Hello, I'm struggling to find out my dcr on my 383 stroker. The motor is a 383, 4.030 bore and a 3.75 stroke. Head gasket is .039 thick. Heads are 64cc and the pistons are .020 in hole. The static compression ratio is 10.6-1 My cam is a summit 1785 . Advertised duration is 272/272 and at .050 218/218. .450/.450 lift at .050 The LSA is a 106. 102 intake and 110 on exhaust. Can this be ran on pump gas? If so what can I do to make it happen? And what's the dcr gonna be?

Thanks for the help, Sean

 

Alot of information missing. Iron or Aluminum heads? What head gaskets? What is the quench distance? What chamber and piston design. Carb or EFI? Mechanical or ECM controlled distributor? Rod length also effects DCR.

I can tell you though my aluminum head, 11:1 383 with rhoads lifters on a 218/228 cam have that cam behaving as a 198/208 at low rpm. Cam is cut on a 108 LSA and installed on a 104 ICL. Cranks at 220 psi and runs on pump gas.

Edit-Missed the head gasket thickness. My thinking is it will not like that 0.059" quench distance at all. Mine is 0.041" quench distance. I have an efficient chamber design and a 2 valve relief flat top piston that is completely flat except the reliefs in the chamber. Alot of quench effect going on inside which helps control the burn. A good fast burn happens which means I make my power with less timing advance.

 

Try this: http://wallaceracing.com/dynamic-cr.php

 

Thanks everyone, but I have found it out. And let's just say I need some changes

 

I like to use Pat Kelly's DCR/SCR calculator.

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

To get the 10.6:1 SCR you state, I used a piston with a 5cc valve relief.
Using that cam as installed on that centerline, it will have a intake valve closing of 58° ABDC. Assuming a 5.7" connecting rod, the DCR works out to 8.9:1.
Just about anything will run on pump gas but I'll say you'll have a fight on your hands with that high a DCR. It can be done sure. (look at what Fast355 has accomplished) but I'll say it's not going be a simple as setting the timing and off you go.
FWIW, I get a theoretical cranking compression of 229 PSI (sea level and 70°F)

 

Ok. So 8.9 isnt all too high. Could I degree the cam in like 4 degrees retarded or advanced to help fix the problem? And how much timing would I have to pull out to safely run on 89 with the summer heat?

 

Aluminum Dart SHP heads. 64cc chamber. Felpro .039 head gaskets from a kit. Carbureted, 750cfm Proform, and a mechanical advance HEI distributor. The quench is.059 I believe. the deck clearance is.020 I believe. And a 5.7 inch rod.

Can this run on 89 in the summer heat?

 

Eh i’d try it as is, as long as you can keep it cool and on the richer side, lower timing to sneak up on it.
assuming aluminum heads. If it has half decent heads id go bigger on cam anyway

 

Ok, I'll start her off pretty conservative

 

I'd say this is key from both an engine operating temperature as well as a cool intake charge.

 

I Plan to out a 160 thermostat in it just to keep her cool. I want her as cool as possoble

 

Carbs have a cooler intake charge than EFI so definately an advantage of them.

That being said timing is going be the make or break. I would start with the heaviest advance springs one can find. Start with the initial timing around 4°. Get a L82 vacuum advance canister that is 10° at 10 in/hg and fully retards by 5 in/hg vacuum and hook it to manifold vacuum. A HEI distributor should have 22° mechanical advance. Start around 26° total advance and tweak for best output without detonation from there. Find a place to make WOT runs at a measured difference, watching for the highest speed. 1/8 mile track on a test and tune day would be a great help here. Once you find the timing that gives the highest speed without detonation you can revisit the springs for the advance curve. Try one lighter spring at a time and watch the ETs. It is entirely possible the car will be quicker with a slower advance curve. I think you will probably end up somewhere around 8° initial, 30° total and probably have full advance in by 2,800-3,200 rpm. At light throttle cruise it will probably like the extra 10° from the vacuum canister and idle best with the vacuum advance hooked to manifold vacuum.

 

Quench aint optimal but might work. With the carb and being wet flow i would think it would help alot, 89 oct may be possible. 93 would be better

 

Before I put that engine in, I would yank the heads and get a set of the GMPP 0.028" MLS gaskets that the Vortec engines use. Would get the quench under 0.050". Over 0.050" and there is no real quench effect. Much easier to do with the engine on the stand than after he finds a detonation problem once its in the car. My $0.02.

 

Yeah, I still got to drive this thing to school. And with how the gas price is heading I would like to be able to shove 89 in it

 

Thats the cons of owning a performance motor. Eat the cost or build something different

 

Indeed. Probably gonna just run 93. But it would be nice to run 89 if at all possible. Including since gas is gonna be 5 bucks a gallons here soon