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Old 02-12-2014, 06:14 PM
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Ron Sutton Ron Sutton is offline
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Hi Chad,

The key to optimizing restricted engines is to not leave anything on the table & take nothing for granted.
Every little bit matters. 10.8 compression is better than 10.7 ... 510 cfm is better than 500 cfm … a few ounces here & there … etc, etc.


A. The 034 bowtie head is the best of those options hands down. I think it flows around 215 cfm, which isn’t anything astounding but it’s the best cast iron GM SBC head.

B. A big deal in these engine is the getting the "squish band" to the optimum number of .035". This means "cold" the piston has .035" clearance to the head surface. This is achieved with a combination of head gasket thickness & block decking.

As an example,

If they run a .041" FelPro gasket, the piston needs to stick out of the block by .006" ... putting the top of the piston at .035” from the head.
If they run a .039" FelPro gasket, the piston needs to stick out of the block by .004" ... putting the top of the piston at .035” from the head.
If they run a .031” FelPro gasket, the piston needs to be down in the bore by .004” ... putting the top of the piston at .035” from the head.

While we’re on head gaskets, run the smallest diameter bore you can. If the engine bore is 4.040”, try to get a head gasket bore around 4.080”. To achieve the optimum squish band, you’ll need a gasket .035” or thinner to meet the "no piston above the deck rule". There are several around .031” See if you can get them with the 4.080” bore. That would be a good gasket for this app with the small 64cc chamber.

C. If the track doesn’t tech carbs with a gauge, there is 30 precious cfm with some TLC. If they do, see if they tech the butterfly shafts. Milling them is worth 10cfm. If the carb has to be 100% gauge legal, it still needs to be reworked.

D. K&N Filters designed a racing filter with a profiled top & bottom that flat out flows more air. Since every CFM matters, you’ll want to use the K&N “Flow Control System” on their 2-barrel. Run the 4.5” tall version & pick the correct one if the carb has the choke horn still on or not.

E. Too bad you can’t switch manifolds. The Edelbrock Victor Jr 2-BBl … is the best mid range Intake manifold I have found through testing. In fact, with our 587HP 2-barrel 410” engines, we went away from it to kill some mid-range (and gain upper end.) But it sounds like a performer it is. Do the rules allow you to run the air-gap version?

F. I see they do not allow methanol for fuel. What about E85 or “Ethanol”? If they allow E85/ethanol, that is your best choice by far. If they require it to be a certain percentage of ethanol, the best strategy is to mix Ethanol & racing gas. Ethanol will flat out build more top end power, so in the 4000-6300 rpm range they’re have an advanatge.

G. Back on the carb again, if they allow E85, I’ve got a guy I worked with that together we developed some good pieces.

H. Comp Cams has some new-ish solid lifter lobe profiles that have more area under the curve while still allowing standard .842” solid lifters. The mistake too many racers make on restricted engines is under-camming them. They think well there is less airflow, so I need to make all my power down low. This is not optimum. When these are the rules, the racer that builds the most total power under the usable rpm curve … and specifically the last 1500 rpm of powerband … will have a faster combination.

Two keys to cam selection is car handling & driving. If we have a poor handling set-up car that can’t carry as much mid-corner speed without pushing … or a driver that parks it in the corner … we can’t optimize the engine. We have to band-aid the engine to build more low end torque to get the turd out of the corner. So 3800 rpm matters more. On the other hand, if we have a well set-up car … with good front end geometry that allows higher mid-corner speeds … and the driver knows how to get optimum corner speed out of the set-up … we don’t have to worry about the very bottom of the rpm curve. We can build a rocket that is “good” at 4200 … but doesn’t blow the tires away … and is “mean” from 4700-6300.

I have three cams in mind, depending on how good you think they are with corner speed.

I. Header & exhaust design are critical here. For optimum power throughout the range, we need step headers & a crossover. Before I make any specific recommendations, I need to know what cam strategy we land on … and if there are any sound decibel limits we need to meet at the track(s) they run.

J. Gear ratio. If we build the “mean” engine that builds better power up top … and less power down around the corner exit rpm … we can run a step more gear in the rear. This is faster. A lot of guys think if two engines put out the same power at different RPM’s … then they can just gear the car to the power band & they will be equal. Not true.

