Gen2(fc) with a V8 Diff problems ??

[Shaq]

hey everyone !

Friend of mine bought a gen 2 rx7 with a v8 engine already in it (I know! Why!) sounds good tho!

He has rover sd1 engine in the car, but the car tops out at 80mph a mechanic who is doing some work on he car reckons the stock diff cannot keep up?!?!

Will a RX7 gen 2 auto diff fit and be better? The mechanic said that it will that this would be a better option

what do you guys think?
do you think he will have a better increase in speed with a gen2 AUTO diff ?
 

please help !


thanks


ShaQ

[yonner]

is he flat out at 6000 in 5th when its at 80???

[20B_boy]

Originally posted by Shaq
but the car tops out at 80mph a mechanic who is doing some work on he car reckons the stock diff cannot keep up?!?!

:rollin

Stock diff \'keeps up\' with the 20B in my TII :rollin - what is he on!

[Shaq]

lol !

thats what i thought, i thought the diff could go through alot before it gives, so what do you reckon it is then why can he only get 80 mph out of it ?


shaQ

[Shaq]

he says it redlines at 80mph?
you think its a transmission problem?


shaQ

[tr8theshape]

Think it must be the diff ratio that\'s the problem, the rover V8 doesn\'t rev like the rotarys,  5 - 5.5k rpm and thats your lot really.

The diff ratio on the SD1 was 3.08:1 (I think) and with that and a 5 speed manual (Rover) 70mph should be around 2300 revs.

having said that a quick calc says that if it tops out at 80 at 5000 revs then if it could rev to 7500 then it would only be doing 120?

[Shaq]

cool,

what do you think he should do ? what does he need to achive more speed?

thanks


shaQ

[grinder]

stick a rotary back in !!

sorry had to be said !

[Sean]

I second thee!

[tr8theshape]

After a quick look on the interweb (bored & lunchtime)!

I see that most manuals have a 4.1 diff wheras the autos have a 3.9 diff (Funnily enough the same as the five speed TR7 which uses the same 5 speed gearbox as the SD1).

So if my memory is correct (going back a few years) on the TR7 90Mph came in at around 4500 to 5000 revs. This means that by swapping the diff for the auto version you will still stuggle to get more than 100Mph out of it.

Unless you can easily get a diiff for the RX which is quite a lot lower then you may be better putting the rotary back in.

Whew - think all that\'s right - going to have to go for a lie down.

[Shaq]

i know thats what i told him to do just stick in a t2 lump in, he wouldnt be having these problems right now, but he was adamant he wanted to keep the v8, when i first saw it i was so excited one of my friends bought a gen2 then he poped the bonnet only to see a V8 with twin carbs on it ....




tr8theshape

thanks for the feedback, so what do you suggest he do ? (apart from stick a T2 lump in!)
100mph is not great !

when you say "get a diff for the RX which is quite a lot lower" what diff do you suggest ?

thank s again


shaQ

[Sean]

tr8theshape seems to know his stuff .....I\'d listen to him!

[tr8theshape]

Afraid I can\'t help there, find out which 2nd Gen had the lowest ratio and put that in.  But due to the diifferent engine characteristics I wouldn\'t expect mega top speeds.

[MikeLMR]

has it got an auto box in it (from the rover of course) ? if it has is he sure its shifting into top ?

[Shaq]

mikeLMR

no its a manual 5 speed.

what do you mean by "shifting into top" ?


thanks

shaQ