Along the lines of the thread...

My 6-port 13b, with the sleeves REMOVED, and some minor exhaust porting dynos at 167HP with a Haltech and MSD direct fire. The exhaust is RB 2.5" and a high flow cat. The sleeves improve port filling at lower engine speeds for improved low end torque but even without them, the engine is much torquier than a 12a.

Your number seems like it just needs some tuning and you'll get alot more out of it.

 

Did you do your modeling with the flow under pressure or vacuum? I tend to view things in a different way, i.e., since I sit next to the Missouri river, my test would be to drop a group of rubber duckies along a tangent line to the banks at a straight section of the river, then watch and record the progress of each one as they float through a bend in the river until they reach the next straight section.

It has been my experience in canoeing that hugging the inside bank of the bend may be the shortest route, the quicker one is usualy off center towards the outer, longer bank. In river dynamics, it is the outer bank that errodes faster than the inner one due to the increased velocity of the water flow being nearer the outer bank than the inner one.

To model this situation, the entire flow path has to be analyzed. This would have to take into account the effect that the primary and secondary ports have on flow when the 2 collide in the housing. The fun part is adding the factor that the rotor comes into play with it's rotation. I've had a theory about this collision in the aspect that if one port had a 90* curve and the other had something like a 45* one, the collision would be minimized and could possibly add to the dynamic intake effect by the 45* port accelerating the 90* intake charge.

Your modeling works fine within the limits of the distances you have set, but it is not what occurs inside the engine. With both the primary and secondary charges taking the path in your model, they will quickly impact each other on the inside of the curve, thereby slowing down the inside velocity and moving the higher velocity to the outer sections of the curve.

Must be nice to have such software to play with. If you can model the entire intake charge that includes both ports and the rotation of the rotor and prove me wrong, I will powdercoat a part for your engine bay.

Nice work, this is fun tonight, I seldom get the challenge to dig deep in the gray matter and bring out 'stuff' that I haven't used in a long time. Beats the hell out of the newb posts.

 

To give you some background, I'm a thermal/mechanical engineer by trade. My masters degree is in engine port flow. I can direct you to my SAE publications and thesis if you'd like to PM me. Fluent is fun software, but I use it at work nearly every day.

The above example that I gave will be the case with any flow that enters a curve at a constant velocity profile, even your river example. It doesn't matter if the flow is driven by positive pressure or vacuum, flow is driven by a pressure difference.

The reason for river meandering is quite different from what you think. It's actually a product of what's known as secondary flow. I can elaborate on that more but we're already way off topic.

 

this is a interesting read, however off-topic from the beginning, since i was going to remove my sleeves to see if i can pick-up any extra power at the high rev's, right now my power really dies off at 5500rpm. i've ruled out all other factors,

guess i'll yank the sleeves and get a feel for it. currently i have a ton of torque but it dies off so quickly, for all i know my 5/6 ports could be cluttered with carbon.

 

jesus christ make your own thread in the LOUNGE, yeah you guys are smart but **** off for jacking my thread

 

I'm pretty sure he's running either 38 or 40mm chokes. When I moved up from 38mm to 40mm in my DCOE I only gained 1 peak hp. I went from 139 in the graph I showed, up to 140whp. Here you can see the exact same problem exists with the sleeves in or out, but without the sleeves there is obvoiously more volume in the port and more port timming...

 

ok whos got a flow bench? caz from my understanding removing the selves hurts the flow......at least this is what i read from paul yaw's web site....and bigger is not always better

and rotary_sex that was very rude of you to tell them to **** off...you are a new member and trochoid is 1 of the ppl that will end up helping you out...when you have other questions you dont know the answers to

 

My point exactly.

 

I've got a bench but I don't have any irons to mess with.

Like I said before, the sleeves will help with low end torque, where port speed (as opposed to flow impedance) is more important to chamber filling and mixing so the timing is shorter. At higher engine speeds, the larger port size is necessary to fill the chamber because the time to fill the chamber is less.


No kidding, he might learn something if he pays attention.

 

He was just messin cause it went way off topic about something that we know isn't the cause of his problem. I didn't run any sleeves and look at my sheats. As far as i know I put more whp out of a stock port than anyone else carbed. Besides pineapple racing who did like 180, but it was build not 200k like mine was.

