speedjohnson

I've got a sbc that I'm using in for C4 roadracing application. I would like to make it as fast as possible, but, more importantly it has to be reliable.

I've had access to a chasis dyno, however, about the only thing that I've been able to do with it is to set up the spark advance and the fuel mixture at WOT.

I've purposely set it up a little fat, trying to avoid a track melt down. I think a few more ponies could be squeezed out of it, but I don't know the "limits" and the parts are too expensive to be used as paperweights, (again).

The engine configuration is: 410ci, Lunati pro-mod 3.75 crank/6.00 rods, JE flattops, 13.7:1 c/r, Brodix -10 RIsp, Brodix intake and Holley 830 carb.

I use race gas. I've got good cooling and a dry sump. The track sessions are 15-20 mins each, several times a weekend. The races are 30 mins.

What total advance/ fuel mixture should I shoot for? Max power or conservative?
Thx. sj

redvetracr

You might consider an exhaust pyrometer, mine came from (I think) Wes-Tach, I bought the single and put into #7 cylinder. Learn to (or try to learn) how to read a set of sparkplugs. ...redvetracr

speedjohnson

I have been trying to read my plugs, however, the race gas makes them look artificially tan. I am definately a little rich by the read, yet at least there's no "pepper" markings on the insulator (which I understand are actually flecks of Al melting off the piston tops).

...#7 exhaust port...I understand that #7 usually a bit leaner than the rest in a carb application.

What is the placement of the pyrometer?...distance from the exhaust port? How hot does it get before it's too hot? Thx sj

redvetracr

SJ,
Do you have the correct magnifier to read the plugs because you should be looking down at the base of the porcelein? I think I am about 6" from the head, my motor seems to like 1250-1275 degrees at full throttle, I think your looking for trouble over 1300. I don`t look at the gauge to much anymore, at the last Road America race I did NOT change a thing or look at a plug, put my car on the pole, led the first few laps and the end of the (important) last one. ...redvetracr

Matt Gruber

13.2:1 in the leanest cyl.
no power gains going leaner, just MPG

SWCDuke

Best power is achieved at about 12.5:1. If you have a fuel injected engine with good mass air metering, you could run as lean as stoichiometric and reduce fuel consumption. (This is often done in endurance racing to reduce the number of fuel stops.) Richening to 12.5:1 increases power about 3 percent realative to stoich., but at a cost of 20 percent increased consumption.

Carbureted engines generally need to run fairly rich to keep the leanest cylinder from going too lean, and this will vary with manifold and carb. design.

Duke


[Modified by SWCDuke, 9:04 AM 12/27/2003]