Getting a dyno tune with sniffer

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Re: Getting a dyno tune with sniffer

Post by EMS »

It is hard to say what the actual drop from crank to rw is. Usually, it is calculated by a percentage. Although, for a given drivetrain, it should be a constant. So, the 120+ guess may be a tad too high.
70mm bore is around 1235cc and 71mm bore is around 1270cc. Any increase in displacement when keeping the same shape of the piston on top and cylinder head will increase the compression ratio, because you compress a larger volume into the same combustion chamber. If you go from 1047 to 1146 (67.5mm bore) the compression ratio with the same domed piston shape rises from stock 9:27:1 to 10:05:1.
Some Wiseco pistons have a flat top in order to reduce the compression and stay with the original ratio. A "higher compression piston" would have to have more of a dome shape, which would be difficult to incorporate into the CBX motor because of clearance to the valves. As a larger bore alone already increases the compression ratio, some larger pistons that keep the stock shape are designated "high compression"
There are plenty of sellers who have no clue and sell all kinds of pistons with all kinds of designations. I have seen the cruizinimage 67.5mm kits being sold as "stock compression", which is just not the case, because the pistons have the same top as the stock units.
I am putting a 72mm bore motor together (1304cc), which would be a 11.3:1 compression, using the stock shape pistons, but I am using a reduced dome piston to keep the ratio at 10.5:1

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Re: Getting a dyno tune with sniffer

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If 103 crank hp ends up 85 whp, then that's ~17% drivetrain loss. To me it seems like it should be expressed as a percentage, because the friction on items like meshing gears and rolling chain links, side plates, etc. will be proportional to the force applied, and I expect those losses to be more significant than things like windage or the drag from spinning gears in oil (which will depend on RPM, not force applied).

With a 17% drivetrain loss, 96 whp would be ~115 crank hp. This is about a 12% improvement. I don't claim to know if that's plausible for basic mods like a 0.5mm overbore, degreed cams, 6-2-1 header, and K&N filter. To me it seems like it's on the high side, but there may have been some porting or head skimming as well. Of course, there could also be a generous dyno...
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Re: Getting a dyno tune with sniffer

Post by wyly »

Syscrush wrote:If 103 crank hp ends up 85 whp, then that's ~17% drivetrain loss. To me it seems like it should be expressed as a percentage, because the friction on items like meshing gears and rolling chain links, side plates, etc. will be proportional to the force applied, and I expect those losses to be more significant than things like windage or the drag from spinning gears in oil (which will depend on RPM, not force applied).

With a 17% drivetrain loss, 96 whp would be ~115 crank hp. This is about a 12% improvement. I don't claim to know if that's plausible for basic mods like a 0.5mm overbore, degreed cams, 6-2-1 header, and K&N filter. To me it seems like it's on the high side, but there may have been some porting or head skimming as well. Of course, there could also be a generous dyno...
it'll be interesting to see what you find when it's opened up, a worn engine that still has 96hp at the wheel is quite good imo...are you thinking that you have even a larger overbore?


my wiseco pistons would have raised compression and my head was planed/decked as well raising it even more...some cam work, dyna coils, pipemasters, without another bike to directly compare to it's hard to know how much you've improved the ride ...not that in the end hp matters much there's more than enough hp and torque to get me in trouble with the law or killed :o :?
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

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Re: Getting a dyno tune with sniffer

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wyly wrote:it'll be interesting to see what you find when it's opened up, a worn engine that still has 96hp at the wheel is quite good imo...are you thinking that you have even a larger overbore?
I think it's more likely that it's had some headwork - porting, good valve job, and a skimmed head to bump compression. A skimmed head would fit with the fact that the cam sprockets were slotted so the cams could be degreed.

I suspect that it's valve guides and/or seals rather than rings given the apparent power output, but that's just a semi-educated guess.
my wiseco pistons would have raised compression and my head was planed/decked as well raising it even more...some cam work, dyna coils, pipemasters, without another bike to directly compare to it's hard to know how much you've improved the ride ...not that in the end hp matters much there's more than enough hp and torque to get me in trouble with the law or killed :o :?
I hear that. If the cylinders are out of round and it needs a re-bore, I'm really of 2 minds about it... On one hand, it's stupid to mod for more power when the bike already has enough. If I wanted a fast bike I could have bought a 10 year old GSX-R1000 for less than what I spent on forks for this bike. On the other hand, it seems stupid to opt for less power if an 1147 or 1163 setup costs the same as just doing 0.75mm over.
Phil in Toronto
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Re: Getting a dyno tune with sniffer

Post by daves79x »

Phil - rest assured (that really doesn't sound right, does it?) that your oil consumption is mostly ring blow-by. Bad valve seals are rarely the culprit with that much blowing of oil. You might even have a broken ring or two. But you will know soon enough, it seems.

