'56 Oval

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T-34
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Re: 36 Hp challenge

Post by T-34 » Thu Nov 05, 2009 2:10 pm

nitro-nige wrote:You can have a look at the USFRA 36 Hp challenge.
http://www.saltflats.com/36_HP.html

"Tom Bruch's small 1378 cc single port 36 HP turbo motor at 103.497 MPH"


Hi Nige, Tom Bruch's 'Small' 1378cc is actually pretty large for a 36hp - the limitation to capacity is the head stud spacing - this has to be retained to be eligible for the 36hp challenge records, other than that capacity is free, although I think there will be an equilibrium between too much capacity and not enough induction as there are limits to heads and carbs that need to be followed too. The turbo would certainly help in this case.

Tom's car is the current 36hp record holder for the NA36 category (New-Age Turbocharged) and is the overall record holder for a Beetle bodied 36hp powered vehicle. The only higher speed recorded is Dick Beiths 129.100 record from 1963 for a 36hp powered lakester.

I've been working with Burly Burlile (the 36hp challenge creator) to try and get a 36hp challenge set up here in Australia. I've spoken to a few of the committee members who will hopefully be reviewing the idea at the next committee meeting. There's a bit more info over at my site where there's a group setup for those interested - http://www.vdubber.com/groups/entry/Saltflat-Racers
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Post by T-34 » Thu Nov 05, 2009 2:11 pm

Forgot to mention - for 36hp challenge entries the gearbox has to be standard cased VW 4 speed, no Berg / 5 speed / non-VW boxes are allowed.
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Post by T-34 » Thu Nov 12, 2009 1:06 pm

OK, Think I've decided to go with the 915 box. It's pretty much a no brainer really - a new box will cost me big $$$$'s but the IRS conversion will cost me next to nothing. I've resolved myself to the fact that cutting the car is the way to go. Just need to source some IRS arms.

Also the 915 box will do for the first outing with stock ratios. I will play about with a different final drive for the following year after I've figured out what works / doesn't etc... This is what I've managed to figure out so far:

The gearbox is from a Stock 1983 Porsche 911 SC - here's the specs

Top Speed : 146.02223mph
Power : 201bhp @ @ 5900 rpm
Torque : 267.0 Nm (197 ft·lb) (27.2 kgm) @ 4300 rpm
Final drive : 3.88
Top gear : 0.82
Rear Tyres : 215/60 VR 15

Radius of rear tyre is 319.5 and the circumference is 2007.48 - Taken from handy calculator - http://www.carbibles.com/tyre_bible_pg2.html

The tyres I'm planning on using are Goodyear LSR's the smallest ones have a circumference of 2111.

So from a little maths the difference that the additional size makes takes theoretical top speed up to 153 mph - for a stock 911 SC runnning at peak revs of 5900 rpm

My main differences are that I have a little more power (hopefully another hundred horses) but probably less revs (I want to set rev limit at 5500 as I don't want to overstress the engine)

This means that theoretical top speed is brought back to 143

All of this is obviously dependent on being able to get the car to that speed (grip / weight / drag / wind etc) But I guess i won't find this out until i get the car out there.

I'm pretty confident I can beat 100mph which is all I will commit to for the first outing, but I would like to think that I could better this by some amount.

My only decision at the moment is this.

Ultimately it would be great to take the bug to 150 - this might take some years to achieve. So do I opt for the taller tyres? (2283 circumference) as this would equate to a theoretical top speed of 155 with the stock 3.88 R&P.

Thoughts. opinions?

Cheers

Mick.
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Post by momec » Sun Nov 15, 2009 9:53 pm

G'Day T34

Take a variety of tyre sizes with you so you have options. In the end the aero will dictate a point where it won't pull any harder or alternatelly will be bouncing on the rev limiter and want a taller ratio. If that ratios at home in the shed your snookered.
Chris
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T-34
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Post by T-34 » Mon Nov 16, 2009 11:25 am

C Hanlon wrote:G'Day T34

Take a variety of tyre sizes with you so you have options. In the end the aero will dictate a point where it won't pull any harder or alternatelly will be bouncing on the rev limiter and want a taller ratio. If that ratios at home in the shed your snookered.
Chris


Sounds like it could get quite expensive - lol

My guess is that I will not reach the rev limiter - and if I do I would be more than happy, but no harm in taking a couple of pairs of different profile speed rated road tyres just in case the LSR's don't work out.

