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Compression height V11 vs. LM1/2

H

Hudriwudri

Tuned and Synch'ed
Joined
May 21, 2010
Messages
32
Location
Genoa, Italy
Hello fellows,

Long time no hear.
Since I finally have again a lil money to spend and more importantly time to continue on my round fin engine I wanted to ask if one of you would know if the v11 sport pistons have the same compression height (pin to piston deck) as the round fin LM/SP pistons.if somebody could assist me with reliable info it would be very kind.
In case of identical compr. height I could save valuable money and get myself some forged 92mm (i know/think thats imho about the upper mentally ;) :lol: sane limit for round bore big bores) pistons almost off the shelf instead of spending zillions for getting some custom made

Many thanks in advance and

Kind regards e tanti saluti da genova

Christian
 
No they are different by 1mm to allow for 2mm longer stroke. You can use thinner base gaskets and shave the cylinders to compensate.
 
hi gray,

thanks a lot for your info.
That was vey kind of you and very appreciated.
I will let you fellows know about further progress.
Pretty soon i should start with measuring, reworking and porting of the Guzzi heads of which im allready really curious about!!

kind regards

Christian

PS: @gray do you plan to eventually also do any competitions in europe besides spa ?
 
You're welcome. Yes at some point I hope to do more racing over there. We are planning on Spa next year. I would love to do Imola again.
 
Hi gray,

sorry for the delay in responding!
Hmm sounds great let me know in case you go again to imola as i might try to stop by as it isnt "too far" from here.
Would be nice to meet!!

kind regards from genoa

Christian

PS: I take it that the V11 pistons also have different squish widths as the V11 combustion chambers are supposedly bigger in diameter?
 
Hi. For sure if I go to Imola I will let you know.

I would recommend using 90mm pistons on the round fin engine. It's what I have on my street bike. It runs beautifully. I'm also building a 90mm square fin race engine which should produce close to 90hp..

Any bigger and the liners get thin. With 90mm pistons the stock liners are approx 2.5mm thick. To use 92mm pistons you really should use thicker liners which a. cost money and b. you have to bore the cases so you are back to spending money again......

With all the hassle of making v11 pistons work I think it would be easier and cost effective to buy a 90mm Nikasil piston/cylinder set from one of the German suppliers e.g., HMB, HT MOTO or Dynotech.

A good compromise is to buy only the pistons from them and use your stock steel liner.
 
Hi gray,

Thanks for your reply!
Ok than let's say some wine together at imola hopefully soon :D
Yup I agree and the 90mm solution it's gonna be most likely in the long run as a kind friend offered me a set.
Although to explain my point clearer:
My goal in mounting bigger diameter pistons is less for the gained displacement but solely a challenge of being able to stuff in bigger valves and have a easier approach at the squish surfaces.
With 92mm I could hypothetically go "hypothetically" all the way up to 50-51mm which is IMHO about the limit within the given limit of the cylinder stud distance bottleneck (~47mm)
The case I have to bore out anyways, but machine work should not be the hindering problem as I have a pretty good equipped shop, thanks to years of saving and being a chronic gearhead haha. ;)
Though after all I'm inclined to think to keep the engine for now a lil bit more timid, and stay for now, with 47-48mm valves lotsa heavy duty porting work , together with lots flow testing (to reach the needed 220-230 cfm) the stuff among other stuff like cams etc, which should be good for about +100 horses regarding my experience with big singles.
Hum hum hum....not easy to take final decisions, but on the other hand, that's what makes tuning such a beautiful endeavour and whileworthy challenge!!! :p :D :D

Have a nice evening and nice greetings

Christian

Ps: for personal reasons I ain't too big a fan of dynotech, while helmut taborsky seems really to be a nice guy!
But there are also other fellows as horvath (now retired) and IMT in Munich, not to forget the fellas in Spain.
Ghezzi unfortunately seems to be missing in action and following other projects like the upside down three cylinder engine.
 
Hi. Wine at Imola sounds great :)

As wonderful as it sounds to go big valve on the round fin I have to say again 90mm is the way to go and stick with 44/37 valves. It's a great set up. Have you thought of 80mm stroke to bump displacement and compression. Probably give you better results :)

If you want to play around with 92mm buy an old California engine.

Regards, Andrew.
 
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