Comp Ratio

[96flhpi]

Let the guy honing my cylinders talk me into 9.5:1 pistons (Wiseco) today.  Didn't disagree at the time cause only other choices close to stock seemed to be V-Twin 8's or Wiseco 7's.  But I'm second guessing now, and have until he orders the pistons (Mon?) to change my mind.  Is 9.5 really high CR in a shovel?  Seems like catalogs don't have anything higher so I guess so.  I'm looking for reliability, not power.

So what do you fellers with more engine knowledge think?  Again, this is my daily commuter, not a second bike to blast around on.  Don't want to spend the season chasing detonation or tunability issues. 

If 9.5 is not the way to go, anyone know about V-Twin piston quality (main reason I went with the higher comp Wisecos was I know they're quality) or should I lose a small amount of CR and go with the Wiseco 7's.  Would rather go with V-Twin 8's but not if they're crap. 

BTW, scoot is '82 FLH 80in.

Thanks in advance - I've been asking a lot of questions lately, first winter with the shovel, you've all been there at some point, no?

[shovelbill]

96,
JE makes 9.5 and 10.5, Arias makes some but i can't get on the site right now, KB makes an 8 and 9.5:1.
can't go wrong with an 8:1 keith black. you gonna do a cam, maybe something small for a bit extra juice?

[monty101]

been runnning weisco a long time and if I was wanting to get more pistons I'd get them again. the keith black have tight specs and I like looser specks on pistons.

[randallwhitman]

I've always heard that you most always get less actual compression than it stated by the manufacturer.  If you're running electronic ignition with a VOES, you'll love more squeeze.

[96flhpi]

Thanks for replies, but I'm more interested in how reliable 9.5 CR would be in a daily driver (and if it's gonna cause detonation or tuning problems) than debating piston manufacturers.  

If Wiseco made an 8 or even 8.5 there'd be no question.  Only asked about V-Twin cause they make an 8.  Just seems to me like 7.4 (stock) to 9.5 is a kinda big jump, but I don't know what I'm talking about so I put it to you guys.  

Bill - put an Andrews J in there last month.  Don't know much about it other than catalog said it was more power throughout the RPM band and it was bolt in.  Spend most of my time between 2K and 3K, almost never get to 4K.  Don't see a lot of cats running it in shovs so I wonder if I made the right choice - seems to be popular in pans though.  Oh well, got me a 5-pack of nose cone gaskets so no big deal to swap it out if it ain't working.  

That brings up another point - I'm not interested in having to match cam with CR and porting heads and high perf pipes and dual plugging heads and so on and so on.  I'm not a builder, just a guy with a torque wrench, some feeler gauges, a manual and some great advisors .  Just want a good reliable scoot I can commute on.  Hell, I'm running the stock Keihin butterfly (I know - crap, but other than a few coughs during warm up it doesn't give me any trouble).  

On the other hand, if I can get a little more juice w/o driving myself crazy or sacrificing dependability I'm not gonna say no.

BTW - dude doing cyl. said he don't like KB, wasn't going to argue. 

Running points Randy.

Any advice is greatly welcomed of course.  Thanks again.

[stroker800]

  I ran a low comp 74" engine for years ,,it was set up properly and it had great power ,good fuel mileage, ran cooler and could burn todays sh%tty gas. The higher comp,,10-1 would still be good power and better mileage, it may run a little hotter but not enuff for damage. I would recommend hi-test gas , single fire ignition and an oil cooler , these are all added performance all shovels should have.
Dave

[monty101]

my 9 1/2 weisco will ping if you lug it. I run 170 lbs of compression. I run premium. It might not ping if I was running dual plugs but I really don't know. I didn't ping much just a little when i lugged it and since they are forged I never worried about it. My old Harley 8 1/2 ran 100 lbs of compression and never pinged and I thought it ran pretty strong to be a stock 74. I have to admt the weisco pistons run great with 4 5/8 t/o torquemonsters and a b cam. Not comparable to the 8 1/2 stock 74. Still gets 50+ mpg too.

[flhswingarm]

I got 9.5 Wisecos for 8 seasons now.......... 160 + per cylinder and still running strong............most importantly, in 01 I dropped a valve.......the wiseco's caved in but didn't collapse and let crap into th bottom end..........I don't know a lot but I know what worked for me................'71 flh that will do anything i ask of her

[96flhpi]

Monty and Swingarm - did you guys have to do anything special to get 'em running right beyond jetting and/or getting the timing right?  Anything beyond that and I really don't want to get that involved - to be honest I'm still leaning towards getting the 8's just to be safe.

Thanks all for replies - keep 'em coming.  Like I said, probably gotta call him first thing Monday.

[crazycanadian]

The 9.5 will run very well .. especially if you put a lil more stick in it.
The mega low compression is 40 year old technology.. with all the new tech available and cams and proper tuning technics there is no reason you can't make it run well!

