Performance Q&A Questions - Performance Q&A

Kevin McClelland Feb 1, 2009 0 Comment(s)

Blue Flame Special
Q
I've been having issues with getting fire from my headers at wide open throttle. I'm hoping you can explain exactly which condition it is, lean or rich. My engine setup is a 383 stroker, a Comp Cams XE294 cam, Sportsman II heads, 12.2:1 compression, a Weiand high-rise intake, a Demon 750-cfm carb jetted at 73 primary with 78 secondaries, and Hooker Super Comp headers with 13/4-inch primaries leading into 31/2-inch collectors. I think they were for a circle-track application, since they come together after the flange and shoot straight out through the fenders, behind the front tires. Total length of the primaries is about 20-22 inches to the collector, then a 10-inch turndown (still 31/2 inches from the collector). It runs on 110-octane race fuel and is in my mud racing truck.

You can really only see the flames at night, not surprisingly, unless it is at WOT. At idle, there are occasionally small blue licks of flame exiting, then when I launch and all the way through the track, there are bright red-orange flames shooting out about a foot and a half. Some of the guys who race there say it is running lean and probably pulling in air from somewhere. I have yet to find a vacuum leak. Others say it is rich, burning off excess fuel. Every time I pull the plugs, they are just as they should be, depending on the day, between ash-gray and light brown. Any ideas?
Brandon
Via email

A
Years ago we ran a 502 big-block Chevy on the engine dyno and stuffed about 300 hp of nitrous through the thing. At the time, I had the dyno facing backward in the cell with the control room window facing the engine front, and the headers came off the front of the engine. We baselined the engine on pump gas and made 670 hp, and then turned up the wick. Well, with a flip of the nitrous button, out shot 2-foot blue flames from both headers and the horsepower needle swept past 1,000 on pump gas! None of us had ever seen header flames in the dyno cell with the lights on.

Back to your mud truck. You will see flames from your headers at night. It sounds like yours may be a little excessive. The short primary header lengths aren't helping matters much. Also, with the color you say the flames are, you could be a little to the rich side. However, the amount of flames, their color, and the exhaust gas temperature are based on many things. The efficiency of the combustion determines how much fuel is consumed during the power stroke and turned into work. How much spark timing are you running? The more retarded the spark advance is, the later the flame is started and the longer it will burn. Fuel doesn't care if it's is doing work or just giving you a beautiful flame show. With your compression and race fuel, you should have somewhere around 36-38 degrees total timing. From the color of your plugs, we'd have to agree with you that your mixture is close. It's tough to set the jetting by the odometer of your truck. It would be easy at a dragstrip, but in the mud it is much safer being on the rich side.

Tell your friends to enjoy the flame show, and ask the crowd for money for the extra thrill. Guess at your track, they don't need jets flying over on the afterburners. Have fun!

Way Over Bore
Q
I bought an engine rebuild kit from Powerhouse for a small-block 350 with 0.030-over pistons. Can a 305 block be bored to my pistons?
Allan McAra
Chilliwack, B.C., Canada

A
The stock bore on a 305 is 3.736 inches. Bringing it out to a standard bore for a 350 would require a 4.00-inch bore, which would remove more than 1/4 inch from the cylinder walls. Production 305 blocks will not accept that much overbore. The good news is that Gen I 350 blocks are very plentiful. Check with the machine shop where you were going to have your engine bored, and I'm sure there's a core 350 lying around or the mechanics will know were you can buy one reasonably. Sorry for the inconvenience.

Budget Builder
Q
I'm writing in to you from the birthplace of GM and Chevrolet! I'm 23 years old and building a '72 Chevelle on a $25,000 salary. I have spent my money wisely and currently have the whole car in primer; I'm dropping in a crate engine, a fresh TH350, and all types of chrome and billet goodies. The engine is a 383 stroker with Vortec heads and 10.2:1 compression. The rearend is an 8.2-inch 10-bolt posi with fresh 3.73 gears, and I've had people tell me that I will destroy this rearend. On the other hand, the guy who built it said as long as I don't put slicks on it and really hook up, it will be fine. I won't be taking it to the track. I'm only planning to cruise it in the summer and maybe run with some guys off a few stoplights. I plan on upgrading to a 12-bolt when my budget allows but want to know if this combo will get me by until then. Thank for your help.
Paul Petronzi
Flint, MI

A
We have a few answers here. Yes, the rearend will live, and yes, the rearend could blow up. Doesn't that help? As everyone knows, you can break an anvil if you try hard enough.

The early 8.2-inch 10-bolts can give you very good service. As you have seen, we've built up several in past issues and they've given us great service. The gentleman who built your rearend is dead on when he says that it will live if you don't hook it up hard. Stay away from slicks and nasty wheelhop. Also, an automatic transmission helps tremendously. The automatic keeps the ring-and-pinion loaded under acceleration. Manual-trans cars tend to unload and load on every gear change and are prone to wheelhop.

If you use your brain, you should get many years of service out of your current combination and it will allow you to save for the 12-bolt you want. Enjoy the many cruise nights, and take a drive down Woodward Avenue for us!

Technical questions for Kevin McClelland can be sent to him at chevyhi@sourceinterlink.com.

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