Inlet trumpets ?????
Discussion
Which is the best solution on a 97/98 450 chim.
1. ACT shortend carbon inlet pipes 48mm - 38mm
2. SC manifold spacer/insulating gasket.
3. 1 + 2
Number 3 would give you maximum room and air flow in the plenum, but is it over kill, considering the restriction in the standard AFM.
So what about changing the standard 3.9/4.2 Hotwire AFM to the GEMS 4.6 20AM?
Sorry if this seems to be a basic question that has been debated on so many other threads all with different views
1. ACT shortend carbon inlet pipes 48mm - 38mm
2. SC manifold spacer/insulating gasket.
3. 1 + 2
Number 3 would give you maximum room and air flow in the plenum, but is it over kill, considering the restriction in the standard AFM.
So what about changing the standard 3.9/4.2 Hotwire AFM to the GEMS 4.6 20AM?
Sorry if this seems to be a basic question that has been debated on so many other threads all with different views
Old skool 45mm alloy trumpets nicely matched and blended through the base and into the top of the inlet manifold is a very effective combination (or even no trumpets at all), the spacer and insulator will do no harm either. Wouldn't worry too much about the AFM unless you're making cam changes or doing major head work with big valves, in which case get rid and go aftermarket mappable ECU and coilpacks etc. The stock throttle plate will flow sufficiently for 300hp so no worries there initially
Quinny said:
SILICONE KID said:
I have the 72mm plenum,45mm flared short aluminium trumpets,port matched inlet manifold,Megasquirt,TVR Power 15 quid thermal insulator and the 5l engine now producing 339bhp.
Bloody he'll Daz, that powder coating must be good stuff to be worth 6 BHP
pbaker43 said:
Which is the best solution on a 97/98 450 chim.
1. ACT shortend carbon inlet pipes 48mm - 38mm
2. SC manifold spacer/insulating gasket.
3. 1 + 2
Number 3 would give you maximum room and air flow in the plenum, but is it over kill, considering the restriction in the standard AFM.
So what about changing the standard 3.9/4.2 Hotwire AFM to the GEMS 4.6 20AM?
Sorry if this seems to be a basic question that has been debated on so many other threads all with different views
The 20 AM is a good unit as it bolts straight in place, but I dont think you can get them new any more. There is also the Bosch AFM thats much bigger, but both have different response curves to the Lucas 5AM AFM, so you either need to modify the voltages given out with a small box of electronics, or rechip the ECU. I have made some electronic units that exactly mimic the voltages given by the 5am, but this has a limitation on big horsepower motors that the 5AM reaches its peak 5 volt output before the motor produces its peak power, so the ECU cannot get any more useful data from the AFM, and this this effect has to be reproduced by the electronics to suit the ECU standard chip fuelling, even though the AFM can flow more air physically, and could liberate a few horsepower more. The advantage of chipping is you can make use of the extra resolution with a bigger AFM to get the full power fueling precise, but its ceratinly not cheap. Ive not power tested the electronic set up, as the primary reason to develop this set up to try and make use of a modern AFM design, and make the fuelling more acurate at low speed to try and reduce the shunting some cars experiance, and if it gains power thats a bonus. Generally however its not worth messing around with bigger AFMs for power unless you are pushing around 270 bhp plus.1. ACT shortend carbon inlet pipes 48mm - 38mm
2. SC manifold spacer/insulating gasket.
3. 1 + 2
Number 3 would give you maximum room and air flow in the plenum, but is it over kill, considering the restriction in the standard AFM.
So what about changing the standard 3.9/4.2 Hotwire AFM to the GEMS 4.6 20AM?
Sorry if this seems to be a basic question that has been debated on so many other threads all with different views
Thanks Guys
So I will bin the AFM change, stick with the original !
thanks blitzracing
Pupp said:
Old skool 45mm alloy trumpets nicely matched and blended through the base and into the top of the inlet manifold is a very effective combination (or even no trumpets at all),
So if I take out the trumpets (ram pipes) the engine will work?
