i'm stuck whether to just get the porsche throttle welded on to the side of the original manifold (where the original TB would be) or to go for this front-mounted jobbie. I don't really want to lose any low-down power (hence why i went for the 268 cam). Plus the front mounted TB will require more fabrication (air intake, throttle cable etc.) But i totally agree that it stands to reason that cylinders 3 & 4 are going to have a less good supply of air with the side mounted throttle. I'm going to be doing this on a p&p head as well, so we can compare what happens.
Cylinders 1 and 4 will still have a worse flow with the front mounted throttle though. Suppose it comes down to experimentation.
nah, the air distribution is fairly even on a front mount manifold apparently, but the important thing is, is that its better than a side on jobbie. Iv just helped a m8 with a mitsubishi colt that now has an FTO lump in it, and he is suffering from the same problem, the highly tuned engine is being robbed everso slightly on the far cylinders. I have just sorted him out with a TB kit which claims to add 42 bhp to the FTO in its current tune (obviously on emerald managment). So give or take the blown up c**p companys spout, should be a safe 30bhp ish. So the theory stands strong. projects on hold for a day or 2 because of work commitments
another thing i toy'ed with today was a double tb setup with a tb on either end of the manifold. (obviously feeding from the same airflow sensor etc etc. apart from relocating the vacuum feed, removing one pair of tb switches, making up a linkage from tb to tb and welding up a Y pipe, cant see it not working, especaily with a really good P&P job done on it. Im getting a bit obsessed with it all now haha!!
I've seen that done before, there are pics of it. No idea what gains he got, though. 99% sure it was an 8v as well.
this sounds interesting to say the least..looking forward to seeing someone have a crack at the pb mani & tb.
well iv scrapped the front mounted TB idea in favour of a twin TB system. Im using a 1.8 PB Manifold and 2 Throttle bodies off a 1.8 8v gti. So far iv cut on end off, and im in the middle of smoothing out the ports inside and the pipes while i can get my hand in . Next step is to weld on a mounting plate for the second TB, and create the linkage to operate the second TB. I am taking pictures along the way, il be putting them on soon, and if my second rolling road run proves a good gain (my 1st run on a standard PB 1.8 8v gti with only a panal filter showed 119.5bhp), i will do a guide. 8v manifolds used and destroyed in the process of development so far....3
hmm.. not sure if it will work with the double throttle body. Common sense says that more air = more power once you match it with extra fuel, but won't too much air just cause the airflow to slow right down, therefore having a detremental effect on performance? I'm not sure, just throwing that idea out there. One idea that i've seen worked on before was from a guy called Ade who i bought a corrado off a few years back. He liked to muck about with throttle bodies, and had the idea of cutting two throttle bodies in half, and welding the two halfs containing the large throttle body together to create one with double large throttles! Apparently the idea worked, he tested it and said it made a decent improvement, but unfortunately the guy that welded it had got the throttle bodies too hot when welding, and the shape of the ports got distorted just enough to allow a load more air in at idle. Hence he couldn't get it to idle at a reasonable RPM, so gave up. Might be worth another go though! Incidentally, my neighbour has offered to modify my current 8v throttle body, porting out one of the throttles and fabricating a larger butterfly for it. I'm undecided whether to get him to enlarge the smaller throttle or the larger one, but i think for the meantime i'm going to give the front-mounted porsche one a blast! Will post pics when i get around to it, as i'll have to blag my neighbour to weld it all for me.....
surely the throttle body isn't the restriction here? and it really won't need double the throttle size, unless you have just bored it out magically to 3L once the hole is big enough, more hole won't help. a 5.0 mustang has a 75mm throttle body i think with 2 8v ones you'd have more area than that...makes little sense really have you read any engine design books, or just watched lots of blue peter
It may produce some good gains in theroy but you'd be better sorting out the known bottleneck in the 8v cylinder head namely the small exh valves and the short radius of the exh ports.
i dont understand why 2 throttle bodies will work any better?? a forward facing body on an AGG manifold is a straight line all the way into the head, there are no bottlenecks. Surely this is just creating more problems, such as linkages etc for very little actual power gain???
with all the fannying around, why not just go straight to throttle bodies? and a known head/cam combo or for the same outlay, a VR6
i'm not so sure on the twin TB idea, but i'll be trying the front mounted porsche TB idea. Haven't started it yet, but watch this space!
haha i love the responses, and im not being funny, but if it doesnt make any difference, so what, the engine wasnt just invented on logic and calculations, theres alot of trail and error and guess work involved. im just tring different things out thats all. Why through good money at other people to work on stuff when i can do it for relativly little outlay. I think some people are missing the point entirely. And nor for some ACTUAL results, i have the twin TB manifold on the car and its up and running with an ugly bodge of a linkage, but it works! feels slightly more eager to rev above 3k, dont know if this is me mentaly making up some performance or whether there is an actual gain, we shall see friday come rolling road time. Noise is a fair bit more too, i like
Are you running both bodies to the original AFM? Be interesting to see if you could use two, though it'd need a bit of electrickery. You might even get a low enough air flow at full throttle that the flap would still be moving rather than maxed out by 4k, so you could get a chip burnt to suit a turbo stuck on the back.
awesome, glad to hear it works. Stupid question maybe, but have you altered the fuelling to compensate for the extra air? Should be interesting come the rollers!! can't wait to see the results
to be honest i havnt alterd the fueling, and i am using the 1 afm (made sure its very clean etc and properly working). It runs fine as it is, but i should imagine a good old retune may see some better results, im freindly with the rolling road guy, hes gunna tweak the fueling as far as possible on the standrad engine to see what real gains are to be had. doesnt seem to be any lack of low down torque atall im not gunna specualte untill run 2 but lets see
