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Last Post 13 Mar 2017 09:33 AM by  loosecannon
EMod MGB-GT build thread
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47CP
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15 Oct 2010 05:53 AM
loosecannon wrote:
47CP wrote:

More unsolicited opinions....

I am not real comfortable with that rearr shock mount on the frame side. The forced is going straight back into the U shaped pieces which goes into the cell mount, but there is nothing triangulated in that direction whatsoever (that I can see). Basically, the force is going into the plane at the level of the top of the cell, straight forward and back and there is nothing but a couple of shirt 1x1 down tubes resisting that.

I am not sure how to fix it, but I think some triangulation needs to be done. Also, if you strengthen it in that plane, that back crossmember for the cell may not be strong enough, depending on the wall thckness of that tube.

All IMO, trying to be helpful, etc. :)

DaveW

You are being helpful :) I was not finished with the bracing. After the earlier fiasco with the bent shock mounts, I had decided to better brace the front and rear mounts, I'll be beefing those areas up significantly. What size bolts do you think I need to fasten the pushrods? M10? M12?

Fasten the pushrods to what? The axle? If it is double shear, I would think the M10 would be plenty. If some sort of single shear, M12. Anything shock related on my car is 1/2", which is pretty standard stock car size down here.

HTH,

DaveW

Dave Hardy
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15 Oct 2010 06:27 AM
What about something like this. Crossmember between the two main rails that is braced longitudinally to the rear of the main rails and vertically to the down tubes. Suspension loads go more directly to the main structure. It would mean that the fuel cell couldn't drop in from above, but it could probably be mounted in the same place, just bolted in from below.
loosecannon
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15 Oct 2010 10:49 AM

DILYSI Dave wrote:
What about something like this. Crossmember between the two main rails that is braced longitudinally to the rear of the main rails and vertically to the down tubes. Suspension loads go more directly to the main structure. It would mean that the fuel cell couldn't drop in from above, but it could probably be mounted in the same place, just bolted in from below.

That looks good. I cut the 1x1 square tube out of the back today and am going to weld 2x2 in it's place, and put some gussets in, too. I'm working on the drivers side header right now and it's really, really time consuming.

loosecannon
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15 Oct 2010 07:20 PM

I went in at 8:00 this morning to get some work done on the car before we opened for business and built the drivers side header. It was very, very difficult to get all the tubes in there and pointed in the right direction and the collector was right up against where the firewall needed to be. The pic is after I tack welded it but before I pulled it out for final welding. I welded as much as possible while still on the car then pulled it off to weld the back side, that's when the trouble started. There were a bunch of spots where I couldn't get the welding gun in at the right angle or close enough, resulting in welds I am ashamed of. Then, when I went to put it back on the car, some of the flanges had shifted and there was no way to get them lined up again-a lot of time and money out the window. That's the bad news, the good news is that, from what I read, this engine doesn't benefit much from headers.
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I also re-did the rear shock mount, it's now far stronger and weighs less than the previous version. I'm pretty excited that when I put the spring on it's stiffest setting, the car hardly moves when I bounce up and down on it, and on the softest setting it bounces pretty good-I think these bike shocks are going to work:
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47CP
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16 Oct 2010 07:54 AM
loosecannon wrote:

I went in at 8:00 this morning to get some work done on the car before we opened for business and built the drivers side header. It was very, very difficult to get all the tubes in there and pointed in the right direction and the collector was right up against where the firewall needed to be. The pic is after I tack welded it but before I pulled it out for final welding. I welded as much as possible while still on the car then pulled it off to weld the back side, that's when the trouble started. There were a bunch of spots where I couldn't get the welding gun in at the right angle or close enough, resulting in welds I am ashamed of. Then, when I went to put it back on the car, some of the flanges had shifted and there was no way to get them lined up again-a lot of time and money out the window. That's the bad news, the good news is that, from what I read, this engine doesn't benefit much from headers.

Headers are a bitch. I cheated and used two sets of stock car headers, one configuration of a chassis header for one side and an adjustable late model deal for the other. I just had to shorten the chassis one and that was still a bitch.

So, did you give up on the headers and go back to the manifolds? That might be a good idea for now just to get the car on the road/track. It might cost some power and weight, but what is the difference between being able to spin the tires continuously from one turn to the next with 1/2 throttle or 3/4 throttle? :)

[quote]

I also re-did the rear shock mount, it's now far stronger and weighs less than the previous version. I'm pretty excited that when I put the spring on it's stiffest setting, the car hardly moves when I bounce up and down on it, and on the softest setting it bounces pretty good-I think these bike shocks are going to work:

This looks much stronger and I think will work fine.

Looking great. You are putting my three year build pace to absolute shame. :(

DaveW

Dave Hardy
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16 Oct 2010 02:38 PM
Looks very nice! Any more info on the bike shocks? Spring rate? Travel? Rocker Ratio? I'm quite intrigued.
loosecannon
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16 Oct 2010 03:43 PM
47CP wrote:

So, did you give up on the headers and go back to the manifolds? That might be a good idea for now just to get the car on the road/track. It might cost some power and weight, but what is the difference between being able to spin the tires continuously from one turn to the next with 1/2 throttle or 3/4 throttle? :) DaveW

Yup, going back to stock exhaust, which is fine because I had serious concerns about melting my shoes to the firewall with the headers so close. There's a lot more power to be gained by changing cams and valve springs.

loosecannon
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16 Oct 2010 03:47 PM

DILYSI Dave wrote:
Looks very nice! Any more info on the bike shocks? Spring rate? Travel? Rocker Ratio? I'm quite intrigued.

