4.0l -v- 3.6l engines

[mickrw]

Could one of our more knowledgeable members please let me know what the differences are, apart from size, between the 4.0l and 3.6l engines? I have a new Tuscan which has the 4.0l engine, is this more or less reliable and how much more or less power does it have over the 3.6l engine? Does anyone know why TVR started to use the 3.6l in the standard Tuscan?

Cheers
Mick

[jonesg1002]

I wondered about this, I guessed the 3.6 reved harder giving its torque and power at higher revs. I thought this might mean it makes some great noises.

Performance wise I don't think there is a great deal between any of the speed6/speed8 options in the real world. Alleged 0-100mph times from 8 to 10 seonds is all very quick.

To me there doesn't seem to be any technical reason why one engine should be more reliable than another. It seems to be more component failure than design error.

[andyvdg]

If I get the figures right :-

Cerbera Speed Six 4.0 350bhp @ 6800rpm, 330ft lbs @ 5000
Tuscan 4.0 360 bhp @ 7000, 310ft.lbs @ 5250
Tuscan RR 4.0 380 bhp @ 7000, 310->330 * ft.lb @ 5250
Tuscan S 4.0 390 bhp @ 7000, 310ft.lbs @ 5250
Tuscan 3.6 350 bhp @ 7200, 290ft.lbs @ 5550

* Various figures presented by TVR. Seemed to settle at 310!

I think the 3.6 revs ultimately higher than the 4.0.
I don't think any one engine is more / less reliable than the others.

Cheers,

Andy.

[fish]

They are basically the same engine. The 3.6l runs a shorter stroke to get the lower capacity which means in turn the lower inertia allows slightly higher reving.

Apart from the slight differences in the torque and power curves thats about it. The 4.0l is a smidgin more torquey but I think most people wouldn't be able to tell.

[Mr Freefall]

Off topic a bit, but if you have bought a secondhand TVR and want spec etc from TVR, you can phone them up with your Chassis number and they will (for £30) pull the file on your car and let you have a copy of the specs etc.

[tuscan_s]

Does anyone know what the max revs are for the 3.6L, and 4.0 Tuscan S engine?

[jonesg1002]

On my S the limiter kicks in at about 7200.

[tigerruss]

I've got the Red Change up light on my 'S' set to 7400 but goes past this with no limiter cutting in. Max revs in computer shows 7600rpm but not sure if that was limited or not

[whitey]

on my Tuscan Red Rose the limiter kicks in at about 7300 on the rare occasion I don't change up quick enough.
There is no point going any higher than 7000 rpm if that is where peak power is.

Cheers
Whitey

[JonGwynne]

fish said: They are basically the same engine. The 3.6l runs a shorter stroke to get the lower capacity which means in turn the lower inertia allows slightly higher reving.

Apart from the slight differences in the torque and power curves thats about it. The 4.0l is a smidgin more torquey but I think most people wouldn't be able to tell.

I've driven both (4.0 in a Tuscan, 3.6 in a Tamora). I think the difference is noticeable but not huge. Personally, I prefer the 4.0* because it has more grunt and give more power lower down. Some people favor the high-revving nature of the 3.6. I think it comes down to personal taste.

Though, based on purely subjective observation, I'd say the 4.0 feels a lot faster off the line. If acceleration is your thing then I'd say the 4.0 is the one to have.

Based on what I have read about the troubles with the Speed Six engines, I don't think there is any reason to assume that either confiuration is more or less reliable.

*I've never driven an "S" or a Red Rose, so I'm talking about the regular 360bhp 4.0 engine here. Based on the figured I've seen quoted, all three incarnations of the 4.0 claim the same torque even with three different bhp ratings quoted.

[s_i_hunter]

After speaking to someone who used to work for TVR power, all engines are 4 litres!!!! The only difference is the inlet manifold.

It is the same with the AJP8 engine, where they are both 4.5 litres, they never produced a 4.2 litre, again just a restricted inlet manifold!!!

Hence why most cerby owners 4.2 and 4.5 say their performance is similar!!!

[joospeed]

I've heard this 4.2 / 4.5 thing before .. is it really true though? .. the 4.2 was in production for 2 years before the 4.5 was introduced .. so if they were thinking that far ahead (TVR usually don't..) they must have been deliberately restricting the 4.2 version knowing they'd be unveiling the 4.5 later. Certainly the inlet is restrictive (up to 15 bhp gain from my mods) but the 4.5 is worse!! I believe the 4.2 system in modded form to be much better than the 4.5 version, it's only when you go 2mm up on butterfly that the 4.5 system reclaims the advantage. I think there's a lot of mis-information and alot of bollox talked about these engines often from people who claim to have worked on them / built them / etc. there's only two places you can put an argument to rest, on the flow bench (been there, done that) and on the dyno (worn the T shirt). See Feb's Sprint (hopefully) for further info.

[JonGwynne]

s_i_hunter said: After speaking to someone who used to work for TVR power, all engines are 4 litres!!!! The only difference is the inlet manifold.

It is the same with the AJP8 engine, where they are both 4.5 litres, they never produced a 4.2 litre, again just a restricted inlet manifold!!!

Hence why most cerby owners 4.2 and 4.5 say their performance is similar!!!

Maybe you could ask your friend why the stroke of the engines are listed as being different? I'm also curious why the performance characteristics of the 3.6L Speed Six engine are exactly what one would expect from a slightly de-stroked engine (e.g. smoother/higher revving and less low-end torque)

You might also ask your friend how TVR get past the various "truth in advertizing" laws (you can't sell a 4.0L car and tell the person buying it that it displaces 3.6L any more than you could get away with the opposite).

If you have any friends who work for insurance underwriters you might ask them why they haven't complained that they're being given inaccurate descrptions of the car when their customers take out policies. Insurance underwriters aren't likely to be too keen on taking premiums based on the car having a 3.6L engine when it really has a 4.0L engine. They'll also be looking for a way not to pay out if that car is involved in any accidents.

Put another way, I think your friend may be mistaken. Just because a person used to work for TVR doesn't necessarily mean they know what they're talking about.

Anyone ever hear TVR offer any official comment on this rumor? Its been floating around for a while.

[Thom]

joospeed said: Certainly the inlet is restrictive (up to 15 bhp gain from my mods) but the 4.5 is worse!! I believe the 4.2 system in modded form to be much better than the 4.5 version, it's only when you go 2mm up on butterfly that the 4.5 system reclaims the advantage.

So, if after your mods the 4.5 reclaims the advantage then it should still be a bigger engine in capacity than the 4.2, shouldn't it?

Have you tried the same inlet manifold on both a 4.2 and a 4.5?

And just how do you happen NOT to have already totally dismantled both engines and meticulously examinated/measured ALL the components, you mighty Joolz "the Cerb man"?!