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Blown Triumph Triple Chopper / Bar Hopper Build

63K views 323 replies 44 participants last post by  knuck39 
#1 ·
I've been waiting to get this build on it's way for far too long but working on another triple build has taken up most of my time.

I well be using a supercharger from a Mercedes SLK, I plan to remove the top cover and make my own better looking version.

I have an SU carb for this build and I will plan to leave the stainless intake pipework raw and bolted together with the star mounts.

So I finally got the engine mounted in the jig. I'm using the stock frame just to get the engine aligned and pitched right. Next is to weld some supports to maintain the engines position and then I will remove the stock frame and bin it and build the new frame around the engine.

I'm going to stick to the stock 30 degree rake and 1426 mm wheelbase to maintain some good handling. This is a bar hopper and I expect to ride it hard.

Things are progressing slower than I would like but sometimes life just gets in the way. Now I have digital readouts setup on my mill and lathe I can start the fun work of building, brackets, mounts and the axle plates and get the frame build under way.

Take a seat.

Cheers Dan.













 
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#246 ·
No.

The BOV is designed to be regulated by vac which is done by throttle. If there is vac on the head side of the carb, that means the slide or butter fly is closed or close enough. The BOV opens with the vac signal and allows pressure to be relieved in a relative manner. Before the carb.

A burst panel or the like, a pop off valve is there for the unexpected back fire after the carb, in the intake before the head. This unexpected, uncontrolled explosion needs a place to go. You dont want it loosening any parts or removing them.
 
#247 · (Edited)
I apologise for being dumb - (it's something I often have to do!) - I don't get the difference between a BOV and a POV. When I search I get the same item.

I totally don't know what I'm doing! :eek:

If anyone can show me how a BOV is different to a POV, I would be eternally grateful - or at least until I've finished this beer.

Hang on - does one let air into the system and one lets air out?
 
#250 ·
No because the POV is purely a safety device as it protects from any over boost and any backfires through the intake, but the BOV is there to stop the now static compressed air from causing problems with the SC, BOV where essentially intended for turbocharged applications as when the throttle is closed the static compressed air reverses direction and stall the spinning turbine which make for more lag as it has to re-spool and can in extreme cases damage the compressor turbine,

SC don't really need the BOV as the compressor veins are direct drive so cannot stall, but in extreme high boost cases can also be damaged.
 
#251 ·
^^^Right.

With a SC, normally your style is a draw through. Making the slide or butterfy be the regulator for air INTO the SC. Consequently that effects the amount if air compressed.

You have installed your Charger to be constantly compressing air only regulated by rpm and dispacement of the Charger itself as setup pully wise and so on.

You have what Tricky-Rickey is describing in a normal turbocharged or centrifugal supercharged blow through application. You will need to bleed off the ununsed pressure. Part throttle and closed deceleration and such.

Look up burst panel in a roots style supercharged application. That is the pop off valve for that application. It is installed in the intake below the supercharger. If there is a back fire, it pops open and releases pressure. If you dont add one of these as well after the carb, you will be picking up your carb at the least, off the ground. This device is regulated only by predetermined spring pressure holding it closed. If the Charged air is at a higher than desired/designed level, it will open. Over boost or backfire.

Quick answer is you can buy a BOV. You probably will have to make or modify your POV. Starting with light spring pressure and increasing till it suits your application.
 
#253 ·
I'm guessing at this point if I had not mentioned BOV this would have been easier.
What you do need is the blower size and drive speed matched to the boost you wish to reach.
You also do need the pop off to vent the pressure in the intake in the event of a back fire.
You do not need a BOV. Although using one between the carb and blower would allow some adjustment to lower the boost pressure.
Timing can be as simple as having fixed timing...or as computer controlled as you like.
Water injection will allow more timing and also cool charge.

I made a correction to my post 229 were I said,.
''Intake side is just open to the inside of the box.''
I missed editing that out before making that post.
The intake manifold is connected to the carb base threw the wall of the box.
My apologies for screwing that up.
 
#258 ·
Wow, thanks for all the input guys - JAWS, I did search on what you said and I am clearer on that now. I can make a pop off now I understand what it is and I found this of one on the Jalopy.



Joe, no worries about your "mistake", I so appreciate you chipping in on this little old build thread. I posted back in #232 a piccy of the carb box and how the carb sits in it. Does this now not stand?



Also Joe, you were bang on with the solid float and Burlen do a solid float for the HIF6 carb I am using - thanks.
 
#260 ·
Wow, thanks for all the input guys - JAWS, I did search on what you said and I am clearer on that now. I can make a pop off now I understand what it is and I found this of one on the Jalopy.

/\This picture shows a crankcase breather on the front of the valve cover. I don't see a pop off valve. In my last post the 3rd picture shows the pop off on the rear of the intake manifold.
 
#265 ·
Well its been a while since i did a blow through carb set up, but the biggest dilemma is boost pressure through the venturi is forcing the fuel back into the tank and the throttle wide open. unless youre using a butterfly valve but fuel problem still stands.

My only attemt at this 10years ago was guided by swedish turbo bike pioneers who did the trial and error work before me.
i used vacuum carburetters, you got to have intake signal from plenum to the top of membrane and boost pressure from a pitot pipe to float bowls and a boost pressure regulator set at 0.2bar fuelpressure. and a biiig bov or the charger gonna wreck havoc on the carbs. all this is quite complicated so i strongly recommend reading up on this in some books or there will be too many questions. good luck!!!
 
#266 ·
Well its been a while since i did a blow through carb set up, but the biggest dilemma is boost pressure through the venturi is forcing the fuel back into the tank and the throttle wide open. unless youre using a butterfly valve but fuel problem still stands.

My only attemt at this 10years ago was guided by swedish turbo bike pioneers who did the trial and error work before me.
i used vacuum carburetters, you got to have intake signal from plenum to the top of membrane and boost pressure from a pitot pipe to float bowls and a boost pressure regulator set at 0.2bar fuelpressure. and a biiig bov or the charger gonna wreck havoc on the carbs. all this is quite complicated so i strongly recommend reading up on this in some books or there will be too many questions. good luck!!!
Now i am used to turbocharged EFI systems and not SC carbed systems but

my thoughts where that using a CV carb on a blow through system under pressure is going to be complicated, i would imagine idle is the only time that there is going to be negative...or at least non positive intake so what happens to the CV side of things as the pressure increases ?
I can understand a draw through system working with a CV carb but under pressure sounds like a nightmare to me.
 
#270 ·
I was going back and re-reading parts of this thread and hit post 215 ( I think) from 64 Dodge 440. Where he stated he had experience trying to use a blow through setup on an SU arb and had problems with the slide hanging under boost. I know Dan saw it cause he responded need to it, but it got me worrying cause I want him to succeed. If he builds the box around the carb is this problem eliminated because the whole carb is operating at the same pressure or is it the force of the boost on the slide itself the problem?
Also on the ignition timing issue, could you not rig the timing plate with a solenoid actuator that retards the plate . Obviously the plate wouldn’t be tight. I saw this done on a drag bike 20 years ago.
 
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