chuyler1

iTrader: (1)

I'm just curious, what is ideal MAP readings under wide open throttle on an N/A 12a street port motor? Should it remain at 99-101 kPa throughout the rev range or will all intake systems eventually start pulling vacuum? I noticed I'm getting about 99-97 kPa up to about 5,000 RPM then it drops to 83 kPa at 8,500RPM. Didn't know if that meant my intake was too restrictive. I have shorter velocity stacks I could try and I haven't quite figured out a good solution for the air filter. I have a basic foam one on there now.

Kenku

Yes, less than 101 kPa at WOT means something is being a restriction. Probably the filter; it's an easy test to just pull the filter and do a pull to see what effect it has on vacuum. Now, how much of a big deal it is? That's a different question. In the real world it's harder to get to "no restriction" than people would like.

peejay

"Velocity stacks"? So, ITBs?

Your throttles are too small. That, or you have "sock" type air filters that have been tested to cause a 50hp performance loss on a piston engine, which is less sensitive to intake restriction than rotaries.

Edit: Peter's Right! Your air filter is a horrible restrictive POS. Throw it away and get something, anything that is an actual air BOX with a pleated element that both throttles can draw from. The larger the better, and yes there is not much room for "wide" but at least get the "lid" part as far from the bellmouths as possible.

Kenku

Who's Peter? I know I know, I should standardize on forumnicks here too.

I really want to build an inlet system based around a K&N 33-2495 element or something; like the GT cars where it draws from the top surface of the radiator feed plenum.

chuyler1

iTrader: (1)

Yeah, the filter I have is garbage, I just wanted to get the car up and running and the K&N filter I tried to use wouldn't fit over the stacks. I have 45mm fuel injected ITBs currently attached to 120mm long velocity stacks. I will eventually develop some sort of intake surrounding the throttle bodies. I was just curious as to whether I went too small on the throttle body size. I guess I will remove the filter and make a run to see how much it changes. FWIW, the MAP signal is getting pulled from the primary runners on the intake manifold.

peejay

45 is a tad on the small side (48s would be better and 52s much better) but it isn't your main restriction, it's those filters. Will explain when I get home.

chuyler1

iTrader: (1)

Let me clarify that this is on a large street port 12a.

I wasn't after every last pony, and the side draft manifold I planned to use already had 45mm openings so I figured I would just go with that. Plus, my best guess power figure will be around 160-180 and this link mentions a Weber with 37mm chokes is good for 170hp and a 42mm choke around 200hp. I know it also mentions the later throttle bodies use 3 45mm throttle bodies...but those are also staged and for a 13b, not a 12a.

peejay

If it's EFI, you really can't go too large. Maybe too large is the 4x42s that I have on a stockport 13B, I can't get the idle below 1400 without retarding the ignition timing.

If you were going for big power you'd have 4x48s

The thing with any kind of independent runner manifold (which is what these are: each barrel feeds a single rotor and doesn't share with the other rotor) the intake tract must be able to flow the "instantaneous" flow for that rotor. This is why you want some form of airbox between the air filter and the trumpets. A nice large filter will be able to flow the average flow of the engine, and the airbox will be able to smooth out the pulses so 72 square inches of cotton gauze (assuming a 6"x3"x4" high K&N) only needs to flow the average flow. If you put a foam sock on the trumpet, you have effectively closed off the trumpet and since the instantaneous flow per barrel might be 2-3+ times higher than the average flow, and you're trying to do that through 1.5 square inches of foam... You can see why it hurts airflow.

I wouldn't run for very long with no filter but for a quick rip up a road (especially if it's rained recently) for a minute, you should be just fine.

Incidentally, I'd once tried putting one of those Spectre air filters on per barrel on a 2-barrel setup and that was restrictive! Was measuring 90kpa at 7000rpm. I use ONE of those filters now, on an airbox, and I see atmpspheric out past 10000...

chuyler1

iTrader: (1)

I wasn't running one per rotor, I had a twin foam filter on it.

I have quad 42s on my stock port REPU. I'm not a fan of the cruising throttle response, so I wanted something more tame for this build. I just wasn't expecting that much vacuum....but I'll run a test without the filter to see where I'm at later this week.

scotty305

iTrader: (2)

It's probably a good idea to add 10-20% to the full throttle sections of your fuel map before doing the first run with the air filter removed. Better to be a little rich if the engine breathes about the same, than to be a little lean if it breathes really well without the filter.

peejay

If that has two holes instead of an airbox, it is effectively the same as a ricer sock. NFG.

