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| Posted: Sun Mar 25th, 2018 03:22 am |
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1st Post |
Brad Emery
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Getting my old Hornet with a Mac 91B1 on alky ready for a test run. Need to know what spark plugs to run. Can I get them local or are they something special. Also, how much oil do I need to run in the alky. Just can't quite remember all these things from 50 years ago. Thanks for the help, Brad
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| Posted: Sun Mar 25th, 2018 04:11 am |
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2nd Post |
steveohara
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Best plug for alky in the 91 series is the Autolite (Motorcraft) AE901. The are hard to find but the Autolite 411 is a suitable replacement.
8 ounces of Burris Castor per gallon of methanol is what I run. Make sure you buy straight methanol, not one of the blends that has additives. For example, VP racing fuels sells three methanol blends, M1, M3 and M5.... you want M1 as the other two have additives that will ruin your motors.
You don't need lab grade methanol, just as long as it is straight methanol you are in good shape.
Steve O'Hara
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| Posted: Sun Mar 25th, 2018 04:13 am |
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3rd Post |
steveohara
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BTW... don't try to run it on 100% methanol/oil with a the stock carb.... very hard to make that work. If you are running the stock intake manifold and reed get a BDC 16 or equivalent double pumper carb for it.
Couldn't switch carbs back in the day but there is no reason you can't now.
Steve O'Hara
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| Posted: Sun Mar 25th, 2018 10:59 pm |
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4th Post |
| Posted: Sun Mar 25th, 2018 11:08 pm |
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| Posted: Sun Mar 25th, 2018 11:56 pm |
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6th Post |
steveohara
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.035 works well.
Will you be using an expansion chamber or simple header?
If its an expansion chamber which make and model?
Steve O'hara
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| Posted: Mon Mar 26th, 2018 12:14 am |
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7th Post |
Brad Emery
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.035 was what I was remembering. but then second guessing myself. I currently have a GEM box muffler on it, but have a 90 deg. and 120 deg. header pipe and had been admiring the PLV S1 pipe on ebay. Would this be a good combo?
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| Posted: Mon Mar 26th, 2018 12:40 am |
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8th Post |
steveohara
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No that S1 pipe is a POS!
Rear cone is much too steep.
A slippy pipe is a much better opotion for the Mac.
How does the motor sit on your kart? Typical sidewinder with the spark plug on the top? Right hand engine mount?
Cast aluminumm header is not a good choice, steel tube is better and you have many more choices as to the shape and direction the flex will point so you can fit the pipe much nicer.
Steve
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| Posted: Mon Mar 26th, 2018 12:45 am |
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9th Post |
steveohara
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look at this ebay auction.... 272509172244
It is the hot ticket for the mac on the road race tracks
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| Posted: Mon Mar 26th, 2018 01:06 am |
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10th Post |
Brad Emery
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I'd been looking at that one also. The kart is a Hornet LP2 I was told with typical right sidewinder configuration. The headers I have are the steel type. The 120 deg one looks like it would be the way to go. Would the slippy pipe be set at one position or operated with a handle of some sort?
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| Posted: Mon Mar 26th, 2018 01:27 am |
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11th Post |
steveohara
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yep, the 120 header and that pipe would be the correct configuration for the LP1 chassis. The internal rear cone would be operated by a cable/handle setup that is easy to set up.
By using the slippy pipe the clutch can be set up to engage at a much lower rpm which saves a lot of abuse.
With that pipe and a 120 header you would want to set it up with very little flex showing... basically as short as the alignment will allow. For long tracks you would gear 4/1 and you want to use the Hartman 20mm wide belt drive system. I used the Hartman engine clutches on the 91 series motors with great success. Engagement speed was around 8,000 rpm and they held up well. I have a bunch of that equipment if you are interested.
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| Posted: Mon Mar 26th, 2018 01:34 am |
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| Posted: Wed Mar 28th, 2018 06:38 am |
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13th Post |
Doug Tenney
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Newbie questions. What specifically is being adjusted on the slippy pipe? Stinger length? Cone locations? The E-Bay auction only shows 1 photo. I can see the bracket for the cable but I can't figure out what moves.
