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Thread: Full Throttle!

  1. #1
    ***Euro-Nova Supporter*** Spacenut's Avatar
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    Full Throttle!

    Hi everyone - its time for an embarrassing admission; for the last 5 years I have not been able to operate my engine with more than 3/4 throttle

    I know, shocking isn't it? All those videos - Nova T33, 2 Novas 2, The Ascent of Little Switzerland, all done on 3/4 throttle. No wonder it looks so slow

    Anyway, yesterday I finally got around to doing something about it. As some of you may know, I am using a hydraulic throttle actuator from Chuck Neil Inc. Popular for drag racing, where chassis twist can result in slackening of the accelerator cable, this neat little device uses a tiny master cylinder and pushrod to operate the throttle bar in the engine bay, and a similar slave cylinder under the throttle pedal. The two are connected together by about 8 feet of hydraulic pipe, and use automatic transmission fluid (ATF) as the working medium.

    For all of the time the Green Machine has been on the road, the master cylinder support bracket, which is bolted onto the top of the engine through two of the water pump elbow bolts, has been positioned so that the pushrod cannot open the throttles fully. I lived with it, as I rarely use all of the throttle pedal, but there were always occasions where this lack of prod was not only an embarrassment, but could be dangerous as well (overtaking, for example). I also reasoned that, in spite of the system being intended to open the butterflies on a 4 barrel Holley, there ought to be more travel available in the pushrod than I was apparently getting.

    So, yesterday I set to work. I removed the master cylinder Hiem joint from the support bracket and then removed the latter as well. I then measured up for a new bracket to reposition the cylinder in a more horizontal orientation, allowing more of the pushrod movement to operate the throttle balance bar. The plate that the bracket sits on had to be carefully reliefed in order to clear the water pump elbow casting. I did this with an angle grinder. I then welded up a suitable support using left-over 3/8" box section. Looks a bit agricultural, but the thinwall tubing (as opposed to the original 4mm steel plate construction) is probably no heavier.

    Here it is in place on top of the engine. Note the close fitting around the water pump casting.





    Once the new bracket was in place, I offered up the master cylinder Hiem joint and bolted it up in a suitable orientation;







    Overhead shot shows the pushrod actuation angle. The picture also shows how filthy the engine got driving through the rain last weekend; I don't know where all this muck came from, maybe the roadworks on the M25...

    Incidentally, for part spotters I can state (for the record) that the rubber bellows protecting the pushrod are branded VW!



    Alternator back in place and belt tension adjusted.



    View from the back, looking forward to the bulkhead.



    Overhead view of the reassembled engine. The new master cylinder location has moved the throttle pedal away from the forward bulkhead, and the pedal itself is now in line with the brake and clutch pedals. This is something I will have to get used to, but is no different to driving an unfamiliar car for the first time.

    Starting the engine with this new arrangement was a revalation; the original thrust angle may not have allowed full throttle, but was quite progressive. Now, the engine instantly barks with real authority in response to the pedal - I now know that I will get all of my 95 bhp when I ask for it!

    However, there was another problem which needed my attention, which was unconnected to the hydraulic system, as it turned out.

    For some while now I have been experiencing the throttle sticking in use, particularly if the engine is running at a constant speed for some time. Initially this form of "cruise control" was quite disconcerting, but eventually I learned to blip the throttle briefly and the butterflies would close properly.

    I thought this might be due to a wear ridge building up in the master cylinder, as there was a bit of unintentional lateral preload on the cylinder from the hydraulic fluid pipe, which is quite rigid. In repositioning the cylinder, my hope was that the pushrod operating point would move to another position in the cylinder, and the stickiness would be resolved.

    Alas, this was not the case - with the engine at idle, gentle pressure on the pedal resulted in the engine note rising and not returning to fully-closed unless the pedal was blipped. I pondered this little problem for a while, with that clarity that only comes with the knowledge that the car would be unusable for the next week unless I found a solution...

    The throttle return spring operates on the balance bar bellcrank, but that is the only return spring in the system. It has to force the throttle butterflies closed, and at the same time force the pushrod back into the cylinder, pushing the hydraulic fluid back into the slave cylinder and pushing the pedal out, against the stiction in the pivot mechanism (which was thick with grease). No wonder the throttles wouldn't close completely! What I needed was a throttle pedal return spring, something to overcome the stiction so that the spring in the engine bay stood a fighting chance. The problem was, I didn't have a suitable spring...

