V8 G27 questions

[rhdv8]

Sorry for all the questions but I thought I'd try and get most of them out of the way in one hit.

1) Is the G27 chassis significantly different for a V8 engined car?
2) Which gearbox and diff is used for the V8 cars?
3) Roughly what is the max torque the drive train could take and what is the weakest link/links (apart from tyres)?
4) Could the chassis its self cope with more power/torque?
5) What sort of clearance is there around the engine?

Many thanks, I'm sure I will have a few more questions but the answers to these ones should get me thinking for a while.

[Darkspeed]

Firstly the G27 was not designed with a V8 in mind and most were kit type builds so the builder did/fitted what he wanted

1) No - but bear in mind that there are 4 generations of the G27 and some variations in between - My V8 G27 is quite special in that its uses mainly G33 running gear.
2) Gearbox usually LT77 or R380 or T5 - Diff - could be Jag IRS / could be a multitude of live axles (Capri Escort Marina) or Sierra IRS
3)Depends on above - could be axle could be box depends what builder used. Weak link on mine is due to silly rear camber setting meaning the 235's have an effective contact patch 3" wide.
4)More power and torque than what? There never was a "standard" V8 G27 - mine sort of copes with 230+BHP and 250+ftlbs
5)None

Andrew

rhdv8 said:

Sorry for all the questions but I thought I'd try and get most of them out of the way in one hit.

1) Is the G27 chassis significantly different for a V8 engined car?
2) Which gearbox and diff is used for the V8 cars?
3) Roughly what is the max torque the drive train could take and what is the weakest link/links (apart from tyres)?
4) Could the chassis its self cope with more power/torque?
5) What sort of clearance is there around the engine?

Many thanks, I'm sure I will have a few more questions but the answers to these ones should get me thinking for a while.

[rhdv8]

Many thanks Andrew,

I was kind of thinking that a GM LS1 5.7 V8 is around the same size as a RV8 (not sure of the relative dimensions of the gearbox's T56 verses the LT77/R380) but I was wondering if the standard 350bhp and 350ft/lbs torque of the LS1 would be too much for the chassis/diff? Or would the limited available tyre width act as a fuse for the rest of the components?

Edited by rhdv8 on Monday 29th June 17:46

[GreenV8S]

Not sure if you mean T56 or T5, but the T56 is quite big isn't it?

I know somebody with a supercharged 5.2L RV8 in a G27, now running on slicks. The chassis is very very soft which meant a rather unusual suspension setup was required to get the handling right. This one uses a Jag diff (which is immensely strong) and an LT77 (which isn't, but seems to cope). Access round the engine bay is generally good. Chassis stiffness around the engine bay is generally hopeless.

[rhdv8]

Yes the T56 which is normally found behind a LS1 is quite big but as I haven’t found the dimensions of a LT77/R380 with bellhousing as yet, and as most of my experience is with the LS1 and T56 I have no idea if it would fit without too much work to the chassis or trans tunnel.

A "soft" chassis doesn’t sound good though with all that torque to hand. Did I read somewhere once that the front screen had a tendency to crack with high torque engines? Or was that another car altogether?

[GreenV8S]

Given the size of the gearbox I guess the prop shaft will be even shorter than normal. Consider whether you could fit a torque tube in there to take out the loads into the diff.

[Darkspeed]

Access to the engine is good but space between the chassis rails for the V8 is pretty tight and to be honest more tubes need to be inserted which would make it even more restrictive.

You would not want to add to the width of the transmission tunnel - its pretty tight in the car width wise to begin with and if needing to make wider you could only go in the direction of the nearside and make it narrow for the passenger and you may struggle with getting the engine over without hitting something

I have 8 inch wheels running 235 section tyres on my car so tyre width is available - but will depend on the series of the car and the type of suspension - as I said my car is pretty rare so may not be possible on the Jag or Live axle or the typical sierra IRS cars

The lack of weight and poor geometry (too much camber) is the real problem with traction on my car

If you can get it too fit with a few extra tubes here and there it would be an absolute hoot - mine is entertaining enough.