Dave

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Re: Getting a dyno tune with sniffer

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Wow! If he has a blow-by in one or more cylinders and STILL makes 96hp rwhp....That has to be quite a motor. 8)

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Re: Getting a dyno tune with sniffer

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Syscrush wrote: I hear that. If the cylinders are out of round and it needs a re-bore, I'm really of 2 minds about it... On one hand, it's stupid to mod for more power when the bike already has enough. If I wanted a fast bike I could have bought a 10 year old GSX-R1000 for less than what I spent on forks for this bike. On the other hand, it seems stupid to opt for less power if an 1147 or 1163 setup costs the same as just doing 0.75mm over.
I would've preferred to keep the displacement it came with but a few frozen pistons and 35ys of rust and an overbore was unavoidable. the tech advised the smaller bore, according to him larger bores could come with cooling problems in stop and go city traffic that I do most of my riding in...

I'm good with the power it has(more than whatever it was stock) as long as it runs like a clock and great throttle response...
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

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Re: Getting a dyno tune with sniffer

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EMS wrote:Wow! If he has a blow-by in one or more cylinders and STILL makes 96hp rwhp....That has to be quite a motor. 8)
The mechanic said probably rings, too, and I had the same thought. If the rings are that bad, then the power # is seriously suspect.

We'll know soon enough.
Phil in Toronto
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Re: Getting a dyno tune with sniffer

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Compression #'s ranged from 145-160 psi, leakdown showed rings leaking on most cylinders, also some leakage on intake & exhaust valves.

I contacted Scott Miller, who remembered the engine. The conversation went something like this:

Me: I'm calling about a CBX I bought that has an engine supposedly build by Scott Miller.
Sandy: Oh, who sold you that CBX?
Me: <guy's name>
Sandy: Yeah, we know him well. Scott says it's been 20 years since that rebuild.
Me: Any chance he would have some notes about what was done to it?
Sandy: All in his head.
Sandy: He says it was just a refresh, 0.5mm over OEM pistons and degreed cams.
Me: Was there any headwork other than degreeing the cams?
Scott (overheard via the phone): That head is kind of a mess - a Honda tech before me damaged the lifter bores, that's why it makes noise when it's cold.
Me: :o

This was all just instant recall by Sandy and Scott. Pretty remarkable considering that he's built literally hundreds of engines since then.


Anyhow, looks like it's gonna be rings & hone at the least, plus a replacement head. Any advice on how to score a good head? Anything I should be doing to prep the head to go back on the bike, other than a valve job?
Phil in Toronto
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Re: Getting a dyno tune with sniffer

Post by wyly »

if he didn't do many cbx engines it would stand out in his memory but impressive just the same that he can recall any details at all...

I know where there was a head just this summer in calgary. Don't know the exact condition I recall it needed some repair, I think the shop wanted in something $200 range for it...

send them an email and find out if they still have it, they had it on ebay for a while but I know it didn't sell then because I saw it in a parts bin
www.oldmotorcycleshop.com/
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

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Re: Getting a dyno tune with sniffer

Post by EMS »

Make sure, the head you are buying has all the cam caps. Especially the one with the tach drive attachment is often broken. Also check the exhaust flange studs. Make sure none are pulled out or loose in the head with a bad thread.
The pinch bolt for the cam adjuster in the front of the head also likes to have a bad thread. Valve guide seals are a must to replace, once you work on it. Also, check the flatness of the unit.
And, taking the experience from the head you have, check the bucket bores for damage. When you install the buckets, make sure the right ones go in the respective positions. As described in the manual.

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Re: Getting a dyno tune with sniffer

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Thanks for the specific pointers, Mike.

If the lifters have been rattling around in damaged lifter bores, should I be buying a head assembly that includes lifters as well for some extra insurance?
Phil in Toronto
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Re: Getting a dyno tune with sniffer

Post by wyly »

with all those requirements it sounds like you might as well buy a complete rebuilt unit...Bert at Six Center could probably supply a completely rebuilt unit... http://www.sixcenter.nl/nieuws/

or Louis if you're just looking for parts
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

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Re: Getting a dyno tune with sniffer

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wyly wrote:with all those requirements it sounds like you might as well buy a complete rebuilt unit...Bert at Six Center could probably supply a completely rebuilt unit... http://www.sixcenter.nl/nieuws/

or Louis if you're just looking for parts
I've been in touch with Louis, and with Bill at TIMS, in addition to a local source who's been dealing with CBX stuff for over 30 years. Thanks for the additional pointer.
Phil in Toronto
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Re: Getting a dyno tune with sniffer

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Syscrush wrote:The good news:
F'n bike made 96hp at the wheel. :o I wonder if that dyno is a bit generous, but that number does kind of fit with my experience.
I now think that the dyno was very generous - having talked to the builder about what was done, there's just no reason to think that the engine makes that much power. When I said that the "number does kind of fit with my experience" I meant notoriously unreliable butt dyno stuff. It seems to keep up just fine with my cousin's VFR800, which should be good for ~90hp at the wheel, and weighs less than the CBX - but we were never drag racing under controlled conditions, just riding together and goofing around. It also feels faster than my old SV650, which had less power but was also a lot lighter. Again, no hard results to compare.
Phil in Toronto
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