WackyRotary

How fast in a 1/4 should a standard bridgeport 12a be with headers and stock hallowed out muffler, stock igition, mikuni 44PHH, 205 50's, stock '85 12a gearing?

I can't get a weber 48mm or better for a while, so I'd like to hear from others who've done this.

If I was loaded which I am not, I would of optimized everything, but with all things being equal, I can not, so do not remind me.

WackyRotary

Anybody?

REVHED

Probably in the mid 14's. With 48mm IDA and free flowing exhaust you should be able to break into the 13's. Shorter diff ratio would help alot too.

WackyRotary

hmmm.. mid 14's is what it feels like, can't find out till I go to the track till spring. I will try it out with out the muffler on sometime this week and see what happens.

pp13bnos

iTrader: (1)

With the proper porting, gears, exaust, fuel system, carb system you should be able to run mid 13s. A J bridge ported 12a should crank out around 260-270hp. Making most of its power before 9,300 range. Hope you're running carbon apex seals. Steel apex seals don't like hi rpms. Your biggest problem will come from trying to keep the motor in the power band. CJ

WackyRotary

yeap, I am using carbon seals. Thats what they need. I am sure the porting is more then reasonibly a optimised standard bridge with port matched rotor housings. I KNOW the carb is not optimized for sure.

Could a half-bridgeport get away with standard steel ones? Meaning porting the endplates not the centers? I think I may want to port into the mildport engine I have since I have it just sitting and the bridgeport engine is more fun. I wish I could just go and buy a weber, but my cash flow is low till the economy bunces back.

rotorhead

hey wacky... just curious, but what kind of fundage would you put towards a used dellorto 48? i've got one in use, but my mechanic has this cool fuelie system i've been eyeing. come spring time, the del MAY be up for sale.

WackyRotary

RotorHead: Yeah, possibly in the spring or later into feburary or march I could probably be interested and able to pay. I am interested in just the carb and not the intake manifold if that is a possiblity. They do bolt up to the same manifold I have. As long as it is set up jetting/venturis/etc for a rotary with oil-metering line connections and nessessary linkages, I would be interested. Fundage? I would say since I'm just wanting the carb and no manifold so in the range of $150-$175. I bought the whole Mikuni system for $225 a few years ago. So that sounds like a rational price range to me without the manifold. What size venturi's do dellerto carbs come with?

peejay

Don't go over 8500 EVER, and orient the apex seals so the corner pieces rub against the center plate if you notch/relieve the rotor housing.

Now. After you do all that, keep in mind that 3mm iron seals WILL CHATTER over 6200rpm... this hurts power as well as really hurting the life of the seals, seal springs, and rotor housings. I haven't pulled out WT's engine (aka "The Diet Coke of Evil) but it blew fairly early in its life, 23k on perfect-spec seals. Could it have been sustained revs over 6200 (going around Nelson Ledges I kept the revs in the 7000-8000rpm range most of the way around, and drag racing it's just 5500-8000 1-2-3 and a big 8400rpm burnout) or oculd it have been over-use of the leading-ignition-only rev limiter the day before? I won't know for sure until it comes out (looking like middle of next month ) but it's something to keep in mind. Until then, I'm putting my plans for a half bridge 12A on hold... if it was high revs that killed it (evidenced by chatter marks and flattened springs) then I'll have to rethink my whole strategy.

Hurley seals are supposedly good to 10k and last longer than the carbon-aluminum seals, but I'm told they wear funny - they "smear" the rotor housings with black crud which eventually hurts compression.

WackyRotary

Thanks PeeJay. I was aware of the orientation problem going with a bridgeport with steel seals. Thats why I planned on building half bridge. That and I already had steel seals with only 20K and wanted more usage from them.
As for high-rpm usage. I use it on the street and don't sustain 7K+ driving except when street racing or doing a top speed run(rare). I did rev my stock rebuild engine way to much and did notice chatter marks. But since this is a dirt-cheap project plan and usage is mainly highway it should be ok one would think.

pp13bnos

iTrader: (1)

Hey Pee jay. I was told that apex seal bounce wich causes (or chattering, what ever you want to call it ) can start as early as 6,500rpms, if the motor is held there for awhile. Never heard of 6,200.

But if your apex seal springs are flattening out, you're either running realy lean, or the motor is getting to hot. When you tear down the engien you'll find out by the colors on the end plates.

Also, the length of the apex seal can also play a factor when it comes to blowing up. The hotter the tempature of the motor, the more the apex seal expands. When it gets to long.....*BOOM*

CJ

peejay

Hmm... something to think about... when the engine was freshly built it ALWAYS ran hot... it would run at 210deg on the highway with the electric fan (1600cfm!) on... going round NL I had to have the heater going full blast as well to keep the temps down. Of course that was before I realized how LEAN the engine was running! After a while it settled down, and towards the end the temps never ever ever went over 180deg, and were usually around 150-160... winter does that to ya. So if anything were heat-damaged, it would have happened early on in its life.

pp13bnos

iTrader: (1)

The break in period is the most important time when it comes to engine longevity. You probably put micro cracks in the apex seal on the break in, then after a little apex seal bounce, everything just comes apart. To be honest, i don't know if it would be cracks or not. But i do know, that Rob at Pineapple has ceramic apex seals x rayed to see if there is any micro cracks. I think he does carbons too...but i don't know about steels. I'll ask him next time i bug him. I guess the only way you'll find out is by tearing the motor down. CJ

WackyRotary

I think the main reason steel seals do damage besides the fact steel is a harder material then carbon seals is the interia of the seal being compressed and decompressed from going through the narrow region of the rotor housing and when it releases more away from the rotor there is more of a time delay because they weigh more the carbon ones. Hence you get that bounce everyones talking about and thus chatter marks. This is just a break down of what I believe happens in the engine..