dwightp

What are the characteristics when going from stock intake to a throttle body such as a TWM? Electronic Fuel injection before and after.

Reason I ask is, most of the TWM applications I am aware of are for hard core race motors. Is this due to the throttle body, injector location in the throttle body or just a "means to an end"?

Thanx,

dwightp

Steve Weiner-Rennsport Systems

Hi DP:

Great question! May I respond?

The main reason to use an individual stack, 6-butterfly intake system is to enhance throttle response, torque and HP at all throttle openings and RPM's. This becomes especially important when camshaft profiles with longer durations and narrow lobe centers are used. This certainly applies to triple-choke carburetors, mechanical FI, and the EFI setups that are referring to.

Risking oversimplification here, the principle is that six small columns of air are easier to accelerate and control their inertia, rather than a common plenum intake for all cylinders and a single throttle. There is no question that the current crop of variable geometry intake systems (Varioram) using a single throttle, works quite well using emissions type cams with little or no duration that causes intake reversion.

Porsche did use a 6-butterfly throttle stack package under the dual plenums on the 3.8 RSR and GT-3R's which use aggressive cams. Porsche engines are VERY sensitive to intake manifold runner lengths and this becomes even more important when using aggressive camshaft profiles.

Hope this helps,

Danno

Also if you measure the cross-sectional area of those 6 small throttle-bodies, it comes out to twice the size of the single throttle. That's to give more high-end flow where the single one can become a restriction. Another alternative is flat-slides and barrel-valves, but those are difficult to modulate at low throttle-openings.

TWM is right down the street from me. They just came out with an axle-less butterfly; when it's fully open, you can't even see that there's a butterfly, it's completely flat! Let me know if you need catalogs or some help picking out a part.

johnfm

Ah ha

some clever guys discussing individual throttle assemblies - excellent (said in the style of Montgomery Burns!!).

Is it any point going to this sort of expense WITHOUT making serious internal mods as well (ie cams, lightweight rods, pistons, porting, knife edging the crank (whatever that means!).

I was considering a MoTec -style replacement management system for the 964, and thought - well if I replace the individual injectors & re-map all the timimg and fuel injection, why would I stick to the individual throttle body??

BUT, with such short induction lengths, would the driveability of the car be compromised - its not a track car, but I like the idea of maximising output without being silly (ie, I don't want a lumpy,engine that is only driveable over 4000 revs).

So, Steve et al. if I was going the MoTeC route, should I also think about individual throttles??

Huntley Racing

Individual throttle bodies are not recommended for street cars. The low speed throttle actuation is too violent for a car that needs to go through bumper to bumper traffic and such. At lower speeds they are very on/off in nature. My 3.6 ltr twin plug injected race motor has twm throttle bodies on it to make power between 7000 RPM and 9000 RPM and thats it. Driving in the pits is almost comical.

maurice97C2S

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by Huntley Racing:
<strong>Individual throttle bodies are not recommended for street cars.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">In themselves they should be fine - look at BMW M-Power engines since the early 80s - all had individual butterflies, give near or above 100 bhp/litre and are very driveable with excellent throttle response. Its the cams etc that take it off the street.

I think Porsche should have moved this way too, but were constrained by air cooling preventing 4 valves per cylinder, and probably packaging reasons in the engine compartment.

Cheers, Maurice

Steve Weiner-Rennsport Systems

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by johnfm:
<strong>Ah ha

some clever guys discussing individual throttle assemblies - excellent (said in the style of Montgomery Burns!!).

Is it any point going to this sort of expense WITHOUT making serious internal mods as well (ie cams, lightweight rods, pistons, porting, knife edging the crank (whatever that means!).

I was considering a MoTec -style replacement management system for the 964, and thought - well if I replace the individual injectors & re-map all the timimg and fuel injection, why would I stick to the individual throttle body??

BUT, with such short induction lengths, would the driveability of the car be compromised - its not a track car, but I like the idea of maximising output without being silly (ie, I don't want a lumpy,engine that is only driveable over 4000 revs).

So, Steve et al. if I was going the MoTeC route, should I also think about individual throttles??</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Hi John:

Good question; The answer lies with you. Its all in what you want to accomplish and what you use the car for.

I'll tell you that individual throttle stacks on any 911 engine; be they carburetors, MFI or a good EFI setup is a well-proven, vast improvement over a single throttle intake regardless of what state of tune the engine is in. There is no question that the amount of HP and torque increase varies with cam profile, compression ratio, displacement, head flow, but the gains in throttle responses at ALL RPM's belies the actual power increase (except for race engines which need such things).

All of the internal mods you mention are SOP for a real race engine; one that sees continuous operation over 7000 RPM. All of those things measurably aid power and durability under such use. Knife-edging the crank means grinding the edges of the counterweights to sharp edges that reduces windage losses from air and oil in the cases.

I would never use Motec without an individual throttle intake system; that would be quite wasteful, and you would not realize the gains from such an investment...

