YPVS how much power

[phil38]

Right, I have an N2 which I've restored and rebuilt the engine. The plan was to go fully standard and then maybe fettle it bit by bit after. The only thing non standard are the reeds which I think are boysen or something similar. Bike is still on std bore, but was honed & new riken rings fitted. Bore size was within spec after hone.

Fitted new yam crank seals, new PV bushes & seals, fully decoked pipes, ultra soniced carbs.

the bike has been run in carefully and since ridden as nature intended. On the Dyno, it's only making 40hp, but revs cleanly out to 9500 and seems to run pretty well, no flat spots although a little rough at very light load around town.

Compression test gives 95psi hot, identical on both pots. Maybe on the low side, but not sure if that's really an issue.

Any ideas? Anyone one got real figures for an N2 or F2 on the Dyno. Book figure is 60PS, so it's way down on that.

[cb250g5]

On Gibsons dyno an untouched F2 YPVS makes 47 out of the box at the rear wheel. I had one & so did Stan () a few years back, both were within a gnats crotchet of each other.

60 is Brochure Horse Power, not Brake Horse Power

[Dieseldog]

Recently had my F2 on Mick Abbeys dyno, oem tune, PWK28's & a set of Mick's pipes made just shy of 51 ponnies

[higgsy]

40 seems a little low to be honest. Different dynos give different reading though, a dyno is a tool to show improvement not really an accurate indication of power unless similar bikes are run against each other for comparison.

But for reference my warmed over engine (slightly skimmed head and opened up inlets on PWK28's) gave 57 on the Bemsee dyno which is a dynapro, that's with Martin 77 pipes.

After I changed the barrels to a set of Uncle Bob's full proddy tune and played around with the inlet length and timing it gave 63 on Bobs dyno which is a dynapro as well.

I would have thought a stock F2 would be high 40's. A set of decent pipes would wake it up a bit, it does sound like the compression could be a tad low. But are the pipes clear and not chocked up, is the air filter good, some of the basics can make a big difference

H

[phil38]

Ok. I feel a bit better about it now. Perhaps it's a bit low but if the target is high 40s not 60, that makes more sense.

The Dyno I'm running on is definitely accurate and not optimistic (it's a government certified one), so perhaps that's a factor too.

Just wanted to know there was nothing very wrong before starting any mods.

Still a bit concerned about the rings with that compression though.

[midlifecrisisrd]

My local dyno had a standard ypvs at 45 horse.

The 60 figure would be measured at the crank, not the rear wheel.

Steve

[higgsy]

Manufacturers power figures are normally A. Taken at the crank. B Optimistic at best. There are a lot of variables in a dyno reading: Air density, heat, loading on the dyno, gear taken etc. that affect the given reading. I take more notice of the power curve and abnormalities in it rather than outright peak power. To go fast, drive is king :-)

Phil I think you might be a bit down, possibly it's the ring seal on slightly worn barrels? but it doesn't sound drastic, it would be worth going over the basics to see if something is slightly amiss. If it's on the standard F2 pipes they seem to suffer from clogging up over the years as well

[slinger]

If ya compression gauge is correct............95 psi is super low, and would indicate you need a rebore.

[steven]

Hi,
I would have thought that 95 psi compression figure is a bit low too, the YPVS compression ratio is slighly less than on a 4L0.
I would say that a YPVS engine should have somewhere in the region of 102 psi - 120 psi, so as has been said, it may be a bit low, but as also has been said, I dont imagine you are using a calibrated gauge.

Did you check the squish band? and if so what are you getting, as from standard they are usualy quite wide.

Did you use a standard or a pattern head gasket? If you used a standard one, swapping it for a pattern one should reduce your squish band and increase your compression pressure.

Only my 2p,s worth as Im not very well read on YPVS stuff or tuning for performance, as I find it hard enough to get a standard LC running properly without going to all the hastle of trying to get a tuned one to run properly.

steven.

[phil38]

I think the bores are good. They were honed and just within max size limits on standard, ring gaps were fine too. Rings are riken, which I know some have said are not as good as yam, but this was the only compromise as yam rings were silly money and norbo doesn't sell crap so I figured they'd be ok. Loads of people run mitaka pistons kits, so I'd have thought he rings make little difference. Both sides were identical, so I don't think I have a bore problem - maybe the gauge was reading a bit low.

Pipes are completely cleaned out (hot air gun, I'll upload the video at some point!).

Didn't check squish, head and base gasket were yam, so perhaps the compression is low?

Sorting out some old microns in the garage, so I'll try them. Snorkel is fitted too so may try pulling that out.

May whip the head off and have a measure up over the winter. What's a safe squish to run with good reliability?

[steven]

Hi,
I measured my squish band with the engine in the frame and the exhausts off.
You can get the solder down the plug hole and rotate the engine using the alternator rotor/flywheel.

With the exhausts off, you can look up the exhaust ports and see whats happening, and if you drop anything down the plug hole, it is easily retreived due to the exhausts being off.

