Trumpets or not

[paul gotts]

Received wisdom from the tuning experts on the inlet side seems to be that, certainly for the larger capacity RV8's, a larger capacity plenum, larger diameter throttle disc and trumpets (unless you've already got a 500) and ultimately multiple throttle bodies is the way to go. However, I was talking to one of the guys that used to work for Rovercraft / Progress a few days ago, and he mentioned that they had seen some of their best power figures on a Griff. 500 running without any trumpets at all. I assume that the purpose of the (flared) trumpets is to speed airflow into the manifold and to even out intake pulses. Has anyone experimented with running without trumpets in a plenum based system?

[350matt]

I believe that this is the basis for TVR powers ' Takara' upgrade, they remove teh trumpets / bits of pipe entirely from the plenum and then flare / broddle the ally base to produce a decent radiused entry. sposede to be worth a bit on its own.

Matt

[Gerry Attrick]

Trumpets are also used to change the resonant frequency of the intake system and move the power boost from the shock wave effect up or down the speed range. Depending on the available space, you can get a useful increase in torque or power, with a loss elsewhere.

[rev-erend]

I believe - the longer trumpets are used to prop up the torque. The curve on the top helps to smooth the air pulses.

Removing the trumpet - will in theory give a small percentage bhp gain but probably would loose some torque and driveability.

SO if using a wild cam - it would not so driveable.

Some cars use this - varying the inlet length.

Longer for low revs - shorter for high revs.

[350matt]

Well bear in mind that even if your're removing the trumpet the intake 'pipe' is still there and the std Rover intake is set for the old cam and and the tuning point is 5250Rpm also by going shorter you stand a chance of catching the earlier or lower number reflection, which tends to be stronger.

INTAKE RUNNER LENGTH
ECD = Effective Cam Duration
RV = Reflective Value = 2 for 2nd reflection 3 for 3rd etc – the earlier the reflection = the stronger the tuning
ECD = 720 - (Adv. duration - 30)
Speed of sound = 396m/sec
intake runner length = ((ECD/360) × (1/(tuned rpm /60))* speed of sound)/(2*RV)
( ((470/360) x (1/6000 /60))*396) /(2 *6) = 0.43mtrs


Matt

[rev-erend]

350matt said:

Well bear in mind that even if your're removing the trumpet the intake 'pipe' is still there and the std Rover intake is set for the old cam and and the tuning point is 5250Rpm also by going shorter you stand a chance of catching the earlier or lower number reflection, which tends to be stronger. INTAKE RUNNER LENGTH ECD = Effective Cam Duration RV = Reflective Value = 2 for 2nd reflection 3 for 3rd etc – the earlier the reflection = the stronger the tuning ECD = 720 - (Adv. duration - 30) Speed of sound = 396m/sec intake runner length = ((ECD/360) × (1/(tuned rpm /60))* speed of sound)/(2*RV) ( ((470/360) x (1/6000 /60))*396) /(2 *6) = 0.43mtrs Matt

Matt - I suspect that there are right ... as there is plenty of power available low down - not many go for a high (solid) lifter cam on this engine .. not really that many benefits - so if you don't go for a wild cam then you won't loose the low down torque and won't need a long trumpet. So just smothing the plenum intake will work.

[paul gotts]

350matt said:

I believe that this is the basis for TVR powers ' Takara' upgrade, they remove teh trumpets / bits of pipe entirely from the plenum and then flare / broddle the ally base to produce a decent radiused entry. sposede to be worth a bit on its own. Matt

Surely you end up with unequal length inlet tracts, or are the varying depths at which the trumpets sit in the base intended to achieve a consistent height from the trumpet top to the roof of the plenum?

[rev-erend]

paul gotts said:

350matt said: I believe that this is the basis for TVR powers ' Takara' upgrade, they remove teh trumpets / bits of pipe entirely from the plenum and then flare / broddle the ally base to produce a decent radiused entry. sposede to be worth a bit on its own. Matt Surely you end up with unequal length inlet tracts, or are the varying depths at which the trumpets sit in the base intended to achieve a consistent height from the trumpet top to the roof of the plenum?

All the trumpets are at various heights - so I guess this makes them all equal length.

With the Takara - they would definately be unequal as they disguard the trumpets.

[2 sheds]

Having trumpets fitted does more than just increase & insure equal tract length, we have the bases machined so that the trumpets are angled out so that you separate the intakes to reduce pulse interuption between cylinders, the theory of tract length / pulse tuning is ok as a guide but you need to factor in the plenum effect, basically the Rover V8 is better with trumpets, yes they will work without but you will loose some of the mid torque.
If the trumpets are running atmospheric (without plenum) the length is more important.
Tim

[johno]

Paul,

Considering your Motec system it should be a straight forward upgrade and remap.

All you need is a larger throttle/multiple trottle body and trumpets, you can then remap according to the new intake.

I reckon you'll probably run out of fuel through injectors before you'll need more air with this set up though, depending on what size of throttle you go for. Considering how much you are already getting from it.

I struggle to believe that no trumpets could possibly be better, given all that air just swiring about in the plenum, and from what I know of engine tuning (very very little) you have bike manufacturers like MV Augusta who are using variable length inlet tracts to give differing engine characteristics. Removing the trumpets removes all of that ability and although these are dynamic systems and ACT's are not they are designed to deliver a beneficial engine characteristic (increased torque/bhp throughout rev's - fair summary Tim ?) There could be differing trumpets dependant on what characteristic you want, but just removing them ??

[johno]

Paul,

Considering your Motec system it should be a straight forward upgrade and remap.

All you need is a larger throttle/multiple trottle body and trumpets, you can then remap according to the new intake.

I reckon you'll probably run out of fuel through injectors before you'll need more air with this set up though, depending on what size of throttle you go for. Considering how much you are already getting from it.

I struggle to believe that no trumpets could possibly be better, given all that air just swiring about in the plenum, and from what I know of engine tuning (very very little) you have bike manufacturers like MV Augusta who are using variable length inlet tracts to give differing engine characteristics. Removing the trumpets removes all of that ability and although these are dynamic systems and ACT's are not they are designed to deliver a beneficial engine characteristic (increased torque/bhp throughout rev's - fair summary Tim ?) There could be differing trumpets dependant on what characteristic you want, but just removing them ??

[350matt]

Has anyone ever made a 'proper' intake for the poor old rover? Apart from a set of downdraughts / throttle bodies they all seem to be based on the std injection set-up which isn't too pretty frankly. I'm in the process of making my own but I'm suprised that non-one tackled it before being as the std manifold has a variety of twists and turns, changes of area etc???

Matt

[Boosted LS1]

The efi plenum on the rover is really quite good imho. It gets all the tracts the same length. It would be better if it was a split plenum and that's been done on the 4.6/4.0. So for torque that's probably the way to go if you have the budget.

Boosted.