Pettersen

iTrader: (1)

So i'm gathering parts for my exhaust, and i was looking for some input on my plan for a exhaust setup.

The exhaust will need to suit the semi pp engine i'm building, wih these basic specs:
20mm PP.
Medium streetported 4 port irons.
Redline at 7500RPM.
Intake with separate tb's for the pp's (so i can have them start open later than the side ports)


My plan for the exhaust: Build it to help get a usable powerband, not just peak hp. The car is daily driven, and only get's out on the track a few times each year so it can't be ridiciously loud.

Rotaryworks 2,25" headers(already have this one)
Will extend the length of the headers a little before they merge into a single 2,5" system with two mufflers, and i have been looking in to a apexi active tail silencer since it will help keep the car quiet when i want it to be.
Going to use 3x 2,5" vband clamps to connect the system.
Everything will be in stainless

So what do you guys think?

jorx7

iTrader: (11)

should be ok. as long as your idle is at 1000 rpm, but will be loud on open throttle. something you could consider are the racing beat rev2 mufflers they are 2 3/4 pipe dia. which will flow very nice, you can run seperate runners all the way or collect to a mid silencer the to there y pipe. or your own. im running fullbridge port t2 n/a block street port exhaust port. using racing beat header to 2 1/2 silencer to the rev2 y pipe and mufflers. sounds so sweet.

Pettersen

iTrader: (1)

If it wasn't for the shipping costs to Norway, i would probably buy something from racing beat. And there aren't any available in Norway, so i need to find some good universal mufflers wich i can get in Norway and use those.

rxspeed7

iTrader: (5)

Vibrant makes pretty decent universal muffler also. That's what I'll be using on my pport setup

lastphaseofthis

iTrader: (8)

personally, something quiet, like you would put on a stock port. and then a exhaust valve before the first mufflers and dump it open atmosphere when the semi pp's open up.

j9fd3s

iTrader: (3)

since an FC has space for two mufflers, i would use it.

stock FC's run a 50mm ID pipe into 2x40mm ID pipes. since you want more, i think header into 65-75mm pipe and then split into dual 50mm pipes should be just about right.

i would run two mufflers at the rear and something in the middle. the center should be straight thru.

if you put a backpressure sensing tube into the collector, you can actually tune your exhaust by backpressure, which actually makes life really simple

joeylyrech

iTrader: (11)

My full bridge with a vibrant mufflers(turbo)was way 2 loud for the street.I install a racing beat presilencer apexi n1 muffler and the thing now is 2 quit!now wide open it does have that deep tone beasty melody.I know yours is periferal but look into the racing beat stuff,is top quality and is worth the money.

ArmyOfOne

iTrader: (12)

I am running a semi pp bridge and the number one sound killer is the racing beat turbo pre-silencer. At the track I dump right behind it and it is still bearable.

John Huijben

iTrader: (1)

You can pack 2 huge silencers in the rear, especially if you remove the head shielding, I believe mine are about 9" x 9" x 18" long or so. Pre-silencer should help too, but make sure it can handle high temps, they get a bit hotter than the silencers at the back, I've seen them glow red hot. About the semi peripheral ports, you should try doing it the other way around, have the semi pp open all the time and open the side ports at higher loads / rpm's. You already have the large overlap, brapping and buckling of the semi pp, regardless of if their opened or not so you might as well use those ports.

Pettersen

iTrader: (1)

The PP's are in my head doing what the 5 and 6 port on a 6 port engine is doing.
My stock mani had butterfly valves for the 5 and 6 port, more or less like the pp's will if i make my intake the way i planned. Wouldn't there just be a constant vacuum in the pp runners?

Anyway, the reason for me wanting to do it this way, is that the 20b Semi pp is running something similar, so imo it's proven to work.

But anyway, when the intake is buildt it shouldn't be much trouble testing both alternatives to see what works best. Would just need to weld injector bungs on the pp runners as well as the side port runners.

Liborek

+1

Constant vacuum sucking exhaust gas which will make engine even more "bad" at low load conditions. IIRC peejay, when he had half-bridge engine, used bridged secondaries for all low-load and idle operation, basically as primaries.

If you mean Logan's engine, he opened peripheral ports based on throttle position, over 50% tps and PP's opened.

Mazda tested combination port engine (full PP with side port) and PP was used all the time - superior torque output through the powerband and side port as additional port area for high rpms.

