Topic: 78 CB750F Turbo, post build review

[Bamboozler]

Thought I'd share thoughts on the new turbo characteristics from what I can gather from my limited 70 miles of ride time on the back roads. 

With a crack of the throttle from a roll the bike sees first signs of boost around 5K, and will see full boost around 6-7k depending on which gear you're in and current speed.  This points to the fact that while improved, the turbo still sits on the larger side. Doesn't it fit the motor? I'm very much liking what I'm seeing and happy with the power delivery, this turbo is staying.  You just have to factor the typical slight delay (lag), but when you what to start moving getting into boost is quicker and less work to find verses the small T3 that it replaced.  The CBs performance brought smiles to my face a few times.

The clutch is still slipping with the Barnett heavy duty springs with stock clutch.  This will need to be addressed.  In a slow roll in 2nd gear a pinning of the throttle to wide open will get you to around 7k and full or just fraction of a second before full boost before the clutch slips sending the revs to the moon.  You can play in the boost a bit more if you roll into it and don't climb through gear in rapid fashion.  Will do some research, but thinking a extra plate will be added and see what happens with that.

For the first ride with the same jetting config from the T3 turbo the tune came in lean when in boost.  I was seeing 12.5-13 at 8-9psi briefly before shutting down and seeing enough to make a jetting change.  The steady throttle was rich coming in at 11.5-12:1 from what I can remember.  Idle is steady and sitting at 15-16:1 with the #35 idle/slow jets.  However, full choke is still too much fuel for it to start on the first few cranks and the throttle needs to go wide open to fire up the motor from the slight flooding.  Jets need to be smaller or fuel mixture screw turned in to help the starting; which doesn't make sense with the A/F past 14.7 (stoic)?

I made a change from the 120 mains to the next step up that I had (and could buy) which was 130s.  This improved the lean out but threw it at the other end of the spectrum with A/Fs coming in at 10.2-11:1 at 8-9psi.  A good conservative tune, but may be able to be improved (~11.2-11.8s) with a 125 main, if some place offers them?

To help the mid throttle cruise I removed one of the two shim washers under the needles and improved the A/F to 13-14:1, I may pull the second shim to see if the no load cruise can hit mid 14 to low 15s for MPG improvements, but it's fine for now.

I tried to change back to my stock #30 idle/slow jets but the new #35s I had installed enlargened the press-in hole to the point where the stock #30s now slide in and out... back the the #35s until new #30s are bought.

I have to address the pitot tubes and pull one of the two tube to reduce the amount of tube area hitting the fuel bowls.  I'm seeing a cruising A/F of 13-14:1 but when you slightly tip in throttle the A/F plummet to the WOT 10.2ish.  I think this is the pitot tube territory and will see if limiting that system slows that drastic drop in A/F.

When I get around to addressing the clutch slip I'll take it to the local dyno and see what numbers it pulls; barring no motor surprises before then .  I'm interested to tie in turbo size, boost pressure, and motor size, and butt dyno to HP number.

LED tail light is just about done and will post on that when finished.

[scartail]

Bam, you're the man!

With a turbo spinning at 80-100Krpm or so, oil gets thin. With forced drainage, it's on the other side. Don't know how you cover that. Is the oil pressure high enough to balance out?

[Bamboozler]

Haven't done anything that folks haven't already done many times before, glad you're enjoying the thread!

I reread your post a few times and I think I'm still missing the balance question.  As you said and I followed, the oil is pressurized by the motor and enters the turbo's CHRA (center housing rotating assembly, center section), processes around the thrust bearing, and dumps (at reasonable pressure) out the drain on the bottom of the turbo.  From here, in the CB's current setup, the oil falls into the accumulation chamber.  The pump's input hose attaches on the bottom of the accumulation chamber via a hose barb and sucks the oil out of the chamber and dumps it back into the top of the valve cover; sorta like a sump pump.  The pump's throughput is high enough to keep up with the volume of oil that is draining from the turbo.  Wondering if this explanation helps or am I still missing your question?

The change that I'm going to investigate is removing the accumulation chamber that is in between the turbo's drain and the oil scavenge pump.  If done the oil will exit the turbo's drain port and enter directly into the hose that connects to the oil pump.  There are people with similar turbo setups that connect the pump directly to the turbo's oil drain and have no reported issues (to my knowledge) with adversely affecting the oiling of the thrust/ball bearings in the turbo.  But as it stands the CB's oil system is working, I'm not seeing any oil being forced through the seals in the CHRA, which you would see if the oil couldn't exit the CHRA quick enough or backed up.  Hope this helps, if not lead me in the right direction.

