Air flow past the throttle plate

[Dqracer]

Hello everyone. I've been around high performance motors all my life, but have never had the time or resources available to invest in porting and airflow research until now...With retirement, time is an abundent resource, so I'm finding myself becoming hopelessly addicted to the mysteries surrounding airflow thru a port. Finding this site has been a big plus..! reading what you guys are devoloping and working on, has answered allot of questions. We are racing 600 cc Mini-Sprints. After hotrodding V-8's for years, I gotta say these jap bike motors are pretty freak'n cool. So, not being able to resist changing the nature of the beast, has taken me down the path of cams, cam timing, compression, alcohol carburation, AFR data ,headers..etc.
A FlowBench is a must have new tool for me..!
My question is, after a guy spent the time to get the optimum flow out of this design of a port,( short & sweet), then you add the carb or TB just upstream,(loaded with alcohol) what turbulent effects does and would the throttle plate add to the equation at anything but WOT. I can see a huge low pressure area behind the top half of the T-plate at part throttle( Y/N )
Would the benefit of small diffuser vanes on the backside of the T-plate have any positive effect...?
Thanks in adavance..
Dallas

[Tony]

The throttle is there to throttle.....

In other words it is SUPPOSED to completely stuff up the flow into the port at anything less than fully wide open.
As long as nothing really bad happens at full WOT, the throttle is just doing it's job.

[bruce]

Something "interesting" to look at on the flowbench with various throttle positions is it effect on fuel signals.

[Dqracer]

Tony,
I agree, it is there to control the amount of airflow and throttle the engine speed, but when you consider the throttle plate for what it is..( a moveable flat restriction) the design aspects of the part itself are not very aerodynamic thru out its range of motion, (be like moving a piece of plywood in a wind tunnel) lots of drag with dirty airflow behind it depending on whatever angle it positioned at.
If proper incoming airflow starts at the tip of the air horn and fllows thru to the tip of the exhaust outlet, why shouldn't the airflow past the throttle plate in (part throttle conditions) be deemed worthy of improvement..? Alot of R&D goes into airflow past the valve seat angle's and the valve, (its a throttle too) If the airflow could be cleaned up as it passes the plate would this not enhance airflow further down stream in the port.

[Tony]

I agree, the throttle greatly disrupts the flow, making it very uneven and turbulent. There will also be a significant restrictive pressure drop.

But deliberately reducing volumetric efficiency, is exactly what the throttle is there for.

If you need say 5% of total engine power to maintain a steady road speed, it does not matter how crudely you strangle the engine, as long as it blocks 95% of the available full airflow somehow.

[Dqracer]

When used on a V-8 with a conventional manifold, I can see where the plates ill effects would be less. however with the intake design of the modern bike engine, having a T-plate the same dia. as the port and located 5" up stream from the backside of the valves, this doesn't offer much of chance for the airstream to settle down after passing by the T-plate.
One more reason to buy or build a flowbench..LOL

Am I confusing myself in thinking of the T-plate as a part in need of areodynamic refinement to stabilize flow thru the induction port.? Or should I be concerned with the overall flow numbers getting into the cylinder..? It seems that the 2 would go hand in hand..?

[Otto]

in a wide open drag style engine we thin the plate and shaft but they are a all the way on or all the way off drivability who cares

[106-1194218389]

I do not know if it would work with gasoline engines, but I used to have a little diesel engine that just had a clear and open air intake tract. All the throttling action was done with the fuel system. The more you opened the throttle the more fuel was injected thus contolling engine power and speed. Just a thought. Honda and GM was working on a gas engine that worked like a diesel called the CCCI engines.

John

[Dqracer]

I was looking at a 62 Jag that had Lucas mechanical injection, (this got me started ) it was outfitted with a throttle slide plate for each intake port, the leading edge of the slide plate was cut at the same diameter as the throttle bore ,so as it opened it created a round hole that progressively got bigger until it was the size of the opening, a better design, but still created a low pressure area (turbulence) on the backside until WOT.
I need to do some flow visulation with a plate in a clear tube, and see what events happen to the airstream.

[106-1194218389]

how about a venturi type device that opens like the iris on a old film camera

[larrycavan]

Throttle plates can kill the flow on a motorcycle engine. Doesn't matter if it's TB or CV carb. They get in the way, disrupt the flow pattern and choke off the port.

Here's a pic of a bored Kawasaki TB with thin plate and modified throttle arm being tested....let's just say mission accomplished....

Some of my old flow data from back in 1985. Same throttle bodies but in stock form compared to Pogue ProFlow throttle bodies modified in similar fashion as the photo.

All at 10"
Stock - 114.7 CFM
Stock w/ Velocity Stack - 125.8 CFM
Pogue -143 CFM
26mm Mikuni Carb w/ Stack - 74.5 CFM

Flow your heads with the throttle body installed and without. It' with that matters. IMO, setting up your porting for a target velocity without the TB's installed is a waste of time.

Done properly, the modified TB will improve flow for you. As for sizing, what you generaly loose is part throttle drivability if you over do the size. It can get snatchy on you..

We have 600's at the local track, PenCan Speedway tomorrow night if the rain holds off....



Edited By larrycavan on 1210900384

[Tony]

Ah... This is what you really want:

[Dqracer]

The expanding venturi idea has bounced around in my head, with the space age materials out there today it could happen...LOL

Larry,,, nice port, are you running gas or alcohol..?


Tony,,that would be nice,

[Moriniman]

BMW had an experimental engine with no throttle mechanism. They used the valve lift and timing to perform the same function. The engine has the potential for very good power, fuel efficiency and emissions. The challenge is to get the valve operating mechanism small enough and cheap enough to be practical. The last time I saw information on the engine, the 'valve command unit' was larger than the engine and consumed too much power.

Lotus used to dyno test cam profiles with an computer controlled valve actuator, but the throttle and valve timing were conventional.

[larrycavan]

That's a gas engine setup for a streetbike. Microsquirt ECU with adjustable pressure reg and the GPz TBs.

I once modeled a head in Cadkey using a rotary valve intake on a 4 stroke. The RV setup was similar to Tony's picture. I still think it could work. We had a disussion about that on Speedtalk a couple years back. Other's had similar concepts.

We have another member, Dean, who works on the 600cc mini sprints. He's probably got some good info on TB flow and setups for them. Hopefully he'll jump into this discussion.

I mostly do classic inline 4 aircooled Kaws and lately big single cyl ATVs. These ATVs are running dual 36mm intake valves.

What motor are you running in your 600?

I just looked at that BMW link. Is that paint in the runners or a serious reversion issue? I suspect the part throttle drivability problem is more an issue of size than it is anything related to the fact that it's a slide throttle arrangement.

IMO, it's no different than the problems faced by motorcycle tuners trying to build big top end power with a carb that's too large for part throttle running.



Edited By larrycavan on 1210927694