Zachmac

First, please read the whole story / post before you start flaming me / explaining how rotary engines work and breath, etc. I have a S4 N/A 13B in a 1959 AH Bugeye sprite that has the RB Holley setup. Stock porting with RB header and 2" open exhaust. I was going back to EFI and had planned on using a stock LIM to get the 6 port acutators back. Alas that ain't gonna happen without pulling the engine and reshaping the passenger side footwell as the clearance just isn't there. I may still do that at some point but not for now.

Contrary to popular belief, not all applications and situations benefit from running the aux. ports open at all times. It is without a doubt detrimental to low rpm intake charge velocity and torque. Don't bother to post all of you arguments to the contrary unless you are a Mazda design engineer and remeber we are talking N/A, not Turbo.

Here is the question. Has anyone played with orifcing the six ports? You could for example simply tack washers into the intake to restrict the flow. This would give back some of the low end grunt but not completely eliminate the aux. port at higher RPM. In theory you could vary the power band versus RPM by varying the size of the hole in the washer / port % open / blocked.

Lastly, since for now I will be staying with the RB intake (Holley setup) is there a supplier of a throttle body assembly that will bolt onto the Holley manifold to replace the carb?

I'll be asking all of the usual suspects these same Q's, RB, Atkins, Pinapple, etc. Just wanted to see what anyone else had done. My guess based on all of the porting threads is the cheese stands alone and I'll mostly get "You want to do what!!!!" Somebody please suprise me!

drago86

I wouldnt think it would work because if you just put a washer in, you would only have a momentary velocity increase (through the washer). The charge would just re expand on the other side of the washer and slow down. All i believe this would accomplish would be making sure hat there was never enough flow for the velocity supercharging effect to occur at high rpm while having no benifit at low rpm.

My5ABaby

iTrader: (7)

I'm not sure where you get the "contrary to popular belief" thing. Nobody (smart) advocates running with the 5/6th ports open all the time for a street car. Alot of stupid people say **** like "just wire 'em open Jim Bob", but ignore them.

RETed

You're just shifting the power band around...nothing surprising.
I guess if you hit the ideal compromise, and you're happy with it, then go for it.
The problem is, I doubt you'd hit this on your first few tries unless you get really lucky?

Proven theory:
1) High intake velocity (i.e. long and narrow intake paths) are good for low-end power.
2) High flow (i.e. short and wide intake paths) are good for top-end power.

It's always is about a compromise between the two.
The Mazda 13B 6-ports was design for this compromise.

You're suggesting trading in some low-end power and top-end power to find a nice middle ground?
Possible...


-Ted

Zachmac

The washer would restrict the flow into the 6 port which in turn directs more flow to the main ports; path of least resitance. The velocity of the flow through the main ports would be increased for any given overall flow rate. It isn't about increasing the velocity through the aux ports, it is about increasing the velocity through the main ports. This is what happens when you close the aux ports off completely in the stock system below the acutation exhaust backpressure. I am simply speculating that one could compromise for a streeet car without the ability (room) to have it vairable (stock system) by placing a restiction in the aux port path versus simply blocking them off totally.

It is simply a way of decreasing the aux port size without going to zero. Clearly the best solution (compromise) is to be able to vary it over the rpm band and that is what you see in many levels and car designs. The stock S4 13B system was basically a two stage, other cars have more complex systems with greater variation over the rpm range. Each increase in variability adds complexity as well so that is a trade off. (An analogous situation to the twin turbo FD turbo swappover rube goldberg, one reason a lot of FDs are now single turbo!)

As someone pointed out, I will probably get better results if I focus on increasing the runner length. That is why I was head toward a DCOE type throttle body setup versus IDA. Now to do that I am either going to have to do the body work to make room for the stock LIM or find a replacement intake that will let me go to a DCOE style setup. The RB upper for DCOE assumes the stock LIM to bolt onto.

The Holley is basically the short runner big hole low velocity setup best suited to high RPM and if I just swap to a spreadbore throttle body on the same intake I will still suffer the loss of low end torque. Maybe though the IDA type setup with the aux ports closed will be okay. Clearly going to take some easter egging for a while.

RotaryEvolution

iTrader: (30)

a better idea would be to modify the LIM to fit actuator rods and reinstall the sleeves, take it to a machine shop with a diagram of what you want to do and they may surprise you at what can be done.

Zachmac

Yeah, nut if I am going to do that it would be easier to just pull the engine and make room for the stock LIM by removing a 4" X 4" chunk of the passenger footwell box. This is the long term fix, I'm just thinking about what I could play with until I do that. I do not think anyone can modify the stock LIM to make it ~2" narrower and still have funtioning actuators. At that depth you are cutting into the flow path. I recall a guy somewhere on this site showing how he cut away all of the "wasted space" on a stock LIM but he wasn't concerned with maintaining the acutaotrs or sleeves and most of waht he was cutting away were the sections necessary to support that.

jgrewe

iTrader: (1)

If the LIM fits at all could you just move where the actuaters are mounted? It looks pretty tight but I know you're dealing with wheel well AND foot box clearance.

Zachmac

Yeah, I thought of that (relocating the actuators and just rigging longer rods) but what you cannot see (I have better pics on the computer at home) is that I have almost no clearance with the RB manifold let alone for the stock LIM without the actuators even mounted. No, it's either cut the footwell and redo it or move on to a fixed port configuration setup. I'll do the latter for now and same the sheetmetal cut fix for later. Who knows, I may get the side draft throttle body setup on it and decide that is fine. Besides, the most obvious fix is to just turbo the hell out of it and run the aux. ports open!!!! Maybe I should just jump right to the big single turbo solution. Now 360 to 300 hp in the 1300 lb. bugeye could get really interesting!!!! At least I allready have the rollcage so I'm ready for the crash.

jgrewe

iTrader: (1)

Holley has a series of throttle bodies that bolt to 4bl manifolds. If you could get just the TB maybe on ebay and then run a megasquirt or something. They have them sized from 650cfm up to 2000cfm so you could find something.

I have an injected 1275 in a '59 that I built for a friend. I see in your picture you have the Midget master cyl set-up so I hope you have the front discs as well!!!

BLUE TII

iTrader: (9)

Since space is so limited why not keep the RB manifold and adapt to TB mounted 2ndary injectiors as mentioned above. The short runners will be better for engine response.

If you want 6-ports actuated you could do it like the European 6-ports were done; add a throttle plate in the aux port runner of the RB LIM down by the flange.

If you wanted to get fancy you could make some countoured aux port sleeves and fix them so they do not rotate.

Zachmac

Assumming I do not cut the sheet metal, I am thinking a DCOE type wrap over manifold (Atkins has one that I think will fit) fed by a TWM 2900 throttle body. That way I can run the stock primary injectors and two secondaries in the TB. This should also give me more low end grunt then the Holley spreadbore or other IDA type TBs. Yes the Holley spreadbore would be faster, simplier, cheaper, but why make it easy?

The next question is what do I do for oil injectors to avoid the pre-mix hassle? Right now I still have the two block feeds and the RB Holley setup meters the two old LIM feeds into one of the float bowls. The Atkins manifold and the TWM aren't set up to address this. I guess I could just bung a couple of injectos into extension runners between the TB and manifold OR have a couple of holes tapped into the inner side of the manifold similar to the origianl LIM setup? Any ideas (other than premix)?

BTW, the more I ponder this the more attractive just pulling the engine and reshaping the sheetmetal to accomodate the first plan is getting!