Good advice. :)
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Post by momec » Wed Nov 18, 2009 8:17 am

Correct rated road tyres are all you need up to 175-200 mph.
Chris
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T-34
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Post by T-34 » Wed Nov 18, 2009 9:54 am

C Hanlon wrote:Correct rated road tyres are all you need up to 175-200 mph.
Chris


After watching a few people spin out this year, i'd prefer to run the rounder profile that the LSR's have - from what I'm led to believe, a bug traveling sideways has the aerodynamics of a wing and will generate some lift, so a squarer tyre may dig in and help promote a roll over - that's something I would like to avoid at all cost.

Plus I figure - use the correct tools for the job - grip is obviously one of the main factors overcoming the drag of the car - so I need every little help I can get. (the CD is 0.38 )

The LSR's also have a taller profile which is helpful to achieve the correct gearing without having to resort to a new differential - (probably the same price)

This is ultimately the plan, but it could obviously change - we'll see how the build progresses.
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Post by Rob » Wed Nov 18, 2009 12:14 pm

Not sure on your rear suspension setup but you may want to limit downward travel if it's the swing arm type. I've rolled two Beetles as a direct result, doing extreme things admittedly but with the swing limited neither would probably have happened.

Roof rails will help kill the lift assuming you spin at a decent speed, my first bug would lift the inside rear but never did spin on asphalt.

Cheers,
Rob
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Post by T-34 » Wed Nov 18, 2009 12:44 pm

Rob - very true and a good point, I used to have a similar issue with my old Triumph Herald - scarily dangerous wheel tuck (and therefore hop) under hard cornering - not good.

The rear suspension will be changed to IRS to be able to use the Porsche gearbox - this means that the dodgy negative camber that you mentioned should not happen as the camber change throughout the suspension travel is minimal.

I will also look to stiffen up the rear end by either welding in a kafer brace system (tie rods that connect the suspension to the rear frame to triangulate each of the points to each other) or by tying the roll cage into the rear frame - not too sure which at this stage. There is a 'LOT' of flex on the rear frame with HI-PO engines under load - probably more an issue for the drags but one that should be addressed.

For those not aware of how an engine fits in a bug - there are two 'horns' the stick out of the rear of the pan - like a two pronged fork - the gearbox bell-housing bolts to the end of the horns - effectively the engine just hangs out of the rear of the horns and the gearbox site in between. There is a front gearbox mount that attaches the nose cone in between where the frame horns meet. Unfortunately the horns have a tendency to flex with the force applied from HI-PO motors. Ultimately this is not too much of an issue as it's a well known problem and there are many off the shelf solutions (such as kafer bars etc)

I was planning on adding limiting straps for the drags, but no harm in adding them for the salt too I guess - they're cheap and will be fitted at some stage anyhows.

I've made a start with the strip down - been taking plenty of pics too, so will post an update when I have uploaded them. There's some more words on my blog too - http://www.vdubber.com/blogs/posts/T-34/category/Oval

Here's a quick pic I uploaded for the blog

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There will be more updates when I've made a bit more progress - lol

Mick.
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Post by Rob » Wed Nov 18, 2009 1:48 pm

I remember having to brace the frame for a mate's beach buggy after we installed the 1835, it had tragic flex but then he had huge rear tyres that didn't help the issue.
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tyres

