There appear to be 2 schools of thought regarding cylinder head > butterfly distance. Brooksters Jenveys are bolted close to head and have long trumpets. Chris Eyre has a `spacer` inlet with short trumpets ! The overall length looks similar in both setups, but I`m wondering what the difference in driveability would be in each case and, in an ideal world, if putting a set of ITB`s on a valver, would you prefer to have the butterflies in the ITB as near the head as sensible with long trumpets, as far away from the head with short trumpets or something inbetween ?
Closer to the head for throttle response and the longer trumpets for torqure. FTW Brookersters are Jenvy DTH bodies as per Badger 5. I used to own the old uber jetta (badger5jetta 2008cc 16v on Jenvy ITB's) and it was amazing on the throttle but havent driven Chris Eyre's set up to compare.
Thats what I was thinking. However, knowing Chris and the research he does into these things, I am surprised if there is no benefit to the longer inlet between head and butterfly he has... Hence my questions. My own investigations have led me towards the short distance and long trumpet solution...
I have the badger-5 dth bodies on my ibiza - its not just where the butterfly is, its where the injector is - injectors far away are good for top end, near to for throttle response - 8 injector setups try and get best of both worlds - the dth injector fires pretty much at the back of the valve so ace for responsiveness but its how these things go with the other engine components that gives the engine its character I spent a whole day on the dyno a few years back and experimented with I think 20-120mm trumpets, about 4 or 5 different sizes, next to no effect on my particular engine, couple hp. The reason was I wanted to fit a cold air box and couldn't do this with the long trumpets because of bonnet clearance. I think the cold air feed would be worth more than the effect of the trumpet length....but that was on my (old) engine. Bill reckoned his engine responded well to longer trumpets. Its never easy. My current engine has cracking throttle response with the 45mm DTH bodies. The same engine when fitted with 48mm bodies on a long manifold (placing the injector further away) gained 15hp, but lost mid range and throttle response. Oh....and it wouldn't fit under the bonnet of the car...... Current experiment being planned is 48mm DTH bodies.
Intersting. So on my 3.2, the injectors are already mounted in the head. so what difference would it make (if any) if was to drill and tap the head to bolt the throttle housings right up, rather than make a manifold to mount them to? or would i actually benfit from mounting the injectors further out along the inlet tract?
Part of the reason my car has long inlets was I suspect down to parts availabilty at the time. The ex-Reeves engine was originally built in 1998, though I believe the origins of the TWM inlet manifold lay with a previous Reeves engine, built around 1996/7. Inlet manifolds available at the time were the rubbish stepped Mangoletsi 16V manifold, which should be avoided at all costs, and this TWM one. The DTH bodies came about in ~ 1999/2000 when Badger5 co-developed them with Jenvey on his Jetta. Jenvey obviously took a standard body, and adapted it to suit the direct fitment. Bill may know more on the maths of the butterfly position and the market they intended to target. So history lesson over, and practically speaking, the DTHs get the job done just fine, and are pretty much the off shelf solution. No one is playing hard enough with high power 16Vs to really back-to-back all of this - or at least put the information in the public domain. A couple of Berg Cup cars had them, and others were generally fabricated, and looked possibly tapered. What precedes all this is the source of power, which comes out of compression, headwork and cams. Otherwise, they literally just use more fuel.
will do!, subscribed to this thread now! one thing i reckon i must consider is that i want to reach my powerband easily, and keep it in there as long as poss. on a valver! must read back through this again lol
depends how you define 'benefit'. Rule of thumb is more top end from moving the injector away from the valve. If you have a wide ratio gearbox, it may be more of a 'benefit' to hae more midrange torque......so keep the injector near the head
From experience inlet tract length hardly has an effect at the power levels we are working at. But the "general" school of thought is big bodies moved further away gives a peaky race engine, chuck an inlet manifold in in there to regain some lost torque. The audi BTCC engine and VW motorsport 16v lumps both have an inlet manifolds and 8 injectors. Moving the injectors further away also has the following benefits, good atomisation of fuel at higher engine speeds and it also has a cooling effect on the incoming air charge. Throttle body size selection is probably the most important thing to get the best throttle response with an all good power. For example I ran a completely standard KR in my mk1 for a while with 48mm bodies, it was completely gutless below 5k rev's, but put those bodies on a slightly tuned engine and things got better...... I hope that helps!!
i have a very close ratio box. but i'm sure my motec can handle mutliple injectors. hmm, keep the ones in the head, but have another set mounted out in the trumpets for high rpm.
Berg Cup photos, and variation seen. Nothing to get hung up on IMO. Class winner, 4 injectors, very long tract, injectors look to be in the airbox/very close to: Difficult to see, but these are relatively short, not a million miles off DTH - second in class: Twin rails (8 injectors) - car's times were average, but driver was first time out in an otherwise highly developed car :
