401 pistons

casey

Hey folks. I finally have a 401!!! :!: Now I need to find some pistons. I have done a search of the net and found there are not as many options as in the past. I want to build for wheeling, not drag racing. So I want durability and low end power. I would also like to keep the compression ratio down in order to run lower octane fuel. Simply because I don't want to have to count on the local stations in E. BF nowhere having super. Someone (I cant recall who or why) said not to use the Keith Black pistons. I've used them in SBC builds and have been very pleased. KBs are wicked expensive to boot. I already have the rebuild kit and RV cam. I'm going to run HEI and GM TBI on it. Stock manifolds, intake and exhaust (non A.I.R.). What would be a good source for an .030 over piston set? Any suggestions? Thanks :t:

Dusty

casey wrote
I have done a search of the net and found there are not as many options as in the past.

There are more options now than there have been in quite a few years. KB makes a good piston, Speed pro. - you can ge the speed pros through fastengineparts.com , mad-dog racing two in the same there but also summit has been having good prices.

the stock replacement or forged 8.5:1 pistons that speedpro makes work well, if you put 51cc heads on instead of your 58cc heads you should find yourself close to 9:1+ a bit derepending on a few things

Use a performer intake. and id probably say the Holley 670 if you opt later to not go with fuel injection.

i know you already have the engine kit and rv cam. but mos tthe rv grinds in the kits tend to be smaller than stock.

I have really liked the H262XE cam from comp but i will say that the howards .479 lift 222 dur @.050 with a 114 lobe seperation has been great in a trail jeep cam idles at 500 rpm tons of torque off the line all the way through. all it is, is a glorified rv grind not far off from stock specs. it works really well with fuel injection. stay with a 112 or 114 lobe seperation for a trail rig it keeps the idle and torque curve smoother as well it keeps vacum up for the accessories and for the fuel injection.

i was running a .512/.512 lift cam with a 274 adv dur 226 @.050 dur and a 112 lobe sep and it never ceased to amaze people how it could idle along on the trail with no low end grunt isses and then still manage to come alive on the sand dunes when it needed too. it worked fairly well with the fuel injection though with a carb ive been alot happier

happyhoppy

I purchased a set of used .030 TRW L2308 forged pistons on ebay a year ago thinking my 401 had to go .030 over - but it was okay at standard bore. Had them checked at the local machine shop and they assured me they were fine to use. They were advertised as very, very low mileage and they appear to be just that. $125.00 and I'll pay the shipping. Can send pictues if you like. (Believe these are 10.5:1 compression.)

82Waggy

I'm using the KB 354's in my 401. I'm unshrouding the valves to open the chambers up to about 65cc's to keep compression down to about 9.1:1. With the standard 58cc heads compression will be up near 9.7:1 with these pistons. Watch compression height with whatever piston you choose and shoot for a zero deck height with an .045 thick head gasket for good quench. This will help reduce potential detonation - as well as other benefits. Hey Dusty, aren't you running fairly high compression with that custom Crower 222dur cam? PS: The troughed head style of that Speed Pro piston is really lousy for quench and flame travel. Unfortunately, off the shelf choices are limited. The KB requires bushing the rods to run their .9272 diameter wrist pins.

a440plus6

I've had real good luck with the Kieth Black Hyperutectic pistons on Mopars. Not forged but imho.....you don't need forged. They are HEAVY.

Dusty

yes i was at 10.2:1 with the edelbrock heads now with cast iron heads im running 9.8:1 roughly and still no gripes. and yes the KB's have a much better design than the Speed pros but price wise the forged speedpro's were $360 to my door

casey

Thanks for the input guys. Dusty, I would like to put new pistons in. Thanks for the offer. I also like the idea of 9:1-9:7 compression ratio. 9:7 being high. Keep it coming. :t:

Dusty

what did i offer? :razz:

casey

Dusty wrote
what did i offer? :razz:

Right! 111!!!

