VAP
03-16-2003, 09:42 AM
Long day yesterday. I was up until midnight flowing this thing then put it on my car thats stock in every way including air filter and exhaust. I only test with a stock platform as any improvement on a stock platform will only be exaggerated, never diminished, by other prudent and meticulously carried-out intake tract mods, ie; cone or panel K&N, port, porting, polishing, extrude-honing, exhaust at al. Yes, they are all related and important for maximum gain. But since I only do TB's I'm restricting myself to TB's tested in a stock car in these narratives and leave the blatantly obvious to you guys.
The flow bench shows a positive increase in efficiency, flow and power up until a CFM equal to 212-215HP on a 2.8 NA engine then the benefits start to take a rather sharp nose-dive. In other words on a car with 200 or less HP it's absolutely better-flowing and noticeably quicker than just doing the primary sleeve alone and it gets to it's redline faster in every gear tho I only tested up to redline in third. I'll leave it on my car and use the higher gears next time I venture out to the boonies. In higher power cars this would be equivalent to throwing out an anchor at anything above 3300 RPM's.
The most incredible trivia facet that came from this is the throttle resolution. The throttle is way way more precise right now in the lower RPM's. You can push the accelerator down to hit 1500 RPM's and it hits it first time and holds it there forever... something my 2.8 has never been able to do before. It's always been a fidgety endeavor before trying to find a higher-than-idle-RPM-and-hold-it-there. And while "resolution" isn't high on anyones list of "must-haves" it's a very very nice thing to have as I'm just finding out. This has to be more related to the location of the secondary sleeve to the primary sleeve and it's influence on air path than any direct affect as the secondary bore is closed while this is happening. Cool side benefit but inexplicable... seems the more I learn the less I know. And like a dog chasing a car... what the hell would I do with it if I caught it!?!
And since some have mentioned it I thought I'd make mention of the plenum found on these cars. I have flowed it and have flowed some TB's while attached to it. The plenum in and of itself is no impedance, restriction or limiting factor in these cars whatsoever. At realistic attainable CFM of air this thing will out-flow the cars all but fantasy capabilities. It flows over 650CFM of air without a hitch and would sustain 372.5HP in a NA 2.8 engine and even more with forced induction (if you could get it to seal). There's no discernable difference in testing TB's with/without the plenum. Audi did their homework on this piece. The MAF on the other hand shows to be the limiting factor in any stock/semi-stock 2.8 12V. Not due to it's electronics but it's physical size limitations due to the internal restriction. It can only flow at/near 370CFM... which is a number I'm easily capable of outdoing on a TB if it were bolted to the right car.
My gut feeling is this throttle body with 35/52mm butterflies was actually designed for either a V8 initially or a turbo application and that it's a smidge too large for our cars and thats why it comes "restricted" from Audi (the primary side). I know this was used in a 91 VW Fox but I'm wondering if a V8 or 5000 turbo used it or it's basic core before that all the way back to 1980. I'm also wondering what size bores are in the 20v cars (I'm betting the same 35/52mm). Audi is a huge proponent of using old core parts with subtle changes on new product lines.
And before anyone asks I won't offer the secondary stage mod as it would drive the price thru the roof and this wasn't a greed-motivated experiment. It was just another way to euthanize a Saturday. The only one in the world will live out it's days in secret in one of many nom de plume silver 96 2.8 12v's out there.
The flow bench shows a positive increase in efficiency, flow and power up until a CFM equal to 212-215HP on a 2.8 NA engine then the benefits start to take a rather sharp nose-dive. In other words on a car with 200 or less HP it's absolutely better-flowing and noticeably quicker than just doing the primary sleeve alone and it gets to it's redline faster in every gear tho I only tested up to redline in third. I'll leave it on my car and use the higher gears next time I venture out to the boonies. In higher power cars this would be equivalent to throwing out an anchor at anything above 3300 RPM's.
The most incredible trivia facet that came from this is the throttle resolution. The throttle is way way more precise right now in the lower RPM's. You can push the accelerator down to hit 1500 RPM's and it hits it first time and holds it there forever... something my 2.8 has never been able to do before. It's always been a fidgety endeavor before trying to find a higher-than-idle-RPM-and-hold-it-there. And while "resolution" isn't high on anyones list of "must-haves" it's a very very nice thing to have as I'm just finding out. This has to be more related to the location of the secondary sleeve to the primary sleeve and it's influence on air path than any direct affect as the secondary bore is closed while this is happening. Cool side benefit but inexplicable... seems the more I learn the less I know. And like a dog chasing a car... what the hell would I do with it if I caught it!?!
And since some have mentioned it I thought I'd make mention of the plenum found on these cars. I have flowed it and have flowed some TB's while attached to it. The plenum in and of itself is no impedance, restriction or limiting factor in these cars whatsoever. At realistic attainable CFM of air this thing will out-flow the cars all but fantasy capabilities. It flows over 650CFM of air without a hitch and would sustain 372.5HP in a NA 2.8 engine and even more with forced induction (if you could get it to seal). There's no discernable difference in testing TB's with/without the plenum. Audi did their homework on this piece. The MAF on the other hand shows to be the limiting factor in any stock/semi-stock 2.8 12V. Not due to it's electronics but it's physical size limitations due to the internal restriction. It can only flow at/near 370CFM... which is a number I'm easily capable of outdoing on a TB if it were bolted to the right car.
My gut feeling is this throttle body with 35/52mm butterflies was actually designed for either a V8 initially or a turbo application and that it's a smidge too large for our cars and thats why it comes "restricted" from Audi (the primary side). I know this was used in a 91 VW Fox but I'm wondering if a V8 or 5000 turbo used it or it's basic core before that all the way back to 1980. I'm also wondering what size bores are in the 20v cars (I'm betting the same 35/52mm). Audi is a huge proponent of using old core parts with subtle changes on new product lines.
And before anyone asks I won't offer the secondary stage mod as it would drive the price thru the roof and this wasn't a greed-motivated experiment. It was just another way to euthanize a Saturday. The only one in the world will live out it's days in secret in one of many nom de plume silver 96 2.8 12v's out there.