× 1-800-946-2642 Home My Account Social / Forum Articles Contact My Cart
Shop Now
Select Your Car Type Sale Items Clearance Items New Items
   Forum Width:     Forum Type: 

 Posted: Jan 7, 2018 05:02AM
Total posts: 9528
Last post: Mar 27, 2024
Member since:Aug 14, 2002
Cars in Garage: 0
Photos: 0
WorkBench Posts: 0
CA
Quote:
Originally Posted by h_lankford
Quote:
Originally Posted by Dan Moffet

(How's the head, Harvey?.... sorry )
worse!
Take two Red Stripes and call me in the morning.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Jan 5, 2018 04:19PM
Total posts: 2036
Last post: Mar 27, 2024
Member since:Aug 29, 2001
Cars in Garage: 0
Photos: 0
WorkBench Posts: 0
Quote:
Originally Posted by Dan Moffet

(How's the head, Harvey?.... sorry )
worse!

 Posted: Jan 5, 2018 04:14PM
Total posts: 9528
Last post: Mar 27, 2024
Member since:Aug 14, 2002
Cars in Garage: 0
Photos: 0
WorkBench Posts: 0
CA
Ahh, looking at the screen shots I posted, I can see what appears to be cobwebs of vapour along the surface of the rams, especially in No. 1 on the No. 3 side. Someone knowledgeable (not me!) in fluid dynamics might explain that there's a pressure differential occurring between the fast-moving intake and the static surface layer on the surface of the ram. (or maybe it's camera shake!)

(How's the head, Harvey?.... sorry )

.

"Hang on a minute lads....I've got a great idea."

 Posted: Jan 5, 2018 03:05PM
Total posts: 9528
Last post: Mar 27, 2024
Member since:Aug 14, 2002
Cars in Garage: 0
Photos: 0
WorkBench Posts: 0
CA
Image Gallery
Harvey: sorry about the headache!

To start with, I wasn't there, so my conjecture is only as good as anybody's.

In the video, I think the injection is into the ports (not direct to combustion chamber), but occurs after the throttle, so if the throttle is partly closed vapour should not escape because vacuum between the throttle and the engine would be much higher than the vacuum at the ram. Amount of fuel per spurt should also be reduced to correspond to throttle position.

The video (as far as I can view it) is not particularly high res and high speed - there's a video delay and the sound does not synch.
Watching it again, on the second acceleration run, as the throttles open, you can see clouds beginning to form in the rams. In the 3 screen captures (cheapo stop-motion) you can see a bit of vapour in the rams as the throttles begin to open.
 At 41 sec. you can see vapour in the rams and and a bit of haze above No. 3.
 At 43 sec. you can see haze over No. 2 and 3 but not a 1 and 4 - the low pressure cell is building in the middle. Road speed is also increasing.
 At 48 sec. there is a little more haze above the rams.

Another thing to watch closely is the haze inside rams 3 and 4 during the second run - the vapour is being pulled in.
But back at 38 sec. the first run has just ended, throttles are just cracked - rpms are low and fuel pulses should be low - and a bit of cloud is still in No. 4.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Jan 5, 2018 09:45AM
 Edited:  Jan 5, 2018 11:51AM
Total posts: 2036
Last post: Mar 27, 2024
Member since:Aug 29, 2001
Cars in Garage: 0
Photos: 0
WorkBench Posts: 0
Dan

I am getting a headache thinking about this

is this correct?
direct injection  - no standoff - injection is in combustion chamber
port injection - too far deep to get regurgitated all the way out to stacks??? But the mini in the video likely has port injection.
throttle body - like carb, fuel is atomized close to the stacks and could get regurgitated. 

poster said " the fuel vapor can be seen to move in the opposite direction of the air flow while the engine is stationary."
(Meaning INTAKE airflow, not airflow over the car. This is what I observed on my 13 hp riding mower engine)

what if BOTH theories are correct?
fuel gets standoffed, and flow over the non-hood at speed is just wafting it away .

If this is the case, then there is a lot of spit-back, just like my 2-cycle boat motor. You would think than in either the 4-cycle case, or the 2-cycle case, that this would be a killer for volumetric efficiency

Edit: I looked at the video again twice. Dan it is hard to see that any cloud (vapor or fuel) forming near the stacks are getting sucked back into the stacks.  Looks more to me like it is being produced and coming out of the stacks, then being wafted back and over the car. CAn the video be played in slo mo? That should answer it.