My bad...happyhoppy..thanks.

donwag

My last 401 build I used stock style pistons and Eddy heads to get the compression ratio to just under 9. Very good torque curve. It runs great on pump gas and plenty of low end power. I am building another 401 and I am going to use the Keith Black pistons and stock heads with the chambers opened up a little to get to about 9 to 9.5 compression ratio. Key is, you have to match all components to your desired use. Don't just select pistions and forget about how they will work with the rest of the engine.

1980_Cj7

Can you get the stock compression ratio pistons in .030 or .040 over? I'm having trouble finding any. I'd like to go hypereutectic this time.

Holeshot

PLEASE use flattop pistons!!! The "stock style" ones have huge valve reliefs on both sides (only needed on one side) and are VERY ping prone. You want to end up with .045" PTHC, as said previously. The MadDog Ross flattops have generic valve reliefs that don't match the valves, get them elsewhere.

AMX69PHATTY

In a year 2000 Badger Piston Catalog they show 390 stock type pistons available in STD, +.020, +.030, +.040, & +.060 as Part #P888. They are cast Flat Tops with only 2 long small valve reliefs. But they have a Compression Hieght of 1.548, rather than 1.495 which is listed for 401 Pistons. The 401 Badger Pistons are part #P894, are listed as available in the same sizes, and are like stock with a .300 deep dish and 4 small valve reliefs. I called and they said they don't show ( 8 ) 390 pistons in stock at this time, but will have more produced sometime in the future, but cvouldn't say when. But they said they did show ( 8 ) 401 pistons in +.040 in stock at thier warehouses available for immediate shipment. Those are the ones with the .300 deep dish the same as stock. Although less than Ideal for quench these may be fairly inexpensive.

http://www.badgerpistons.com/Company.htm
Badger Pistons
944 Highway 15 North
New Albany, Mississippi 38652
Phone: (866) 534-7601 or (662) 534-7601
Fax: (866) 834-2332 or (662) 534-2332

What you said in the other thread about the cam gear being installed with the Key in the Sprocket Bore Oil Passage Groove is amazing. Can't imagine what that would do to Cam Timing.
#-o

1980_Cj7

Holeshot wrote
PLEASE use flattop pistons!!! The "stock style" ones have huge valve reliefs on both sides (only needed on one side) and are VERY ping prone. You want to end up with .045" PTHC, as said previously.

The MadDog Ross flattops have generic valve reliefs that don't match the valves, get them elsewhere.

Aren't flat tops gonna give us a way high compression ration though? Like Fuzz's, he has something like 12:1.

Holeshot

That's why you need to increase the combustion chamber volume via unshrouding the valves (increases flow & performance) & "open chambering" the combustion chamber. My heads came out to around 72cc after the mods, which dropped the 13.5~1 pistons down to around 11~1, so should drop 12~1s to around 9.5~1 or so (a stout cam will bleed off some compression as well). The AM engine is fairly compression tolerant when open-chambered & fed enough fuel & MSDd, 11~1 is the number that comes up frequently as the limit for a performance cammed engine with .045" quench & tuned correctly. Using stock-style pistons will make the above engine ping itself to death.

JERSEYJOE

AMX PHATTY: I RECENTLY TOOK APART A 401 THAT SOME BRAIN SURGEON INSTALLED THE BADGER 888 390 PISTONS IN. IN WAS IN A CJ 7 AND ACCORDING TO THE OWNER: IT BLEW UP ONE DAY IN A WATER HOLE. I TOOK IT APART AND 4 OF THE PISTON DOMES LOOKED LIKE SOMEONE BEAT THEM WITH A HAMMER. THE MOTOR HAS LOW MILES AND IS .030 OVER. 4 OF THE PISTONS ARE PERFECT AND I WOULD REUSE THEM. THE BAD 4 HAVE BROKEN UPPER RING LANDS. A WHILE BACK I ASKED ON THE FORUM WHAT THE STATIC COMPRERSSION WOULD BE WITH THIS COMBINATION. IT HAD THE 1.68 EXHAUST 58CC HEADS. I ALSO CALLED BADGER AND THEY REPORTED NO 888 PISTONS AND NO PRODUCTION DATE. IF I GOT MY HANDS ON 4 OF THEM I WOULD REASSEMBLE THIS ONE

