Stockish 340 upgrades, cam needed

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Agreed, you have to be accurate to within a half cc per one tenth (0.1) of a point of compression by the “hand grenades and horseshoes on line calculator”. The criticality of how close the compression is between the 9.8:1 and 10.5:1 is going to be dependent on intake valve closing, altitude, and fuel octane rating.
So far I’ve refrained from mentioning the dreaded alternative fuel route. Some TRW domes milled for a final compression of 11-11.5:1 with some e85 on a “close enough tune” with the fuel available during the time of the year it’s going to going to be driven the most (bring it varies from 70-85 % from winter to summer blends!) would be the best route to take the atomic cylinder heads to some resemblance of true street ability. Big DCR with the somewhat short duration cam and it could probably be idled out from a stop.
 
Km your cr is in the ballpark to run any of those Lunati cams mentioned
You first need to know the rev range she want in driving that stick with the 3:23 gears
If you go with the bigger cam you might up the cr a little
with the short one you should be ok in any case - you are fine tuning trying to keep as much pressure as possible
when giving the final info put it all in one post with the dome , ht above deck etc etc
 
Wyrmrider said:
Km your cr is in the ballpark to run any of those Lunati cams mentioned
You first need to know the rev range she want in driving that stick with the 3:23 gears
If you go with the bigger cam you might up the cr a little
with the short one you should be ok in any case - you are fine tuning trying to keep as much pressure as possible
when giving the final info put it all in one post with the dome , ht above deck etc etc
Click to expand...

That's why i put all the math in post 69
All he has to do is add his true discovered cc's and we have a compression ratio.
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Cudafever said:
You can us a online calculator, but there are thing that you need to cc before you can get a accurate compression reading.
For example my 4.10 bore piston stuck up .017" above the block(so it take away from the top dead center reading because it removes head space) How Ever! because of the valve reliefs in the head was larger than the .017' pop up of the piston, it became a number that was add to the head volume. bore and stroke are set! the head volume make the compression ratio)
hope that wasn't confusing.

So here we go
head cc 70
head gasket cc 8
10.5: compression piston cc 7.35(in the hole even though it a pop up piston because of valve relief in piston)
above head total
85.35cc

Bore X Bore X Stroke X .7854 =43.70 X 16.387(convert to CC)=716.12 CC
Below head or bdc volume
716.12

716.12+85.35=801.47 cc Divided by 85.35=9.3903925
Aka my 10.5:1 piston equiled a actual compression ratio of 9.40:1
Compression Ratio = 9.40:1.

So let us you head cc on my .060" over bored 340 motor
65 head
8 head gasket
piston 7.35
total 80.35
80.35+716.12=796.47 divided by 80.35=9.9125078
New compression = 9.91:1

I used the felpro .040" thick head gasket , So your compression will be slightly lower........However, you decked and leveled your block, so it might be real close.
Edit: for math! Bore X Bore X Stroke X .7854= 43.70
Click to expand...

NOTE CC below deck is added to head volume and CC above deck are subtracted. Example is a domed piston would have X amount of cc subtracted from the head volume. and your .015 pop up would also if there was no Valve Reliefs in the piston.
Even though The piston sets .015 above the deck there is more cc in the valve relieve than the piston pop up. 7.xx cc for the piston is added to the head volume. hope that make sence.
 
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Here is the valve relief machined. Kim

E47B986B-13CB-4A9A-B170-DC591252596B.jpeg


9922E18C-1D99-46C4-9AB6-E92FB676406F.jpeg
 
I think probably just radius the sharp corner a little for detonation resistance and it will clear.
 
Howards grinds the cam mentioned in post 146
IDK who grinds the Hughes Whiplash
I'd e-mail howard and ask for the .006 timing for the 711651-10 (110LCA) and the 711451-08 (108 lca)


you can compare the 451 against the .842 lifter design 411021 on page 142 of the catalog

the 451 is definitely a MOPARgrind it's up 7 degrees at .050 and .056 lift

which head cc is the right one?
 
