327, 4.040, 11.2 CR, max RPM 7250, Crower Sportsman rods, forged crank, forged light Ross pistons.

 

I ran my 302, twisted it harder than your motor, with the minimum alowable total deck that NHRA said you had to have. .021.

 

depends on the piston to wall clearance. use a dial indicator on both edges,top and bottom, with ther piston at TDC and rock the piston back and forth to see how much it is above or below the deck.

 

I am .006 in the hole with a 5.3cc pop up piston, .022 gasket and 62.5cc heads

near 12:1 with a 151 cam and have no issues.

 

I have asked the same question, and most have told me to keep the quench above ~0.030"... if you have good parts and good measurements. If you measure all the bearing clearances (main, rod, piston pin) and all the thermal growth (rod & piston crown & crank throw vs. later block expansion at start up) with piston rock and a rod stretch guesstimate you really do not need much more than ~0.020"-0.025". The most critical time for potential contact is after a cold engine start, when the block is cold and the reciprocating assembly is growing in length due to rapid warm up and rpm, and the block temperature and growth has not caught up to the expansion of the hot moving parts (like when dropping the hammer on a cold engine). The key, again, is good measurements (and a good machinist, with a little driving care).

There is a lot of caution when throwing out a number because a piston rocking in a loose bore and uneven deck can ruin the clearance in one cylinder (and boom).

In a stock rebuild (no deck work to even the distance the pistons are down the bore) you need to work around the tightest chamber, and most causal engine builders do not measure to check the clearances. This is where the common 0.040" and 0.045" quench range numbers came from, to allow room for builder/owner error and ignorance (and to justify the standard Felpro 0.041" gasket and the standard Corteco 0.047" gasket, even if the pistons are way down the bore at TDC).

Some people also believe the quench issue is moot, because theory allows for over 0.070" quench in a 4" bore before it becomes a detonation problem (in theory). Practice (real world testing) indicates that anything less than ~0.050" in a 4" bore is more resistant to detonation than the loose clearance, and an even tighter quench only provides better compression (with minimal additional detonation resistance benefit, but good for power if your cam and fuel can take the resulting dynamic CR).

The hardest issue for me was finding the real world compressed gasket thickness for the standard pieces. The custom copper gasket thickness info is easy, the more economical MLS and composite gasket thickness is not (I had to call the manufacturers and have them read back to me the specs and readings from CAD drawings and in-house testing).

My new 350 has: forged flat-top pistons 0.006 above the even deck, 67cc chambers, 4.86 cc valve reliefs, billet rods and forged crank, yielding just over 10:1. I get 0.033" quench with the Felpro 0.039" gasket or 0.041" quench with the 0.047" Corteco gasket. Both gaskets are good for 600 hp or ~13.5:1 CR (per the manufacturers). The engine's DCR is over 8:1 and I have to live with 91 octane pump gas, so the compression & expected power difference between 0.033 and 0.041 quench is not that great to really worry about offsetting the safety of more clearance (not like what I would be concerned about when assembling a pure-stock engine like Donny's or a potential class record contender).

Assemble the engine with clearance anywhere between 0.030 and 0.050 quench and it's not likely to be a problem. Just be careful on the tighter end of the quench range (be very careful with parts and clearances - and warm up time).

 

Hey Donny...what do you have to run for gas with that dude??


I think everyone answered question well. Lighter the parts, stronger the rods, tighter the wall clearance...the tighter you can go.

My 540 has .0045 wall clearance, pistons .009 OUT of the hole and a .037 gasket for a .028 quench. The pistons just slightly *polish* the heads. You can see it....but you can't feel it. I spin 7000-7500 rpm regularly. I surely can't go any tighter on mine and I have to be very careful of the head gaskets I use. Also you need to actually measure some compressed gaskets. The ones I have used for years compress .008 more than the package says.


JIM

 

Jim, the L79 cam has so much duration, it bleeds off cylinder pressure.. I can drive around town on 93 octane with the timing set on stun... no detonation.

I run 1/3 to 1/2 110 race fuel and 93 on race day... the desktop dyno shows that the L79 cam is too much cam for such a short stroke motor, it makes it hard to use the static compression.

 

Piston clearance will probably be .030.........standard, I think for a lot of forged aluminums. I haven't selected pistons yet, and I will need 4.040 buckets with about 7cc dome. Right now, the decks are uneven at about 9.010 plus/minus about .005. They will be surfaced flat, but haven't selected gasket yet, because haven't selected cam yet. Looking at the Lunati 60141, which likes about 11.5 SCR.