I understand that the desirable squish band for a 350 LC or YPVS should be in the region of 0.9 - 1.2 mm.
You will find that in the real world most LC,s left the factory with the squish band in the region of 2.0mm - 2.5mm or more due to the problems encountered reaching production tollerances on mass produced pistons, con rods, and cylinders, etc so they deliberately made them with wide squish bands.

I faffed about for ages with mine changing heads etc and gaskets, my standard engine was about 2.8 mm or something like that before I started.

Eventualy I got mine down to about 1.8mm or so by using a pattern head gasket which is thinner than a genuine one, and a standard cylinder head that gave me the tightest squish band, I was amazed at the differences in standard un-machined cylider head sizes.

Appart from being re bored my engine is totaly standard and shows 130 psi, its been on the road since last year, and so far so good.

I think to get the sqush band down to 0.9mm - 1.2mm, machining of components is probably required, which is a route I did not want to go.

From what I read, if your bike has a slightly wide squish band, it will not make full power, but unless you are racing it you will probably never know.

steven.

[mikee]

You should be looking for nearer 150 psi on a comp test , 100 is way low

My 31k motored mito makes just under 54 rwhp on uncle micks dyno

[bare]

clumsy fingers sorry

[bare]

Sept 27, 2014 12:48:58 GMT 1 slinger said:

If ya compression gauge is correct............95 psi is super low, and would indicate you need a rebore.

There You have it :-)
95psi is silly low comp. In fairness tho every Comp test will result in a differing number with different individuals testing.
On the other hand 150 psi is into 'start worrying' ranges.
In MY testings Riken rings are Sketchy at best, Producing 15 LESS psi than OEM rings under exactly identical test conditions.
As for Boysen Reeds? Please.. Oem steels are Far better performers.
Dyno numbers can be all over the place.
Dependent on type/quality of the Dyno Contraption used.
Then there are the Operator input 'correction ' factors.
Hardly Tablets from the Mount.. readouts :-)

[phil38]

Sept 29, 2014 4:21:21 GMT 1 bare said:

Sept 27, 2014 12:48:58 GMT 1 slinger said:

If ya compression gauge is correct............95 psi is super low, and would indicate you need a rebore.

There You have it :-)
95psi is silly low comp. In fairness tho every Comp test will result in a differing number with different individuals testing.
On the other hand 150 psi is into 'start worrying' ranges.
In MY testings Riken rings are Sketchy at best, Producing 15 LESS psi than OEM rings under exactly identical test conditions.
As for Boysen Reeds? Please.. Oem steels are Far better performers.
Dyno numbers can be all over the place.
Dependent on type/quality of the Dyno Contraption used.
Then there are the Operator input 'correction ' factors.
Hardly Tablets from the Mount.. readouts :-)

I had seen in other posts that you tested the Riken rings back to back (this was a while after I'd fitted them). It's surprising they are that different (and it was only one set you tested I guess?), but then if I have 110PSI (15 more than I have), I wouldn't be concerned. I think I need to try another gauge to be sure.

Boysen reeds are a guess at what's fitted. They're fibre ones and were on the bike when I got it (it wasn't a performance mod I was expecting to get some improvement from, but at the same time I didn't feel inclined to change back to standard)

I'll measure the squish next as a very large clearance will also give low compression pressure and lower power.

It is an N2 so they have lower compression ratio than LCs and 31Ks and apparently can be pretty wide on squish

[slinger]

Try another gauge and see if your readings are different!

If I've read your post right it sounds like you had the bores honed out to the max limit (example 64.10mm) and used the same pistons but new rings.
This will not be helping your comp readings at all, the ring gap maybe with in spec but your have quite a lot of piston rock.Personally unless your going to address the positive deck height,thick gasket and massive chamber volume it ain't going to matter what your squish gap is.

[phil38]

Sept 30, 2014 19:46:28 GMT 1 slinger said:

Try another gauge and see if your readings are different!

If I've read your post right it sounds like you had the bores honed out to the max limit (example 64.10mm) and used the same pistons but new rings.
This will not be helping your comp readings at all, the ring gap maybe with in spec but your have quite a lot of piston rock.Personally unless your going to address the positive deck height,thick gasket and massive chamber volume it ain't going to matter what your squish gap is.

You are correct. Bores were honed to remove some light scuffing caused by stuck rings and came out just on the top limit. Don't think piston rock should be a big factor on a comp test considering the long skirt, it maybe.

Your points on deck height gasket and chamber volume are presumably referring to the engine design? Surely measuring the squish will tell me where my engine is (considering the tolerances) taking the first two of those into account?

[higgsy]

It is an N2 so they have lower compression ratio than LCs and 31Ks and apparently can be pretty wide on squish

? ? ? ? The motor is the same as the F2. All stock Yamaha have large squish clearances, all powervalve models are the same as far as piston to head volume is concerned, don't take any notice of the supposed different heads with Y1, Y2 etc. All measure up the same.