Wyrmrider said:
Howards grinds the cam mentioned in post 146
IDK who grinds the Hughes Whiplash
I'd e-mail howard and ask for the .006 timing for the 711651-10 (110LCA) and the 711451-08 (108 lca)


you can compare the 451 against the .842 lifter design 411021 on page 142 of the catalog

the 451 is definitely a MOPARgrind it's up 7 degrees at .050 and .056 lift

which head cc is the right one?
Click to expand...
65.1-.2 CCs at present. Finding cam specs to see what DCR we could reach.
 
1 head is 65.1. Other 65.2. I’m pretty sure we’re gonna take .020-.030 off the heads to help out the low end as I’m sure the big ports will make it lazy. Kim
 
I've done some more calc's and am coming up right in the 9.9-10.1 compression zone with a .030 cut on the heads when including the overall piston head volume. The cam timing calculations show that the with the ICL of 106 degrees the intake closing is going to be very close to 62.5 degrees ABDC, The cranking compression at 2260 should be between 151-154 PSI and DCR should fall in between 7.9:1-8.1:1. This will help crutch the low velocity charge fill issue at and off of idle, but will be a little much with 91 octane under hard acceleration. But, with a probable static timing requirement of 32-34 degrees with the tight chambers and .038 quench, a slow mechanical advance curve should be able to control spark knock under load.
 
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@AJ/FormS, Care to double check me thus far? Factoring in for the 91 octane makes me a little nervous here with the potential need to maximize compression for the slow low speed port velocity.
 
Thanks for the update! And that really puts it into perspective, I’m surprised that they’re only 20ccs extra! You weren’t kidding when you mentioned the low rpm lag in port velocity. Those as cast heads, 9.8:1, and the .506/[email protected] would easily meet goal requirements and then some. If these are the actual heads going on it, I’m not nearly as concerned about exceeding dynamic compression now! What are the port window dimensions there? I’m wanting to calculate at what RPM that much port window actually starts to work at on a 346 inch small block. The .506 lift, 1.6 rockers, and the .903 cam are going to help, it’s going to need the valves opens as quickly as possible just to get that huge column of mixture moving. And are those 2.02/1.63 valves? I’d be surprised if it’s any lower than 3500 rpm... One advantage of the LD340 ( especially if the ports haven’t been touched, hopefully it hasn’t been opened up any) is the reversion dam back into the manifold by the port mismatch and the manifold exit velocity at the flange. Just keeping the mixture in suspension looks like it’s going to be a challenge. I’ve read about a few 10.5:1-11:1 static 91 octane builds with careful tuning, and this is close. 10:1 looks pretty good now more because it will probably take more timing curve than I originally anticipated off of idle. All I can think of when I look at those heads is how well they would work if you could fill the port from the floor 1/3 of the way to the roof. and filling the bottom of the manifold to match.
 
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711451-08. Four degrees advance ground in cam. The intake closing is coming in at 59-1/2 degrees, so no more than 9.8:1 with the small port heads on 91 octane, and could go as low as 9.5:1 without significant torque loss to get the car moving.
9.8:1 yields a DCR of 8.1:1 and 155 PSI cranking compression, right at the practical limit of 91 octane. Going together with 65 cc heads and close to 9 cc of piston head volume including the ring gap and the .052 thick 12.5 cc neighborhood gaskets gives right at 9.5:1. This gives a comfortable DCR of 7.8:1 and about 147 PSI cranking compression. That will allow a good performance mechanical advance rate and allow for the maximum static timing.
 
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If he still insists on the CNC heads, give the port window at the intake face dimensions so I can get some idea of how much to crutch the compression to make it play nicely at low rpm. But, he needs to know if it's made to work as intended at low rpm, it's not going to work well at high rpm unless he gets some 98 octane fuel or better in the tank.
 
good luck kim
conflicting hardware
choices have to be made
go conservative
pretend it has stock flowing closed chamber heads
he can't use the alure of those nice heads
 
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