 Posted: Jan 5, 2018 07:25AM
Total posts: 9528
Last post: Mar 27, 2024
Member since:Aug 14, 2002
Cars in Garage: 0
Photos: 0
WorkBench Posts: 0
CA
In support of Rosebud's position:

The vapour clouds in the video occur above the axis of the stacks, not in line. Aerodynamics of a Mini: Below the slam-panel the Mini pushes air at speed. The air escapes to the sides and upward. On a Mini with a bonnet in place a low-pressure area occurs forward of the windscreen - an eddy from the up-rising air. Without a bonnet, the flow over the engine is much less aerodynamic, so the eddy would be above the velocity stacks. On wide open throttle, the stacks are sucking from this low-pressure area, which would explain why the clouds are above the stacks. Assuming the fuel injection in the video is timed for maximum flow while the respective intake valve is open, atomized fuel would be drawn in.

In consideration of Steve (CTR)'s situation, he may have had stand-off (though I'm not sure how slicks would have an effect ). Was this a cross-flow head or a down-draft carb behind the head?. If a carb in the conventional location, it would be sucking from the same low-pressure area. WOT would increase the pressure reduction, producing clouds. The more throttle and rpm, the greater the cloud. Lifting off the throttle would reduce the draft at the rams, reducing the area of lowest, cloud-producing air pressure and the clouds would shrink towards the rams.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Jan 5, 2018 06:13AM
Total posts: 4134
Last post: Oct 13, 2020
Member since:Oct 8, 2011
Cars in Garage: 0
Photos: 0
WorkBench Posts: 0
US
I can tell you my autocross mini ran 13.3 to 1 CR, ST 643 camshaft, 48 IDA with roughly 2 inch rams, 4.35 CWP, SC/CR tranny, GoodYear slicks on 6X10 Revs. As I recall this happened flat out in third gear on a 1500 ft straight. I could lift slightly and see it sucked back into the carb. This was about 1974 and I was talking with Vizard on the phone and he was sending me pre publication copies of his work to proof read. I think I'll stick with stand off in my case. I'm not sure it's the same thing we see coming off the wings of an airplane. Steve (CTR) 

 Posted: Jan 4, 2018 11:57AM
Total posts: 1368
Last post: Jul 20, 2023
Member since:Jul 15, 2008
Cars in Garage: 0
Photos: 117
WorkBench Posts: 1
US
Image Gallery

The video of the Arden 8-Port has gotten 11,000+ views and hundreds of comments on my FB page. The question seems to be: Are we seeing a water vapor cloud created by low pressure around the velocity stacks, or is it fuel (fuel standoff) caused by an overly aggressive camshaft with extreme valve overlap? The consensus is split down the middle; 50% insist that it’s fuel, 50% are convinced that it’s water vapor. I was of the opinion that it is water vapor, but after reading several astute-sounding posts by readers I began to rethink my position. Not to put too fine a point on it (too late), the difference is that if it’s fuel it’s a serious fire hazard, not to mention that a lot of horsepower is being left on the table. If it’s water vapor it’s not a problem.

 

After doing a little research and re-reading Vizard on the subject, I am even more convinced that it is in fact water vapor. Here’s why…

 

1) Fuel standoff results from a combination of valve overlap and short (or no) velocity stacks in carbureted engines. We can only guess about the cam in this engine, but the stacks are fairly long and the engine in the video is fuel injected.

 

2) Fuel standoff results in a backflow of aerosolized fuel. Water would appear as a vapor [link]. In the video showing a true fuel standoff condition [link] we seem to be seeing an aerosol. In the Arden 8-port video [link], we are clearly seeing vapor.

 

I’m sticking with water vapor.

 

Michael, Santa Barbara, CA

. . . the sled, not the flower

      Poser MotorSports

 Posted: Jan 1, 2018 11:37AM
Total posts: 1368
Last post: Jul 20, 2023
Member since:Jul 15, 2008
Cars in Garage: 0
Photos: 117
WorkBench Posts: 1
US
Quote:
Originally Posted by CooperTune
...around 70/80 mph at constant RPM a large cloud would form over the horns. Steve (CTR)   
Here's another example...

