How's it going everyone?
Would bridgeporting my 12a completely kill my fuel economy? Someone said that I'd be driving from petrol station to petrol station filling up but I just thought I'd get a second opinion.
Cheers,
Mat

 

Yes. I suggest 25-30 litres per 100 km[9mpg] would be typical but have heard of a case of 125km per tankful around town[5mpg]. Remember its primarily a competition set-up where fuel consumption does not matter.

Also engine wear wll go up by a factor of 5.

A 12A stock set-up will give 9 litres per 100km average use. On another thread you were askung about a turbo for a 12A. Out of interest the offical consumption for a 12AT is 7.7 litres per 100km highway, 13.5 city.

 

I managed 14.6mpg average for a 12a bridgeport for a country person I am I guess. No real changes in MPG occur driving light or hard, so its clearly the overlaps fault a bridgeport has. So ofcourse, I drive hard always, and keeps the carbon cleaned out.

Its a long ways between towns for me and were you need to go, so I spend significant time on the hwy, but I always keep it above 3500rpm NO MATTER WHAT and fluctuate a lot because crusing speed causes it to jump around like you Aussi's say: a Kangroo!! LOL!

On a road course near here, I managed to get down to 8mpg, which the road course where speeds up to 90mph on the straights MAX and some tight corners are in so a lot of time braking actually will help mpg somewhat I suppose. But I'd guess you could get worse on some Tracks. My absolute best hwy mpg for the bridgeport was 16.9mpg ALL HIGHWAY. But that is definitely not typical of most people driving a bridgy on the street daily since they majortiy live in urban areas and stoplights are allways tempting.

 

3500rpm does not give much torque on a bridgeport, most don't get any significant numbers until at least 6000rpm.

The trouble with 3500rpm is you are over the legal speed limit in 5th, dropping a gear to a useable rpm pushes up fuel consumption.

I have a feeling most so called street bridgeports are in practice only 1/2 bridgeports with a limited increase in port size.

 

If you are worried about gas mileage you don't need to be asking about a bridgeport.

Just my opinion; if i could afford to drive around at 9000 rpm all day then I would be doing it. . .

 

If you have ask the price you can't afford it, unfortunately Woolworth fuel discounts are not that great!

 

Your abslulotely right. I'm saying it should be operated above 3500rpm at any time except idle. I would almost keep it in a gear that keeps it from 4000rpm+ for crusing. I said 3500rpm because I can hold 70mph there, but if you need to accerate, yes you'd need to downshift to get into the REAL power band.

As for the cost of the bridgeport, if you can do the porting yourself, you already saved some money there. ... and if you skimp on essentials like harden stationaries and just get a HP oil regulator and carbon seals, it should go well on the street since you won't be holding 8000rpm all day I assume which is why mine is still together.

 

my bridgey gets about 11mpg even when i make a few 1/4 mile passes.

 

i'm looking into a bridgeport for the 12a that's gonna go into my racecar.

anybody have power numbers and pics of the ports on their motors to share, i'd like to do the porting by myself, but i dont know if i can.

i'd also like to prep it for 10k rpm usage, so i'd need the HP oil stuff and hardened gears, and carbon seals/race springs.... sound about right?

for exhaust, i was thinking of the RB dual header, then dual 2" all the way back, neck it into 3" single before the axle, and then into an SS N1 style "muffler"... this should be free-flowing enough, and not be as loud as a fully open exhaust.

 

guys, I get 100km to 10litres of fuel if i just cruise....
its all about how u drive....I've got about 180horses at the wheels too

 

The past weekend`s fuel consumption wasnt that bad.
(Dragwars thread)

I used 32 l and drove 105 miles,comes to 5km/l
I drove 80 mph most of the time on the highway.

I dont know the formula from km/l to m/g.

Karis

 

Silly question, but are all these numbers for carb'd cars?

Would be interested to see what the EFI numbers are like

 

My 12a J-Bridge just dyno'd 205hp to the wheels with 42mm chokes in the Dellorto. We figure 20% drivetrain loss for a RWD helical gear tranny = 246 at the fly.

