Ok you guru's it's time to put on your thinking caps!

My current build is a flat top 355, ported stock heads (64cc), comp cams 212/218 (112) with 1.6 rockers, HSR, TES headers, with a 5 speed and 3.27 gear. Aiming for 350-375 bhp.

I'm at the point of spec'ing head gaskets and chamber cc's, and I need help with the DCR calculations based on the intake valve closing. I have a pretty good handle on calculating the SCR and an understanding of what DCR is and why it's important. I'm just not sure how to fit the valve closing event into the equation. For example- If I.V. closes at "x" then the piston is at "Y"... which gives the amount of dynamic "swept" volume... then calculate DCR.

Also, I understand that for a iron head 355 max SCR should be around 10.5, DCR should be 8.5, and quench at 0.040 when running 93 octane (with close attention to timing, fuel ratio engine temp etc.) Sound about right? I'm wanting to push this to the max and any recommendations would be appreciated.

 

heres some differant calculators & info

given the info you posted ,your scr is aproximately 9.8:1 with that cam your DCR is aproximately 8.9:1


http://www.crower.com/misc/valve_timing_chart.html

http://cochise.uia.net/pkelley2/DynamicCR.html

http://www.diamondracing.net/cocalc.htm



http://www.kb-silvolite.com/calc.php?action=comp2

http://www.wallaceracing.com/dynamic-cr.php

http://www.smokemup.com/auto_math/compression_ratio.php

http://not2fast.wryday.com/turbo/com...pressure.shtml
average the results



since your trying to maximize the combo ID suggest you talk to ERSON CAMS and get a cam like this, (hydrolic roller) and get a 3.73-3.90:1 rear gear ratio

E119847, Duration: 226/234, LSA: 112, Lift: 584/584

read thru this

http://www.idavette.net/hib/camcon.htm

yes you can reach the goal with a flat tappet solid or flat tappet hydrolic lifter cam, at a lower cost, but youll be far happier with the hydrolic roller and the stiffer rear gear ratio, talk to the guys at ERSON,CRANE,CROWER and get thier imput

 

Wow thanks for the info. I've breafly read through some of it and I'm sure it will be helpful. It looks perfect.

You stated that you estimate of my DCR is 8.9 with my cam and combo. Do you think this is too high?

You suggested a longer duration cam too. Is this only to reduce my DCR or do you feel I need that much cam to reach my power goals?

 

Question - define ported stock heads, 64cc?

 

"You suggested a longer duration cam too. Is this only to reduce my DCR or do you feel I need that much cam to reach my power goals?"


I also suggested swaping to a 3.73-3.90:1 rear gear and talking with three differant cam companies, but yes, a slightly longer durration and slightly larger cam will both increase your chances of exceeding the goal and decrease cylinder pressure to reduce detonation tendencys, the cam suggest and ones of similar specs have worked in similar combos in the past but its up to YOU to ask the questions and check and verify the clearances and valve train geometry. your stock springs and clearances will NOT work, you will NEED to have the heads reworked, clearanced and larger springs installed, but the benefit is much improved power potential
just don,t get dumb and cheap and expect to throw a cam in the engine with no other changes ,(yeah WE ALL FOUND OUT THE HARD WAY THAT DOESN,T WORK)and have anything but problems. too use a larger cam the combo and clearances and heads being machined to the correct specs MUST match and the drive train must match the raised and extended rpm range and greater air flow thats producing the higher power

 

This started out as an intake manifold swap! I purchased a Holley Stealth Ram and, well things got kinda out of hand and I'm pulling the engine to freshen things up, port and upgrade the heads and maximumize the variables I can.

Yes, unfortunatly budget restrictions do affect the decision on some componenet selection. However the HSR, modest port size heads, cam selection (212/218-.520/.528 w/1.6) was based on the 3.27 gear and the daily driver use. I've been running 9.7 SCR with this cam and have not had any problems that I'm aware of. My horsepower goal may be a bit optimistic. Regardless, I am going to reuse the cam and valvetrain and flat top bottom end. This is why all the little "details" are so important. I can still tweek the variables such as final combustion cc, gasket thickness, cam degreeing and the like to achieve the most ideal results.

In regard to the heads. They are the stock 64 cc iron heads (083's I believe) and they are being ported according to guidelines set out by David Vizard in his book "Max performance Chevy small block" and another members 3 part article on these heads. I have ported 4 or 5 sets in the past with sastisfactory results. I am also installing 1.94/1.5 SS under cut valves, screw in studs and reusing my Comp Cams springs/retainers for the stated cam.

Currently I am planning the head port and valve work, adjusting the head gasket thickness to achieve 0.040" quench, possibly milling the heads and/or opening up the chambers to achieve the highest useable compression (10.5:1?), adding 1.6 rockers, degreeing the cam and installing the HSR.

It seems from what I've read and experianced;

1. DCR is more important than SCR and 8.2-8.4 should be my target for 93 octane.
2. 0.040" quench will give me the best performance and minimize detonation.
3. Polishing the chambers will help deter detonation.
4. Keeping the engine cool (170'f) is very important.
5. Doing all this stuff is a blast!

Do you agree?

 

Yes yes and yes, I agree. The 083's will have 1.94/1.5 valves stock, i'd upgrade (at least the exhaust side).
Are you looking at sitting bulls info on this? I'd recommend reading the guys article where he got 270cfm out of the 083's (unless that's the one you're talking about).

For your setup, you're somewhat "underheaded". So i'd recommend bigger on the cam, it won't feel that large. 212/218 is WEE. I'd definitely recommend an upgrade.