Trumpet curve

[TVRleigh]

Any reason why the Trumpets are lower at the side to the middle.
I know the tubes are the same length, but just sit further down.

but was wondering if there was a reason, I know the early plem's was curved, but the later ones was square.

Thanks
Leigh

[sidecar]

Any reason why the Trumpets are lower at the side to the middle.
I know the tubes are the same length, but just sit further down.

but was wondering if there was a reason, I know the early plem's was curved, but the later ones was square.

Thanks
Leigh

Sometimes different length trumpets are used on the same engine to tune each cylinder to a different peak in the torque curve. The engine will therefore produce less of an out right peak in torque but the spread of the torque curve will be better. Basically it's a slight de-tune of the engine which may result in a better road based engine. (As apposed to race based).

Either that or they can't fit all long one's in the air box!

Pete

[TVRleigh]

So its ok to have them all the same length and depth,

As planning on having the base skimmed and having bigger trumpets fitted.

even the tuners seem to have them in a curve though, see
http://cgi.ebay.co.uk/Chrome-Morgan-SD1 ... .m14.l1318

Need to be 100% before I get it chopped.

Thanks
Leigh

[russell_ram]

It's so that each of the eight inlet tracts end up being the same length. The short ones feed the cylinders that are furthest away from the plenum, the long ones feed the nearest cylinders. You should keep the relative difference in heights in any mods you do as far as possible else you'll have some cylinders 'on song' at different rpm to others.

Russ

[Ian Anderson]

Don't suggest that unless you are changing the roof of the plenum

The distance between end of trumpet and plenum roof should be the same on all trumpets. If not the reverse pulses will cause havoc.

Ian

[sidecar]

Well there you go, they are different lengths so in fact they are all in fact the same length as far as the engine is concerned!

The different length thing has been done on engines before now to flattern and spread the torque, I promise you!

Pete

[TVRleigh]

ok,

I'll get them to keep them the same relative distance.

the plenum roof on the later 4.0 P38 cars was flat, though and they still had the curved trumpets.

But makes some sense to have the same inlet track length.

but also I remember Eliot at http://www.mez.co.uk/ having a 1" compersit trumpet base. was just a 1" think lump of plastic with the 8 holes and a trumpet style blend.

and he said that worked very well. and they was all the same length and very short.

[Eliot]

but also I remember Eliot at http://www.mez.co.uk/ having a 1" compersit trumpet base. was just a 1" think lump of plastic with the 8 holes and a trumpet style blend.

and he said that worked very well. and they was all the same length and very short.

One of my flat blended bases was dynod back to back against an ACT carbon trumpet setup - the trumpets worked better.

[Ian Anderson]

Look at the back of any original GT40
4 webber carbs and a flat metal plate above them

This was done as they found they had leaning out problems between the different cylinders when the engine bay was closed up and the rear windscreen closed the gap to the back 2 carb trumpets.

The simple plate meant they could tune the carb in normal way and then put the plate on and it would not change after the rear was closed.

They did vary the height of the plate for different tracks to move power band up and down - but that is another story

Ian

[TVRleigh]

but also I remember Eliot at http://www.mez.co.uk/ having a 1" compersit trumpet base. was just a 1" think lump of plastic with the 8 holes and a trumpet style blend.

and he said that worked very well. and they was all the same length and very short.

One of my flat blended bases was dynod back to back against an ACT carbon trumpet setup - the trumpets worked better.

Was the rest the same, Inc the bore of the flat blend base compared to the ACT trumpets.

Thanks
Leigh

[chodjinn]

At the end of the day though, anyone even considering spending £345 on carbon trumpets needs a punch in the face!

IIRC, with forced induction the trumpet lengths don't matter as much, and I would have assumed eliot's blended base would be a good option in such a case?

[Eliot]

Yes, 44mm base.

Its available for sale if anyone wants it (he didn't want it, because the trumpets came out better)

[TVRleigh]

Thanks for the replies

Still a little confused on the best route.

One Last question do you need to worry about the 4 small drain holes.

as I want to make the base shorter.

Thanks
again
Leigh

[Eliot]

dont worry about them.

there's some info on the net about it somehwhere, they mgb guys lower them.
Dont go too low, otherwise you might foul the injectors or rocker covers.

[chodjinn]

yeah there is a guide somewhere on the net; and the 'how to V8 your MGB' book gives exact dimensions. I can find out and PM them to you if you wish (I have the book at home!). IIRC its about 22-25mm total you can remove (trumpet base and manifold combined). And yes the fuel rail gets in the way if you go any lower.

Personally, I've not reduced my inlet manifold or trumpet base, mainly because its a pain and i can't afford to, but also because I have a spanky ACT carbon plenum sticking out of the bonnet!