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Author Topic: Bugatti Type 37 Build  (Read 26317 times)

StefanN

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Re: Bugatti Type 37 Build - engine cooling
« Reply #120 on: 02 July 2020, 03:10:19 pm »
Given the engine has a fan, Iíve built a shroud around the inlet and then will feed cold air in.  The idea is that a positive pressure of cold air is better than recirculating hot air.   Will it work?

Chris Brown

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Re: Bugatti Type 37 Build
« Reply #121 on: 02 July 2020, 03:24:25 pm »
Yes it'll allow you to draw cooler air from outside the engine compartment, but the cross sectional area of the inlet needs to be more than the total area of the intake slots in the fan shroud. If it isn'y you'll restrict your airflow, and to some extent negate the advantage of cooler air.

StefanN

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Re: Bugatti Type 37 Build
« Reply #122 on: 03 July 2020, 09:11:42 am »
Yes it'll allow you to draw cooler air from outside the engine compartment, but the cross sectional area of the inlet needs to be more than the total area of the intake slots in the fan shroud. If it isn'y you'll restrict your airflow, and to some extent negate the advantage of cooler air.

I was wondering about that Chris.   The first thing I noticed is that the fan, which is supposed to pull air in the centre and then accelerate it out to the edge, has "inlet" slots exposing the fan blades along quite a bit of the radius - which presumably then spills air?   Wrt cross sectional area, I'm working on the basis that one large inlet is much more efficient from a flow perspective than lots of turbulent, lossy narrow slots....but the new inlet size is a complete guess...errr experiment!   Time will tell.  Hopefully I'll get to run the engine again in the next few days and will get a feel for it then.

Chris Brown

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Re: Bugatti Type 37 Build
« Reply #123 on: 03 July 2020, 10:58:40 am »
Just as well I've got ahead of myself by buying engines! I've just checked, and as I thought the fan is within the shroud area, so all the slots in the pull start housing are inlet. The inlet to your cool air feed needs to be more than the total area of all those slots.

Feeding cool air in should not only improve engine cooling, but also the temperature of the air exiting the shroud should be lower, reducing the heat build up. As Rhys points out though letting the hot air out is just as important, and as it's volume is greater a larger cross sectional area of vents is needed.

When I build an enclosed kart I'll do some experiments on heat extraction, the Morgan is a different proposition as the engine and exhaust will not be enclosed by the body.

RhysN

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Re: Bugatti Type 37 Build
« Reply #124 on: 03 July 2020, 01:02:49 pm »
Quite a bit of the airflow is directed across the cylinder head fins by the fan. I believe that most of those slots in the housing are to draw air in. It might be interesting to do some testing on a running engine to check, smoke a a method? I don't have one running right now or I would try that this afternoon.
It would be a good exercise for those with video skills (Hint :) )

Chris Brown

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Re: Bugatti Type 37 Build
« Reply #125 on: 03 July 2020, 02:05:03 pm »
I think you'll find all of the slots draw air in, they all feed into the suction side of the fan. I've got a digital differential manometer which I can bring with me when I can next get to a gathering. That'll allow approximate airflow measurements to be taken on both inlet and outlet sides.

StefanN

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Re: Bugatti Type 37 Build - remote choke
« Reply #126 on: 06 July 2020, 10:46:08 am »
I wanted to make a remote choke for the Mikuni carb.  I experimented with using a cable pull to the existing lever, but didn't like the way it looked.

So, I drilled a 2mm hole down the middle of the shaft of the plunger and then an exit hole for the wire. A blob of solder on the end stops it coming back out. I then drilled a bit of brass 5.3mm to take the end of the sleeve of the cable. At the other end I drilled it so it could fit over the shoulder on the end of the original brass nut and soldered these together. Seems to work. Adjustment will have to be at the lever end of the cable.

Would have been even simpler to make a new piece to replace the original nut but couldn't figure out what thread it was so went this route.

StefanN

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Re: Bugatti Type 37 Build
« Reply #127 on: 17 July 2020, 08:24:33 pm »
I finally managed to fit the smaller tyres to try on the Bugatti.  3.25 down to 2.5 should make for an interesting comparison. 

RhysN

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Re: Bugatti Type 37 Build
« Reply #128 on: 18 July 2020, 07:41:00 am »
Stefan, have you changed all 4? Are they the same make as previously? It will be interesting to see what differences you feel.
I have noted that the guys in the US now talk about different makes and versions of tyres, grip vs wear and such, so perhaps a straight size swap may give other knowledge.

StefanN

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Re: Bugatti Type 37 Build
« Reply #129 on: 18 July 2020, 09:00:19 am »
Stefan, have you changed all 4? Are they the same make as previously? It will be interesting to see what differences you feel.

No Iíve only changed the rears so far.   Thatís partly cost but also because I always scuff up the rim when changing tyres.  Also, Iím still working on weight distribution and understeer, so for the purposes of this test, keeping the weight and contact at the front will mean Iím not changing too many things at the same time.   Itíll probably look odd and will change the angle the ck is sitting at a bit .... hmmm thatíll give me more caster!

As you say, will be interesting to feel the difference.

StefanN

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Re: Bugatti Type 37 Build - tyre size comparison
« Reply #130 on: 18 July 2020, 09:36:18 am »
The smaller tyres change the diameter of the wheels from 600mm to 570mm.   That'll give a 5% change in gearing.  Changing just the back tyres for now will increase the caster at the front by 0.5 deg.

A rear wheel with the 3.25" tyre weighs in at 6.2kg.  With the 2.50" tyre it weighs 5kg.  To me, that's a surprisingly large difference.
« Last Edit: 18 July 2020, 02:14:02 pm by StefanN »

RhysN

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Re: Bugatti Type 37 Build
« Reply #131 on: 18 July 2020, 06:08:06 pm »
What is the main aim for making the change. Those bigger tyres in some makes are a whole lot heavier, but that surprises me too. Is it because you are going from a full motorcycle tyre to more of a moped one?

StefanN

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Re: Bugatti Type 37 Build
« Reply #132 on: 19 July 2020, 09:07:21 am »
The aim of the changes is to get the car handling in a way I enjoy, and have fun experimenting along the way.   With the current setup I have both rear wheels keyed to the axle.   Also the weight distribution is a little too much to the rear.   As a result it understeers badly and with the extra grip itís difficult to get a controlled drift.

The other effects (weight, ratio, caster) Iíve noted above are just observations and the caster difference will be temporary; I just wanted to check I wasnít get an unhelpful effect from running different size tyres during initial testing.

Other possible tweaks I may try are:
- Dropping the seat even further
- Moving seat bottom and pedals forward
- Add weight at the front
- Playing with track width at the back (narrow like the GNís or wider for more stability)


RhysN

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Re: Bugatti Type 37 Build
« Reply #133 on: 19 July 2020, 10:52:49 am »
For me it's the fiddling that appeals the most, and your analytical approach interest me.
Have you tried playing with tyre pressures? They do have a huge effect on the CK.
The narrowing of the rear track, I am sure, would be the most beneficial of those you mention. AFN did loads of experimenting. The GN and later Fraser Nash always had solid drive axles, and narrower rear track.
One change at a time :)
« Last Edit: 19 July 2020, 10:55:45 am by RhysN »

StefanN

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Re: Bugatti Type 37 Build
« Reply #134 on: 19 July 2020, 11:04:58 am »
Yes did lots with tyre pressure and it helped, but not enough.   I have a suspicion that pushing the rear tyre pressure up might have contributed to my spokes loosening at the end of last year.