Dyno plots

[spondontrx]

Hi Mark, unfortunately the dyno man only gave me this one and I still haven't asked him for the files or another print.
However I have this one to show you made earlier on the same dyno ,the blue line from this one is also printed on the newer chart .
Changes in between these runs are a airbox that I made ,the cdi from Over (not a big improvement) , some changes to the carb's and no alternator (For track use I charge the battery in between sessions)
The beautiful bigger valves are still waiting on my desk to be fitted

[cobbadiggabuddyblooo]

There's that familiar drop around 3500 rpm ... I noticed the same on mine at 4500 and killer bought this up also .. I have an idea killer was working on it being a spring on the acc. Pump??? Any thought why this seems to be appearing...

[spondontrx]

I forgot to mention that the older (second) plot is without the acceleration pump (Keihin FCR41) . the newer plot is better in that area so maybe . The dyno man suggested the clutch slipping.

[sanddune51]

Thanks Theo, converting Newton-metres to pound-feet torque measurement shows your 90.75 Nm is just about 67 pound feet of torque. Reading off the graph this is at around 6700rpm.Thats nice .

I'm hoping my top end build will give equally impressive torque output at or just past 6000 revs.

Thanks for posting.


Mark.

[cobbadiggabuddyblooo]

You maybe able to talk the torque but can you walk the walk Baby..

[sanddune51]

Cobba, I'd really better hope I can or I'm not gonna be a happy camper .
Seems some pro tuners end up with bikes making power at high revs when they were expecting the opposite.
One things for sure ... theres no guarantees.

Oh, nearly forgot to mention, the engine I thought was an 878 high compression,turns out to be +1mm oversize with fairly deeply dished piston crowns (not good for my compression quest ). All this transpired after I'd already bought new JE 878 rings to refresh it
It seems at best I'm looking at an 868 low comp. big valved engine . I don't think I'll be reaching the stars with that,but it's what I've got.

I'm also wondering if 3VD +1mm pistons have a deeper dish than +1mm 4UN's

Mark.

[cobbadiggabuddyblooo]

Bummer Man..thats not fair after all you've done... TTS do a good deal for the 878 piston kits.. I'm sure someone out there would take the rings for an exsisting 878 rebuild if you went down that path... Gotta follow your dreams mate.. (I've been chasing those twin blondes all my life )

[misterdimwiddy]

Cobba, I'd really better hope I can or I'm not gonna be a happy camper .
Seems some pro tuners end up with bikes making power at high revs when they were expecting the opposite.
One things for sure ... theres no guarantees.

Oh, nearly forgot to mention, the engine I thought was an 878 high compression,turns out to be +1mm oversize with fairly deeply dished piston crowns (not good for my compression quest ). All this transpired after I'd already bought new JE 878 rings to refresh it
It seems at best I'm looking at an 868 low comp. big valved engine . I don't think I'll be reaching the stars with that,but it's what I've got.

I'm also wondering if 3VD +1mm pistons have a deeper dish than +1mm 4UN's

Mark.

Stock pistons in my used motor are pretty much flat topped, certainly not dished. Can post pics if it helps. Don't see why +1mm oversize would be any different?

I thought I had seen an 868 motor using stock pistons at 12:1 on here some where which sounded a good alternative to the JE.

If my motor stays together at Brands nxt month I may have the JE rings from you as a spare set. Hoping to never have to strip the thing again but you never know.

[Killerwhale]

Cobba, I'd really better hope I can or I'm not gonna be a happy camper .
Seems some pro tuners end up with bikes making power at high revs when they were expecting the opposite.
One things for sure ... theres no guarantees.

Oh, nearly forgot to mention, the engine I thought was an 878 high compression,turns out to be +1mm oversize with fairly deeply dished piston crowns (not good for my compression quest ). All this transpired after I'd already bought new JE 878 rings to refresh it
It seems at best I'm looking at an 868 low comp. big valved engine . I don't think I'll be reaching the stars with that,but it's what I've got.

I'm also wondering if 3VD +1mm pistons have a deeper dish than +1mm 4UN's

Mark.

Stock pistons in my used motor are pretty much flat topped, certainly not dished. Can post pics if it helps. Don't see why +1mm oversize would be any different?

I thought I had seen an 868 motor using stock pistons at 12:1 on here some where which sounded a good alternative to the JE.

If my motor stays together at Brands nxt month I may have the JE rings from you as a spare set. Hoping to never have to strip the thing again but you never know.

TDM piston crowns are concave, my 900 one´s laying around has a big slope in ´em...

[sanddune51]

Quote -"Stock pistons in my used motor are pretty much flat topped, certainly not dished. Can post pics if it helps. Don't see why +1mm oversize would be any different?

I thought I had seen an 868 motor using stock pistons at 12:1 on here some where which sounded a good alternative to the JE.

If my motor stays together at Brands nxt month I may have the JE rings from you as a spare set. Hoping to never have to strip the thing again but you never know."

Phil,
It seems early (3vd) Tdm ('92-'96) runs a lower C.R. than the Trx, hence the dished piston. The issue is not the piston oversize but the model the piston is intended for.Later pistons for the '96 on Tdm 850's and the Trx850 are marked 4NX and appear without the dish.
Of course this only applies to OE Yamaha parts,not aftermarket parts

Apologies for highjacking your dyno plot thread

This is my dished +1.00mm,clearly marked 3VD



Mark.

[cobbadiggabuddyblooo]

Here's the JE 878 piston for a comparision ..

[Killerwhale]

Tax refund at 1200£, guess the funding for the large valves are here....now just up to mech to shake up some time!!