hey that's just about right

 

Trying to find the SAE chart where they showed the tradeoff between exhaust backpressure and BMEP, comparing side port to peripheral port engines. Can't find it.

I think the crossover was at 400mm-Hg, which seems awfully high, but they're the scienticians doing experiments, while I'm just some guy putting cars together and sometimes they work and sometimes they don't.

I can't imagine that even 2psi is "good", but it's better than 4.

 

peejay, can i need to ask you a question that im sure you could answer for me. i know that you have driven/owned both bridge ports and peri ports and was curious if you could be honest with me about the difference in power bands between the 2 engines? im planing a peri port as you know sincing i had started this thread lol. someone had explained to me that i might want to reconsider, that a pp has a much shorter powerband than a bridgey does and has really had me agitated lately at the idea of am i making the right decision?i mean, weren't bridge ports made clearly to use when pp engines were not a loud? i figured that you have personal experience with both and could shine some light onto the subject for me. the pp will probably be 45mm for reliability reasons (by what i have read a pp bigger than 45mm is less reliable) unless you can clear that up for me lol? and the bridge port (that i was planning before i started asking questions) would be a standard bridge port with chamfered housings to help flow to those eye brows lol. which should have the broader power band? peak hp is not a goal, thsi car will be primarily used for solo 2 and later solo1. power band is the goal here and turbos as you understand peejay, are not on the menu. if you could explain to me the dfference in power bands between the 2 engines it would help me clear up confusion. dyno sheets would be amazing (either in here or in a pm, i understand sharing dyno stuff on na engines is a difficult task but i have to ask). anyhow, thanks in advance, im sure you can cure me from stupidity that others have shined onto me.

if anyone else has personal experience with both a standard cut bridge port (not a half bridge, a j bridge or a monster bridge, but a standard bridge) feel free to share your experiences and knowledge please. i only emphasized on Peejay because by what i have read he has owned both bridgeys in the past and currently a pp.

mind you this is power band comparisons with track quiet exhaust (under 103 db's ?)

thanks guys and i know that i ask a lot of questions but it's the only way to learn, and who better to ask then the ones who have personal experience.

 

I USED to have a fabricated peripheral port. I NOW run bridge-ported engines. It's less screwing around.

Ask j9fd3s about the straight skinny since he has MFR housings. I didn't care about top end power at all with my peripheral port, i wanted broad powerband as low as practical, and it was soft below 2000 and then woke right up. That said, I went too small on the throttle body and it was choking power even at lower RPM.

All of my engines are for SCCA RallyCross which needs a broader powerband even than Solo. On pavement, you don't have to worry about wheelspin, and then getting traction pulling your engine down out of its powerband.

 

Found the chart.

Top right of page 2.

2.3psi is about 120mm-Hg, or basically at the minimum backpressure that Mazda tested.

Of course, a peripheral port engine (trying to) make 300hp is a lot different from a 180hp engine, but still the RB exhaust system does look pretty promising.

 

I've never seen anyone post anything about being able to swap out the fifth on the Miata. I've heard that you can take the 5th from the Miata and place it on the FC to get the same gearing in 5th as the GTUs (iirc) which is what you want when running a stock FC box with a 4.88 or 5.10 rear end.

Mind pointing me towards what salvage yard search engine you're using. Only thing I could find nearby when I last searched last year was in the $400 range in OKC.


btw No clue what you titled your youtube video but all the linked vids after it are house cats that are purring.