 

**** i was drunk when i posted that. sorry dudes didnt mean any harm, im not a new member either, i have over 4000 posts under a different alias

 

SSSShhhhhhhuuuuuut uuuuuuuupppp!... LOL

 

I have to say that this thread rocks.

 

rotary_sex dont use any sleeves. My gslse with no sleves, racing beat exhaust, msd 6a, and 48 DHLA puts down 150 horses at the wheels. I still need a little tuning. It sounds like youre just in need of some tuning. Check into your timing. I advanced mine and got a ton of responsiveness out of it. 26 degrees of total advance is nice . I am just running mechanical advance on my distributor.

 

I surrender. I had a feeling I was over my head, then you drop the flow diagrams on me. It's been fun though, nice to get the gray matter stirred up and bring a little science to the forum.

As a I am a man of my word, PM me and we will discuus the part you wish powdercoated.

Btw, I am impressed with your knowledge on flow. You should trot it out more, you could certainly contribute to porting and flow, whether it be in port design, intake or exhaust.

Thanks for the education.

 

damn 26 advance, im running 5 advance, stock ignition, once accel super coil (leading) and a stock coil for the trailing, no vaccum advance.

thinking of hunting down a jacobs ignition box

 

You may want to rethink some of this stuff. It is not all 100% accurate or at least to my knowledge.

 

26 degrees advance is probably maximum centrifugal. Run the engine speed up until the timing quits advancing (generally, over 4000rpm) and *then* read it. With a stock distributor, 26 degrees "total" is about 6 degrees at idle, depending on which distributor is being used.

You might want to reconnect your vacuum advance (use ported vacuum not manifold vacuum) as it does wonders for part-throttle driveability and fuel economy. If you don't like the look of vacuum hoses, bend up some hardline and paint it or shine it up, fuel's too expensive to leave the vacuum advance disconnected.

The jacobs box is junk, their company is 100% hype.

 

Peejay, could you explain the difference between ported and manifold vacuum, and where ported vacuum is. You lost me on that one.

 

Manifold vacuum should be self-explanatory... it's the vacuum sourced direct from the manifold.

Ported vacuum is from ports in the carb, specifically from just above the throttle plate. When at idle, the throttle is shut and the ports see no vacuum. Once the throttle is opened a few degrees, it is exposed to manifold vacuum.

Generally you don't want to use manifold vacuum for the vacuum advance because it makes the idle unpredictable. High manifold vacuum causes lots of advance which makes the idle high. Load the engine down, or just start the engine without touching the throttle, and vacuum drops, causing advance to drop and idle speed will drop (and vacuum will drop, causing advance to drop...) and the engine will probably stall (or not start).

Also, using ported vacuum as the source, when you tip into the throttle, you get a nice boost of timing right when you need it, and you'll find that you won't need nearly as much accelerator pump as you thought you did, and the engine feels crisp and lively. Use manifold vacuum as the source, and you *lose* a bunch of timing right when you need it and the engine responds like complete ***.

On a Holley carb, the ported vacuum take-off is the nipple above the choke-side idle mixture adjustment. On the Nikki, you have to take it from one of the nipples on the carb spacer. I don't remember which one I took it from, I just connected up a vacuum gauge to the nipples and used the first one that showed no vacuum until I blipped the throttle

 

very good stuff peejay lol im aobut to go check to see what vac line i have it hooked to on my holley...altho i think i got it right witch means i still need to work out alot of bugs err

*edit* damn it i knew i had it right err

 

Thankyou Sir, just what I was looking for.

I understand manifold vacuum too well. When I hooked up the vacuum gauge to the rear intake port on the bp, at idle, the needle vibrated so bad it was just a blur. This was due to the overlap, and the overlap made worse by still having part of the stock exhaust system. I recently completed a full header back 3" system and the needle has settled down a bit.

Since I'm running the Mikuni, I'll have to check if it even has a port I can use. I have the vacuum advance unhooked.

 

Rotary Sex, my apologies, here I am jacking your thread again.

 

well im running 5 advance over stock at idle, so close to what your running, no vaccum advance, i get 18mpg religiously and my car is as streetable as a stock gsl-se. low end is fine, a little weak but its smooth. i can cruise 35-40 in 4th gear a just slide

 

haha no prob, your one smart dude, but it doesnt help me at all