Post by David Leikvold » Wed Nov 18, 2009 6:23 pm

T34, thank you for racing a VW. Wait till you price all those Goodyear LSR tyres, you may suddenly find the VR and ZR road tyres much more appealing. As for the LSRs having more grip, I doubt it. They are built round so they have a circular cross section which keeps them in shape with the high pressures they're supposed to run to be safe at 300mph, which is a long way from where you're sitting. That gives them a very small footprint on the salt. I think a good ZR with a wet weather racer style tread pattern (Goodyear Eagle F1 or similar) would work better at the speeds you're hoping to achieve. They also come in a useful variety of diameters and widths. They would be more likely to stop you getting out of shape in the first place than the LSRs and more responsive to any attempt to catch a slide too. If you lower the Beetle to within an inch or so of the salt there'll be very little air getting under it anyway so your fear of flying would be minimised by building the car as cleverly as possible in the first place. Very hard suspension with good shocks and absolutely no bump steer is a good place to start. Good luck.
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Post by T-34 » Wed Nov 18, 2009 10:32 pm

Thanks for the thanks :D

I was originally intending on running my Type 34 Karmann Ghia, but then found out that I needed to put a cage in it - I was hoping to run it in the street class as it's a road going car but then found out that the street class is no more - The Type 34 is where the engine and box I am using in the bug come from.

I've already priced the LSR's - they're about $750 a corner. ( :shock: ouch - I know!!)

I know the bug will probably never get anywhere near 300mph, but the tyres will get used on another project once the bug has been pushed to it's limit - let's just say that there's plans in the pipeline for something a little more aerodynamic :wink:

I will take a look at the VR / ZR rated tyres to see if I can get something the same overall rolling radius. Would be interested to hear what others have found success with too.

Mick.
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Post by T-34 » Thu Nov 19, 2009 1:51 am

OK bit of an update....

Finished stripping the shell. The doors, glass, wings interior etc are all safely stashed in the garage. Next stage is to unbolt the body from the floor pan and raise it up on trestles so that the floor-pan can be rolled out from underneath it.

Once the pan is out I will replace both pan halves as there is not really any point in trying to patch up the existing ones. I will also trial fit the 915 gearbox as it's easier to do this with the body off, but I will need put the body back on to check clearances before finally mounting the box in position.

When the pan is sorted i will re-mate it to the body and send it off to get the cage built. One benefit of the bug is that the body can be lifted to weld the tops of the cage - no holes in the floor pan required.

There's more wordy stuff over at my blog - http://www.vdubber.com/blogs/entry/Stripped-Naked

Here's a few pics...

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David Leikvold
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tars

Post by David Leikvold » Thu Nov 19, 2009 11:08 am

Mike,
Goodyear makes (or made a while back) a 185/50ZR15 tyre which, at a nominal 565mm, is the smallest diameter ZR tyre I could ever find. This is a whopping 50mm smaller in the radius (not the diameter) than the original 165R15 radial at 660mm that most beetles had. That's 50mm closer to the salt than standard before you even start on the front suspension. That size tyre would still put a decent footprint on the salt and wouldn't interfere with the front guards when you wanted to turn the car either.
Cheers
Dave
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Re: tars

Post by T-34 » Fri Nov 20, 2009 12:04 pm

David Leikvold wrote:Mike,
Goodyear makes (or made a while back) a 185/50ZR15 tyre which, at a nominal 565mm, is the smallest diameter ZR tyre I could ever find. This is a whopping 50mm smaller in the radius (not the diameter) than the original 165R15 radial at 660mm that most beetles had. That's 50mm closer to the salt than standard before you even start on the front suspension. That size tyre would still put a decent footprint on the salt and wouldn't interfere with the front guards when you wanted to turn the car either.
Cheers
Dave


Thanks for the info Dave, I will look into it. Originally I was simply going to lower the front and keep the rear height stock - pretty much standard stance for drag racing, but with the IRS there is no reason that I cannot also dump the rear suspension too. This is not possible with swing axle due to the effect it has on camber. Being able to tune the suspension a bit better I might look to get it as low as possible.

What's everyone's thoughts about running a narrower tyre up front - say 135 / 145 ? This is pretty common with drag racers, is this seen as an advantage on the salt?
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