 

its hard to compare, because you can cut the bridge so many different ways, and then the intake/exhaust lengths matter a lot too, so there are a LOT of variables.

i think the "short powerband" thing is kind of a myth, or a mis-statement. if you take a MFR engine, it makes peak torque @8k and peak power @9k, so that looks narrow. however the part that is deceptive is that the MFR engine makes more power than the stock engine from like 2000rpm up.

i've driven my 12A P port back to back with a modded stock 12A, and it feels like if you limit the P port to 4,000rpm it'll still blow the doors off the stocker. i could tow with the P port.

my bridgeport experience is a little short i admit. check this out, full instructions, https://docs.google.com/file/d/0Byot...dXM/edit?pli=1


bridge ports were used when P ports were not class legal because they make too much power. for instance Mazda won big @daytona in 1979, and IMSA added weight, and then said you can run a PP at a higher weight, or run a bridgeport at a lower weight.

i put an exhaust on my car with a stock engine, and then used it with the PP for a while, and it was just as loud...


the apex seal needs to go over the hole for the port, and if the hole is too big, it'll actually bend into the port. this is why the stock exhaust ports have a chamfer around the edge

hope that helps!

 

Not sure if it was this thread or another I was reading but wasn't it decided that unsprung clutches weren't the best route to go with out trannys in the first place?

 

faaar oouuuuut. That's a goofy looking port. They close the main port at 50 and the bridge at 65 degrees? Were they thinking that compression by-pass would blow fresh charge down into the chamber to help flush out exhaust residuals?

Interesting that nowhere in that manual do they give recommended or maximum RPM, coolant temp, oil temp, or oil pressure, just that too much RPM/temp and not enough pressure is bad. I infer that they wanted to limit revs to about 8,000.

And now I finally see what RICE RACING was talking about about ten years ago with the modifications done to the old thick carbon-aluminum seals to make them live at high RPM.

 

Here you go.

That would get you a shorter, not taller, 5th gear.

Really, 5th with an FC box and FC-height tires and the 4.78s is slightly LESS RPM than 5th with a 1st-gen box with 1st-gen height tires and 3.91s. And not all 1st-gens had 5-speed transmissions. In short, there's nothing wrong with turning 3500 down the highway. Hell, my VW turns 4000, and it's got a long-stroke five in the poor thing. (I specifically don't exceed 4000rpm on the highway because the poor thing has about 350k on it. Powerband's dead at around 5200 anyway)

 

Hey, show me where you can get a sprung clutch discs for a Quartermaster 7.25 or 5.5" twin disc clutch setup and I'll consider it.

 

Details details

I bet the engagement and slip characteristics of a small diameter double disk clutch are a lot nicer, too. As well as the intended purpose.

(Now, if you want fun, how about those really tiny "clutches" that are really just a pedal operated spline, and just enough clutch material to get you moving before full engagement?)

 

I have a triple plate Quartermaster on my Cougar. Great clutch, easy to modulate, but good lord don't try to slip it to get the car moving. I let another, (read inexperienced) guy drive the car for a couple of track sessions and then load it on to the trailer and he wiped it out. Its going to cost $400 for new discs and plates as it was custom made. Grrrrrrr.

I like big beefy stock style clutches now.

Eric

 

im speaking more of a standard bridge port. not cutting the water jacket but extend porting the primary port/ adding chamfer onto the rotor housing to allow airflow to the port better. what should give a broader power band? im not looking for 300 rwhp although 250 would be amazing but realistically i know its nt going to happen while being quiet lol. this car will be used for autocross and later time trials or maybe wheel to wheel racing with nasa. either way, both pp and bp are legal bjut trying to decide which would be the better route to go.

peejay, i can't believe you went back to a bridgey. can i ask how much power does it put out? i was originally thinking bridge port but then some guys on here detered me towards a pp explaining that the pp will make more hp and tq and will be easier to drive apposed to the bridge port (i know that with fuel injection you can get a bridgey pretty tame). what do you think would be better for this application? i mean if i bridge port,later if i need more power i could fill the ports in and pp it right? Peejay went back to a bridge port for a broader power band. i trust your judgement peejay, you've been in the game for a while. wish i could see a comparison of dynos sheets ...but i doubt that could happen lol. when i say standard port i mean something like this

http://www.google.com/imgres?q=racin...11,s:133,i:169

only to the edge of the housing and add chamfer to help flow. i need reliability, im not going to half *** anything, going to get full balance anf clearance and lightweight flywheel and gilmer pulley. going to be running efi 60mm itb that tapers down to 55mm at the base. will be tuned in AlphaN with a ms3. which do you guys think would be the correct port to go with

part of me is thinking just do the bridge, worste case sceneio at least I can post dyno charts and show people what is really capable of, not just word of mouth with no dyno's. i dunno, just some ideas.

