the combustion chambers in a shovel are large and flat tops would drop compression a fair amount. Shovel pistons is what I would use. Not sure what the problem is with cast pistons but there is no reason to run forged pistons. The deck height of the cylinders may be different from a shovel to an EVO and therefor the piston may travel beyond 0 deck height. This would not be good.

 

the combustion chambers in a shovel are large and flat tops would drop compression a fair amount. Shovel pistons is what I would use. Not sure what the problem is with cast pistons but there is no reason to run forged pistons. The deck height of the cylinders may be different from a shovel to an EVO and therefor the piston may travel beyond 0 deck height. This would not be good.

Assuming that you check the deck height as mentioned by Mr. Springer, I like the idea of the flat top pistons iin your case. I'm just guessing but I sounds like you probably have some pretty high compression.

My Shovelhead is a stock 80" with stock low compression pistons. It's probably around 7.5:1 compression. Another guess, but Harley was probably thinking about detonation with the fuel that was available at that time. Mine will run perfectly on 87 octane. The low compression idea is a good one if it will enable you to keep the bike going and not detonate.

Even with the low compression, my bike will still do a good honest 100 mph. It's not all that fast getting up there but I'm not into high performance anyway. The bike is an old friend and I just want to keep it running as long as possible.

I would consider staying with cast pistons so that you can set them up fairly tight. Let us know what sort of pistons you come up with that will work in your Shovelhead.

 

Springer .. well .. I don't like cast pistons for one reason .. it's possible to burn 'em pretty easy .. I've seen several holed cast pistons in shovels and pans, and long ago holed a piston myself in a sportster .. all it takes is pushing too hard ona hot summer day, and/or an intake leak or some other mechanical disorder to do it .. forged however is bullet proof and they last longer IMHO .. I've put forged pistons thru hell an back with no physical damage to the pistons themselves .. yea, they can be noisy. and you do have to run them loose .. but I like the peace of mind of knowing that burning a piston is one thing I don't have to concern myself with when rolling thru 100+ degree temps far from home .. like Arizona for instance .. ever tried towing a trailer full of camping gear with a shovel, with poor "pump puke" fuel and the mercury over 100 degrees ? .. lol .. it'll send your nerves on edge the whole way and make an otherwise enjoyable trip a white knuckle teeth grinder .. forged pistons can take a beating when cast would have turned to fuel .. for this motor forged is only available in 9.5:1 static compression which is at least a point higher than I'd like to run .. I surely don't wanna shave the domes .. so .. since lower compression forged pistons are not redily available, I'm left with the choice of making the motor even taller with FAT gaskets, which won't do much, or having pistons made, which sounds expensive, or trying a flat top piston off the rack that'll clear the 4 5/8" stroke .. there is also the fact that big bore shovel pistons are only available up to .030" over .. I might need to go .040" and buying new barrels right now is not an option .. S&S big bore barrels are NOT cheap .. this is a budget rebuild .. need one more bore outa these jugs before I possibly go to fresh 3 13/16" barrels .. perhaps someone who's tried flat top pistons ina shovel can shed some light on my questions about trying it .. if it works good, I might try it with my "go fast" 11:1 motor .. thx

nomad

 

NewUltraClassic .. yea .. I'd run cast except for the reasons that I've outlined in my above post to Springer .. it'd be an easier solution, and would lower the compression to a workable # .. but, I'm set in my mind about forged .. I've seen too many holed cast pistons and have never seen a forged turn to fuel .. so .. unless I can figure another way, flat tops seem worth a try .. the heads I plan to use are single plug, and another reason to use flat top pistons .. I want to use these basically stock single plug heads simply cause they're fresh .. fresh guides and Manley valves, then I shelved them .. LOL .. bout time I put them to use and get some miles outa them .. they're no good for a high performance application, but should work well for what I want out of this motor .. this motor is for touring .. torque is my goal, not top end HP .. so these stock heads should work ok with the moderate lift short duration cam I plan to use .. still haven't picked out a cam .. gotta get past the piston thing 1st .. thx

nomad

 

flat top pistons in a hemi head motor would be good for maybe 5 to1. H.D. used to sell stroker plates to drop compression. cast pistons been around forever. If you run with intake leaks alot forged pistons arent the answer.

 

flat top pistons in a hemi head motor would be good for maybe 5 to1. H.D. used to sell stroker plates to drop compression. cast pistons been around forever. If you run with intake leaks alot forged pistons arent the answer.

High Compression is not always the answer to all things. It's ironic that two of the fastest motors that Harley-Davidson ever produced had not much more than 4:1 compression. The 1940's WR and 1950's-60's KR track bikes. Of course they were flatheads but both models were getting 125 mph out of 45 cu. inches. They were designed to breathe and rev close to 7,000 rpm.

Lots of folks are now using flathead pistons in Shovelheads and older simply to conserve the motors. My 1980 engine is completely stock and will still do close to the notorious "ton". (100 mph) That's plenty fast for me.

As to the forged pistons, the only thing I have against them for the street is that they generally have to be set up with higher clearance. That leads to more noise, greater wear and generally shorter life.

