged Crank - Hot Rod Forum : Hotrodders Bulletin Board
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Old 03-24-2008, 10:39 AM
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#7416, BBC forged Crank

Hi
I am trying to get more CR with my 454 with changing pistons.
I have .030" bore, milled 063 close chamber heads that were 101cc
now 95cc. My deck height is .040" which isn't too good. It has a cast
crank in it now. I have a chance to get a 7416 steel crank. My question
is, "is there differences/tollerences in 454 cranks steel or forged even though they are
both 4.00" stroke that would lesson the deck height from .040" to .010" or
.005" or 0 deck height"? or even if I change out the cast for the forged with
new bearings, ARP rod bolts etc... will I still end up with .040" deck because
the pistons are .030" cheap rebuilder ones? I doesn't seem like it, but going
from .040" to .032" or less changes my CR a lot and would help in getting up
around 9.5:1 or more.
Thank you

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Old 03-24-2008, 11:25 AM
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I posted several comments on your previous questions regarding some possibilities as to why you have such extreme deck clearance. You mentioned originally that you had a reman'd engine. Its been my experience having to go back thru engines that were of this type of origin, that there machining practices are not of the highest standards, as compared to a real professional engine shop. I'll mention several scenarios and let you decide on how to move forward with your situation. I'll answer your most recent question about the steel crank. No, the tolerances are the same for manufacturing as far as stroke goes 4" on the cast,and 4" on the steel. However , I will say that one possibility for your excessive deck height could be partially the reman'd crank. The crankgrinder at the reman shop, could have gotten the stroke off when he/she or it, reground the crank. I think I recall you saying that it was undersized .020 or .030 already(I cant positively recall). But that is one strong possibility for the deck height. The next possibility is the connecting rods. When you recon a normal rod that hasn't had a bearing turned or anything abnormal has happened to it. You take about .003-.004 of material off the mating surafce of the rod cap to close up the housing bore, retorque, and hone the housing bore back to its standard dimensions. This unfortunately, shortens the rod by some amount, usually only a few thousandths. But,not knowing their procedure for this, one can only speculate as to their practice. I will assume for conversation sake that they are really into high volume production, and they bore the housing bores in the rods, instead of honing them. The operator might have mistakenly set the center to center dimension on the machine too short, or could have been "smoking his lunch"....we dont know. But i'll bet if you check the crank stroke and rod lengths, you'll find your answer, and know how you should proceed! The only other piece to check is the piston, are there any machining marks on the top to indicate it has been modified by flycutting or belt sanding ? If a part # or oversize is visible on the top, then I would say it hasn't been tampered with and probably not part of the problem.Keep us informed on what you find out.....
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Old 03-24-2008, 11:37 AM
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CR vs deck height

Thanks CNC-Dude for the info.

Yes I read your previous message. the engine is
in short block condition. I only have the heads off
to switch them out with my rebuilt 063's.
Yes there is a stamped .030" on top of each piston.
My crank queston was just that...a question. I do not
want to pull her apart. Down the raod a peice when I have
the $$ I am going to go through it all out, but for now I just
want to throw the 063 heads on it. They have to be better
than the stock 122cc emission heads. It is a pretty stout engine
4 bolt, has about 45-50K on it, everything looks good. When I switched out the oil pan so it would fit in my 65 Malibu I popped one a the caps off
to look at the mains...looks ok I guess for 50K and oil change neglect
from the previous owner.
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Old 03-24-2008, 12:14 PM
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Quote:
Originally Posted by Fastest65
Thanks CNC-Dude for the info.

Yes I read your previous message. the engine is
in short block condition. I only have the heads off
to switch them out with my rebuilt 063's.
Yes there is a stamped .030" on top of each piston.
My crank queston was just that...a question. I do not
want to pull her apart. Down the raod a peice when I have
the $$ I am going to go through it all out, but for now I just
want to throw the 063 heads on it. They have to be better
than the stock 122cc emission heads. It is a pretty stout engine
4 bolt, has about 45-50K on it, everything looks good. When I switched out the oil pan so it would fit in my 65 Malibu I popped one a the caps off
to look at the mains...looks ok I guess for 50K and oil change neglect
from the previous owner.
If you were pleased with the open chamber heads, then I wouldn't agonize too much over the deck issue,"it is what it is", put the other heads on and keep having fun. This will just give you more to look forward to at a latter time to change, and make even more improvements then for a better combo....
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Old 03-24-2008, 12:52 PM
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If you keep everything organized and are very careful when you take it apart, you could just have the decks milled then put it back together, I mean if you are thinking about changing the crank anyways you might as well as long as you are in there.

Of course if you change the rods and pistons down the road then you might have pistons sticking out of the bores, which won't work with your closed chamber heads.
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Old 03-24-2008, 01:00 PM
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CR increase, Deck Height

Double V23 thanks.

Yeah I have beat this horse dead already. Just trying to put
something together that will bump up the performance some.
I cannot even run a nice cam with the low CR. With my calcs
I am coming up with 9.14 to 9.28:1 CR. But with the close chamber
heads I may have VP clearance issues if I go to big on cam. I just wanted
to snap it up a bit with the smaller cc heads and a lopy cam.
Yes...when I get the $$ to rebuild I have a set of 049's waiting for it. so
a small dome won't be a issues.
Hopefully for now the close chmaber heads will surprise me and snap it
up a bit for now.
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Old 03-24-2008, 02:47 PM
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I may have mentioned this already but I am only running 9.5:1 compression on my 496. It has .660 lift and 284 dur @.050 (solid roller) I am running open chamber heads with flat tops with 1 valve relief. The pistons are .010 in the hole and I don't have any P/V clearance problems.

It is making 575 HP and 690 ft/lbs at 5500 rpm. So don't let anybody tell you you can't make decent power with low compression.

The thing drives and idles beautifully
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Old 03-24-2008, 03:35 PM
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Deck Height, CR, Cam

Double V23...thanks again for the knowledge.
you have .010" in the hole I have .040" in the
hole that makes a huge difference in CR. Without
running a solid, "what hyd cam would you suggest"?
I kind of want to go with the Isky #396281, 280/280,
232/232 @ .050", 108 Lobe sep. I want rough idle, BUT
also want it to go as good as she sounds. It is in a fairly
lite vehicle 65 Malibu. Want to go 4 spd, but have PG and also
have T400. I don't care about buying another stall say 2500.
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Old 03-24-2008, 09:24 PM
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I know but you said that your compression ratio will be around 9.2:1. That is almost the CR I have. So if you do that and use the hydraulic cam you listed you should be alright. The quench won't be the best at .060 or so. But that just means you will have to run a little higher octane.

Here is the thing about Big Blocks...they aren't nearly as sensitive as small blocks. Those big cubes really smooth out a big duration, big lift cam.

Especially with a 4 speed you can make the car drive just the way the cam likes. That is the nice thing about a manual...cam calls for a higher stall? Just rev it a bit before you launch. Cam says you need bigger gears? just downshift. Between the BBC, the 4 speed, and the light car you will be quite happy.

If you want a good suggestion on camshafts call ultradyne/bullet cams and chat with one of their tech guys for about 15 minutes. They are super friendly and don't mind giving you every single spec on the cam. Even if you don't plan on buying one, but their support is excellant and you might just end up buying the cam they suggest.
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