[scartail]

Maybe I was thinking of it wrong. I was thinking, say at idle (thinking back, 80Krpm wouldn't be idle), you don't have alot of oil pressure pushing oil into the turbo, and conversely you have the pump sucking, could you dry out the cartridge? Maybe it doesn't matter. And on the other end, with less oil, could you run the savenge pump dry?

I haven't seen any reference on why running the pump on all the time wouldn't be good. I was just trying to think through possible reasons on why.

[Bamboozler]

I see where you're coming from now.  

That question you have is the same that I had when figuring out how to handle the oil system (would the pump negatively affect the oiling of the turbo's bearing).  I saw a turbo bike build use an accumulation chamber with vent port and thought it was a good idea because it prevents the scavenge pump from applying a vacuum on the turbo's oil line/system.  The turbo gets oiled from the feed line and drops into the accumulation chamber, the pump's vacuum stops at the bottom of the chamber.  If that vent hole in the chamber was plugged then vacuum could reach up and into the turbo's cartridge, and even beyond into the oil feed line and motor if the pump pulled a strong enough vacuum.  But the accumulation chamber is at atmospheric pressure because of the breather tube's hole to the outside and doesn't clamp down on the turbo's cartridge.

However, as I noted in the post above, there are people that have a pump hooked directly to the turbo's drain and the vacuum seems not to bother the abilities of the oil feed line from properly lubricating the turbo's bearing.  I'd leave the chamber in place but I'm not fond of that breather port being able to bypass the oil onto the road if the pump stops.  Maybe I'll just extend the breather line up to the top of the gas tank and have the oil puke over the top of the tank if the pump stops... at least I'll know immediately when things are going south with the oil system..  Though I think a reasonable solution would be to have a indicator light turn on if and when the pump stopped working for what ever reason.

The pump is a self priming diaphragm pump and can be ran dry.  So if a trickle of oil is all it gets fed with (idle) it shouldn't cause the pump any problems.  This faq covers the pump the CB is running http://www.scavengepump.com/faqs.shtml, both the CB's and the one offered at that link are what look to be rebadged Surflo pumps.

[scartail]

brother... double thumbs up!

A couple years back, I was blowing through turbos on my integra. My boss (an old lube guy) told me I should run a scavenge system with a pump. I'm on my third turbo, maybe I should have taken his advice.

That pump being self-primed (lube & temp) would be a good solution. And venting the chamber would be good right? It's better that the oil be pushed out the vent (pump failure), and blowing through your turbo seals. Atleast you can recognized it to some extent (oil puddle or oil-wetted legs).

[Bamboozler]

I like the idea of venting the chamber because it disconnects any affect the pump has on the turbo's oiling system.  I don't like what I currently have because if the pump would stop working I wouldn't notice the oil pouring out the chamber's short vent tube up in front of the bike where I can't see it.  If the pump would stop the chamber would fill up full, oil would pour out the vent tube, and as you said oil would be forced past the turbo's oil seals.  The only sign I would be able to catch is the exhaust that has been turned into a mosquito fogger via the mirrors (or stop and go traffic as smoke drifts by), or by the time the red oil light comes on.  I think as you noted the turbo would not fair too well. It seem that once these turbo's have their oil seals breached a rebuild is needed, or from what I've read at least.  I think, as you also noted, if you can extend the chamber's vent tube to a place that would be noticed immediately if it were puking oil it would be a win.

Another some what important idea it seems to follow regarding turbo longevity is having a restrictor on the oil feed line.  It seem to be more noticeable reading threads discussing the Chinese turbos that having a oil restrictor has helped people have positive results in preventing oil seals from becoming breached.  You will get those that get away without, but I've generally heard much better success when installing one.  Garrett's site says its more of a band aid and in most cases not needed with a journal bearing CHRA (but says a 0.040" restrictor for a ball bearing center).  I agree with this to an extent, a restrictor can compensate for having a poorly returned oil drain system that can't dump enough oil fast enough (so slowing down the feed helps the poorly ran drain system keep up).  I welded my adapter fitting shut and drilled a 0.062" hole to mimic what journal bearing restrictor ATP turbo sells (0.065") and it seem fine for almost 100 miles on the new turbo and around 300 or so on the old one.  I think if the restrictor was too small I would've had a sick turbo within the first 10 miles or so.

Lastly, seeing we're talking turbos, through reading quite a few threads to evaluate how well these Chinese turbo's are holding up for folks I come across the general consensus that they do not seem to live long after they are pushed past their maximum rated boost pressures.  This is something that a Garrett and other good quality turbo brands seem not to have much problem with.  A few times I've read of people having no problems for some time with their Chinese turbo when running a conservative boost pressure (teens low 20s psi), and then crank the boost up to the upper 20s low 30psi and have it sick within a few weeks afterwards. If that holds true the CB's turbo should live forever..