    Now I apologise if this gets a bit surreal, but I had a flash of inspiration. Why not make a suitable spring? To do this, I needed some sprung steel wire, and a suitable mandrel to form it on. The former came from a dismantled egg-whisk, bought from Woolies before they went bankrupt for the S.K.W.I.D. project. SKWID stands for Submersible Kinetic Water Immersion Device, which unfortunately didn't succeed due to some technical difficulties producing a sound watertight seal without proper machining facilities. But that's another story - back to the egg-whisk. The whisking bit consisted of half a dozen sprung steel wires, formed into a U shape and held together at the top by a tubular handle. Removing the handle provided the wire I needed for my return spring.

    An offcut of M10 threaded rod, clamped in the vice provided the mandrel. Then it was a case of having a go...



    Whoops! Not a very good first effort, but you've got to start somewhere Now for the Mk2...



    Ah, much better. The coil fits around the pivot shaft of the pedal, the big hook goes around the pedal itself, and the little hook slots into a convenient hole in the pedal box flange.



    And here it is in place. In oder to engage the little hook, the spring has to be pre-loaded, so the pedal is always trying to pull itself away from the bulkhead. The pedal shaft passes through a steel boss welded to the chassis, and is threaded at the other end. I used a reversed M10 Nyloc nut to locate the shaft while at the same time providing a little bit of endfloat. Also, all the grease is gone - from now on I will be using oil on the pedal shaft!

    Now the pedal returns smartly to the closed position, no matter how gently I operate the throttle, and perhaps more importantly, the pedal goes all the way to the floor without the spring becoming coil-bound.

    Right - now to put some (cautious) miles on the clock to check out my handiwork!

    Lauren
    only Pythagoras can save me now!

  2. #2
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    Re: Full Throttle!

    Hi Lauren. That was a very interesting article. In a way it must be quite exciting to suddenly find out that your car can accelerate a lot faster because of something like the throttle only going so far with room for more. That exact thing happened to me at some point at the end of the 90's when I discovered the throttle could go another inch or so. It was because my cable was not short enough.

    Make sure you go easy now that you have more power available.

    I'm intruiged to know how you actually made the return spring. What technique did you use to bend it around the bolt? And if it was sprung steel how did you manage to bend it and it stay put in the coil shape?

    I need a better return spring on my accelerator, which incidentally I need to write about on my re-build post, but I'm waiting to see what Rusper come up with at the other end first as there will be natural 'return' from the engine throttle bar.

  3. #3

    Re: Full Throttle!

    You never cease to amaze us with you talents Lauren, keep it up
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  4. #4
    ***Euro-Nova Supporter*** Spacenut's Avatar
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    Re: Full Throttle!

    Quote Originally Posted by NovaF4
    I'm intruiged to know how you actually made the return spring. What technique did you use to bend it around the bolt? And if it was sprung steel how did you manage to bend it and it stay put in the coil shape?
    Hi Giles - sprung steel has a limit of elasticity, same as any other metal. If you bend it beyond that limit, it becomes permanently deformed. The difference of course is that sprung steel is a lot less ductile than other metals, so is not tolerant of mistakes - if you try and reform a sharp radius it will probably fracture due to work hardening. In the case of my return spring, the number of loops determines how much "springiness" there is, through the axial twisting of the ends. Each loop deforms slightly within the limit of elasticity, so when the axial load is removed, the spring unwinds.

    I actually formed the spring by hand, starting in the middle of the wire and carefully making the first loop around the mandrel so that there were no kinks. Then I just continued winding the wire round the mandrel until the spring was long enough. The large hook was formed around the mandrel as well and then bent through 90° with needle-nosed pliers. The small hook was formed with just the pliers.

    Lauren
    only Pythagoras can save me now!

  5. #5
    Senior Member bushboy's Avatar
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    Re: Full Throttle!

    Laure,
    Only getting patial throttle remindes me of a Kart racing incident back in Australia when I was 16. In those days, us Juniors raced the most powerfull racing 2 strokes avaliable. Mine as a DAP 100cc rotary valve putting out about 22BHP at 16,000rpm.
    We had been practicing all morning ready for the race meeting to start & the thing was down on power, people were running rings around me, it wouldnt reach max revs. We had all sotrs of advice from race engine tuners, even one that built them for a living, we had the head off, the barrel off, advised that the piston might be in the wrong way round, the rotary valve was out of time, but nothing worked.

    It was not untill my elder brother turned up on his Z1R casually walked into the pits after watching from the bleachers & said, it don't sound right, it's not loud enough. OK smarty I said what's wrong with it cause we are about to pack up & go home. His reply was your are not getting full throttle. He is not known for his mechanical expertise & after we scoffed & laughed at him, he took a screw driver, removed the foam air filter & said, there take a look at that. 3/4 throttle at best. A quick adjustment of the peddle stop & I was racing again.