Shocks are Ohlins off the back of a Yamaha R1 sportbike. Spring rate is 525 lb/inch, travel is about 3 inches at the shock but more when the pivot is factored in. Yamaha lists shock travel as 5.1 inches but that must be the wheel travel. Don't know the ratio but from the pivot to the bolt on one side is 4 inches and from the pivot to the other side is 3.25 inches.

loosecannon
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19 Oct 2010 01:13 PM

I worked on the brackets holding up the front fenders and supension, and I weighed the car again. The bad news is that it weighs 1800 lbs without wheels/tires/radiator but the good news is that the weight balance is 46% Front, 54% Rear and will probably be perfect once I add the weight of the rad and fluid up front.

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loosecannon
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20 Oct 2010 05:08 PM
I'll admit it, staring at where a firewall should be, I am intimidated by how complex the thing is going to have to be. I decided to start at the back and work my way forward, so here is the transmission tunnel, done without a metal bending tool:
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47CP
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20 Oct 2010 06:00 PM

You aren't going to do all of that in steel, are you? And you are gonna need a brake soon. :)

The footbox area was an absolute bear on my car and took about 3 full weekends to figure out.

Here it is 90% complete:

DaveW

loosecannon
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20 Oct 2010 07:00 PM
47CP wrote:

You aren't going to do all of that in steel, are you? And you are gonna need a brake soon. :)

The footbox area was an absolute bear on my car and took about 3 full weekends to figure out.

Here it is 90% complete:

DaveW

Wow, that is almost a dead ringer for my pedalbox. I don't have any way to weld aluminum but I guess I could rivet aluminum panels together. I am comfortable with steel so will probably go with that, despite the weight penalty. My MIG has a kit that can convert it to weld aluminum but the guys at Welders Supply said that if anybody is going to see the welds, I better not because they will be ugly.

47CP
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21 Oct 2010 05:56 AM

I would highly recommend aluminum. It is lighter and easier to work with. You can get a cheap brake at Harbor Freight (I think mine was $200) and a hydraulic pop rivet gun for $50. You just rivet it all together and it is plenty strong and easy to change or remove later if needed. I don't have better pics handly, but the entire interior of my car is riveted aluminum with only the slightest steel frame in a few key places. No aluminum welding.

An .040 or .035 aluminum panel of reasonble size with a 90 degree bend on one edge is pretty strong.

IMO, you will be adding a bunch of weight with steel.

DaveW

Bullitt2954
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21 Oct 2010 11:56 AM
47CP wrote:
An .040 or .035 aluminum panel of reasonble size with a 90 degree bend on one edge is pretty strong.

IMO, you will be adding a bunch of weight with steel.

DaveW

IIRC the equivalent gauge in aluminium weighs about 1/3 that of steel. It's only about 1/3 as strong - but for this particular application, I would think them shiny-silver-panels would be PLENTY strong enough.

47CP
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21 Oct 2010 12:09 PM

Here are some more pictures of my footbox.

There were all taken before I disassembled the whole car and painted the frame so nothing is riveted together. On final assembly, I riveted all that stuff together and it is plenty strong. The trick is always joining one panel to another with a 3/4" (19mm :)) "flap" that is bent 90 degrees and rivets to the next panel.

DaveW

loosecannon
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21 Oct 2010 12:22 PM
That looks fantastic. We don't have Harbour Freights in Canada but I'll see if I can track down a brake. I'm not comfortable working with aluminum, though.
loosecannon
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21 Oct 2010 08:19 PM

Built seat and seatbelt mounts today. I was planning on putting in a harnass guide bar and attaching the belts to the rear frame rails but looking at the instructions included with the belts, I noticed that I could wrap them around the guide bar. So, I decided to build the bar out of rollbar tube and make it look nice:
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loosecannon
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22 Oct 2010 07:53 PM

I found a Ford 9" rear end on e-bay that was the right width, the problem was that it was built for a 2000 hp dragster. Here it is with ladder bar and wheelie bar mounts, I'm pretty sure I won't be needing those ;)
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I sliced off all the mounts I didn't need, welded on the ones I did and cut holes in the braces to lighten things up a little.
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Here are the 4 piston aluminum calipers that came with the rear end, you can see the trick rotors on the left in the first pic:
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Here it is in the car. I shortened the bars to get to the MGB stock wheelbase of 91" so now I will have even more weight on the back tires than the 54% I had earlier:
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And from the side:
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vinax
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22 Oct 2010 09:31 PM

Amazing craftsmanship.... I wish I had your fabrication skills.

Car weighs 1800lbs already? It must have contracted STEELITIS


loosecannon
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22 Oct 2010 09:39 PM
vinax wrote:

Amazing craftsmanship.... I wish I had your fabrication skills.

Car weighs 1800lbs already? It must have contracted STEELITIS


Thanks :) I could have made the car lighter by going with smaller brakes, smaller rollbar tubing and lighter engine but I didn't want it to be a one trick pony. I want to participate in solosprint, lapping days and maybe even a hillclimb and I needed more robust and heavier parts. I'm sure I could be at the class minimum by swapping engines but for now I'm going to have some fun with the V12.

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