[ivanhoew]

in case it helps bam ,

i run into the same enrichment problem on the 500 ,

to solve it , i put a adjustable bleed valve in the fuel pressurisation line from the intercooler to the fuel pressure regulator ..with this , i can turn the valve while riding ,bleed off pressure to atmosphere ,and lean out the mix .

it only needs to open a little to have an effect ,but make sure its still rich enough on boost ...

 if you open it too far its possible to have the engine start to cut out as boost comes in ... in fact if you open it wide you can sit at the lights with the throttle wide open and the engine sitting at 4k rpm missfiring like its got launch control ,at night the entire headers glow bright orange ....but then they do that on my bike at night at any speed over 60 

regards
robert.

[traveler]

I'd be interested in a non-intercooled setup for my 550.  about 4-5 psi, draw through with a single carb.

Looking for an ATP kit....no luck thus far.

May have to fab it together.....which is TOUGH for this guy.

~Joe

[wannabridin]

GREAT looking bike man!  it came together so well!!!  can you elaborate on your tank and seat finish?  looks brushed?  this looks like a really cool alternative to painting silver!! 

[Bamboozler]

Hi Robert, hope all is well. That’s a pretty crafty method of fuel control having the bleeder value drop your fuel pressure regulator.  I will definitely keep that in mind when I get off my butt and address the enrichment again.  I’ve been kinda slow to get to wretch out and instead have been enjoying a running bike too much.   I’ve gotten around 1400 miles on it this spring so far and been having a blast; trying to ride whenever the weather permits.  I realized what is most likely attributing to part of the enrichment problem, that being the accelerator pump on the Keihin PD42 carbs.  I thinking pump is squirting my A/F ratios rich; at least with a decent twist of the throttle.  However this doesn’t explain why it’s still staying in the 10s with a constant throttle, this I think may be the pitot tube, diameter too large?
 
I have removed the last shim under the needles and blocked off one of the two pitot tubes.  Both failed to change the plunge to the 10s with a tip-in throttle.  Removing the clips lowered the low load/speed cruising a half a point or so leaner and the removing of the pitot tube didn’t change anything noticeably. I think my single pitot tube may be too large a diameter itself.  I haven’t taken the small amount time to hemostat clamp the silicone pitot tube and see what change occurs and reduce the hose diameter to adjust if it does effect the enrichment (like it should be).  I mostly see it pegged in the 10s when at highway speeds and up a slight grade when the motor is sitting at 0.5-1.0 psi of constant boost (i.e. pitot tube territory).  Again, interesting method of leaning the fuel you noted and will keep it in mind for a potential tool.

Hey Joe, Do you have any access to a mig welder that you could frame a turbo exhaust up with and pass it to a local welder tacked up to be TIGed?  Aluminum intake could be ordered or cut/fitted to size and taped up and passed to a tig welder for final weld, just a few ambitious thoughts? 

Thanks wannabridin!  The tank and seat is an area that is soon to be addressed.  The finish is natural brushed mild steel; there is no paint just a clear.  I do really like the finish, it shines nice in the sun, but there are some issues with it.  I sanded both the front and rear tanks down to 220 grit (I think) and when I was finished I wiped them down with acetone and sprayed them with Eastwood’s Diamond Clear.  I coated the fuel tank alone with several light/medium coats, just about a whole rattle can worth.  In later May I got stuck in some rain close to home and for whatever reason the water somehow got through the clear and the tanks developed small light spots of oxide; the gas cap lid being the worse. I’m not sure if it prepped it incorrectly, should have used Eastwoods “special” prep or what, but somehow there were microscopic pin holes or a breach in general to have moisture work on the metal under the clear across the majority of the top surface (sides not so much??).  It’s disappointing, because I like the finish.  One other thing is without a primer for a base it scratches down to metal much easier than paint.

Instead of the clear I’m having a local acquaintance (does good paint work) take the two tanks and hit them with a coat of paint/clear.  Leaning on silver with some smaller size metal flake to keep the same look as it is now.  This also gives the opportunity to bondo out the slight dents in the rear tank and maybe a slight one or two in the front.  Wish the clear with bare metal worked out better, but it just seems too difficult for it to bond to the bare metal and be durable as well; sucks.