AMX69PHATTY

The lady on the phone from Badger said thier system showed none on hand in any of thier wharehouses and wouldn't give me a date or timeframe either as to when they would be producing more #P888 390 pistons but lead me to believe they would be making more. Yeah it's kinda strange that they can't give a date as to when they will be available. Maybe they're waiting to see how many calls they get. Wonder how many sets BullTear would have to buy / order in order to get them to produce them ? ( just kiddy Matt :?: ) Maybe I'll call'em again next week and try to find out more. On compression, I guess things nowadays seem to imply AMC had it backwards, small chambers in the Heads and dished pistons down in the hole some. So to go with "todays knowledge" which is Flat Tops at or near zero deck clearance, they only way to achieve that is to increase the size of the combustion chambers in the heads. The good thing being that apparently the way AMC heads were casts there is enough material there to allow one to do just that, unshroud the valves and open the chamber volume.

82Waggy

Static compression ratio is not the whole story. CR needs to be matched with cam timing since it is the intake valve closing point that controls the level of cylinder pressure you will actually make - pressure does not start to build until the intake valve has closed, and the valve does not close until some number of degrees after bottom dead center. This is why running long duration cams with stock compression ratio (typically 8-8.5:1 on smog generation motors) usually results in a loss of power across the board - the later intake valve closing point results in a reduction of cylinder pressure. It is also why you should increase compression with long cams so as to maintain cylinder pressure and not lose bottom end torque - the limit on cylinder pressure is detonation resistance on the type of fuel used for a given loading condition. The late intake valve closing point reduces cylinder pressure by allowing the compression stroke to back feed the intake manifold while the valve is still open. Too much of this results in a loss of vacuum and rough idle, loss of fuel economy, and difficult drivability at the lower rpm ranges. At high rpm this can sometimes help force the charge into the next cylinder on the induction stroke and build more power. A single plane manifold makes this even more critical as it is then possible for a cylinder on the induction stroke to also draw exhaust, through the open plenum manifold, from another cylinder that would be at TDC on the exhaust stroke when both the intake and exhaust valves are still open (the overlap phase) - not generally what you want in a Jeep or tow vehicle but usually helps a drag car trying to make max hp at high rpm. A dual plane manifold seperates the cylinders so that at no time can the overlap phase of one back feed exhaust into another on the induction stroke. I've wandered off into another topic, but the point is you need to match piston CR with the cam and intake system for the intended operation. Leave high compression, long cams, and single plane intakes at the drag strip if what you want is rock crawling and towing power. More to the point of this discussion, a D-cup dish piston is an excellent way to control compression ratio and still maintain good quench and flame travel characteristics. A flat top with good quench distance is almost always going to result in too high a static CR for non-drag strip uses.

Holeshot

A flat top with good quench distance is almost always going to result in too high a static CR for non-drag strip uses.

That is exactly why using flattops & opening up the chamber is THE way to go. You get better flow & the proper .045" quench.

A big boost in power across the range & eliminate the ping. One of the few cases where you can have your cake & eat it too.

1980_Cj7

So who can open up the heads? Is it something we would want to try ourselves? How much does it cost to have it done professionally? Is there any downside like getting too thin anywhere? Not sure what route we are going to take when we put our engine back together, just trying to consider all options at this point. A big part of me says to just copycat what Donwags did. His engine is tried and proven and even dynoed. Just a reminder, this engine is in a CJ-7 used for rock crawling, not beating ol' Fuzz, although I'd luv to be able to do both. If the butcher shop steps up to the plate and does the right thing, I'm thinking custom pistons are looking better and better, to avoid going any bigger overbore than absolutely necessary.