The engine needs a plenum between the trumpets and the filter element, the larger the better.

chuyler1

iTrader: (1)

What about something like this until I have the time to build an airbox? Better or worse than the "ricer sock"?

https://www.pegasusautoracing.com/pr...asp?RecID=9425

j9fd3s

iTrader: (3)

those do not flow any air, but they do filter, so its valid to use em if you need it.

j9fd3s

iTrader: (3)

btw i like the AP1 S2000 air filter, its a nice big paper cone. 17220-PCX-003 is the Honda number. its cheap, availability is good

peejay

https://www.pistonheads.com/gassing/...f=66&t=1373996

If you read down, someone found those mesh things to cost 18hp on a 200hp V8 engine. And they also don't really filter the air, they just keep birds and large insects out.

chuyler1

iTrader: (1)

Here's where I'm at now.
124hp at 6500 on a Dynapack.

Tuner says it typically reads low but I have read the opposite. I'm not concerned so much about the power output as I am the RPM. It basically falls apart over 6500 and that ain't right for a balanced big street port.

This is with 120mm air horns and the air filter removed. We're going to try the 50mm air horns tomorrow but it's looking like the throttle body and manifold just aren't flowing enough....it's that or the Racing Beat street port exhaust is too restrictive because it's got plenty of fuel and timing.

mikey D

The itg filters should be fine untill you realize you always suck 120+ degree air. I was ok with the performance sucking hot air. What you describe sounds like intake restriction. I don't know why filter makers don't rate their filters for cfm. Kinda pisses me off.

I pull 99-101 kpa to redline. Even with the new airbox on.
I haven't expeirimented enough to notice any cons to running an airbox. I'm always pulling in near ambient now, once I get a chance to Dyno I'll try and do a itb only pull, a cold air intake pull. Unrelated but I also want to do a 10 degree split and a zero degree split and a -5 split pull pull.

I'll share the results. My builds nothing special so the results would apply to most people

mikey D

A stock port 12a optimized should be able to get 150 flywheel hp. The itb won't really gain you peak power, mostly it's drivability.

Its 1/2 price margarita night so I'm only half reading the posts and do the remember what all youve do e outside the it and ecu. Sorry. =)

mikey D

Take the filter off and Dyno it. Some other things cause power to roll over also. Timing??

chuyler1

iTrader: (1)

This port job should be good for 160-180 flywheel based on the builder's other motors that have made 200-215 with a Weber down draft. I told him to keep it streetable.

One other option I have is to try the shorty side draft that Atkins sells. That'll work with a 45 DCOE as well and all I'd have to do is cut longer fuel lines and make sure my injector connectors will stretch.

chuyler1

iTrader: (1)

The numbers and graph I posted above was without the filter. You may have missed it (have another margarita

They tried timing, it's not that. Ignition is IGN-1A direct fire.

mikey D

I don't think you want to switch manifolds.
I don't see any graphs.
120mm is pretty long on a dcoe style intake but that doesn't seem like the problem your having.

I run the racing beat exhaust, not sure what it's called any more. It's the dual primary that collects at the muffler. I could pick up power with a louder config but maybe not enough to be worth it.

chuyler1

iTrader: (1)

Here is the graph. Again this is with the 120mm air horns, no air filter, on the wrap around side draft 45 mm DCOE. I don't have a baseline graph for this dyno so I don't know whether it reads high or low, I just know that peak power at 6500 doesn't seem right.

mikey D

I think I'm getting too old for half-price Margarita nights.

I don't think where you are peaking is a problem I wish my horsepower peak that early. Shorter stacks will help with that a little, a dcoe is already pretty long and doesn't need long velocity stacks.

I don't have any helpful advise though. If you factor in 20% drivetrain loss your making 150+ hp.

chuyler1

iTrader: (1)

Update: with the shorty air horns, see photo, it made 132hp at 7,000 RPM. I don't have the chart but that's an 8hp gain. So I'll stick with the shortys. I got to drive it today and it is pretty tame until about 6,500 on my tacho (not sure how accurate it is) then it pulls hard to 8,500 before tapering off. Both tuners are in love with the car. She's good to go now, except for an air filter. Next stop, deals's gap.