What series car are you thinking of?

Andrew

[rhdv8]

Andrew,
to be honest I haven’t got as far as thinking about what series of G27 but I would be more tempted by as late as possible as I would guess there has been a progression in terms of suspension/chassis etc. Also I’ve never been a fan of the pop up headlamps but I'm guessing that a later bonnet would be adaptable to the earlier cars.

My original thoughts were tending towards a V8 engined car to begin with but if the chassis are much the same it may not make a difference.

As you’ve said your G27 has the running gear of the G33, what are the differences between the two? And why are you not able to adjust for your tyres?

I would think that a G33 would be a better choice for the LS1 but I've always liked the shape and size of the G27 and by the looks of things they are considerably cheaper to buy in the first place. Also it would be a shame to swap an alternative engine into a car with such a limited production run.

I take it that the latter cars utilised the Sierra diff and that all versions including cosworth type of diff would fit? If so, any idea of the limits of the diff taking into account the light weight of the G27? Also what half shafts and UJ’s are used?

Also one last thing is there any good literature or places to do some research on the differences of the various versions of the G27?

Thanks again guys.

[blitzracing]

You are nuts to try and put huge horse power into these chassis. They lack a basic back bone so the whole lot twists across a relatively thin floor pan and chassis area. Just try jacking one corner up and see what happens to the door shuts ! A flexable chassis is not a good mounting point for accurate suspension geometry either. Although the G33 chassis can be made to handle in an acceptable manner, the aero dynamics make the cars go light at the front at 100mph plus, and thats not easy to fix. I think to story about cracked windscreens is an old wives tale, as the windscreen and surround is not really tied into the chassis so has little chance of taking any load. Before you go any further get a trip out in a G33 at speed, and then once you have changed your pants, have a rethink.

Mark

[blueg33]

Probably easier to get a G33. Its already got V8 power and is pretty quick.

[rhdv8]

So the answer to my original question number 4 would be a no then.

blitzracing said:

You are nuts to try and put huge horse power into these chassis. They lack a basic back bone so the whole lot twists across a relatively thin floor pan and chassis area. Just try jacking one corner up and see what happens to the door shuts ! A flexable chassis is not a good mounting point for accurate suspension geometry either. Although the G33 chassis can be made to handle in an acceptable manner, the aero dynamics make the cars go light at the front at 100mph plus, and thats not easy to fix. I think to story about cracked windscreens is an old wives tale, as the windscreen and surround is not really tied into the chassis so has little chance of taking any load. Before you go any further get a trip out in a G33 at speed, and then once you have changed your pants, have a rethink.

Mark

[blueg33]

rhdv8 said:

So the answer to my original question number 4 would be a no then.

blitzracing said:

You are nuts to try and put huge horse power into these chassis. They lack a basic back bone so the whole lot twists across a relatively thin floor pan and chassis area. Just try jacking one corner up and see what happens to the door shuts ! A flexable chassis is not a good mounting point for accurate suspension geometry either. Although the G33 chassis can be made to handle in an acceptable manner, the aero dynamics make the cars go light at the front at 100mph plus, and thats not easy to fix. I think to story about cracked windscreens is an old wives tale, as the windscreen and surround is not really tied into the chassis so has little chance of taking any load. Before you go any further get a trip out in a G33 at speed, and then once you have changed your pants, have a rethink.

Mark

Mark, I am not sure I agree with you about the car going light at the front, certainly not until you are up at 130mph plus. I have drven mine at 151 mph and it still felt ok. This year at le mans several of my mates who tried the car commented that it felt much more planted than they expected. Maybe full corner weighting has helped with this?

I agree that the chassis can be a bit soft, but handling can be set up fine.

Personally I cant see the point of putting much more than 300bhp in these types of cars unless you are trying to turn them into something they are not (drag racers?) Suspension set up makes far more difference in terms of a-b down a public road than power, the same also applies but to a slightly lesser degree for hill climbing.