    So back to your story Laure. I was thinking, as I was reading your progress & looking at the pictures, that there did not seam to be much in the way of return springing, for all of the reasons you said while describing your solution. I must say that your spring bending is very neat. The little hook for the bar looks very professional. I do like a good, this is how I done it write up.

    Now that you are getting full throttle, may I suggest you start saving for a new set of rear tyres

    Bushboy
    "Always do what you are afraid to do"
    "I can accept failure, but I can't accept not trying"

  6. #6
    ***Euro-Nova Supporter*** Spacenut's Avatar
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    Re: Full Throttle!

    Hehe - well, my current tyres have only got a couple of thousand miles on them, but I know what you mean. I don't think 95 bhp is going to shred them just yet - although the Alfatune engine will be a different matter altogether

    Actually, I've got a funny story about 3/4 throttle too. When I had the Barracuda I used to hang out with Jeff and Karen Marshall down at their workshop, and a really nice car came in - a late Forties Buick I think. Six cylinder flathead. Anyway, the throttle response was really sluggish and the transmission wouldn't kick-down, and the owner wanted to know why, so we popped the hood and after a bit of head-scratching it became clear that the bellcrank operating the butterflies, which was mounted on the top of the engine casing, was limited in its travel by the chrome dome-head bolts holding the cylinder head down. Just out of curiosity I wiggled one and it came off in my hand - it was a chrome dress-up kit! The actual cylinder bolt heads were flat and the bellcrank simply passed over them.

    Lauren
    only Pythagoras can save me now!

  7. #7
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    Re: Full Throttle!

    Awesome work Lauren!!! Brilliant!

  8. #8
    ***Euro-Nova Supporter*** Peter's Avatar
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    Re: Full Throttle!

    Having issues with my hydraulic throttle too but trying to work it out before binning it and going back to cable. The slave tends to stick when closed and takes a fair bit of push to get the thing moving. I am using brake fluid at the moment but you using ATF gives me hope that the thicker fluid will be better and not so prone to leak and rotting seals. The return spring on the slave is barely adequate and I may back it up with secondary pull springs on the other end of the DellOrto throttle spindles. MY carbs are reversed so the linkage connections are at the back with the throttle rods behind the shroud where there’s a lot more room. I have fixed the slave to the back of the shroud and the pivot to the hole on the front of the crankcase centre line behind the clutch.
    I have a return spring on the pedal but I think I need a lot more power to it to ensure a snap shut scenario.

    Locost pedal set up I now have a coil spring simular to yours to the left of the throttle pedel on the boss part.


    Linkage and pivot


    As you can see nothing on the rear of the carbs or having to thread under the alternator which is now central
    and would have screwed up a normal set-up across the rear.
    The opinions expressed in my posts may not be made in a sound mind and should be taken in the spirit intended, Jack Daniels is fine. Autism isn't something you get or can be 'cured of', it is the way we are wired, differently.

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  9. #9
    ***Euro-Nova Supporter*** Spacenut's Avatar
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    Re: Full Throttle!

    Hi Peter - I'm not sure of the relative merits of using ATF instead of brake fluid. The CNC throttle only specifies ATF as the working fluid, but I was wondering about using brake fluid because of the one major flaw in ATF - it expands as it is heated!

    (which means that when you are stuck in traffic the throttles start to open and idle speed increases. I solved this problem by opening the bleed screw when the fluid was hot, but I may come across the same issue again now that I have re-positioned the cylinder).

    I can't think why you might have that initial stiction in the pedal, unless the angle of the slave cylinder in relation to the pedal has anything to do with it - that's going to result in a very small movement of the pushrod, if that is translated into a movement large enough to operate a pair of Dellortos, there must be quite a lot of amplification in the system, if you'll pardon the electrical terminology. Maybe the system is too sensitive to pedal movement?

    It has taken me several years to get round to sorting this problem out, and the issue with the sticky throttle was nothing to do with Chuck's hydraulics, I just had to eliminate all of the other problems one by one!

    My hillclimbing friend Graham doesn't like the idea of hydraulic throttles and has recommended I go to a cable system too. However, his main objection seemed to be based around my (incorrect) supposition that the hydraulics themselves were to blame. He actually had a sit in the car and tried the throttle with the engine running, and was pleasantly surprised by its response. So it would seem that the hydraulic system does offer the benefit of smoothness in operation that is noticably better than Graham's mega-sorted competition cable system.

    In any case I'll be sticking with hydraulics for a while yet

    Lauren
    only Pythagoras can save me now!

  10. #10
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    Re: Full Throttle!

    Hmm, I'm still trying to get to grips with your spring. Three things - What did it look like to start with? How strong is it? For example, how far apart could you pull it by hand? What's a mandrel?

    G

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