Low Engine C of G / Inverted Gearboxes

[Lee]

I think I've found an advantage of the Hitech over the GTD!!
I'm assuming the original builder didn't modify the chassis and as it stands, my gearbox is about 5-10mm clear of the bottom of the chassis, which puts the crank c/l at about 210mm above the bottom of the chassis. I am running with about 80mm of ground clearance, so my crank c/l is within 290mm of the ground. How many GTDs with unmodified chassis have their engine that low?

No flames PLEASE. I know the GTD has various advantages, but it's nice after all this time to find an occassion where mine has one. /ubbthreads/images/graemlins/grin.gif

But then again, just thinking about it, many of the GTDs with Porsche and ZF boxes are probably lower.

 

[Lee]

Frank

Would I be correct in thinking that Andrews gearbox is slightly lower than the chassis and/or the assembly is slightly tilted to keep the box above the chassis?

 

[Frank Catt]

Lee, the bottom of the gearbox, lowest part by bell housing, is level with the underside of the chassis, the engine sits perfectly level. I can do you photos of drive shaft angles etc when I put the gearbox back in the car, Andrew broke the box on the start line at Brighton on Saturday. Frank

 

[Brian Magee]

Lee

The thing that dictates how low you can mount the engine in the car is the size of the flywheel. Even with say a 4" deep dry sump, the bellhousing will still be lower if you have more than an 8" dia. starter ring. My starter ring is a fraction over 12" dia. and from the centre line of the bellhousing to the bottom is 6.5" (ZF gearbox) which is the same as my sump. This lines up with the bottom of the chassis so unless you want to risk taking the bottom of the sump off on a speed hump that is about as low as you can go.

Brian.

 

[Gary Gibbs]

You can also go with a low ground clearance flywheel clutch combo from Tilton Racing for example. They make clutches as small as 4.5" diameter with ring gears just a bit larger. The problems as I see are the requirement of a custom belhousing and the starter location. If you look at there site you will see for the low ground clearance options that the starter is mounted from the trans side which could be a bit tough. Both problems could be engineered out I suspect.

 

[Julian West]

FWIW, the answer to the question 'how low can you go' depends entirely on how much engineering you are prepared to do. There comes a 'point' when you're doing an awful lot of engineering for very little gain & probably wasting your time! How much pain for how much gain is up to you!! /ubbthreads/images/graemlins/smile.gif

I know all this has been done before in the GTD club, however I like to suss things out & make my own choices & this is my opinion. I haven't actually proven any of this to myself yet so I may be talking toffee!

Working within the constraints of the GTD chassis & R21T trans, the engine & trans can be lowered & levelled so the crank C/L is 205mm from the chassis floor. To do this 'some' chassis mods are needed, but you can keep the engine, trans, bellhousing, clutch, suspension, etc 'standard'.

If you want to go lower than 205mm, you need to do alot more engineering & look harder at either cutting into the bellhousing, or inverting the transaxle, shortening the A-arms, and/or heavy mods to the chassis, probably a combination of all of theses items will be needed. As Gary points out, you could even engineer in smaller flywheel/clutch assemblies with reduction gear starters.

The GTD chassis has a transverse member right under the flywheel which makes things a bit tricky. Not all GT40 reps have this member, so if you want to go with a super low engine & trans it may be easier to start with a different chassis.

here's a side on view of the standard GTD setup;

 

[Julian West]

Here's a similar view with the engine sitting level in the chassis with the crank centerline 165mm from the chassis floor.

I'm sure it's possible to sit the engine & trans this low, but I'll probably raise it 40mm to reduce the amount of engineering needed & also to reduce the driveshaft angles.

 

[Gary Gibbs]

What oil pan are you using and how high/low is the bottom of the pan relative to the bottom of the chassis?

 

[Julian West]

I'm using a GT40 pattern sump from Armandos oil pans. It's 165mm deep.

With the engine mounted as shown in the second picture the crank centerline is 165mm from the underside of the chassis & hence the sump would be flush with the underside of the chassis.

As I'll probably be mounting the engine with the crank C/L 205mm from the chassis floor, the sump will be 40mm higher than the chassis underside.

 

[Kevin Box]

I am following this line of discussion with interest.
Does anyone out there make a bell-housing for the inverted UN1 or have all the inverted GT40s had custom built bell-housings?

cheers KB

 

[Neil]

For what it's worth, I use a KEP (Kennedy Engineered Products) adapter to mate my Donovan (think small-block Chevrolet) to an inverted Porsche G50.... but my car is not a GT40.


Regards, Neil Tucson, AZ

 

[Terry Oxandale]

KEP also was my choice for the inverted 930 behind the LS motor (non-GT).

 

[George]

I used a Kennedy adapter on my 302 and inverted G97. Very easy to setup only requiring a minor modification to the tranny housing for the starter.