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Hi all!! I'm building a new engine for my C3. I wanted a 383ci, totally street, compatible with 95ron gasoline.
I've choose these components:
- Heads 64cc
- Dished pistons +18cc
- Deck Clearance 0.016
- Gasket thickness: 0.039
Before I get flamed for bragging or being a know it all, stating facts is not bragging and sharing your knowledge and experience is not being a know it all!
Quench or squish, whichever you choose to use, is very important and does have large effects on the engine. I have built race winning and record setting engines from small 2 cycle engines, Pro Stock, road race, land speed and Top Fuel, naturally aspirated, turbo charged, supercharged, gasoline, methanol, and nitromethane, as well as decades of street engines and years of dyno testing.
The statement "The closer you get to zero quench, the more it is prone to detonation." couldn't be more wrong! Tight squish absolutely makes the engine less sensitive to detonation. Engines with tight quench will run more efficient, burn cleaner, sound crisper, need less timing advance and will make more power.
I do not consider .040" on a SBC to be a tight squish. Beyond .040" is where quench begins to have little positive effect. I like to run as tight as possible without the piston colliding with the head. I run .034" on my engine in my signature. I have run as tight as .025" in engines before. In race engines I used to keep tightening the quench until the piston and head would just start to shine each other a little where they touched and then back off about .002". How tight you can run depends on a lot of things like rod and piston weight and material, stroke, block material and rpm the engine will be spun to.
There are other things that come into the equation like quench to bore ratio. A low rpm engine may run as much as 55% quench to bore ratio whereas running that much on a high rpm engine would cause a pumping loss and may even put the flame out. High rpm engines do better with between 35% to 40% quench to bore ratio. At extremely high racing engines rpm, quench becomes less of a concern because of such short combustions times and the speed of the intake charge. Of course this is not of concern to the OP or most street engine builders. Run between .035" and .040" quench and you will be fine. You will get the benefits of a tight quench.
Smokey Yunick professed the merits of a tight quench all the way back in the early 60's, so this is nothing new. He liked to set engines up so the piston and heads were just starting to shine the surface of each other. There is no wonder where I got that idea!
Hi all!! I'm building a new engine for my C3. I wanted a 383ci, totally street, compatible with 95ron gasoline.
I've choose these components:
- Heads 64cc
- Dished pistons +18cc
- Deck Clearance 0.016
- Gasket thickness: 0.039
The CR should be about 9.4:1. How many HP I should expect with this configuration?
Thx!
quick comp calc ~ 9.37:1
but that gasket is too thick because that makes poor quench height. (0.016 + 0.039 = 0.055" = too much). You need thinner gasket to make quench closer to 0.040-0.045" Yes that raises compression but the quench is importanant.
Both GM & Victor Reinz make a nice gasket about 0.028" thick ... that'll make ~ 9.59:1
First, quench is Not some obscure factor with little practical importantance or significance. . It's real and important. Look at the tallest part of your piston ... opposite the valve reliefs. Imagine, at TDC, how close it comes to the flat of cylinder head. That measurement at TDC is "quench" . To be effective it needs to be 0.040-0.045" ... "effective" means creating more swirl in combustion chamber at/near TDC .. that more efficiently keeps gas molecules droplets in suspension ... helps make a more efficient burn. Seems this is first you heard of this and I'm Not the best to try to explain. So, please google "quench" and find what others can explain better than I.
Jackson, thanks for the patience, any explaination or aid it's very valuable for me! I just read an article about the quench height and how this parameter affects the combustion. I could be wrong but what I understood is that with concave designed pistons as mine (+18cc), the quench height is not so significant. Am I wrong?
But if you think that the problem is so notable, I could change the head gaskets. I'm not so happy because the engine is closed.
...OK, you could answer that I could have done this question before!
Jackson, thanks for the patience, any explaination or aid it's very valuable for me! I just read an article about the quench height and how this parameter affects the combustion. I could be wrong but what I understood is that with concave designed pistons as mine (+18cc), the quench height is not so significant. Am I wrong?
But if you think that the problem is so notable, I could change the head gaskets. I'm not so happy because the engine is closed.
...OK, you could answer that I could have done this question before!
Yes, wrong. Look at your picture of the KB pistons ... at the Bottom ~5oclock position is the large curved FLAT area ... that is the "quench" pad. Other type dish piston don't have that pad. Yours have the good profile for quench. Change the gaskets. Calculate your CR. Then someone else will have needed info for cam advice.
gasket 5746 will make yours about 9.63:1 CR with about 0.042" quench ... all very good.
that 2102 grind is marketed by dozens of cam maker as an "RV" cam ... pretty small.
I think you could use more cam but I suggest let the others chime in ... tell us more about your heads and the valve train ... did you but the heads new and already assembled? Which brand & part number for those heads
I would go with a larger cam as well, that one will run out of power pretty early on, maybe 4800 rpm or so. Look for something closer to a 285 duration advertised on a 110* or better yet a 108* lobe separation. You could expect 450 HP or slightly more with that.
technically quench is the action of heat transfer from the piston to the head. Squish refers to the distance from the piston to the head.
in either case the distance is important for detonation prevention. Detonation limits cylinder pressure and is destructive to the engine.
We want as much cylinder pressure as possible without detonation to achieve max available torque. Proper squish distance is critical to achieving this.
With those parts that engine is going to make about 375 horsepower and about 460 ft/lbs. torque......with a flat Kansas torque curve.......you are leaving about 60 horsepower on the table with that cam and intake......
