Visit The Dirt Forum for More Information

Author Topic:   Need more power for 406 ?
Tim Weiss
posted December 03, 2003 07:54 AM
We are running a 406 with a stock crank x rods flat top forged pistons all balanced midwest 2 cam dart wilson intake ported world heads 208 160 valves 62cc want to go with roller cam and dome pistons. will the stock crank be ok for this? the heads came off a roller motor. running a 2900 lb clip car 180% headers also run alcohol 6800 to 7000 rpms. we have run this motor for 3 seasons with no rebuild it just started to get some blowby last couple races.only rules are iron block and iron heads.what size cam would work best? looking for a little more torque and hp. we run on a 3/8 medium bank dirt track

posted December 03, 2003 11:58 AM
Sounds like you have a lot of room for improvement/horse power gain. Your budget will be your main limit , so I would first establish that . After that you need to consider your rules . Can you use any steel head? As for cam , there are VERY few book grind cams that will take full advantage of an engine burning alcohol. So a custom grind should be included in the budget. The crank will not work , or not for very long anyway. I will wager that after 3 seasons on your stock crank , it will be cracked in every journal . Once again crank choice will depend on your budget. I'd basically decide how far you want to go , and what your budget will be . At that point , you can get a pretty close idea of what you can build .


Hendren Racing Engines
Rutherfordton , NC

posted December 03, 2003 01:30 PM
As mentioned above, budget is the biggest factor.

Some food for thought:

Scat 'low end' steel crank $400
Crane solid roller cam (248/256 .630") $275
Lifters $230
6" Eagle bushed SIR rods $225
Keith Black hyper pistons (flat top of small dome) $300
Angle mill heads for 13-14:1 $250

That's just some ideas. Flat top pistons with small chamber heads will make more power than a large chamber head with a big domed piston. Something like a .100" dome and heads angled to 58cc would work pretty well. KB129's with 58cc heads would be about 14:1. Pretty good for alkie.

After that, spend the money on better heads and/or port work. But the best heads in the world won't be worth much if a rod or the crank snaps. A splayed cap 2 bolt wouldn't be a bad idea either.

posted December 03, 2003 04:08 PM
Thanks for your replies. we are thinking about buying a balanced rotating assembly but have not decided on what kind. quality at a good price is what Im looking for. the only rules are iron block and iron heads. we do plan on using the same heads we have now. we are looking for 500 to 550+ hp. any input would be helpful. this motor had lots of power but we need a little more.

posted December 04, 2003 11:49 AM
Originally posted by zeroracing:

and he has not tld me what to think about the kieth black pistons but alot of guys were talking about them and they had alot of problems with breaking them. so i would look into a different piston and not a scat crank.

Most people that break KB pistons do so because they don't read the instructions and/or don't know how to file fit rings. You need around .030" end gap on the top ring of a KB piston. I run .032"-.033" on mine (4.030" bore x .080 gap factor = .0322" endgap) The one motor ran half the year with either a blown headgasket or pinholed block losing water and running at 260+ degrees everyweek. Never butted a ring or broke a piston. Not saying that's the way I like to run a motor, but in August I didn't have time or funds to build a new one. Figured I'd run it till it blew... made it all year. I've yet to tear it down and find the real problem, but it was using about 3 qts of water every 20 laps.

Back to the Archives