Vitesse engine

Darkspeed · Post by **Darkspeed** » Tue Mar 25, 2008 12:08 am

How good are Vitesse heads when compared with later 3.9 versions?

I have just picked up a stripped 31A 9.75 engine - no idea it was a vitesse engine it was only bought for a source of a manual flywheel and a front cover - but having a look at the inlet ports they look larger than the 3.9

Also is the Vitesse cam different?

Cheers

Andrew

CastleMGBV8 · Post by **CastleMGBV8** » Tue Mar 25, 2008 1:02 am

Andrew,

The Vitesse and 3.9 heads were very similar but I think on the Vitesse heads they did a liitle more work to open up the throats just behind the valves. If your ports are bigger they may have had some additional work,

The head specs are given in the cylinder head, exhaust and inlet section under the subject cylinder head numbers.

The cams i think were standard SD1 but I think a few had a slightly hotter cam for homologation purposes, and the number W9 rings a bell

Kevin.

ChrisJC · Post by **ChrisJC** » Tue Mar 25, 2008 8:17 am

My understanding is that the heads were the same, it was just the valves that were different. The Vitesse ones had waisted stems.

Chris.

Post by **katanaman** » Tue Mar 25, 2008 9:30 am

What Chris said the heads are the same. Most of them should have the wasted stems as well unless it was a carbed 3.9.

Darkspeed · Post by **Darkspeed** » Tue Mar 25, 2008 12:53 pm

I have read the info on the heads on the board and the info in the Hardcastle and the Hammill books and in general they raise more questions than they answer in a lot of area's - Vitesse spec's seem to be one.

A stock 9.35 SD1 puts out 155 and the Vitesse 190 - for a change in valves and injection fueling thats a 22% power increase for not a lot of work and if the same heads are on a 3.9 and a similar cam why are the 3.9's only rated at a similar power output to the Vitesse 3.5

Perhaps dropping some of that meltable mould stuff down the ports of the Vit and the 3.9 is in order.

Cheers

Andrew

TVRleigh · Post by **TVRleigh** » Tue Mar 25, 2008 1:11 pm

I'm sure the 3.9's used a different Cam and C/R

ChrisJC · Post by **ChrisJC** » Tue Mar 25, 2008 1:41 pm

TVRleigh wrote:I'm sure the 3.9's used a different Cam and C/R

They did - the standard SD1 was 9.35:1 and the Vitesse was 9.75:1

Chris.

Darkspeed · Post by **Darkspeed** » Tue Mar 25, 2008 8:21 pm

Compression ratio alone will make a negligible difference to the power but if the cam is such that it develops power at a much lower rpm then it makes sense why the 3.9 would have a lower output.

But that begs the question of how mild is the 3.9 cam compared to the SD1/Vitesse if they are the same.

Hammill's book it just pathetic with regard to standard cams except to rubbish them all.

Hardcastle gives the SD1 and the 3.9 as same and timings lift but the 3.9 is swung by 2 degrees.

It does not add up - by what's printed all you would do to a have a firebreathing 3.9 is fit tin gaskets and re-time the existing cam 2 degree's

I dont think there is any other option but to have a very close look at the cams and head in the Vitesse. Unless anyone has any definitive answers about cams in the two engines.

Cheers

Andrew

kiwicar · Post by **kiwicar** » Tue Mar 25, 2008 9:42 pm

The extra 2 deg advance, .4 on the CR, waisted valve stems, very slightly better ports, better mapping on the EFI (RR map is very lean at certain points to get through emisions) and better plenum set up and slight improvment on the exhaust will all add up especially when the heads on the 3.5/ 3.9 are the real limmiting factor. The heads as standard only flow enough to produce limited torque, in the case of the SD1 that torque is produced at higher rev's hence it produces roughly the same power as the 3.9 the 3.9 just produces it lower down, the heads are about maxed out in both cases. To demonstrate it further, a mild cam improvment on a carbed 3.5 with SD1/RR heads and a very mild clean up and a set of headers with SUs on the standard su manifold but a needle upgrade will give you the same 200 ish BHP it is also why sticking a huge great bucket of a 4 barrel and a much better inlet manifold on a rover makes very little difference to the output (compare it with the gains from a carb upgrade on a 302 ford). Put that lot on the 3.9 won't give you the gains of the 3.5.
Mike

Darkspeed · Post by **Darkspeed** » Wed Mar 26, 2008 12:16 am

Looking at the cam spec's its the lift thats the problem and why the power tops out on the Vitesse 3.5/3.9 as you say with the same cam and the same lift and the same head will only flow the same air and therefore the capacity increase is wasted apart from lowering the rpm where maximum power is produced.

For the SD1 / Vitesse 22% power increase the difference in the heads must be a little more than those waisted valve stems.

Cheers

Andrew

CastleMGBV8 · Post by **CastleMGBV8** » Wed Mar 26, 2008 1:12 am

The mods done to the Vitesse heads are basically the same as Peter Burgess's Econotune heads which he states +30BHP. add .4/1 increase in compression ratio say 5BHP and your at 190BHP

A 3.9 with the same heads and a slightly hotter cam would be good for 230BHP assuming a decent induction system and a free flowing exhaust.

http://www.mgcars.org.uk/peterburgess/page18.html

bren · Post by **bren** » Wed Apr 02, 2008 8:57 pm

Compression DOES make a big difference - many years ago I had a single plenum Vitesse and I could'nt understand why it felt flat - in the end I just got used to the torque. However, when I broke it for spares it turned out that the original 9.75:1 motor had been replaced with an 8.13:1 unit from a range rover. That explained everything.