[traveler]

Sounds like it's coming along......I'm thinking about getting the setup off of a Seca 650 turbo, and then modifying the manifolds to work......also playing with the idea of setting up a sin=gle carb draw through system.  In the J&P Cycles catalog, there is a company that makes a carburetor that has ALL jetting adjsutments made via screws accessible from the outside of the carb....so all you do is adjust the screws and that's it!  I just want a 4-5 psi kit that will work on my stock motor and will add a little juice, be unique and the 550 mill will survive it!

~Joe

[ivanhoew]

Hi Robert, hope all is well. That’s a pretty crafty method of fuel control having the bleeder value drop your fuel pressure regulator.  I will definitely keep that in mind when I get off my butt and address the enrichment again.  I’ve been kinda slow to get to wretch out and instead have been enjoying a running bike too much.   I’ve gotten around 1400 miles on it this spring so far and been having a blast; trying to ride whenever the weather permits.  I realized what is most likely attributing to part of the enrichment problem, that being the accelerator pump on the Keihin PD42 carbs.  I thinking pump is squirting my A/F ratios rich; at least with a decent twist of the throttle.  However this doesn’t explain why it’s still staying in the 10s with a constant throttle, this I think may be the pitot tube, diameter too large?
 
I have removed the last shim under the needles and blocked off one of the two pitot tubes.  Both failed to change the plunge to the 10s with a tip-in throttle.  Removing the clips lowered the low load/speed cruising a half a point or so leaner and the removing of the pitot tube didn’t change anything noticeably. I think my single pitot tube may be too large a diameter itself.  I haven’t taken the small amount time to hemostat clamp the silicone pitot tube and see what change occurs and reduce the hose diameter to adjust if it does effect the enrichment (like it should be).  I mostly see it pegged in the 10s when at highway speeds and up a slight grade when the motor is sitting at 0.5-1.0 psi of constant boost (i.e. pitot tube territory).  Again, interesting method of leaning the fuel you noted and will keep it in mind for a potential tool.

.

yup alls well ,just spent the day on the lathe , making a one off clutch for a turbo austin mini ...in 34 degrees ,dont you just hate flat roofs in the sun lol.

those problems you describe are just like the ones i had ....rich cruise and tip in ..the bleed valve brought that area down from 10 to 13 to 1 ,.. its the air velocity in the pipe that makes it so rich .

regards
robert .

[Bamboozler]

Sounds like it's coming along......I'm thinking about getting the setup off of a Seca 650 turbo, and then modifying the manifolds to work......also playing with the idea of setting up a sin=gle carb draw through system.  In the J&P Cycles catalog, there is a company that makes a carburetor that has ALL jetting adjsutments made via screws accessible from the outside of the carb....so all you do is adjust the screws and that's it!  I just want a 4-5 psi kit that will work on my stock motor and will add a little juice, be unique and the 550 mill will survive it!

~Joe

I hear what you’re wanting Joe, very alluring adding such a potent power adder.   If Robert’s (ivanhoew) 400/4 is any indication of what power these motor’s can manage you probably will be tempted in no time to see what just a bit more boost is like.  I like the idea you have with the draw through.  That carb sounds like money when you don’t have to disassemble anything to make a fuel adjustment; pays for itself in convenience. If you need any help getting something started just ask, would like to see your plan in motion!

yup alls well ,just spent the day on the lathe , making a one off clutch for a turbo austin mini ...in 34 degrees ,dont you just hate flat roofs in the sun lol.

those problems you describe are just like the ones i had ....rich cruise and tip in ..the bleed valve brought that area down from 10 to 13 to 1 ,.. its the air velocity in the pipe that makes it so rich .

regards
robert .

Uhg Robert, must be a labor of love crafting the mini clutch in a boiler room!  Sounds like an interesting project boosting a mini, that’s a big power to weight win!  You’ll have to pass a link to the build thread if/when one exists.  Hope a cold pint or two is/was in your future!

I agree with you that the bike needs a bit of boost reference adjust.  I’m thinking that installing a valve on the pitot tube just as you have done on your fuel pressure regulator boost reference would be a good solution that should give results.  I don’t know if I would need to bleed it to atmosphere but rather use it as a variable orifice.  The valve would be much easier than changing silicone tube or steel pitot tube diameter, thanks for promoting the idea!

