Hi new member here i am planning to install some throttle bodies onto a 1.4 16v engine, and i am unsure on the basis for working out inlet tract length their are 2 kinds of throttle bodies im looking at both jenvey (40mm)93mm and 118mm in length and i have about 10" from the mounting face on the head to the bulkhead (inlet is at the back) what should i go for? do i want to have a long as possible? and what aboiut airhorns/trumpets? is it better to use the shorter bodies and longer trumpets or the other way round? cheers ! Edited by: jtothez
This is a bit of a "how longs a piece of string" question. The ideal length is dependant on loads of other factors. Your best bet is to go for the shorter manifold and then use different length trumpets to tweek it. You can always go longer with the trumpets but can't shorten the manifold. The basic rule is that a longer inlet will give better torque and a shorter better top end, but that's only a very rough guide, there are so many vairiables the only way to tell is to get a selection of trumpets and book a rolling road.
There's a calculator here to give you a very rough idea of lengths, but don't take it as gospel. There are too many factors at play to be able to say 'the right length is X', and it's also complicated by you, and how you want the engine to drive. For each gain you get from tuning the inlet length there is also a corresponding loss somewhere else in the rpm range, the trick is to find yourself a balance that you're happiest with.
ok i see so it is far more about the way the power is delivered than theactual power output i will opt for the shorter ones then, i have seen some 90 degree bend trumpets, as i think these could be the answer to fitting a long tract length. does standard inlet tract length figure anywhere in deciding on some trumpets to use? saying that standard length is about 20 inches!
Sharp 90deg bends are poo for airflow, and will also likely disrupt the pulses going up and down the inlet, so you'd effectively just see the distance from the head to the bend for pulse tuning effects. I'd steer clear and spend the time trying to fit some straight ones in. If it was me i'd be looking to get the inlets as long as I can fit in the bay.
ah ok, no bendy ones then! for long ones i will more than certain i will have to make an airbox for them whats the best way to do this? either have a large foam filter covering the trumpets then enclose this and have a feed from a decent airsupply, or make a box around the trumpets and a long pipe with a cone filter at the end of it?
There is a wee bit about this on the Jenvey site, but tbh, there are books out there on this subject alone, so you probably aren't going to find the total answer on here. You will need more than 10" though. Time to cut the scuttle panel out!
Cut a big hole in the scuttle panel with a jigsaw. Seems a bit brutal initially, but its the only way i'm afraid.
your being serious? but, i suppose with the trumpets thier, they can actually breathe rather than being pinned against the bulkhead
Exactly. No point in spending money on the right bits, then gaining nothing through compromising the installation. You can make a really neat job to be fair. Just think it out and take your time.
