Forum Donations
Search
VTF Google Search
 Click Here

750 and 920 cylinder heads

Technical Virago Help Topics
  • Advertisement

Post a reply

750 and 920 cylinder heads

PostAuthor: dazthebiker » Tue Jun 04, 2019 8:06 am

Does anyone know if the 750 and 920 heads are the same?

Owing to a ruined gearbox in my 750 i have decided to swap to a 920 engine, but i spent days porting the 750 heads and matching them to the inlet and exhaust flanges, and im wondering if they are the same so i could put the 750 heads on the 920? If they are machined with smaller chambers to suit a smaller bore then they might end up increasing compression a little, which would be no bad thing.

dazthebiker
Junior Membership
Junior Membership
 
Posts: 74
Joined: Sun Feb 11, 2018 11:16 am
Location: England Flag
Bike year & model: 81 xv750
Sex: Male

Re: 750 and 920 cylinder heads

PostAuthor: nanno » Tue Jun 04, 2019 8:32 am

dazthebiker wrote:Does anyone know if the 750 and 920 heads are the same?

Owing to a ruined gearbox in my 750 i have decided to swap to a 920 engine, but i spent days porting the 750 heads and matching them to the inlet and exhaust flanges, and im wondering if they are the same so i could put the 750 heads on the 920? If they are machined with smaller chambers to suit a smaller bore then they might end up increasing compression a little, which would be no bad thing.


No they are not the same, but yes they fit and yes they increase compression. And due to the smaller valves, they increase gas-velocity in the ports improving low-end torque.

(It's what I did with 700 heads on my stroked (Xv1100 internals) TR1.)

Cheers,
Greg

P.S.: As you will find some numbers, once you start looking. In most c/r-calculations people forget to figure in that the piston sits low in the bore and that the headgasket has got some height too. 700 heads on my 1063 engine results in approx 10.25:1 compression ratio. (Without figuring in the above you end up in the mid 12s)
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
User avatar
nanno
Silver Membership
Silver Membership
 
Posts: 1236
Joined: Thu May 26, 2011 4:06 pm
  Flag
Bike year & model: 1981 Yamaha TR1
1982 Yamaha TR1 Turbo
1977 XS 750 Sidecar
1984 XT500 4Valve (Austrian Tax saving edition)
1979 RD250/R5/DS7-hodgepodge (in bits)
Sex: Male

Re: 750 and 920 cylinder heads

PostAuthor: nanno » Tue Jun 04, 2019 9:36 am

dazthebiker wrote:Does anyone know if the 750 and 920 heads are the same?

Owing to a ruined gearbox in my 750 i have decided to swap to a 920 engine, but i spent days porting the 750 heads and matching them to the inlet and exhaust flanges, and im wondering if they are the same so i could put the 750 heads on the 920? If they are machined with smaller chambers to suit a smaller bore then they might end up increasing compression a little, which would be no bad thing.


No they are not the same, but yes they fit and yes they increase compression. And due to the smaller valves, they increase gas-velocity in the ports improving low-end torque.

(It's what I did with 700 heads on my stroked (Xv1100 internals) TR1.)

Cheers,
Greg

P.S.: As you will find some numbers, once you start looking. In most c/r-calculations people forget to figure in that the piston sits low in the bore and that the headgasket has got some height too. 700 heads on my 1063 engine results in approx 10.25:1 compression ratio. (Without figuring in the above you end up in the mid 12s)
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
User avatar
nanno
Silver Membership
Silver Membership
 
Posts: 1236
Joined: Thu May 26, 2011 4:06 pm
  Flag
Bike year & model: 1981 Yamaha TR1
1982 Yamaha TR1 Turbo
1977 XS 750 Sidecar
1984 XT500 4Valve (Austrian Tax saving edition)
1979 RD250/R5/DS7-hodgepodge (in bits)
Sex: Male

Re: 750 and 920 cylinder heads

PostAuthor: dazthebiker » Fri Jun 14, 2019 10:32 am

excellent, thanks nanno!

dazthebiker
Junior Membership
Junior Membership
 
Posts: 74
Joined: Sun Feb 11, 2018 11:16 am
Location: England Flag
Bike year & model: 81 xv750
Sex: Male



Post a reply


  • Advertisement

Return to Virago Help "Tech"

Who is online

Registered users: chrismalm