Something that’s kinda related that I thought I share.  At the end of last summer I talked with the son of the owner of a cycle shop in New York State. This individual tunes the fuel injected bikes while his father works on the carbureted.  He’s tuned a bunch of boosted bikes on the shop’s dyno and noted that he shoots for an descending A/F passing through the value of ~12.3:1 or so as the motor is at 1-2psi on its way up to full boost (and the A/F on the way to a richer full boost value too).  I have never achieved this yet as my A/F has been in the 10s at this point, but wondering if there’s something to be gained by following suit.  He noted that customers sometimes note that it seems as if bikes feels slower after tuning but their actual mph at is much faster and the same given time; a smoother more powerful power delivery.  Being too rich, or lean for that matter, makes the bike sluggish and then “yanks” you on the handle bars when the peak boost and A/F merge/align into harmony and the power peaks (making it feel more power but slower overall).  I thought this was interesting bit of insight from someone who had quite a bit of experience on the matter.  It would be interesting to see if this sweet spot can be confirmed to be a good rule of thumbs tuning reference.

[ivanhoew]

now you'v done it  !

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=10207

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=10263

http://www.youtube.com/user/legrandphromage

that should send ANYONE to sleep !

[Bamboozler]

now you'v done it  !

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=10207

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=10263

http://www.youtube.com/user/legrandphromage

that should send ANYONE to sleep !

Haha, sweet, there is some great fabrication and customizing in your mini!  Being able to pull near 200hp out of that small guy is awesome to see.   Thanks for posting the links, like the video of the Mito, hope to see more of it too!

Jason

[Bamboozler]

It's November and I finally took the time to hit up the dyno.  Mark the guy who provided the TIG work for final welding on the bike took purchase of a DynoJet dyno this September and this weekend I swung by with the CB.  The bike had 4 pulls and successively increased the horsepower a bit more and more each time. This was in part from Mark raising the peak RPM from 9.25k to about 10k on the last pull.  The numbers were as follows.

87 RWHP
94 RWHP
96 RWHP
101 RWHP

This is with 93 octane pump gas, 8 PSI, stock spark timing and still stock motor.  I'd love to wake up that turbo a bit more and sit it at 12-15 psi with race gas and some spark timing yanked.. but I'm not 100% if the motor would start to object sooner than later if it's allowed to play there?.  All in all I'm pleased with the results!  I'll post the dyno graph when I get the .jpg of it. Forgive my 30min crash course with video editing.. work in progress. 

http://www.youtube.com/watch?v=Q3wsQRz2R60
[youtube=425,350]http://www.youtube.com/watch?v=Q3wsQRz2R60[/youtube]

[Flying J]

SO from a stock HP of 68 thats pretty good. It must be a beast to ride.

[Jerry Rxman Griffin aka MuthaF'er]

Nice all around job on the bike.

Stock, huh. I believe I'd unstock it with some Carrillo rods with that kind of HP! It'll cost you way more to rebuild it after it throws a rod!

[Bamboozler]

Thanks

I hear ya in regards to throwing some internals into it.  For one it will as you said reduce the chance of putting a more expensive possible hole in the side of the case, but it will also allow the bike to play in the higher boost range.  So far there's been 2500+ miles logged with it at 8psi from this summer, and plenty of full 8psi upper RPM fun and games.  Make you wonder how much HP is OK with the stock motor??? It seems it's OK with occasional dips in 80+ HP.  But ultimately there no better peace of mind that to have it supported properly...and you can then run more boost...

Bike is a blast to ride, a little late on the boost onset, but is easy to find. I'm playing around with a Garrett GT15 and another header as we speak and some other toys.  I'm curious as to what quicker boost will provide...

[MRieck]

SO from a stock HP of 68 thats pretty good. It must be a beast to ride.

68 would be a great day...a "GREAT" bike would come in at 52 stock on a rear wheel dyno (which weren't available in the day). The average would be about 47 to 50HP. These engines did not make a lot of HP

[Flying J]

Yeah but he started with a 750F, the best and most powerfull 750 ever built!

[bwaller]

I'm not sure if it's your runners beginning to smoke just before you back out of it or if maybe its off the back tire. Not an expert but I wonder if the rear end should be strapped down against the roller for the last ounce of hp.

[Bamboozler]

The smoke you see is the crank case blow by, the hose from the rear valve cover bung is ran down under the bike by the source of the smoke.  A fresh motor would reduce this a bit with good sealing rings.  I welded a bung in the exhaust for a crank case evacuation tube which I purchased (Vibrant), just have to weld a fitting to the tappet cover and give it a try.  I'm curious if it will reduce the amount of blow by and or free up some power as well.  The first attempt to weld to a ebay bought tappet cover didn't work because the aluminum was some odd pot metal that did not want to take to the nice aluminum on the AN fitting.  I have to get that guy finished, the AN line has been ready to thread from the exhaust bung to the valve cover since August, it would have been nice to have it finished for the dyno runs.. next time.

[BrianAdair]

This is way to cool....!
I have been considering turbocharging my CB750 later on.

I'm bookmarking this thread.

SWEET build man!