[blitzracing]

I dont think its as simple as corner weights (tried that), and fitting spliters does help. It was picked up on the origional design, and was due to be looked in by Ginetta. The best description I can give it is "floaty". Not that dangerious and I know some cars dont show it, but mine does whatever Ive tried so far.

[rhdv8]

blitzracing said:

Before you go any further get a trip out in a G33 at speed, and then once you have changed your pants, have a rethink.
Mark

I really wanted something a fair bit brisker than I already have which is a 350+bhp LS1 Mazda RX7 which with its original 250ish BHP and not a great deal of torque rotary engine is quoted as going from 0 to 60 in 5.1 and on to 159ish so I think I'm covered in the pants department

[GreenV8S]

blitzracing said:

I dont think its as simple as corner weights (tried that), and fitting spliters does help. It was picked up on the origional design, and was due to be looked in by Ginetta. The best description I can give it is "floaty". Not that dangerious and I know some cars dont show it, but mine does whatever Ive tried so far.

I know somebody who has thoroughly sorted the handling and aerodynamics but it took quite a lot of ingenuity. It's not the sort of thing that can be sorted just by changing suspension rates and geometry.

[blitzracing]

I dont think you could ever fully sort the setup, only make it work well for one purpose (hill climb, track or road etc ) and compromise on the rest. Ive certainly been in a G33 that handles well on the track, but Id suspect it loosens all its bolts and the drivers teeth on the way home !

[GreenV8S]

blitzracing said:

I dont think you could ever fully sort the setup, only make it work well for one purpose (hill climb, track or road etc ) and compromise on the rest.

Fair point. I meant that the handling vices had been overcome. It wasn't actually *that* uncomfortable, but was definitely 100% dedicated to track work by the end.

[Darkspeed]

G33 is wider and longer than the G27 - Its not that I cannot adjust - the G33 suspension used on mine is all rose jointed where the wishbones meet the uprights - I have not yet got around to making the required changes.

G33 has much more room to work with being a significantly bigger car - but as they were all factory built "production cars" they are more expensive - rarer than the G27 but strangely easier to find !!

I'm a fan of pop ups one the G27 - anything else looks wrong on them IMHO

As far as I am aware the later cars used the Sierra diff and typically the 7" not the Cossy 7.5 although it will fit - lets face it anything can be made to fit if necessary.

Shafts on mine are shortened bolt on shafts.

Literature and info - afraid not very much at all - The John Rose books are probably the best reference but not sure how much info on the G27 is in there.

Andrew

rhdv8 said:

As you’ve said your G27 has the running gear of the G33, what are the differences between the two? And why are you not able to adjust for your tyres?

I would think that a G33 would be a better choice for the LS1 but I've always liked the shape and size of the G27 and by the looks of things they are considerably cheaper to buy in the first place. Also it would be a shame to swap an alternative engine into a car with such a limited production run.

I take it that the latter cars utilised the Sierra diff and that all versions including cosworth type of diff would fit? If so, any idea of the limits of the diff taking into account the light weight of the G27? Also what half shafts and UJ’s are used?

Also one last thing is there any good literature or places to do some research on the differences of the various versions of the G27?

Thanks again guys.

[blitzracing]

Jsut a note on the Diff on the G33 setup. The cosworth unit is tough enough, but the fixing Ginetta used bend and break. On initial inspection they appear to have only have fully fixed it on one side, but it appears this was done because there was fractionly less space than needed to fix the extra brackets needed on both sides without an hour's extra fiddling. It is possible to reinforce the whole lot but space is really tight between the chassis rails.

[jamesG20V6]

blitzracing said:

Jsut a note on the Diff on the G33 setup. The cosworth unit is tough enough, but the fixing Ginetta used bend and break. On initial inspection they appear to have only have fully fixed it on one side, but it appears this was done because there was fractionly less space than needed to fix the extra brackets needed on both sides without an hour's extra fiddling. It is possible to reinforce the whole lot but space is really tight between the chassis rails.

That goes for the G27 and early G20 too. I snapped a diff mount with circa 200bhp.