Slinger has hit the nail on the head. You need new pistons. Maybe a rebore. Reducing your squish and upping the compression will help, but it will only mask the real problem

[steven]

Sept 30, 2014 19:46:28 GMT 1 slinger said:

Try another gauge and see if your readings are different!

If I've read your post right it sounds like you had the bores honed out to the max limit (example 64.10mm) and used the same pistons but new rings.
This will not be helping your comp readings at all, the ring gap maybe with in spec but your have quite a lot of piston rock.Personally unless your going to address the positive deck height,thick gasket and massive chamber volume it ain't going to matter what your squish gap is.

Hi,
What should the "deck height" be ? Should it be a positive or a negative reading?
I looked for different thickneses of base gaskets when I was doing mine, but found no one selling different thickness base gaskets for LC,s or Ypvs,s, I suppose you could make them up yourself to the required thickness if you wanted.
I have never seen this figure written down or mentioned for an LC or a YPVS, is it the same figure for 4L0 and Ypvs?
Thanks,
steven.

[midlifecrisisrd]

Oct 1, 2014 10:20:06 GMT 1 steven said:

Sept 30, 2014 19:46:28 GMT 1 slinger said:

Try another gauge and see if your readings are different!

If I've read your post right it sounds like you had the bores honed out to the max limit (example 64.10mm) and used the same pistons but new rings.
This will not be helping your comp readings at all, the ring gap maybe with in spec but your have quite a lot of piston rock.Personally unless your going to address the positive deck height,thick gasket and massive chamber volume it ain't going to matter what your squish gap is.

Hi,
What should the "deck height" be ? Should it be a positive or a negative reading?
I looked for different thickneses of base gaskets when I was doing mine, but found no one selling different thickness base gaskets for LC,s or Ypvs,s, I suppose you could make them up yourself to the required thickness if you wanted.
I have never seen this figure written down or mentioned for an LC or a YPVS, is it the same figure for 4L0 and Ypvs?
Thanks,
steven.

Search for banshee base gaskets. You get one piece ones that are different thicknesses.

Steve

[phil38]

Oct 1, 2014 5:25:12 GMT 1 higgsy said:

It is an N2 so they have lower compression ratio than LCs and 31Ks and apparently can be pretty wide on squish

? ? ? ? The motor is the same as the F2. All stock Yamaha have large squish clearances, all powervalve models are the same as far as piston to head volume is concerned, don't take any notice of the supposed different heads with Y1, Y2 etc. All measure up the same.

Slinger has hit the nail on the head. You need new pistons. Maybe a rebore. Reducing your squish and upping the compression will help, but it will only mask the real problem

You may well be right. Should maybe have re-bored rather than accepting the engine at max limit with a hone, but it was nice to have and engine which hadn't been re-bored and with gen yam pistons (can't be many about), not to mention saving the cost of a re-bore and two new pistons.

I though comp ratio on F2/N2 was a bit lower than 31K, certainly lower than an LC. And yes, they will all have large squish. It's highly unlikely that mine is an outlier in terms of squish clearance, but there is a manufacturing tolerance on con-rod length, crank case, barrel height, piston height, head & gaskets. With all of those things selected at random with the engines assembled you'd expect a squish of about 1.9mm, but there will be a built tolerance. If Yamaha measured each engine or graded different parts to ensure engines all fell within a narrow range then it's unlikely any engine would be very wide. Saying that if the optimum squish is ~1.0mm and the average (nominal design) is 1.9mm, then maybe the tolerance is 1.9mm =/- 0.9mm so worst case is 2.8mm?

My logic is probably bollox, but if an engine ended up at ~2.8mm, the compression ratio would end up about 5.3:1 (according to my rough arsed fag packed calcs). So if a good bore does 120psi at 6:1, then one with a max tolerance squish will be about 105psi.

OK, I need a re-bore! (assuming the gauges are OK and I don't have a freak engine with 3.5mm squish!)

[slinger]

Oct 1, 2014 10:43:01 GMT 1 midlifecrisisrd said:

Oct 1, 2014 10:20:06 GMT 1 steven said:

Hi,
What should the "deck height" be ? Should it be a positive or a negative reading?
I looked for different thickneses of base gaskets when I was doing mine, but found no one selling different thickness base gaskets for LC,s or Ypvs,s, I suppose you could make them up yourself to the required thickness if you wanted.
I have never seen this figure written down or mentioned for an LC or a YPVS, is it the same figure for 4L0 and Ypvs?
Thanks,
steven.

Search for banshee base gaskets. You get one piece ones that are different thicknesses.

Steve

There,s no given rule what the deck height should be to be honest, you work with what you have most of the time. If you remove the head gasket skim the head and re-work the chamber to get you 20cc volume and .8mm squish gap you end up with 140 psi static comp at sea level with a stock 1UA exhaust port height.
If you machine the deck height you can increase the static comp along with the geometric comp (which go hand in hand). A +4mm stroke crank I use a positive deck height and machine the head to run the piston up into it.

At 6000 ft above sea level using 20cc chamber volume and giving 130 psi static comp made 5 WRhp over a stock head when dynoed on the same day.