 

for the most power from a bridge you won't be filling in any gaps later.

 

For what its worth, my buddy Al (01racing) had a monster j bridge in his car when he bought it. I believe that after tuning it to within an inch of its life it was making between 225 and 230 rwhp on a Holley 650 double pumper carb. After a couple of years of hard race use it passed on and rather than do the same thing again, he built a strong PP using all new pieces, balancing, blueprinting, clearancing and a 51 IDA Weber. Al was a Mazda Dealer at the time so it was only horribly expensive.

His new PP consistently makes over 260 rwhp and has shown over 280 rwhp when wound out (10,000 rpm+) and leaned out. I can tell you that it has decent torque and just where my set up starts really pull (+ 4500 rpm) his just screams. Other than the mega rpm he pulls, the car seems more tractible than mine and more flexible. The only negatives I can see are the noise it makes (intake and exhaust) and the fact that it is a bit fragile as its pulling tons of rpm.

Send him a P.M. I am certain he would be more than happy to give you a real world back to back comparing a monster bridge to a PP.

Eric

 

im not even talking about a monster bridge though, just a standard cut one. the j bridge is way to big and unreliable for what i want. i'll try pm'ing him. is he still an active member? and true, i didn'tthink about it. if i were to add chamfer on the housings to helps the bridge breath then i wouldnt be able to fill those later. it's shameful how so little adjustments in the intake and exhaust can completly change the nature of the beast. i was asking for a comparison in the broadness of the powerband between the bp and the pp... but i guess one small change in the intake length or exhaust length can easily change the length of the powerband on either engine.

Peejay, you went from a pp to a bridge, how much broader is the powerband between the 2 that you have raced?

 

I never ever once said that.

I went to bridge ports because it is a lot less screwing around. All you have to do is port - no massive ordeal of fabrication. It took me almost two years of free time to make my peripheral port. I bridge ported my TII engine in about sixteen hours of work, including pulling and reinstalling the engine.

Engines are not monuments, at least not for me. I get 30k out of an engine, or maybe 400mi, depends on a lot of factors. I've pretty much solved my dust and cooling system issues, so I'm tending more towards 30k than 400mi B ut, an expendable item should be cheap/easy to replace, not be a big long ordeal of fabrication.

In 2009 (maybe it was 2010?) I went through three engines, and rebuilt two of them twice. My current engine (100% stock GSL-SE shortbloick save for the porting - I had NO good parts left over from the previous stuff except for oil pans and timing covers!) has been in the car for something like 30k, and it's getting tired, so I'm currently in the process of putting the next engine together. I don't have time to be doing custom this and fabbing that, I need to get the thing back on the road so I can drive to work

If I had $6000 or whatever to put together a store-bought peripheral port, times at least one engine per season and possibly two or three or five, I'd spend it on entry fees and maybe a tow vehicle! Maybe... mmm maybe not a tow rig, I hate driving trucks

 

thank you Peejay, i guess i misunderstood. i plan to clearance the engine. this will be my first build (i have an experienced friend thats going to help put the engine together). i have a complete 4 port motor (s4 tII) and was trying to figure out which would be best. i never thought about so much fabrication after the ports are made. maybe the intake? i have a friend with a welder. if you have had better experiences with a bridgey over a pp i think i should join you on that. i dont have the funds to keep rebuilding the motor. 30k miles without needing be opened up would satisfy me.

thanks Peejay, your input is always appreciated. you have a lot of first hand experience. that's whaty i was asking for. not enough NA rotary guys anymore.

 

oooohhhh fancy! Sad to say I've hit that site up for info on many occasions previously but obviously hadn't seen that page before.

I'll bookmark that away with the rest of my transmission data.