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Author Topic:   Pistons, hypers or forged.
FS93
Dirt Roller

Total posts: 8
posted October 02, 2001 11:11 PM UIN: 3107810
IS there a significant advantage in a IMCA modified engine in using forged vs hypereutectic pistons. I am getting ready to start on a backup motor for next year. I want to keep the cost down, but dont want crap in the motor. The 406 that came with the car has forged pistons. I am thinking of building a 383 or 377 and am looking for ideas.

WILDphil
Dirt Roller

Total posts: 6
posted October 03, 2001 10:52 PM
Hypers are more cost effeicent and the have closer tolorences than forged because the way they are formed, a hyper will on the average on loose 1.0 cfm on a motor that has some laps on it, forged pistons will loose again on the average is 3.0 cfm. with some laps on the motor.
So I would say go with the hypers. They will work quite well for your application.

sdhnc29
Dirt Forum Racer

Total posts: 81
posted October 03, 2001 11:49 PM
Unless your on a tight budget , Hyperexplosives should not be used in a race engine . *Just my opinion*

jammin
Dirt Administrator

Total posts: 3426
posted October 03, 2001 11:54 PM UIN: 16262997
The weight is the biggest factor when looking at hypers. I have a couple of motors with Speed Pro's in them and have had no problem. Even had some major carb problems on a motor last year and never melted one. I can say that they are very, very durable. But, on the other hand, they are also heavy. This will affect your acceleration a little, but for a claimer, it is the best alternative. For a better engine though, I would use forged aluminum because of the weight and durability it offers. If you spend the money on lighter internals, then you should spend it on the pistons for a complete package. Dont skimp on hypers if your spending the money. But for basic stock applications, hypers are hard to beat.

jammin

istock59
Dirt Roller

Total posts: 17
posted October 04, 2001 08:02 AM
If it's for a claimer motor (IMCA), hypers are hard to beat. Just remember to open up the top ring gap. I exploded a set of Speedpro hypers last year because the machineshop told me to not file the top ring....

smayo964
Dirt Newbie

Total posts: 4
posted October 04, 2001 09:15 AM
Hey istock59. Question for you concerning your statement about opening up the top ring gap. What gap is recommended and what gap did you have when the engines detonated? Just curious. I've blown a couple this year for some unknown reason. Also, does anyone know what the max compression ratio is for the hyper type pistons? Thanx

istock59
Dirt Roller

Total posts: 17
posted October 04, 2001 10:55 AM
smayo964, checkout www.kb-silvolite.com for recommeneded top ring gap. I know that's Keith Black stuff, but I used the same top gap in my second set of Speedpros. 20+ races on them with no problems.

On the set that came apart, I used just the standard drop-in ring gap. Probably around .018 I suppose. I asked the machineshop about the ring gap when I put it together, but they told me that Speedpros didn't need the extra gap like KB's. But, I got the carb a little lean, the engine a little hot, and ripped the tops of a couple pistons off the skirts.... Oops..

Never again. All my hypers get the top ring gap opened up now!

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