GTD_Webers

Gents,

My GTD w/ 302 and UN1-13 is mounted with a nose down attitude, and I am trying to find out the history as to why. I am not saying this is wrong or bad, just want to know the reason. I remember seeing a thread about it having to do with the UN1, but I can't seem to find that again. Also, do all the manufacturers have this same issue? Pictures can be deceiving and it is sometimes hard to tell if everyone's motors do the same thing with varying degrees of incline.

I ask, because I want to add Webers, but am concerned with the clearance towards the rear.

Thanks
Robert
 

Mike Pass

Supporter
The engine is a bit nose down on a GTD with Renault transaxle because of the position of the output shafts on the UN1. The gearbox height is determined by the output shaft position and hence the driveshaft angle. If you lower the transaxle too much the driveshaft angle on take off in first gear at full throttle is too much and this can break the driveshaft or UJs.
So the transaxle height is set. In order to reduce the centre of gravity position of the motor the only way to lower it is to tilt it downwards because the transaxle iheight is fixed. On my car the downward tilt is about 5 degrees. To compensate for this I use a wedge plate under the Holley to bring the carb back level. With Webers the tilt may not be a problem. The issue of the rear carb and the rear window will be dependent on IDA or IDF carbs, the length of intake trumpets, the manifold and the rear window position. I have seen lots of GTDs with Webers so I guess it should be OK.
Cheers
Mike
 
I can't speak to why GTD mounted their engines as they did, but my Tornado did/does not mount front low in either SBF or Coyote configuration. I never broke a half shaft or damaged a CV joint. My half shafts were/are ever so slightly outboard CV high @ a 4.5 inch rear ride height.
 

Mike Pass

Supporter
The standard positions used by GTD do not cause any problems.
IF the Renault transaxle is significantly lowered then the driveshaft angle does cause driveshaft breakages especially on a car which is used in sprints which involve many hard launches. A friend of mine will testify as he has done at least three shafts but the car has had some serious "use".
Cheers
Mike
 
The other solution could be inverting the gearbox, this should lower the input shaft quite a bit, thus the motor (which then should be put level).
I've seen that done on a GTD, the owner had to modify the motor mounts and change the oil pan (He told me that it lowered the engine about 15cm. He then set the gearbox 4-5cm higher to save some ground clearance, for a total lowering of the engine about 10cm).

He put webers on it and you could only see the stacks through the rear bulkhead window when seated at the wheel (not the entire carb + stack). No more clearance problem about the rear window...(and the protrusion of the water pump pulley through the firewall was reduced to almost nothing), he was also able to put some nicer crossover exhaust and correct turkey pan. I must admit the general feeling was far better, when you opened the rear clip : looks like closer to the original stance.

I'm considering doing that on mine, in the future.
 
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Tim Kay

Lifetime Supporter
before I swapped my UN1 trans with a G50 in my tornado i had a slight nose down attitude with Weber IDF's. no issues but had I considered IDA's there would've been clearance issues at the rear most weber air horns against the rear plexi. Further, the IDF air horns were only about 60-70 mm tall with low profile air cleaners.
 

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Hey Robert,

I had a GTD GT40 back in 2005 and had the UN1 transaxle with 289 and 44 IDA webers. No issues with clearance see attached pics. By the way I now have a CAV GT40 and Sam Watson in McKinney has new CAV also so we should get together some time.
 

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Tim Kay

Lifetime Supporter
The pics above are IDF not IDA, quite different. In addition, looking at gary's engine position, it appears to be mounted more forward than usual, at least in my very similar Tornado tube chassis. notice the 'relieved' tube under rear cabin window, dizzy clearance. Also, in the pic of the rear clip closed you'll see the carbs appear more forward therefore more clearance of the flat deck fiberglass, under the the plexi, to the rear carbs (more plexi clearance as well)

Here's a pic of IDA's in my SPF, even with the bodies (without air horns) being taller than IDF's you'll see they don't exceed the bottom of the cabin window.
 

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Great information Gentlemen........Thanks

The Edelbrock 4 barrel I have also has a wedge shim below it to level it out. From the top of the manifold, it rises over 9" to the top of the air filter and clears the glass in the middle. Mr Inglese tells me he can make IDFs 9-7/8" tall with no issues versus the standard 10-7/8". I assume this includes the intake. So in theory, this should work.

Robert
 
Oh Dear Oh Dear Oh Dear, what nonsense ! We have been lowering and levelling GTD engine / gearbox units for many years in the UK, nothing to do with drive shafts etc etc, units can be lowered up to 100 mm and set level with an easy modification to the chassis, removing the narrow and kicked up chassis members under the gearbox and widening them to accommodate the gearbox between them. This shortens the lower wishbones by 40mm but with other geometry changes has improved the rear handling substantially. This can be a "do it yourself" modification ( provided you are or have a qualified welder to help you ) and gives the opportunity to set the tops of the weber IDAs below the rear bulkhead window. Frank
 

Mike Pass

Supporter
Don't completely agree with that. John Bate's GTD - ex Andrew Fordyce has the lowered setup and has broken several driveshafts. He keeps a spare in the car when competing in it.
Cheers
Mike
 
Sorry......they were 44 IDFs as I recently purchased 48 IDAs for my CAV. This GTD I had back in 2005 was one of GTDs two display cars they built back when they were in business.
 

Malcolm

Supporter
Southern GT do a chassis conversion for GTD at the rear which is well worth having. It will solve the issues above and is cost effective for the improvements in handling and looks.
 
I totally agree with Malcolm , but if you don't want to ship a part chassis to the US then it is doable locally, it is a fairly simple conversion with big benefits. Frank,
 

Malcolm

Supporter
I'd ship it if it were my decision as all the design work has been done for you and is proven to be very good. You will probably save on labour costs versus the shipping costs as Southern GT are set up to produce this stuff with jigs and each piece of frame already sitting on a shelf.
 
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