[if this is the case why were they in there in the first place]. Why has no one else removed these pipes, and why the big debate on shunting, as everyone seems to agree there is not enough air on the top of the trumpets so removing them will create space and better air flow? Or am I just thick and should 
I do not have loads of cash to throw at this problem, all I am asking for is an effective solution to make the car a little easier to drive around town, I know all TVR’s seem to be different but there has to be a core thread leading to a mild solution.
So I will bin the AFM change, stick with the original !
thanks blitzracingPupp said:
Old skool 45mm alloy trumpets nicely matched and blended through the base and into the top of the inlet manifold is a very effective combination (or even no trumpets at all),
So if I take out the trumpets (ram pipes) the engine will work?
[if this is the case why were they in there in the first place]. Why has no one else removed these pipes, and why the big debate on shunting, as everyone seems to agree there is not enough air on the top of the trumpets so removing them will create space and better air flow? Or am I just thick and should I do not have loads of cash to throw at this problem, all I am asking for is an effective solution to make the car a little easier to drive around town, I know all TVR’s seem to be different but there has to be a core thread leading to a mild solution.
Think you will need to speak to Mark Adams..If you dont change the inlet manifold you will have a step between the trumpet base and inlet manifold.I was going to buy the TVR POWER plenum spacer but 100 quid for a bit of plastic...you need your head testing if you have bought one!!!
Edited by SILICONE KID on Wednesday 17th November 19:27
Putting it in its simplest terms, You need the trumpets to both smooth the gas flow and maintain gas velocity into the inlet ports, as once the inlet charge has reached a reasonable speed down the trumpet , its inertia will continue to push air into the combustion chamber even as the valves close. This effect also helps counter act pulses of exhaust gas that try and escape back into the plenum chamber during the valve overlap period. These effects will only occur at certain rev bands, so the trumpet length is tuned to maximise the torque at what ever RPM is needed. As a rule of thumb, long trumpets give low down torque, and short ones are better for higher RPM, and ultimate power, but how much effect this has on the ancient RV8 head and port design with stock trumpets is open to discussion. Wider trumpets will give better ultimate flow, but removing them completely may not be such a good idea due to the lack of the ram effect. There are some rolling road tests from the past on the Griff forum if you dig around enough. As for chipping, just changing the inlet trumpets wont throw things out enough to matter.
Edited by blitzracing on Wednesday 17th November 20:30
I`d agree with Blitz, he`s a clever chap you know
removing the trumpets altogether with a blended base gave no benefits at all when tested on a dyno, the 45mm trumpets work well, as for porting and matching the inlet manifold save yourself a fortune, take yours of the car and do it yourself, pretty simple to do, and make sure you fit an insulator plate before refitting the plenum, it helps enormously to reduce heat soak into the plenum.
all this talk of remaps makes me wonder, I fitted 72mm plenum, 45mm trumpets, blended the inlet manifold and ran it afterwards no problems, remaps only needed when changing the afm, no matter what you do, you are still trying to suck air through a 55mm hole!
removing the trumpets altogether with a blended base gave no benefits at all when tested on a dyno, the 45mm trumpets work well, as for porting and matching the inlet manifold save yourself a fortune, take yours of the car and do it yourself, pretty simple to do, and make sure you fit an insulator plate before refitting the plenum, it helps enormously to reduce heat soak into the plenum.
all this talk of remaps makes me wonder, I fitted 72mm plenum, 45mm trumpets, blended the inlet manifold and ran it afterwards no problems, remaps only needed when changing the afm, no matter what you do, you are still trying to suck air through a 55mm hole!
Alexdaredevilz said:
roysum said:
topsparks said:
Roy,I would be interested in your trumpets,as I have a 45mm ported inlet manifold and stage 3 heads but no trumpets yet!
Sorry topsparks, someone got in before you by PM.Regards, Roy.
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