Well I'm gearing up to pick out pistons/cam for my 383. Im using the downloadable DCR calculator that has been posted on here, and LS1 tech. I was shooting for around 8.5:1 and got it with 8.6:1 at sea level, and more like 8.2-8.3:1 during the racing season. 11:1 SCR and a XE284 cam (ivc of 68*) and a 5.7 rod. Im trying to mimic Joe Sherman's 539hp pump gas build, but push it a bit farther. If his cam really was very similar to a 282HR then it has a IVC of 73, so even more pump gas friendly, but with another point of compression. (he ran 10:1scr)

I was taking a look at various combos online, and saw the aluminum headed SBCs were pushing it to 11:1 scr, but the dynamic worked out to be 9.2-9.6:1 and run pump gas (possibly 93)

Im still taking a look at the Iron headed combos, but something I did find what, how often does someone bolt on 64cc heads onto a 350, and stick with the stock cam, or something similar for a while? Well they work out to near the 8.4-8.7 mark depending on how mild of a cam (212-218 range) and they dont complain about pinging on 91.

So what do you guys think? I see lots of threads about DCRs but no estimates on what DSR will run on what octane range.

 

You haven't found the magic number because it doesn't exist. It will be different for every setup. Rod length, valve overlap, deck heights, quench area and what type of fuel you will run will all change what you can get away with. With iron heads I would keep it below 10.2:1 even on the more forgiving setups for pump gas. It's all about cylinder pressure, not CR. If you're building a street motor and not looking for the last .1 at the track keep it safe. No need to push it. It'll live longer that way.

 

I get what your saying, but I guess something I didn't mention is how everyone looks at the static compression vs the working (DCR). I understand that you can set up a engine with 10.2:1 static, and get there with a true flat top, but a gasket thats over .050 thick, with a 0 deck hight, killing your quench. I was setting mine up with a .035-.038, and a 5.7 rod

Yes I want the motor to run safely on just regular jane Pump 91. I will have a MSD retard dial in the car to turn it back if I do get a bad tank, but of course I don't want to have to do that as a bad aid fix all the time.

 

If you are referring to Joe Sherman's motor in the Engine Masters Series remember that motor only had to run for maybe 10 seconds. Those motors are far from steetable and are run on the ragged edge.

Not sure what type of racing you are doing but I think you are getting into the danger zone with DCR's you are mentioning. You had better have a real good cooling system.

 

some of the major factors in your engines potential power, is the volumetric efficiency (how efficiently you fill and empty the cylinders) and the octane of the fuel used, compression ratio and detonation limits,
With detonation, prevention the main factors are
Ignition timing
Quench
FUEL OCTANE
DCR
and cylinder heat level
you�ll be fairly safe if you stay under
8.5:1 dcr at 170f degrees
8.25 dcr at 180f degrees
7.8:1 dcr at 210f degrees
and keep the quench in the .036-.043 range
heres some differant calculators
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

the numbers are for 92 octane premium gas run at a 14.7:1 , best POWERS usually closer to 12.7:1 A/F ratio, at that a/f ratio you can run SLIGHTLY more compression , but keep the chart in mind

BTW heres a VERY SIMILAR GRAPH

 

Thanks grumpyvet, Ill keep all of that information in mind. As far as the cooling system goes, I had no troubles at all with the 31x19 griffin radiator, air dam in place, and the stock single V6 fan in 110* heat, and the car stayed right around 160-170 (mech gauge, checked with two otheres) when I had the 160 thermostat in there. The fan only had to be on when I was going slower then 20mph for extended amounts of time. Guess I will try to error on the safe side, with a DCR in the low 8s then.