 

Michael, Santa Barbara, CA

. . . the sled, not the flower

      Poser MotorSports

 Posted: Jan 1, 2018 06:38AM
Total posts: 4134
Last post: Oct 13, 2020
Member since:Oct 8, 2011
Cars in Garage: 0
Photos: 0
WorkBench Posts: 0
US
Back when I was running SCCA Solo 2 all over the country I tried a 48 IDA down draft on my car. First couple of times I tried it without an air cleaner, just the ram stacks sticking though the bonnet. Some where around 70/80 mph at constant RPM a large cloud would form over the horns. The IDA set up is very hard to dial in on a mini. I sold mine on and currently have another complete set up that has been sorted for a full race MEB power unit. This one has a monster K&N filter. Steve (CTR)   

 Posted: Dec 31, 2017 04:40PM
Total posts: 1368
Last post: Jul 20, 2023
Member since:Jul 15, 2008
Cars in Garage: 0
Photos: 117
WorkBench Posts: 1
US
Quote:
Originally Posted by h_lankford
thanks

"standoff"

see
//www.enginelabs.com/news/engine-theory-quick-fuel-standoff/

They blame aggressive cam/overlap/harmonics for some of this, but I have seen it on a one cylinder 13 hp Briggs and Stratton with the air filter housing off. It definitely does not have an aggressive cam and peak rpm is only 3600. 

Maybe all it takes is a tiny bit of overlap or intake valve backflow to do it. Or.....just the intake valve flapping shut and not leaking at all, just causing a momentary hold-up of the flow from the intake into the cylinder. That cannot be smooth, it is pulsatile at all rpms. Staccato.

Someone else with more fluid dynamics knowledge can help me out.
Yeah, there's a lot going on here—perhaps some fuel standoff. But I can't help but think that the majority of what we're seeing is simply a low-pressure vapor cloud. In the enginelabs link it's clear that standoff is occurring; the fuel vapor can be seen to move in the opposite direction of the air flow while the engine is stationary. In the Arden/Lucas video, the car is moving at 30 to 60 mph, yet the vapor is hovering in and around the stacks. It can even be seen forming 6-8 inches above the stacks. I say it's mostly water vapor, but fascinating all the same.

 

Michael, Santa Barbara, CA

. . . the sled, not the flower

      Poser MotorSports

 Posted: Dec 31, 2017 04:13PM
Total posts: 1007
Last post: Jul 19, 2022
Member since:Jul 24, 2014
Cars in Garage: 0
Photos: 0
WorkBench Posts: 0
Great sounding mini! I had an old 650 Hirth twin 38 mm Mikuni 2 stroke snowmobile that would soak you with fuel running with no air box in the same way. Seems reed valves stopped that on newer machines.

 Posted: Dec 31, 2017 03:53PM
Total posts: 2036
Last post: Mar 27, 2024
Member since:Aug 29, 2001
Cars in Garage: 0
Photos: 0
WorkBench Posts: 0
thanks

"standoff"

see
//www.enginelabs.com/news/engine-theory-quick-fuel-standoff/

They blame aggressive cam/overlap/harmonics for some of this, but I have seen it on a one cylinder 13 hp Briggs and Stratton with the air filter housing off. It definitely does not have an aggressive cam and peak rpm is only 3600. 

Maybe all it takes is a tiny bit of overlap or intake valve backflow to do it. Or.....just the intake valve flapping shut and not leaking at all, just causing a momentary hold-up of the flow from the intake into the cylinder. That cannot be smooth, it is pulsatile at all rpms. Staccato.

Someone else with more fluid dynamics knowledge can help me out.

 Posted: Dec 31, 2017 03:29PM
Total posts: 1368
Last post: Jul 20, 2023
Member since:Jul 15, 2008
Cars in Garage: 0
Photos: 117
WorkBench Posts: 1
US
Image Gallery

Dramatic video of a Mini with and Arden 8 port head & Lucas fuel injection. The ram stacks are pulling so hard they're creating their own weather system. [link]

 

Michael, Santa Barbara, CA

. . . the sled, not the flower

      Poser MotorSports