It is a full J-Bridge with ceramics, none of this half bridge or eyebrow port stuff. look around @ yawpower.com Paul still has some pics of his bridge there.

you're right on about the oiling system. You also need to clearance the rotors and e-shaft and balance the entire rotating assembly including both couterweights.

that exhaust will have great flow and be really friggin loud. i say go for it but be prepared for the track sound meter guy to stop by.

 

I'm going to be building a new motor fo my 83 is bridgeport streetable? What I really mean is where do htye idle at? And how hard are they to drive on the street? Could I take a date out in it or would it just be emarrasing to try to get it to run without ripping the tires at every stop? That kinda thing, I'm willling to give uo hte gas milage but I want something that I can drive everyday.

 

with a bridgeport the power comes in at 5000rpm with hardly anything below.

It is primary a race engine set-up but you could just about use it in the street but not as a daily driver.

You would have great problems getting it past any authority due to emission and noise levels.

Not really the set-up to take a date out unless its to the track to see you perform. Try small talk at 5000rpm without a muffler, and your first present would have to be a set of diamond studded ear plugs from Tiffanies.

 

Thanks, I guess I'll be doing a street port.

 

You set the idle of a bridgeport to where it lopes up and down real smooth. brapp - - brapp - - brapp - - That turned out to be 1800rpms on my motor. I could have set it to 1200-1500 but it stumble's and hiccups at those rpms.

My Full J-bridge kicks and bucks under 4000rpms so you need to rev it over that otherwise your fillings rattle out of your teeth. I bet a 'standard' bridge would have less overlap and would kick at a lower rpm.

You need a very free flowing exhaust to get the most out of a bridge. Most streetable exhaust will choke the bridge and you'd make about the power of a streetport give or take. Lots of variables.

If you want great power for a street car thesedays you're best off going turbo streetport. The Noise Police are too abundant any more, esp. here in SoCal.

 

I seriously don't know why would anyone that has ever had a bridgeport would even concider of getting another one unless it's purely for racing even than i still don't know about that. They are so impractical in every way you look at it.

All new seals $800
Porting time just for bridges 20 hrs
Intake $500
Exhaust $400
End plate lapping $150
Balancing $afraid to find out
Bell Housing Shield $175
Clutch & Pressure Plate $250
Ignition $130 or more
Noise-Tons of it
Fuel Mileage-8-10 mpg
Drivability-Almost None

All for what, a miserable 230hp at 7k rpm.

 

So i should street port, no doubt about it huh? Sounds like i could get about the same out of that.

 

As for price, you gotta pay to play.
drivability, noise and gas mileage are not street driving friendly

i got 246hp @8800rpm. and another 10-20 are available with a bigger carb or efi.

they make GREAT race motors, last year a 12a bp rx-3 almost won the national GT3 title. most other little motors trying to put out this much power normally aspirated have a narrow powerband located @ high rpms.

 

What can I expect from a street port?

 

My 13B Bridge with a weber in a rx-3 coupe
used 28l/100kms

 

a 12a streetport if full scca e production race trim maxes out @ 225 flywheel hp. 38mm chokes in a weber IDA and an exhaust with typically just one high flow muffler (LOUD, barely 103db legal).

power goes down accordingly when you muffle it. I'd be happy to see 200 fwhp street driven.

in a lightweight car that's a lotta fun!

 

I am shoting for 1hp per 10lb ratio. I take it I'll need a turbo or some juice huh?

 

LOTS of people here put 86-91 Turbo ][ motors in their 1st gens.

It might be more economical to do a turbo blow-thru carb setup. Robert does nice work on these and comes reccomended.

http://24.5.223.119/website/home.asp

He has a factory 12a Turbo in the Used Engine section too!

FWIW in my Rotary Truck pictured below I have a 13b Streetport with Dellorto carb, 41mm chokes, aluminum flywheel, Centerforce ][ clutch, 4.625 ring and pinion and a real nice high flowing straight through exhaust.

It's a nice little package that makes good power and revvs up like nobody's business! It's easy to bounce off the redline buzzer.

With a semi-close ratio tranny ala Miata or RWD 626 + MSD ignition and cold air induction it'll really scoot along. Never underestimate the acceleration that gearing can give you. Especially if you've never driven a properly geared rotary!