×

Notice

The forum is in read only mode.
Welcome, Guest
Username: Password: Remember me
16 Dec 2020
The Joomla and Kunena packages have been updated to the latest versions.
Forum for GFR
  • Page:
  • 1
  • 2

TOPIC:

GFR power figures 10 years 2 months ago #3540

  • Valdeziscoming
  • Valdeziscoming's Avatar Topic Author
  • Offline
  • Premium Member
  • Premium Member
  • Posts: 99
  • Thank you received: 0
Does anyone know why (or if) the Crono makes more power than the GFR? The Gilera manuals quote a Crono Max power of 23 PW @ 9750 rpm and 22.5 Nm of torque at the same RPM. The GFR manual quotes 22 PW @ 10750 and 20 Nm of torque @ 10500 rpm.
Now I always assumed the GFR made a bit more power than the Crono because it was the last incarnation of the model and because Gilera revised the porting on the GFR which runs 194 degrees of exhaust port duration against the Crono's 186 (although transfer duration is 2 degrees less for the GFR at 128 degrees while the Crono's is 130). The GFR runs more ignition advance, 18 degrees instead of the Crono 16 degrees and a slightly higher compression ratio at 13:1 against the Cronos 12.5. Both bikes run a Delorto VHSA32ES although the GFRs main jet is bigger and there are other differences.

So if the quoted figures are good am I correct in thinking that by raising the exhaust port height the engineers have made the GFR engine rev a bit more but at the same time slightly lowered power and torque. Can anyone explain the reasons for Gilera doing this or is there something that isn't shown in the figures?

Also the bikes run the same internal gearbox ratios but the Crono is geared for higher speed as it runs a one tooth bigger front sprocket and a one tooth smaller rear. The GFR is also heavier than the crono by a few KGs. So the GFR revs a bit more but makes less power and torque but the GFR gearing will compensate for the slight power/torque loss, is this right?

Leigh

Re: GFR power figures 10 years 2 months ago #3541

  • 72degrees
  • 72degrees's Avatar
  • Offline
  • Administrator
  • Administrator
  • So many menus and buttons - so little time
  • Posts: 779
  • Thank you received: 17
Dunno! My older GFR runs a gearbox sprocket 1 tooth smaller than standard which I put on to do a couple of hill climbs. It was still a bit like a slug off the line and needed 'clutching' on hairpins.

The newer one has the legs on it though on standard gearing. This may be just because it has a new top end and the old one has 40000 Kms on the clock. Although Pat Sproston made some cryptic comments about it being 'special' in some way I don't think it has trick reeds or similar.

Anyway, name your dyno for a shoot out - or bring a Crono to Curborough in July and do an NHCA Give it a Go and we'll see which can get the highest speed through the finish. ;) The speed you take the last right hander has some bearing but the straight is long enough to make up for that if there is a real power difference. For comparison my lad's YZ125 managed 77 mph.
"Do not adjust your mind, there is a fault in the reality"
1957 175 Sport

Re: GFR power figures 10 years 2 months ago #3543

  • Kano Nordi
  • Kano Nordi's Avatar
  • Offline
  • Platinum Member
  • Platinum Member
  • Posts: 1728
  • Thank you received: 22
My Jedi was clocked over 100 at the Curbo' finish line :laugh:
As 72 said choose your Dyno to see if they are ponies or carthorses, revised ports, more compression and bigger jets were not changed to go slower
John

Re: GFR power figures 10 years 2 months ago #3544

  • Valdeziscoming
  • Valdeziscoming's Avatar Topic Author
  • Offline
  • Premium Member
  • Premium Member
  • Posts: 99
  • Thank you received: 0
Hi John,
That's the mystery for me, Gilera made changes to the GFR (in order to give more performance you'd think) and then quote lower power and torque figures. I've got to think the figures they quote are correct so I would like to understand the reasoning behind them and what's going on inside the engine.
I'd like to see power and torque graphs for the two bikes as this may show a more complete picture than just the Max power and torque figures.

Guess I'll have to wait until a GFR comes up for sale buy it, get both motors to the same condition and compare them back to back. Or meet up with 72 degrees in July!

Leigh

Re: GFR power figures 10 years 2 months ago #3545

  • Joachim
  • Joachim's Avatar
  • Offline
  • Platinum Member
  • Platinum Member
  • Posts: 1026
  • Thank you received: 42
The sad thing is that the GFR seems to have another connecting rod. I just cannot remembe rif it's some mm longe ror shorter.

Also the Crono has a different exhaust.
BTW it's much havier than the GFR one.

Also keep in mind that Luigi has to struggle with other italian brands.
Looking at those Aprilia and Cagica 125 'racing' bikes for young man, he may think some horses more and kilos less may be a good argument selling more of the Cronos.
Of course all those bike mags doing dyno tests will catch him.
So he says... sorry ;)

Beside this, you believe in italian data?

;) Joachim

Re: GFR power figures 10 years 2 months ago #3546

  • Valdeziscoming
  • Valdeziscoming's Avatar Topic Author
  • Offline
  • Premium Member
  • Premium Member
  • Posts: 99
  • Thank you received: 0
Hi Joachim,

Yes, the GFR connecting rod is different, slightly longer I think and runs a bigger crank pin. The steel exhaust can on the Crono is heavier than the alloy item fitted to the GFR, but the wheels on the GFR are quite a bit heavier than those fitted to the Crono!

Do I believe Italian data? Well of course sales brochures don't mean anything do they but I would like to think they would tell the truth in the technical manuals. No point in tell fibs in the maintenance manual is there, and anyway Gilera needed the GFR to sale well against the other Italian 125 rocket ships so one more little exaggeration wouldn't have done any harm.

Where is our inside man in Gilera to give us the truth the whole truth and nothing but the truth?

Leigh
  • Page:
  • 1
  • 2
Time to create page: 0.041 seconds
Powered by Kunena Forum