Ive been reading and reading about Dynamic compression ratios and quench distances and frankly ive been getting more and more confused. What does Dynamic Compression Ratio Really effect as far as drivability/power go? What about Quench? What is too small for either?

Here are my specs and some of the results I've gotten from Dynamic Compression Calculator By Patrick Kelley.

Camshaft: Advertised Duration: 279Intake/286Exhaust 113LSA 113ILC
Stroke: 3.750"
Rod: 6.0"
Head cc: 59cc
Piston to deck clearance: .010" (for calcs NOT set in stone YET!)
Head gasket: .039" crushed 4.125" bore (For calcs not purchased yet)
Pistons: Wiseco's Flat w/valve reliefs (-5.4cc)

When i do the Calculatons I get the following:
Static CR: 11.44:1
Dynamic CR: 8.55:1
Quench: .049"


The thing that gets me is that i DRIVE my car allot! My Z28 is my daily driver, so i decided on the 383 and the smaller camshaft for streetability(good throttle responce good low end) Is that DCR and quench going to work for street driving on premium 93 pump gas. Ive been told that 9.0 was the general limit, but i want to be safe.

I could also change a few things and use a dish piston to bring the DCR down but I feel it just looks TOO low, At least i think. Here are the calcs for the dish:

Camshaft: Advertised Duration: 279Intake/286Exhaust 113LSA 113ILC
Stroke: 3.750"
Rod: 6.0"
Head cc: 59cc
Piston to deck clearance: .000" (for calcs NOT set in stone YET!)
Head gasket: .029" crushed 4.125" bore (For calcs not purchased yet)
Pistons: Wiseco's Dish (-20cc)

When i do the Calculatons I get the following:
Static CR: 10.18:1
Dynamic CR: 7.64:1
Quench: .029" (but isnt it more because of the dish?)



Which way would be better to go? I do not plan on using a turbo or supercharger on this car, but I MIGHT put a 50 shot of Nitrous Oxide on it. Ultimately I want this to be good on the street and handle my daily abuse and last me a good long time. This motor's ability to run on pump gas(93 octane) and not have detonation issues is also important to me, i will be having a good dyno tune done.


So in summary:
1: What does Dynamic Compression Ratio Really effect as far as drivability/power go?
2: What about Quench?
3: What is too small for either?
4: Which pistons/setup would be better for my needs?


I'm SO very sorry for the length, but as usual THANK YOU GUYS FOR YOUR INSIGHT AND HELP ON MY PROJECT!!!!!!



THANKS,
T.C.

 

If anyone has any help, it would be very appreciated. Im waiting on buying my pistons and sending my block to the machinist.

Thanks,
T.C.

 

Well Quench is measured from the flats on the pistons to the deck surface on the head.... Those two things will cause the quench. You're talking about the 2 pieces that will be closest together and the distance between them. .029 is REALLY close probably not a good idea. If you have a zero deck block you can do a Fel Pro and with a .010 in the hole setup one of the thinner gaskets. That should answer 2&3

I would go with flat tops and a slightly larger cam. A few things are needed to run a DCR higher than 8.25 effectively, good quench, good cooling, good flow thru the water jackets of the heads, good timing/tuning and maybe good coolant. You can do it but the rule if you are not going to tune the snot out of it would be to stay under 8.3:1. I don't follow this rule most times cause I like to push it on the DCR on LT1's since it's a good way to make TQ when you have no runner length in your intake manifold.

DCR effect on drivablity is that is increases TQ and it increases vacuum, both of those things help the way the motor drives.

Bret

 

I went through the same thing that you are dealing with about 2 weeks ago when I was getting my engine rebuilt with a LE H/C setup. My suggestion since your car will be N/A, would be to go with the first setup you described. My motor is running a DCR of about 8.8 and my quench is around 0.045. I don't have any problems so far with detonation. The real test will come in the summer here in Texas when it gets really hot. With a good tune I think you will be fine tho. I'm sure someone else can chime in with exact explanations to your questions as far as what would be to small of a quench, etc.

Anthony

 

I have a question for you Bret...In your opinion, would you think it to be better to:

1. Run a higher DCR on pump gas with a say .040 quench and an extremely cold running engine, say below 180 or..
2. Run slightly lower DCR with identical quench and a hotter engine, closer to 190.

Reason I ask is Ive been told that engines ideally run best between 180-190*, which makes sense if you think about it logically if the fuel doesnt atomize as well at lower temps, and the air doesnt expand as much once it gets into the cylinder as much.

My 381 was running no hotter than 170 ever, most of the time it ran at 165, and it seemed to want to run richer than it shouldve been.

 

this is coolant temp, correct? where is it measured at in your car?

 

Drivers head. Autometer electric gage.

 

Where its measured is important....

Think about the fact that we have injectors and not a carb. To me heat is the enemy except when you are trying to keep it where it helps, in the chamber. Even a carb setup that is running with a intake manifold that is at ambient temps will make more power, you just have to tune it properly for that.

The good thing about the design of the LT1 is the reverse cool, we can keep pumping cold water thru the heads let it heat up and then exit out thru the block.

The threads on Evans NPG has some good discussions on coolant temp.... with higher temps you can gain mechanical efficeincy but loose VE, but still eak out higher HP numbers. If you keep that intake cool so you don't loose VE thru heatsoak then you see even better numbers.

Bret