My .02

 

High Compression is not always the answer to all things. It's ironic that two of the fastest motors that Harley-Davidson ever produced had not much more than 4:1 compression. The 1940's WR and 1950's-60's KR track bikes. Of course they were flatheads but both models were getting 125 mph out of 45 cu. inches. They were designed to breathe and rev close to 7,000 rpm.

Lots of folks are now using flathead pistons in Shovelheads and older simply to conserve the motors. My 1980 engine is completely stock and will still do close to the notorious "ton". (100 mph) That's plenty fast for me.

As to the forged pistons, the only thing I have against them for the street is that they generally have to be set up with higher clearance. That leads to more noise, greater wear and generally shorter life.

My .02

I didnt say anything about speed. I believe 39 knuck went 136 in 39 (I think).KR were hybrids yeah they could rev real high. check out the bearings in them. My wifes buell blast will carry my 270lb ass to 100, course if you time it through the 1/4 with a calender. I dont think a flat head will rev to 7grand.

 

I didnt say anything about speed. I believe 39 knuck went 136 in 39 (I think).KR were hybrids yeah they could rev real high. check out the bearings in them. My wifes buell blast will carry my 270lb ass to 100, course if you time it through the 1/4 with a calender. I dont think a flat head will rev to 7grand.

The KR's often revved to 7,000 grand. I was involved in flat track racing via the pits for many years. They were damn fast.

I'm not sure what you mean by KR's being hybrids. They were available through dealers to anyone who wanted to race who could afford one. The factory team ones were special but the standard trackers were available.

 

The KR's often revved to 7,000 grand. I was involved in flat track racing via the pits for many years. They were damn fast.

I'm not sure what you mean by KR's being hybrids. They were available through dealers to anyone who wanted to race who could afford one. The factory team ones were special but the standard trackers were available.

I suppose one could call a motorcycle a "hybrid" If it was derived from the 1952 k model street bike. the kr was first noted in 1956 it was a ridgid, no brakes, ball bearing motor, flat out race bike and your right anyone could have one, if say in 1956 you and 28 of your friends could have bought the entire production run. so what would you call it?

 

WLA -vs- WR

The WLA had 4.5:1 compression ratio, The WR & WL (w/aluminum heads) are at 7:1 CR The WLA was lucky to run 65 mph for sustained distances. the WL could do 70 pretty easilyand top out at 80, and the WR speaks for itself...

 

The WLA had 4.5:1 compression ratio, The WR & WL (w/aluminum heads) are at 7:1 CR The WLA was lucky to run 65 mph for sustained distances. the WL could do 70 pretty easilyand top out at 80, and the WR speaks for itself...

I've never heard that the WR's were that high in compression. They were also relieved and I think the one that I had was lower than that. I had a 1946 WR when I first came to California. It had brakes and had been raced on TT tracks. It ran 92 mph on a quarter mile one time. Don't remember the elapsed time but it was doing 92 mph half way down the strip. Those things were quick for a little flathead and the KR's were even faster.

This may be heresy but in any case, I prefer lower compression for touring, especially with the price of gas these days.

I think that forged pistons need to be set a couple of thousandths looser than cast so that would rule them out for my bike. That would probably translate into greaer noise and oil consumption.

I had my Shovelhead bored at the local HD dealer about 6 years back and, at my request, they fitted the pistons very tight with stock low compression cast pistons. I broke it in carefully and it's still very quiet with no oil burning whatsoever.

 

I've never heard that the WR's were that high in compression. They were also relieved and I think the one that I had was lower than that. I had a 1946 WR when I first came to California. It had brakes and had been raced on TT tracks. It ran 92 mph on a quarter mile one time. Don't remember the elapsed time but it was doing 92 mph half way down the strip. Those things were quick for a little flathead and the KR's were even faster.

This may be heresy but in any case, I prefer lower compression for touring, especially with the price of gas these days.

I think that forged pistons need to be set a couple of thousandths looser than cast so that would rule them out for my bike. That would probably translate into greaer noise and oil consumption.

I had my Shovelhead bored at the local HD dealer about 6 years back and, at my request, they fitted the pistons very tight with stock low compression cast pistons. I broke it in carefully and it's still very quiet with no oil burning whatsoever.

92 mph halfway down the strip, that would be an 1/8mile right? do you really believe some of the things you post or are you just b.s.ing? even 92 in the 1/4 come on , figure the gear ratio to get a 45 flattie to do 90

 

92 mph halfway down the strip, that would be an 1/8mile right? do you really believe some of the things you post or are you just b.s.ing? even 92 in the 1/4 come on , figure the gear ratio to get a 45 flattie to do 90

Sorry, it was quarter mile. It was also 45 years ago so I may be weak on my rememberance. Those bikes would do 120 miles per hour into the corner on a mile track so it doesn't matter what the gear ratio was. The things I post here are from my memories as well as I can recall.

I suggest that if you doubt the items that I post you should put me on your ignore list.

 

Sorry, it was quarter mile. It was also 45 years ago so I may be weak on my rememberance. Those bikes would do 120 miles per hour into the corner on a mile track so it doesn't matter what the gear ratio was. The things I post here are from my memories as well as I can recall.

I suggest that if you doubt the items that I post you should put me on your ignore list.

what fun would that be? seriously though, check out www.beautyofspeed.com

 

what fun would that be? seriously though, check out www.beautyofspeed.com

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