Chad Landry got me to thinkin about my comp ratio on the rebuilt engine now that I'm going with the vortec heads.

I've tried to run the info through Pat Kellys DCR program but, I not sure of what to enter for some of the info such as "(dish/vavlerelief/Dome Volume positive cc") or the piston to deck clearance (we never measured it).

.030 350
Hyper Speedpro flattop Pistons with 4 valve releif
Comp 268H
268 adv. duration.
.454 lift.
110 lobe sep.
28 ADV intake closing angle


I plugged in .019 piston to deck clearance and 00 for the dish/valve releif and .039 gasket thickness and the specs from my I'm getting 10.77 DCR & .058 Quench and 3.335 as dynamic stroke. I'm pretty sure that is not correct.

Can anyone help without knowing the exact piston to deck number.
The block wasn't decked. Is there a "close" number I could plug?

Would somebody please double check for me.

Thanks

Dwayne

Try using 6cc for the valve pockets and click the flat top button. 6cc is pretty common. If the deck is uncut, use .025" for the deck (hopefully the pistons are not de-stroker pistons). 28º is not the intake closing. 60º is the right number if the cam is installed at 4º advance that is the ICL is at 106º.

The intake gasket should be .039" or .041" with a bore of 4.166" for a composite gasket. If you're using a shim, use .015" or .018", depending on the shim. The shim's bore is 4.100".

Give this a try and see what you get.

Thank you Pat!

OK, I re-ran it with your suggestions, now I'm getting 8.4955 calculated DCR w/.064 Quench. Thats with a .039 composite gasket. I'm guessing this isn't an optimal set-up.

With a .015 shim it gives me 9.029 DCR with .040 Quench.

Now, if this is correct I should probably go with the shim right?

Do those numbers look close?

Thanks

Originally posted by New68SS:
OK, I re-ran it with your suggestions, now I'm getting 8.4955 calculated DCR w/.064 Quench. Thats with a .039 composite gasket. I'm guessing this isn't an optimal set-up...sounds fine to me

You are probably going to have to make some changes to your setup or go to a bigger cam if you want to run this thing on pump gas. That is of course if your numbers are correct.

I don't see the chamber volume for your heads.

Troy.

somethings not right..your SCR should be around 9.66-1 and the DCR should be around 8.00-1. Ive run that same combo b4(with 64cc fuellies) thats with 5.7 rods and a quench of .064 and 8.49DCR and 10.2SCR with a .040 quench

OK, heres the numbers I used

Crank = 3.48
Rods = 5.7
ADV intake closing = 60
Dynamic Stroke = 2.812
Distance of piston from BDC = 0.6672

ADV intake and exhaust dur = 268
Lobe sep = 110
intake lobe Centerline - 106

Intake Seat timing = 28 BTCD & 60 ABDC
Exhaust " " = 68 BTCD & 20 ABDC
overlap = 48 total cam advance = 4

NUmber of Cylinder = 8
Bore dia. = 4.1256 (is that right for .030 over?)
Stroke 3.48 or 2.81279 Dynamic
Combustion Chamber = 63cc
Head gastket = .039
Head gassket bore = 4.166
Piston to deck = .025
Flat or dish piston
dish/valve relief = 6

Anybody see any obvious mistakes in the above numbers?

If not, it looks like the Vortecs are not going to be ideal with that cam.

What would you do? Put the 76cc smoggers back on? I hate to do that but I don't want build a dog

Thanks for all the help so far.

Dwayne

A .030 over 350's bore is 4.030". I get 9.77 for the SCR and 8.08 for DCR. Which is excellent. However the quench sucks.

Victor makes a .020" shim (4.1" bore) that would improve the quench (.045"). However to use it you would need to install the 268 cam with no advance (110 ICL). This makes the DCR 8.24. This might be a good way to go. If the crevice space above the top ring is considered and the cam is installed at 108º (2º advance) the DCR is 8.3 using the .020 head gasket. This would work, particlarly with Vortec heads since they are more detonation resistant. Setting the cam at 108 ICL would require using a 2º bushing and the -4 position on the timing set since the cam is ground with 4º advance in it.

Thanks again Pat,

What would the results be if I just ran it with the .064 Quench?

I'm using a non-adjustable timing set. If I were to change the timing set, can I just install it with the bushing and be good to go?

Thanks

To run with the .064" quench, you might have to take some timing out. But maybe not. The ZZ4 engine has a .076" quench and runs pretty well but it has aluminum heads.

You can use the standard timing set but you'll have to use a bushing. The bushing would need to be installed to reduce the advance by 2º. This would look like the timing set is retarded 2º but cam would be at +2º advance. Do you follow this? If you decide to stay with the .039 gasket, install the cam with the 4º advance (straight up on the timing set with no bushing).

So, If I leave the cam the way it is now, that would be considered straight up? And the problems I’m facing with the .064 quench is the likelihood of detonation not necessarily poor performance, unless the timing has to be retarded to prevent detonation and thus results in less than optimal performance?

I do follow what your saying about installing the bushing to reduce the advance, and thats probably not out of the question, and may be my best remedy.

Just for kicks I ran the program using the 76cc heads I'm removing and still get a .064 quench. So, using the 76cc heads are not really going to help in that department correct?

Sorry for all the questions. and thanks for your patience.


Dwayne

Quench is the distance from the top of the piston to the bottom of the matching flat spot on the head. Chamber size doesn't affect it. The advance of the cam is measured at the intake centerline. A 110 LSA cam installed at 106 is 4º advanced. All Comp street cams are made with this advance built into them so a standard timing set can be used and the cam will have their desired advance. You, as the engine builder, can change the amount of advance. Since the cam has 4º advance using the standard timing set (zero advance at the timing set), retarding the timing set 2º leave the cam with 2º of advance. Properly used, the term "straight up" means the cam has no advance regardless of what the timing set is set at. This is definitly a matter of some confusion.

If you stay with the .039 gasket, there is no need to change the cam timing. If you go with a thinner gasket to improve the quench distance, you'll need to re-time the cam to 2º advance.

The more advance the cam has, intake closing earlier, the higher the DCR will be. Taking some of the advance out lowers the DCR.

OK, say I do want to install the bushing and run the shim gasket.

Is it as simple as revoming the timing cover and pulling the gear set off and installing it. Or will I need to rotate the cam or crank. In other words will the dots still line up?

And, if I understand correctly, the engine should perform the same as with the .064 quench but with less liklyhood of pinging?

Dwayne

the tighter the quench the better it will run...not 30HP better but more effiecient<sp>

I've not used a bushing but it's not hard. The cam gear has to be drilled for the bushing (the bolt holes might need to be slightly enlarged, but maybe not for 2º). With the bushing in place the cam will be rotated a slight amount (2º). Just line up the dots and you're done. Only the cam gear has to come off. What the bushing does is relocate the dowel hole in the cam gear. The dots will line up the same as before. I recommend using blue (non-permanent) locktight on the cam bolts and be sure to install a lock plate.

Thanks for all your help fellows.

I think the bushing is the way I'm going to ga.

Thanks again.

Dwayne