K. Ignition timing will be more critical with the 10.8-1 compression. I’d start at 37° with this combo. Don’t mess around with advance curves. Ideally in race engines, you want to have full timing at idle. Just use a retard feature for starting it. For these engines I like the MSD E-Curve billet distributer. You can set it up to retard the timing 24° to start … then it goes to full timing at idle once the engine is running. It runs smoother, doesn’t load up, gets rolling easier, gets around the pits better, and handles low speed caution flags better.

If they can afford $200 to put the car on a chassis dyno, you can get the last 20hp of the engine by fine tuning the jetting & timing. Tune for optimum power from 4700-6300 & give up some in the 4000-4300 range so it doesn’t spin the tires easily. This allows the driver to roll the throttle on quicker and get the acceleration cycle started earlier. This is key both to good lap times, but also setting up passes. You can’t pas someone if you can’t get off the corner well enough to get along side them.

Dyno test the timing … up & down from 37° … and whatever timing builds most power from 4700-6300 will be your number. Make 2° changes at first, then fine tune it with 1° changes. 1° matters, especially in restricted race engines.

L. For oil, I strongly urge them to run a “blend” over full synthetic or full petroleum based oil. The “good” petroleum based oils offer better lubricity, for less wear, longer time between rebuilds & frankly more power over a longer period of time. The synthetic part of the blend offers a higher level of heat protection. Thicker viscosities add more friction. Super thin viscosities offer less protection. I’d like to see them run a 10w40 or 15w40 … depending on the rod & main bearing clearances. If you keep them .0015” - .0018” that would be my choice.

M. Blueprinting the oil pump is strongly suggested … or simply buying it that way. Getting the rotors deburred & the clearances optimized so the pump is “low drag” is the goal here. You don’t need a ton of volume or pressure in a SBC turning 6300 rpm. Buy a quality pump, but don’t get carried away with pressure or volume. Both are HP reducers.

O. There doesn’t seem to be a timing chain rule. At a minimum, go with the tru-roller from Cloyes with the index-able gears. If budget allows, I’ve seen better power & extended engine life with the Comp Cams belt drives.

P. I can’t say enough about making the rotational assembly light. If the crank rule is 48#, for Pete’s sake get down right to it. Target 48.5#.

Q. Several manufacturers offer light pistons. I think JE has them around 375 grams with standard pins.

R. An area not tech’ed is piston pins. This thing won’t build major power, so you can run thinner wall, light pins.

S. A little out of order, but whatever cam I recommend, they’re going to want 1.65 roller rockers.

T. With only 6300 rpm, they don’t need big ol’ pushrods. Here is an opportunity to go small diameter & thin wall chromoly & lighten the valvetrain. (Hardend tips.)

U. Spend the little extra for titanium valve spring retainers. They will pay for themselves plus some with extended life of the valvetrain.

V. Probably not a big issue, but make sure the valve springs are set-up close to coil bind to reduce oscillation & bounce. (Remember, the engine doesn’t make compression until the intake valve stops bouncing & actually seals. )

W. Once we land on a cam, valve spring pressure is critical. Too little & we have power loss along with durability issues.

X. Don’t cut corners on the valve guides or seals. We need it sealed with as close to zero oil contamination in the cylinder as possible. Some people justify the cylinder need lubrication, but the low tension oil rings already take care of that.

Y. If we end up on gasoline, run as cold of a plug as possible, like a 1 on an Autolite scale or a 10 on an NGK scale & dial in the jetting & timing. If we run Ethanol, run 1 step hotter … like a 2 on an Autolite scale or a 9 on an NGK scale. Stay away from the trick of week 2, 3, 4 or 987 prong spark plugs. I buy $3 race plugs so I can read them & throw them away. Buy plugs with the strap cut back or cut it back yourself. Gap them at .035" & index it so the gap opening is pointing straight down to the top of the piston or just slightly towards the intake valve.

Z. Frankly, an ignition amplifier won’t build any more power here unless the jetting is too rich. But make sure they have a top notch coil 7 new wires. Replace the wires every season. Don’t wait for them to “go bad.”

Get me answers to my few questions above & we’ll get working on cam & exhaust.


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