Tried another set:

 

That's really interesting. It would make since that using a smaller diameter would increase velocity into the engine, but changing the port diameter on a PP motor would also change the timing and duration of the intake cycle. I wonder what gained you that mid range, increased velocity or port timing?

 

Ah, I should have been clear. The port size was a 48mm D-shape, the original runners/throttle body was 55mm, we reduced them to 48mm. The port did not change.

The peak wasnt all that special, but was the same for both at around the 9k.

Looking back on it (this was 2001), I believe we probably could have gotten more with larger throttles and a tapering type manifold.

This reminds me of a question Ive always had.

What are peoples thinking on the effects of going larger vs smaller. As in regards to Bernoulli's theorem? I know smaller is higher velocity, but what about the pressure change? Does one effect outweigh the other? Obviously the bigger you get, the slower the air is, but the higher the static pressure will be. Less dynamic pressure = more static yes?

 

There comes a certain point where larger isn't going to gain you anymore ultimate power and will only hurt you in most places. You found it. Nothing surprising about that at all.

 

Well, after some reading about tapered runners, I came to conclusion, that slightly tapered straight runner with fully radiused velocity stack is best for broadening and enhancing VE curve in whole rev range. Same peak power can be achieved with non-tapered runners, but tuned length is different (shorter) and average power suffers.

Velocity and consequent momentum of charge (idealy both air and fuel, as evaporation of fuel further increases VE), plays huge role in engine´s VE but so does acoustic tuning (which weakens with change in cross section). When we imagine two same engines, one with tapered runner, other with non-tapered, but with same diameter at port face, we can make wild guess that velocity in this point is probably same. So this on its own doesn´t tell us why tapered works better.

Maybe the condition where airflow speeds up along the runner creates smaller pressure losses than flow maintaining high velocity along whole runner Or maybe part of negative pressure wave traveling up the runner changes its sing and direction to positive pressure wave along whole runner forcing more air into the engine befora arrival of strong return wave


I would say that good baseline is runner of same cross section area as port opening, ie exactly what you´ve done in your example. And if anything has very possitive effect on setting up the in flow of air to the runner, then its properly done velocity stack. As air doesn´t flow just from above, but from every angle with higher pressure than in runner itself. And I think that very high velocities along runner surface are very good for charging efficiency, as long they remain laminar.

 

Just noticed this thread, looks good in the development. Mechanically staged semi p-ports do seem to work extremely well. Or staging in the sideports should work equally as well. Personally I would advise against making 9 throttle bodies, but that is just my experience. If you make above 400rwhp with external injectors, you will need more fuel than 6 x 550cc. I ran out using 6x550 and 3x 270cc at 420 or so.

Good luck with it, semi p-ports are awesome

 

Hey Gto, nice to hear from someone who has done what you have. I read all your threads and am very impressed. From what I was told about the 20B ports, I will not make above 400whp with them, but with the semi-PP playing on my mind now, maybe it will just get up near there?

Maybe it would be safer to go a bit bigger? I could still use 550 primaries and maybe up the secondaries to whatever is required?

 

Haha, just realised those latest set of headers go nowhere near fitting with my runners!! Look cool tho!!

Ive redone the set that go underneath and will probably have to go that way. Problem is I have no idea how much room I have to work with as Im not even in the same country as my car at the moment!!

If anyone could give me a rough measurement of the room below the exhaust ports, that would be much aprreciated.

 

+1. there is graph of secondary runner size vs VE @6000rpm, from 30mm to 38mm, and 34 and 36mm are about the same, but 38, 32 and 30 are all lower.

there is an optimum range for the size of the runner at a given rpm and outside of that you loose.

the trick is sizing the runner so it works in the power band you want, if 6000rpm was the redline, you'd go with 34mm, if the rev range needs to be higher, you'd choose bigger....

 

So Im thinking 3x550cc primaries and 3x850 secondaries, that should cover me incase I do actually manage to fluke low 400's at the wheels.

Also what is everyones thoughts on running a Haltech PS2000, with 6 X D585 coils?

 

Thanks I think possibly 400rwhp is a reality with just the 20b ports. We have made 360rwhp sideport only not trying too hard. But this is something that has taken me years to figure out.

Semi p-ports reward well engineered intake and exhaust setups, and punish poorly made ones. With lots of tinkering 400rwhp shouldn't be difficult.

I switched to 1000cc secondaries, and have 550cc primaries. Then of course 270cc tertiary injectors. Seems to work great.

 

Thats seems like alot of injector! What sort of duty are you on with the 1000's?

I am keen to get those secondaries on early and doing more of the work, hopefully maximising the point of stand offs.

 

almost 78% duty cycle on all of them. I am pretty sure the walbro fuel pump was giving up on life though. Should have been a bit lower than that.

 

Was this just set at the standard 43.5psi? Or do you think it was actually dropping off pressure during the runs?

 

Add me to the list, Ill take one for sure! haha
Maybe if you wanna fab one for a 13b, that would rock too. Being that my turbo 3 rotor build is already a headache. Figure the FB might like a sweet little N/A motor. Just stuck between a hyperlight car with a 13b, or more powerful 20b. Eitherway, Much win on the design!

 

Did someone say 13b?



I got bored...

 

Water cut aluminium flange plates for the carbon fibre trumpets turned up today!!

 

Ordered linkages today, hopefully should look something like this:

 

Alright, after thinking about the semi pp I had setup there and reading a bit, there is another option.
I didnt like the fact of splitting the semi-pp runner off the secondary runner.

Now I know its not new, but I am thinking of going with 45mm Peripheral ports and still using the 40mm primaries, Bridgeported.

It would make the manifold alot easier and its stops the secondary runner from splitting.

Something like this:


Thoughts welcome.

 

45mm PPs would look something like this:

 

Had a different idea for if I was to run the 9 ports.

Tried moving the interference for the semi-pp runner up top near the throttle body. This would allow me to get inside the pipe and make sure the join is nice.



However, this makes the semi-pp runner have more bends and is longer. It would also make the rest of the pipe hard to fab.

Here is what the hole on the inside of the 45mm runner would look like. I think for splitting the pipe, this would be a good place, however drawbacks as mentioned above might not make this worthwhile.


cant say that this would be staying inline with the KISS principle!!

 

Heres another idea if I go with the larger PP and blocked secondary port.

If it is a consensus that the 45mm may be too big with the BP primary, I could have the PP insert machined down from a 45mm entry to a 40mm ID on the face of the housing.


Whats peoples thoughts on that?

For info thats a 4deg taper.

 

I got bored...... did someone say ECU activated RPM triggered slide throttle semi-pp's? (no-one would say that...thats a ridiculous sentence). But anyways.



Course this would need some sort of linear actuator and its own airbox/filter or some plenum with plumbing to the main airbox......yeah Im not doing this.

I just know Logan is smiling right now..



Looks cool but hey?



HAPPY NEW YEARS FOR TONIGHT EVERYONE!!!!

 

Lol, I picked a good day to stop by the n/a section. Did make me smile There are some very simple ways to acheive ecu controlled, rpm triggered semi p-ports. That was actually always the plan with mine, still havent got around to it. Once I get a photo of the setup I can send it over to ya.

Oh, finally sent you a reply in PM.

 

There are some very simple ways to acheive ecu controlled, rpm triggered semi p-ports. [/QUOTE]

That's why I love my Haltech. I have all kinds of aux outputs to control stuff. ;-)