Maurice is correct,......A properly designed 6-butterfly (or slide) intake system can be very streetable. Just look at how well a good carbureted or MFI system runs. Using a race type intake merely requires good air filtration, injector placement and throttle linkage geometry. I've never seen any of the normally available individual throttle intake systems that were so short as to compromise drivability, given the RPM range that 911 engines operate in. In some cases with aggressive cams, we'll space the throttles up to gain some mid-range torque.

IMHO, the main complaints from some EFI systems lies with a poorly designed linkage and bell cranks that make the throttle opening very erratic and unlinear.

Bottom line: If you are considering MoteC, then budget for an individual throttle intake system, and if this is street car, make certain that its provisoned for good quality air filters. If this is mapped properly, you will be very pleased and you gain the flexibility to use whatever camshaft you please, at a later date.

fusionsport

To kinda wade in here- yes individual throttle bodies can be better than a single- it is the theory that a stack of air will move through the a smaller hole faster than a big hole- but that is way to general a term- and it kinda goes back to the olden days when everyone argued against FI for carbs because on the dyno the carbs made a cpl more high end hp- but in truth a plenum type intake manifold even close to properly constructed can and will flow as much air more evenly and with less flow issues than any individual throttle body you care to stack against it- and whats more the individual throttle bodies will not transition from part to full throttle as cleanly as a plenum type intake- the plenum type intakes are not an emissions fix as much as they are a sound, powerband, efficiency(this doesnt mean fuel economy but rather engine efficiency at various loads, which as a by-product increases power and fuel economy) Now if you are building a motor operating in a 2000 rpm band then individual throttle bodies are ok, and can be made to work passably well througout most of the powerband- however they are expensive and not nec for 80 percent of the club racers out there.
What I seem to see people forgetting is they are a pain in the *** to get synched- even with efi the linkage is sensitive and has to be checked regularly or you get issues, and even when synched can have strange turbulence to the flow. Bmw did manage to get them to work on their M-motors, but honestly a mere 100bhp per litre from a car with that much technology is embarrassing- and I wouldnt mention it if I worked for BMW(as it happens I DO have a World Challenge Touring Car BMW I am mapping now), not ever. especially when the now nearly ten year old Honda B-16A motor made 160 plus on pump gas-not premium- from 1600cc without having to rev the **** out of it- and they did it with a stock throttle body and intake. Resonance tuning, reversion, laminar flow- all these things are what make an intake work, not to mention low-pressure charging from aero effects, which by the way the Porsche motors are highly sensitive to- just ask anyone who has ever tuned a n/a motor on the dyno then had to add fuel when at the track because of a lean condition.
Bottom line is that I would-and have just tonight- recommend for the average racer and hot street car the following-
3.0-32 litre engines- 3.2 Motronic intake,ported and flow-tested, Motec or DTA ecu
3.2-3.5 Motronic or Fabricated Intake, Motec or DTA ecu
3.5 and up, turbo cars- factory ported and flow-tested intake, or fabricated twin throttle body plenum intakes, Motec or DTA ecu

I prefer the twin TB intakes for turbo cars and bigger motor becuase of what I can do with low and high speed flow numbers, but that is just me.
Under 3.0 litre cars need a fabricated or modified factory intake, but can really benefit from modern efi. The worst thing you can do is simply bolt on a set of individuals and then go tune, as you can have all sorts of issues with flow, and though efi can compensate for it- if you have a flaw in your air pump(engine in other words) you need to fix that first rather than try and band-aid it with mapping.

johnfm

Aw Marge, now you're just confusing me (said in the style of Homer!!).

Luckily, I am a few months off any engine upgrades, so have some time to decipher these opinions.

My current thoughts for a road car: MoTeC & big bore throttle body/throttle bodies.

Huntley Racing

The 'Homer' version of what Fusion was trying to say is: run your stock manifold with EFI for your street car. Good luck.

fusionsport

Actually I was really just saying that unless you are building an unlimited race motor that you would be better off using a simple plenum intake- and nicely enough the factory has one made for the job- and fabricated ones work nicely too- so in a Bart voice- "Dont have a cow man!"

fusionsport

By the by- I have a source for exceptional individual throttle bodies at reasonable-but not cheap- pricing- please enquire if I havent disuaded you from individual throttle bodies for your racing car. I have them in bores ranging from 40 to 70+ mm with one or two injectors, various tapers, and of course anything custom can be done with the appropriate sums. TWM are wonderful throttle bodies- I just thought I would throw out an alternative. Again enquire if you are interested in any price quote for either single plenum or multiple individual throttle bodies for any four or six cylinder Porsche, turbo or not- or for any other engine for that matter. Cheers

Tim

I would definately be interested in throttle bodies.Ive been looking at the TWM Weber replacement.

fusionsport

Tim I sent you an IM on here.

johnfm

Hey

clever engine tuners, would twin injection solve the problems of resolution (ie fine metering of fuel) at idle and mass fuel delivery at WOT?

I read about using two small injectors, instead of one big one. I expect it could be controlled via MoTeC, DTA or similar. I expect you would need a custom throttle body, but that probably isn't a big deal. I expect the biggest headache will be management.