If you are encountering a lil pinging.. put one heat range colder plug in it and round off the electrode your ping will go away 9 times out of 10.

I've got evie and twinkies going out my shop door with 11.1 to 11.5 on pump gas and no ping.. all in proper engine building and tune up!

[tbkickstart2]

  With the head's off now, I would set my head's up for more lift now, that way you can put any cam you want to try later with no problem's with the lift. I'f it was mine, I would use the 9.5 piston's and put a electronic ignition that I could use a VOES switch to help with the detonation and use a cam with more duration than the J cam does. Andrew's B cam or the new B2 cam would work better than the J cam. I have not used the new B2 cam so I can't say much about it, maybe somebody has and they can help you out. Just something to think about.....TB

[flhswingarm]

96flh..........
No, I did not do anything special with the 9.5'ers............ while I had the heads off I clearanced them to accept the cam I bought at the time..... Crane "c"........ Anyhoo...........no ping at all with the Wisecos

[monty101]

I cut 1/16 of an inch off the skirts because of the add'l stroke clearance needed to run 4 5/8 flywheels. I ran revtech tall stroker cylinders. I also lightly ruffed up the piston domes with 400 grit wet dry sandpaper to get the "new" off. since I only cut 1/16 off I didn't weigh them. They were close enough and t/o who dynamically balanced the assembly said they didn't have to be exact weights. Both cylinders are both running I remember last time I checked after the rings seated 170 lbs of compression. The add'l compression is definitely worth running better gas in my books even though it never really had what I consider a pinging problem. The hgher compresiion means you run down the road and can keep up with the other traffic without running high rpms  because you can gear up your scooter to highway gears. I run 2.8 or so final drive ratio and the 89 incher pulls it fine. I run in 4th after I slow down to 40 mph just like a stocker but that's because of the heavy t/o flywheels. I don't think anything above 89 inches will still get 53 mpg on the highway like the 89 incher does. I know my 96 incher is runing a 2.5 rato and it only gets 42 on the highway and its even got a 6 speed.

[monty101]

yeah that 278 duration and cam overlap the c cam will probably lower the comp and make it easier to start and stop any pinging. I got a b cam with a lot less duration and lift. It's got a lot of compression. I did run a c cam for about a week but I took it out. I put it back in the box because I run in the lower rpm range because of the 2.8 final drive ratio and I need the torque that you get from the b cam at the lower rpm. If you decide to run the lower comp pistons you can always get the base of the cylinders machined down to increase the compression to what ever you want. Truett and Osborn did mine because in my  96 incher I put some s&s pistons made for 4 1/2 inch strokers and I wanted at least 9.5 to 1 compression . I forget but they can tell you how much they would need to shave off to get you comp up to what ever you want. I know some of those pistons that are low comp have only 7 to 1 or so comp ratio. good luck....I would suggest going with the 9 1.2 weisco and if the pinging is a issue buy premium gas or install some 1/16 inch stroker plates. That would be a cheap fix for any pinging problem and I think paying a little more for gas if you elect to will be well worth the extra power.

[shovelbill]

it's monday 96, what did you do?

[96flhpi]

Bill,
Went with the 8's.  Seemed like most of the advice to run the 9.5 was "all you gotta do is run voes or single fire or this cam or that cam and have the engine built right" and so on.  Like I said not interested in building an engine and don't know enough even if I did want to.  Also, kinda like to keep it simple as possible.

Only doing cyls. cause have the heads off already and the cyls were scored.  Kinda stupid not to take care of that while I'm already this far in.  Just want to bolt it all back together and be ready to go without worrying about this or that.

Do wish I could have used Wisecos over the V-Twin though.  Machinist said he uses them without problems but we all know they aren't the same quality.

Thanks to all for replies and advice.

[shovelbill]

for what you're doing with the bike i think you did the right thing, cast 8's are just fine. IF you want to do something else in the future, maybe look into a CV carb. lots of guys been raving about the swap and it's not very expensive. from what they've been saying, great fuel economy too.

[hotham]

I am running close to 9-1 in my 93"er.  Dual plugs and Compufire Elite ignition.  It runs great on 89 octane.  Jetting and tune up are perfect as the pipes have been on for over 10 years and they still look like new.  I am convinced the best thing you can do for a Shovelhead is dual plugs.  If you want quick starts and still be able to run a stock starter.  Two things I found are necessary.  A pair of fine wire battery cables an AGM type battery and a cam with later closing specs on the intake.  An ignition, like the Compufire is great, because you have so much adjustment to play with. 

[randallwhitman]

Hotham......I'm with you regarding that Compufire ignition.  Had the "high compression" version in my dual plugged 103 for years with a VOES......great stuff.  Randy