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Martyn123 wrote:

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Hi Major,

Just about to start welding my chassis and whilst the car is in bits have given some thought to bringing the car more up to date, with your experience so far on your build some advice would be appreciated.

Last week i visited a company local to me in Birmingham who do a lot of work on LS engine conversions (they had 3 in the workshop in progress) inc a T$%4V%^&R's and having showed him a Mantula chassis he thought that the design looked quite sturdy, he was quite confident that with the bottom engine mount chassis rails replaced with a thicker box section and some corner bracing on the top rails a LS1 would fit no problem and recommended a T56 gearbox due to their size, he showed me a T56 on one of their cars and it did not seem much bigger than my Rover gearbox, we then talked about the rear end and he was of the opinion that as long as the car is not raced on slick tryes, any excessive power would cause the rear tyres to loose their grip first rarther than overloading the diff unit (LSD ZF type), I intend this to be a road car only.

My car when originally raced had a 5.0 engine and whilst not having the BHP of a LS1 wondered just how much chassis work was actually really necessary to cope with the extra power, I have been trying to get a picture of a bare Mantis chassis without success to make comparisions to the Mantula chassis, i seem to recall reading somewhere that there was not that much difference in them.

This car of mine i intend to rebuild only once and will see me out so do not want to go to all the trouble of a rebuild and regret not going that extra mile later on,

Should I be all sensible and stick with my Rover engine 3.5 with carbs although blueprinted, Crane cam and lightened flywheel, with the many $$$ later uprating it or go for the "you only live once so go for it" option,


Regards,


Martyn.........
www.marcosmantula.com

Hello Martyn123
All I know is this. Putting an LS1 into the road going Marcos, (Chassis's all pretty similar) is pointless unless you are prepared to change the diff.

My Rover V8 standard 5 speed box and Ford IRS diff in the Mantula (as was) meant the engine was over revving from the start. Pointless really but great when you wanted to do a traffic light start and annoy the hell out of the GTI brigade. Running a 3.5 litre engine with the torque and power my humble 3.5 had was almost wasted running at 70 - 80 mph as the fuel economy went through the floor.

When I found the Chevy LS engine I knew that the back end had to change. There was no point in contemplating 5.7lts and 350 bhp when you were going to be screaming the nads off it at 70 mph.
The gearboxes I have looked at are all pretty much ratio-ed the same. Simply because they are designed for road use. (I guess) That leaves the diff. The only one I found that had an off the shelf ratio markedly different from the standard Marcos was a Jaguar Diff. It will act like an over drive. I am hoping that the sheer power of the the LS1 will negate the sluggish effect the diff will have compared to a 3.09 ratio-ed diff. (my diff is ratio-ed at 2.88:1) This means its going to be a cruiser, more economical and if desired a much higher top speed.

That's the diff sorted out then. Now the engine. As far as I can see, the LS1 is longer than the rover. Not by much but enough. possibly about 2 inches. If you rover people look at the crankshaft pulley and the steering rack chassis beam you'll see there is not 2 inches of spare room down there. So the engine has to go back. Mine will go back a good way as I am putting a different steering wishbone structure in the front. so the engine bay is sort of going to be re designed to get the Jaguar/Chevy wheels and the Chevy engine to sit under the bonnet. Also I am creating side pipes so as to get rid of the ground clearance problem my Marcos had.
All this and I am attempting to do the lions share of work myself. Despite my best efforts, on occasions I have to undo some of my work because I missed out a detail.
I bought the Mantula back in the days when I had the choice to build it myself. I still have this crazy longing to do exactly the same thing second time around.

The engine chassis rails I am fitting are 80 x 40 mm box sections and heavy duty. The scallops taken out of my Mantula chassis by the factory for things like starter motors bell housings probably don't lend itself for strength when you are slotting in a 350 bhp motor with all the added torque.

I think I know where I am going with this project, but the road is long and there is many an adventure ahead on its way to completion.

More soon.