Pettersen

iTrader: (1)

Ok, thank you both. That was realy helpful

Just to have all my intake questions answered, would opening the pp's and sideports at the same time be better or worse than opening the pp's first and then having the side ports open later?


Edit: yes i meant Logan.

j9fd3s

iTrader: (3)

yeah that does work, we ran one on the race car. installing it we went from 103DB to like 96 or 98. i should put one on my PP

John Huijben

iTrader: (1)

Some more thoughts about this,
I added a picture to clarify the idea further. (excuse my poor 1min paint skills) Top half of the engine sees a low pressure, intake channel also sees low pressure. Bottom half of the engine sees high exhaust pressure. Because of the pressure difference hot filthy exhaust gasses dilute the intake charge screwing everything up. Your's probably wont be so bad though since the p-port is very small, but same principle applies. By opening the p-port up your reducing the low pressure in the intake runner, which should make things a bit better. Opening the side ports first and the p-ports later should also work, but doing it the other way just might work a little bit better as far as idle / low end drivability / fouling sparkplugs is concerned. I think opening the ports staged will work, makes port flow velocity higher at lower rpm's / throttle positions, which is good for fuel atomization (Be sure to stage the injectors accordingly though if your doing this) It's not 100% neccesary though, opening everything at the same time will probably also work pretty good concidering the small p-port and assuming your using a nice standalone efi system. Also depends on how 'medium' your side-ports are ported.

j9fd3s

iTrader: (3)

good explanation, John. that IS the problem with the engine, all the pressures are the reverse of what we actually want. at low engine speeds, there is no inertia so the pressures have a big effect, and you get brap brap brap, at high speeds its just the backpressure vs inertia.

in the middle though we have low backpressure and inertia of the gasses is high, so basically anything works

John Huijben

iTrader: (1)

Yeah I know :-), it's really no wonder why these engines love a low backpressure free flowing exhaust, and why getting the intake runner length right is just so important!

Pettersen

iTrader: (1)

Thanks john.

peejay

That is exactly why I made my half-bridge engines idle on the secondary ports, by replacing the factory throttle body's secondary stop screw with a much longer one. They still idle "lumpy" but when driving it's great. I did have to move the brake booster source from the secondary to the primary side since the secondaries basically never built enough vacuum for the brakes to work.

It's also why my current full bridge engine doesn't have "secondary" at all. All four barrels open at the same time and rate. Drives very well, actually. (I just drove it ~950 miles/1500km to Oklahoma - posting this from the hotel room )

I SUSPECT that this is why a lot of people bridge the primaries in a half-bridge. It works better for drivability.

joeylyrech

iTrader: (11)

Isnt worst having all four butterflys opening at the same time?Wouldnt that affect air velocity at lower rpms and cause more bucking jerking and loss of low rpm driviability torque?I like your idea of idleling bridges on secondaries ports,i am gonna try that on my fd throttle body and see if it works for my setup.
To the op sorry 2 hijack your thread my bad

j9fd3s

iTrader: (3)

the bucking is from intake vacuum sucking up exhaust gasses like a giant EGR valve. less intake vacuum = less exhaust gasses in the intake = less bucking.

peejay

Nnnnope.

I mean, you'd think that it does hurt torque, but any theoretical benefits you'd have from having more velocity in two ports is more than negated by the losses from having vacuum in the other two ports pulling exhaust up.

I was pulling the steepest grades on I-44 through Missouri in 5th gear, accelerating UPHILL from 3200 to 3500 (~80mph) at part throttle. Just enough throttle that you could hear the intake bark over all of the other noise. Needed to get around those trucks... This, by the way, is with so much gear in the car that I had to pull the passenger seat out, so that plus me = maybe 3300-3400lb.

joeylyrech

iTrader: (11)

Okay pj so what do you suggest to do so i can get some more torque low end driviability out of my setup.
Full bridge,real bridges with notched housings and extended 2 the water seals.FD motor with ported tb and a divided 72mm setup.

peejay

Divided 72mm setup? You mean like a turbo? Throw that junk out! And get rid of the FD intake manifold.

joeylyrech

iTrader: (11)

yea is turbo

Pettersen

iTrader: (1)

Since i was going to only use the PP's i was going to use 2*42mm tb's for the pp's, but if they are going to open from start i have some questions.

Won't the 42mm tb's need to be openede very little before the 20mm pp's are maxed out? And wouldn't that be a bad thing?

Wouldn't it be a better idea to run the two pp's of one single 42mm tb?