 

Ya really really really got to taqke the DCR charts and all with a big grain of salt. take what you read in Hot Rod and car craft with an even bigger grain of salt. maybe two grains.
They tend to embelish and leave out details.

i run the XE284H in my 400. It makes serious power and torque. The compression ratio is 9.8:1. I normally use Sunoco 94 which can tolerate a bit more compression (around 10.5+/-). My car also seems to run fine on 92(Esso)
Trouble with trying to max out the compression is that as soon as you have just a little too much, its a lot too much.
Forget about what people use with aluminum heads. Its not relevent to cast heads or how much power yu'll make with cast heads.
An engine that pings will make less power and not last long.
It really messes with the rings.
If you'll be using 91 octane gas I would not build for more than 10:1. My best advice is to keep it a little under 10:1 like I did. That last bit of cr is just not worth it.
Joe Sherman builds some amazing stuff. has for years. But his motors that he sells to the public do not run as high a cr as the ones he runs for a few seconds on Engine Master dyno contests. He fully realizes that real world road conditions are very different than on the dyno. A customer will not be happy if the motor he buys will not operate in the real world on the available pump gas. Fortunatly the difference in net power is very small. The differnce in reliability is big. If you want , why not consult Joe directly to get his best advice. Not being Joe Sherman but being old enough (built a few in my years) to remember ariticles about Joe and his cars from way way back I can tell ya, go easy on cr reguardless of what DCR theory suggests. there are lots of other factor to consider and some real world practical limits.
Consider experimenting with the installed intake C/L of your cam. 106 is stock but the motor may well like 103-104 or something like that. Nothing wrong with moving it around a bit. Consider ordering a custom grind using the same lobes but tighter LSA. A 383 may well like a 105 to108LSA more than 110 (especially if you run open headers and collector extensions). Probabily much more power to be had there then trying to max out the last bit of compression ratio. Comp cams or maybe even Joe Sherman can help ya with that.
I suggest trying a 107LSA, if you're willing and want some more power/torque. Further, try 1.6 rockers on the intake side. (Split ratio) Shouldn't have to pay much or any more for this custom cam. The Last XE284H I bought had to be made by Comp and shipped out as there was no local stock. Same price. Many good shops like the one I deal with are well hooked up with the factory (Comp Cams) and "special orders don't upset them".
Ya probabily won;t make quite as much power as a hyd roller using a flat tappet cam but optimizing the LSA and trying 1.6 rockers will help. I'll bet $$$ joe uses a custom grind cam with LSA very simular to what I suggest.
You might also consider running a solid cam. they tend to make more power and torque and cost little or no more than a hyd. They sure do rev higher. Food for thought.
One thing that the appliation of popular DCR theory does not address is establishing the exact "running duration" of a camshaft. the exact point that the valve in the running motor actually open a close. This exact running timng point is not the same as the "Advertized Duration" Unless you know the actual intake valve closing point in the running engine the dynamic compression cannot be calculated or presdicted accurately enough to say what is the max you can run with this cam or that cam.
Further dynamic compression theory does not predict the actual in cylinder pressure at peak torque (max volumetric effiency) Overlap, exhaust dilution, etc etc effect the power and octane limit some. how much is hard to perdict.
Thats why we have dynos.
There are just way too many other factors.
I'm very curious as to how the Protopline Vortec heads work for ya. Did ya flow test them?

 

Nope didnt flow test them, its actually kind of hard to find much information on them anymore becuase ProTopline got bought out, but they are supose to out flow the Vortecs from GM with a bowl clean up, and stock valves. When I pull the heads off to get rebuilt, I might see if I can have them flowed.

Thanks for the input guys.

 

RHS now sells the former Protopline stuff including two versions of ProAction Vortecs. have very impressive advertized flow numbers.
Just wondering how accurate the production heads actually are. I realize they test them on a large 4.125' bore.
if they are half as good as they advertized they are a rockin head. http://www.racingheadservice.com/

please let me know what yours flow. russ_q@homail.com

 

FWIW, i'm running 10:1 static, 8.5:1 DCR (last I checked...). Engine never gets over 180*F, and i'm at 4000' elevation. No detonation on Mohawk 92 octane, with fairly aggressive timing.