Anybody have reports about this brand new cam yet? It is ground on a 110 LCA, but, INCREDIBLY, if I open up the LCA to 118, it performs at peak with my Engine Analyzer program. I will try to find a better modeling program, because I don't think that EA accurately reflects the very fast ramps on this cam. I'm thinking of having it ground on 111 or 112 rather than 110 LCA for my 327 with 2.02 intakes.

So, looks like Donny has .028 and hotrod also has .028. Donny probably using FM pistons, which require .030", so no contact, and hotrod using .045, and so the contact. It looks like I'll be shooting for .030-.032.

Joe

 

Let's review one more time. When I raced in stock you had to use a lot of stock parts, like rods and pistons. So my 302 with 20 over stock pistons and stock rods, stock heads and valve train, with .021 total deck that I built myself would turn about 8K 11.80 at the local strip on 9 inch tires with slapper bars.

I was trying to get every bit of poewer out of a small motor and it seemed to work just fine. It kepts the pistons clean

 

When you say "total deck", you mean gasket thk plus/minus piston to deck distance, right? For instance, if you used a .022 gasket, then your pistons were .001 in the hole?

 

http://www.csgnetwork.com/compcalc.html this is a nice calculator for compression ratio

 

remember with street driven cars you will get carbon build up on that part of the piston and at high RPMs there could be contact if you start off with too little clearance

 

You might try modeling the Lunati cam with the "lifter profile type" set to "aggressive solid flat cheater" (on the cam/valve train page). The plot's initial ramps are slower than the Lunati and the 0.300" duration is longer, but it's the best you can do with the basic program.

If you can find the advertised 0.006" duration numbers for the cam you use them for a cross check and adjust between the 0.050" & 0.006" numbers to find a guess-average for the performance. It's all a guess (a model) and all the other cam profiles will have the same comparative error after the same adjustment for the lifter profile type that best matches the cam data.

I liked the Lunati 60141, as I found it the best model for an off the shelf cam for the broad range of average power. I understand that some of the circle track guys run the cam for good midrange torque (quick off tight corners & short tracks). It works with short stroke & short rod lengths and restricted intakes, so it should work with a stock intake & bottom end that has some compression. The caution I was given is you need gears on the deeper end (3.73 & 4.11) to keep it in the rpm it likes to run. It performs better than the LT1 above 2000 rpm, but it will also keep running the rpm up until it's happy (and with a TKO's overdrive or 3.08 gears it can demand attention & be a ticket attractor).

In the end I talked to a number of cam people and selected a similar grind, an Isky 530A ground on a 110 degree LCA. It's also an aggressive cam grind used in circle track cars for enhanced mid-range, and we pushed the LCA out 4-degrees (to 110) to overcome some of the exhaust manifold & muffler restriction (to raise the DCR to work with the flat-tops compression, and lower the overlap to values similar to something in-between the LT1 & 30-30). I have a single plane Vic Jr with little intake restriction, so I do not need to go wider or worry about reversion (it's there at low rpm anyway, so a wider LCA will not help me much).

I was warned to avoid pushing the LCA out as far as the EA program recommends. I was told the wide LCA models work better for the LSx series engines with ample intake and exhaust ports, and can work to improve the midrange of a mismatched engine with oversized ports (i.e. using a head with a 215cc intake on a 327). The problem is the ultra-wide LCA softens the peak torque enough to lose the bulge in the torque curve. With the 461/462 160-172cc heads the engine needs some overlap to help with the mid-rpm+ rush expected of a short stroke small block (similar to that 3500 rpm increase in torque & kick from the 30-30). The dyno and first hand driving reports are the engine loses it's performance small block character if the LCA gets too wide (good if you want a 300hp-327 feel, but not if you want an L76 feel).

I often heard that if you want more midrange select it with a milder cam, or just stroke the engine to a 350 or 383. The guys that were building 327's for short track use and road racing in the 60's are almost all retired. More than a few told me to build the 327/350 for rpm, or put 1.6 rocker arms on the Duntov 097' cam and run it till it quits (and to build a 383 or larger if I needed more mid-range). Almost all told me that the fun of a 327 is the mid-range rush of power, and the high rpm sound that you cannot get with a 383 running camel hump heads. You will not win stop light races with a 327, not even against 383 Nova's and Camaros, so they recommend going for the feel and sound you like (for the comforting blast down a country road).

Good Luck!