overlap doesn't matter. only thing that does, is when that intake valve closes.
i noticed that jordan is from texas. damn hot down there this time of year, especially at texas motorplex.

i also read through the dcr thread and i got quite a bit from it. i think the best of the man's knowledge is being kept to himself (mr hp) so read into it what you will. if you live in a really hot-summer place like texas, you might want to be a little more conservative. a lot of little things could be help in running a higher comp. a cowl hood that will let some heat out will help a good deal as would an electric high flow water pump and an efficient cooling system.

JB

 

11.8 to 1 here w/ 93 octane..no problems at all.

Cody

 

Thanks for all the replies fellas...I have spent most of last night and a bit of today cramming my brain with all the info I found in advanced tech for DCR. I don't have all the specifics of my build with me, nor can I D/L the calculater to my work computer out here(offshore). I did talk to my shop today and we are considering the XE236/242 on a 112 myself, which sure be plenty safe, but if anyone feels the need to calculate it...you are welcome to.

Here is a basic route that I am going-

Scat Cast Crank
forged 6" I beam rods
forged flat top pistons
spin balanced assembly
11.8:1 compression ratio
ported LT1 Heads w/2.00I 1.54E valves
Comp Cams 987 springs (depending on which cam I choose)
Comp Cams 1.6 Pro Magnum roller rockers
Hardened chrome moly pushrods
Comp Cams lifters
Meziere HD water pump
L98 true roller timing set

 

97 RedSS- You have any #'s on that beast?? by your sig, it is really close to what I am building...though I was considering more cam.

 

I am not going to re-hash the entire DCR thread. But just offer a word of advice. Unless you have the time and $$$ to experiment with motors, stick with something that is known to work.

One other thing, overlap does not figure into DCR, but it does influence octane tolerance, as young Trey suggested. On an NA motor a narrower LSA will increase cylinder pressure under WOT/low rpm conditions. This is ripe for promoting detonation. Obviously, you shouldn't drive a high compression/high performance motor at WOT at low rpm, but I have seen a lot of people do it.

Rich Krause

 

That is what I am saying...seems more than a few are running a 306 and it is working fine. I have asked repeatedly for a cam that I can run safely with this combo that I came across cheap. Which I am just gonna call tha cam companies and talk it over with them, and use what they suggest. and yes I agree that if you want to learn about DCR...just search it in advance tech.

 

Hi guys. I'm experiencing some detonation issues and was wondering if you
guys can help. I'm running a 396 LT1 ported heads, custom pistons 11:8 compression
custom cam, .658 int .618 exhaust 236-244 duration on a 112 lobe separation.

I have already detonated this thing running pump gas, and have torn it down to do a complete check through. I ended up running this thing on the dyno with a LT1 carburetor intake since I wanted to get some power numbers and dynoed at 515 horsepower at 6000 and 525 ft lbs of torque at 4250. This was with no real tuning and a dual plane intake manifold. His dyno can't measure any lower than 4250 rpm's too so I know the torque would pick up too.
But anyway I think with the injection back on and proper tuning, I should be in the neighborhood of 550 horsepower.

I was wondering if someone here can give me any input as far as where you guys think I should set my timing and if your running the knock retard or not.
Can you guys give me a heads up or some information onto how I can make this
motor pump gas friendly. What fuel are you guys running too if your running race gas that won't hurt the o2'S? I will definetely be spraying a 175 shot
on top of all this too.

If anyone is doing this already with this kind of compression, is there anyway some one can e-mail their file since I have LT1 Edit so I could have a starting point.

Your guys help is greatly appreciated.

Thanks

 

How about a bit more information chap.

Are you sure about your static compression? Can you give us your combustion chamber size, piston dish volume, gasket thickness, compression height, etc.?
What is your quench height?

Maybe we can make some headway with a bit more info.

Mike

 

i am going to venture a guess that "some real tuning" could help your cuase

 

Ok, going off on a tangent, but what is the reason for such high compressions to begin with. The HP advantage (from what I understand) become minimal as you increase. Heck isn't 10.4:1 pretty good to begin with?


Just wanting to know.

Ben

 

The reason for high static compression is that when using a big cam, the DCR will be proportionally low. More comporession is good, as long as it does not result in detonation. 10.4:1 is a high CR for a relatively large bore, "old tech" motor like an LT1. But that's with a "small" stock cam. Put in a cam with a later intake closing point and the DCR drops and power is lost.

How much hp? Depends a lot on the details. But one of David Vizard's books on SBC's indicated a couple of percent or a bit less when going from 10:1 to 11:1. That's with the same cam, etc. There's a whole table in the book that lists the expected changes with different CR's. I can dig it up if people are interested.

Rich Krause

 

Rich,

That explains it and I can understand that. I have seen a graph of diminishing returns based upon increase CR also and hence why I brought up the point.

I guess it is just others trying to get the optimal setup where I am in the arena of pretty much a stock car.

GL to you all with your high CR.

Ben