How does the driver control the slippy setting? A small lever or paddle under the steering wheel?
The driver gradually pulls up on (or lets go of) the lever as the revs build coming out of the turn?
Doesn't the driver have to become hyper vigilant with his gauges to avoid roasting his engine?
Just curious!
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| Posted: Wed Mar 28th, 2018 07:18 am |
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14th Post |
steveohara
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Doug,
You pretty much nailed it. A slippy pipe has an internal, movable convergent (rear) cone with the stinger attached. The big end of the cone is supported by the large diameter straight section of the pipe and the stigner is supported by the small end of the outer rear cone. When the kart accelerates from a standing start or out of a slow corner the engine rpm will be at the stall speed of the clutch which is generally set just a little below the peak torque rpm of the engine. To optimize the acceleration the rear cone must be further from the exhaust port at the lower end of the rpm band and for maximum top speed the cone needs to be closer to the exhaust port. The relationship is pretty linear as far as the distance so you would expect the range of adjustment to be in direct proportion to the width of the rpm band of the engine. However, that was not always the case because the volume of the pipe is also important to the performance of the engine. Exhaust pressure will result in the rear cone position pushed as far from the engine as the design allows and that is where the cone needs to be for the hard pulls off the turns. as the engine speed increases the driver pulls the rear cone toward the exhaust port thereby reducing the tune length of the pipe and the volume simultaneously. Typically on a road race course the pipe is pulled all the way in on the long straights and the driver will release the handle when he lifts to brake for a corner. As the kart accelerates off the corner and gains speed the pipe is pulled back in. As you imagined, if the driver is too early with the pull he can cause the motor to overheat and seize up. Too late on the pull and power is lost. Use of the slippy pipe is an art and just like tuning the needles on the fly some drivers were better than others at sensing the needs of the engine and developing a feel for when and how much to pull the cone in.
Steve O'Hara
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| Posted: Wed Mar 28th, 2018 09:21 pm |
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15th Post |
Brad Emery
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Were/are these used only on long tracks? I recently spent several years running 250 2 stroke micros, and we were pretty much into getting the right pipe but we never even thought about something like this. It would keep you awful busy doing this process twice in a 12 second lap, especially if you were shifting gears also. This is good stuff!
Sorry Doug, I just grabbed that pipe on ebay.
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| Posted: Wed Mar 28th, 2018 11:03 pm |
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16th Post |
Doug Tenney
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No problem Brad. I can't rub my belly and pat my head at the same time, so running a slippy pipe in sprints would not go well. I might as well be texting at the same time!
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| Posted: Thu Mar 29th, 2018 06:09 am |
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17th Post |
steveohara
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Guys,
Slippy pipes have been tried many times on sprint tracks without success. They are only effective on long road racing tracks that require a very tall gear ratio that results in very slow rates of acceleration and long stretches of flat out top end running.
SteveO
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| Posted: Thu Mar 29th, 2018 10:29 pm |
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18th Post |
Doug Tenney
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Some detailed drivel related to your original question:
If you need a colder plug, try NGK B9HS. They also make a B10HS and I assume it's one step colder. (NGK goes opposite the other mfr's; their plugs get colder as the numbers increase. NGK B8HS is approx equal to Autolite 411).
Your post says you have a Mc91B1. I believe that's the first Mc91x to use 12mm (.472") reach plugs. Look closely and you should see tiny text cast right into the head, next to the spark plug hole, saying to use 12mm/0.472" reach plugs.
Mc91B and earlier Macs use 9.5mm (3/8") reach plugs, and there is no text cast into the head. For those, McCulloch recommended Champion J2J (coldest), J4J (middle), J6J (hottest).
J2J crosses over to NGK B9S.
J4J crosses over to NGK B7S or B8S, or Autolite 353
J6J crosses over to NGK B6S or Autolite 303
I heard that some guys keep things simple by running Autolite 411's in all of them.
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