You need a cam with 230 or at .050 and .500 lift........and 2107 does not come up as a good intake part number.
I put that exact cam in a warmed over 305 with ported stock heads for a 54' Pickup and with the 2101 Performer, Headers and tune.....it was done at 5400 rpm.....in a 305. Torquey little bugger though.....spins the hides no problem......feels like a good running 350.
From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
This is only my opinion, but don't get hung up on the ".040" quench" myth. I run a .080" quench on my 383 and it runs mid 12s with "CROSSFIRE INJECTION". So, if you want to run a .040" quench have at it and knock yourself out, but the motor will run just fine. The closer you get to zero quench, the more it is prone to detonation. Personally, I would have also used 6" rods with a 383, but that's just me and 5.7" work OK. What are you using for fueling, carb or EFI, what size carb if it is a carb? Ignition...MSD, DUI? What year C3 is it? Again, this is only my opinion and I'm sure others will differ, but I would have went with ALL forged rotating assembly for piece of mind since your going to spend the money on the build, it only makes sense if the budget can handle it.
Last edited by Buccaneer; Apr 3, 2019 at 10:18 PM.
Combustion Chamber Volume (cc): 64 cc
Intake Runner Volume (cc): 190 cc
Intake Port Shape: Square
Exhaust Port Shape: Square
Spark Plug Style: Straight
Comp. Valve Job: No
Intake Valve Diameter (in): 2.020 in.
Exhaust Valve Diameter (in): 1.600 in.
Intake Valve Angle: 23 deg.
Exhaust Valve Angle: 23 deg.
Outside Diameter of Outer Spring (in): 1.450 in.
Damper Spring Included: Yes
Number of Springs Per Valve: Dual
Retainers Included: Yes
Retainer Material: Chromoly steel
Locks Included: Yes
Lock Style: 10 degree
Valve Stem Seals Included: Yes
Valve Stem Seal Style: Positive stop
Rocker Arm Nut Thread Size: 7/16 in.
@REELAV8R and @Jebbysan I considered a cam with similar data that you suggest but the vacuum to activate brake, headlamps and other services, will be enough?
@Buccaneer the primary priority for the design of this engine was the possibility to run in the worst conditions (heat and load) with 95ron gasoline. I have a friend with a 383 and 10.1cr, who can run only with 98 or 100 ron gas. And in Italy is very expensive and worst, hard to find. So, I prefer to have some less HPs but the sureness to refill anywhere the tank. I will run the engine on my '74 with an Holley 4777-2 650cfm DP carburetor and HEI ignition.
My 406 has a 244@.050 cam and 10-11 inches of vacuum and all of my stuff works just fine........BUT.....you have to make sure the system is not leaking ANYWHERE.....this is a problem for most.....a large cam brings out problems that were not showing up on a 19-20 inch of vacuum stock engine.....
The cam specs I suggested will give you about 13-14 inches......no problem. You will be disappointed with that pea shooter cam........
And as far as quench goes......tighter the better.....the closer you make it, the less prone to detonation it will be BUT it that only becomes an issue if you are right on the edge....10.5 to 1 is the limit with a fast burn chamber.......you need to ask Pro-Comp if these heads have that updated chamber.....
This is only my opinion, but don't get hung up on the ".040" quench" myth. I run a .080" quench on my 383 and it runs mid 12s with "CROSSFIRE INJECTION". So, if you want to run a .040" quench have at it and knock yourself out, but the motor will run just fine. The closer you get to zero quench, the more it is prone to detonation. Personally, I would have also used 6" rods with a 383, but that's just me and 5.7" work OK. What are you using for fueling, carb or EFI, what size carb if it is a carb? Ignition...MSD, DUI? What year C3 is it? Again, this is only my opinion and I'm sure others will differ, but I would have went with ALL forged rotating assembly for piece of mind since your going to spend the money on the build, it only makes sense if the budget can handle it.
Give this man a cigar^^^^^. Agree with everything said.
I would not get hung up with the quench issue, either. I did not worry about quench with my L-82 355 at all and the motor runs terrific with zero detonation on 89 octane with AFR heads and roller cam. I would also have avoided hyper pistons like the plague and used forged everything like I did, personally. The power is in the heads, cam, and compression, everything else is not so much on sub 450 Gross HP, give or take a few HP, except LTH's.
So, your 383ci will have about 9.63:1 static compression ratio with aluminum heads which probably have springs which allow about 0.500" valve lift ... engine builder always must verify valvetrain can accept valve lift of cam.
a larger cam can also "effectively" bleed off (reduce) some of your compression if it has a longer duration (see static compression calculator like REELAV8R linked)
Summit cam & lifter kit pn SUM-K1102 is virtually same cam as edelbrock pn 2102 ...both have relatively small aka short 204/214 duration and both are essentially one step up from either OE 350 cam or SUM-K1101. https://www.summitracing.com/parts/sum-k1102?rrec=true
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of course, all flat tappet cams require extra attention during break-in period ... and throughout their life ... this is discussed ad nauseum here and elsewhere ... pay heed!
Last edited by jackson; Apr 4, 2019 at 11:33 AM.
Reason: changed edelbrock cam pn 1102 to correct pn 2102
nobody is saying quench doesnt matter, it is ideal..but most times you can get away with more provided the valve timing/tune/cyl pressure isnt way out of the ballpark.
Mines "idiot proofed" some....should ping according to some but wont.
Think another 20 deg of cam timing would make the op real happy
How many HP?
