The V8 Owners Forum -

Some more questions for my conversion (MGB with Rover 3.9 V8)

Starter motor:

I need a starter motor before I fit the engine to the car and am unsure what to get. I don't want a standard one as I know they sit close to the manifold and can suffer from overheating. I've seen two other options; a hi-torque compact starter (expensive) or what looks to be a short body standard starter (that would give more exhaust clearance).

So from people's experience what is best to get?

2. Where is best in the UK to get the rubber engine to body mounts?

3. Just out of curiosity, is a V8 with LT77 box and a 3.9:1 final drive useable at all?

Many thanks

I would have thought that a 3.9:1 diff will leave your setup quite 'revy' If your wheels have a smallish rolling radius it will be worse still!

The normal sized RV8 starter motor will work ok, even with block hugger manifolds. BUT you will need the one with the starter solenoid on the bottom.


The 3.9:1 diff ratio will give you about 70mph @ 3000rpm in 4th gear assuming the lt77 has 1:1 for 4th gear?
This is on standard MGB sized tyres at around the 24" diameter.

Wrap the exhaust manifolds in heat wrap and it will save you some aggro later on ?

Better still. Cut the inner wings and fit RV8 style manifolds. You can buy fittings to make the rest of the system yourself or fork out on a complete RV8 style system which aint cheap !

1st gear will be almost useless with that diff ratio, but you may be able to pop little wheelies

You can either buy a V8 spec (remanufactured )axle for about 600 notes or if you have access to the right equipment you could buy a crown wheel and pinion and attempt the mod yourself ?

Regards
Perry

If the MGB people are so worried about exhaust heat why do they not ceramic coat the headers.

So much neater than wrap and longer lasting, stops the bits rotting and really works

Ian

mgbv8 wrote:The normal sized RV8 starter motor will work ok, even with block hugger manifolds. BUT you will need the one with the starter solenoid on the bottom.


Regards
Perry

Thanks all. Interesting Perry, why's that and how can I tell which starters have a solenoid on the bottom? (from pictures I mean)

Cheers

Ian Anderson wrote:If the MGB people are so worried about exhaust heat why do they not ceramic coat the headers.

So much neater than wrap and longer lasting, stops the bits rotting and really works

Ian

I had a new set of headers camcoated inside and out, cost a fortune,
Three years later,rust came through !
I've now gone stainless,I would never use it again

With regards to the diff and the LT77 box you won't be doing 70 MPH in fifth gear at 3000 RPM, check it out using a gear calc...

http://johnmaherracing.com/calculators/ ... alculator/

sidecar wrote:With regards to the diff and the LT77 box you won't be doing 70 MPH in fifth gear at 3000 RPM, check it out using a gear calc...

http://johnmaherracing.com/calculators/ ... alculator/

4th gear Pete!
I dont know about the 77 but I assumed 4th would be 1:1 and 5th might be an overdrive gear??

Welshie wrote:

mgbv8 wrote:The normal sized RV8 starter motor will work ok, even with block hugger manifolds. BUT you will need the one with the starter solenoid on the bottom.


Regards
Perry

Thanks all. Interesting Perry, why's that and how can I tell which starters have a solenoid on the bottom? (from pictures I mean)

Cheers

Hold the starter motor and look at the flywheel end. Hold it as though it would be mounted on the engine, with the open side facing your left as it would be when fitted. The solenoid will be at the bottom. Others will have the solenoid on the right hand side.


See the one at the top of the picture. Solenoid on the bottom when fitted to the engine.

http://www.rimmerbros.co.uk/ItemImages/ ... 007939.jpg

Ok will do, seen some online that look to have a shorter body too.

So does the solenoid go underneath for better access or?

Welshie wrote:Ok will do, seen some online that look to have a shorter body too.

So does the solenoid go underneath for better access or?

The underneath one is generally know as the SD1 type. There were two types - interchangeable on the SD1. The early one is longer than the later.

mgbv8 wrote:

sidecar wrote:With regards to the diff and the LT77 box you won't be doing 70 MPH in fifth gear at 3000 RPM, check it out using a gear calc...

http://johnmaherracing.com/calculators/ ... alculator/

4th gear Pete!
I dont know about the 77 but I assumed 4th would be 1:1 and 5th might be an overdrive gear??

Hi Perry,

Yeah I know you mentioned fourth gear, my point is that it won't even cruise at 70 MPH in fifth gear at 3000 RPM which is a 0.83 overdrive (usually) so in fourth gear will be even worse!


I'm at home now so I have access to the gear calc that I used when working out my ratios, I've bunged in the LT77 ratio's along with a 3.9 diff and a 24 inch diameter wheel.....

3rd gear at 3000 RPM = 37 MPH, at 6000 RPM = 73 MPH
4th gear at 3000 RPM = 55 MPH, at 6000 RPM = 110 MPH
5th gear at 3000 RPM = 66 MPH, at 6000 RPM = 132 MPH


Just for reference I run a 4.6 stage III lump in my Cob with NOS,
I run 235-45-17 wheels and a 3.36:1 diff along with a T5 close ratio box, the figures are below:-

3rd gear at 3000 RPM = 53 MPH, at 6000 RPM = 107 MPH
4th gear at 3000 RPM = 67 MPH, at 6000 RPM = 135 MPH
5th gear at 3000 RPM = 77 MPH, at 6000 RPM = 155 MPH

My Cob is as aero dynamic as a brick!

Double post!

Interesting, I'm not sure of my LT77 ratio's though so can't really work it out yet. I just wanted to know if I can get away with using the 3.9 ratio withough it scrreaming at 40mph for a bit.

Would a starter like this be suitable?

http://www.ebay.co.uk/itm/221009564102? ... 1423.l2649

If you want one that sticks out from the block sideways by the minimum amount, you need an SD1 type.

The SD1 V8 manual used a 3.08:1 final drive and 14" wheels. So a 3.9:1 on hopefully a lighter car would likely feel very under geared. But at legal speeds in the UK, the only thing that will suffer is the MPG.