Carl

iTrader: (2)

I just did a dyno test on my Spec7/Pro7. Compared the Spec7 exhaust (late stock manifold with 2.25" tubing to glasspack muffler at rear bumper) with a Racing Beat Street Header (2-into-1) and presilencer dumping under the car in front of the rear axle. Got about an 8% increase in horsepower. The intake is still california smog legal. The absolute horsepower numbers were lower than when I tested the same base configuration a few years ago, but that may just be a difference in atmospheric conditions, since the car is probably faster than it was back then.

As a side note, got almost 4% increase by opening the hood during the test. Kind of a good sign for using a cold air intake. The increase probably wouldn't be quite that big while racing with a cold air intake, because more airflow while racing would keep the underhood temps cooler than sitting still on the dyno. Probably still get 2% or so with a cold air intake.

Anyway, I hope someone finds this interesting/useful. It is useful to me since it gives me my 10th post so I can post some cheap 1st gen parts on the for sale forum.

Carl Johnk

Kentetsu

Good info, thanks for posting.

PercentSevenC

Interesting information, especially with regards to the hood.

DivinDriver

iTrader: (15)

Very good to know that the reality pretty closely matches the theory!

vipernicus42

iTrader: (4)

Interesting mention about the hood, because it's different from what I found, though my intake is radically different.

On the dyno, the difference between hood open with no airbox and hood closed with my ISC Airbox that has a K&N was approx 1-2hp, or so small that it wasn't accurately reproducible and well within the margin of error for the dyno I was on.

What that tells me is that
a) the stock airbox is very restrictive, but my ISCRacing airbox and K&N aren't much different than an open carb and

b) With RB headers, my e-fan going and the fan in front of the car pushing air at it, heat doesn't tend to build up a lot in my engine bay. I would imagine this would make sense since the stock exhaust manifold looks like cast iron and tosses a huge amount of heat compared to my RB header.

I didn't dyno RB header vs. any other exhaust so I don't have any feedback there, but those numbers are pretty impressive.

I'd be interested to know what kind of numbers you ran. A Cali-legal intake is radically different from my Sterling on a ported manifold, and my RB Street Port exhaust is equally different from your Spec7 setup.... but I have 220,000km on my motor and run compression readings that are borderline (6.9kg/cm2 on all faces of all rotors at 250rpm), though I still put more hp to the rear wheels than it had at the flywheel stock... not much more, but enough that it counts.

Jon

thunkrd

iTrader: (1)

i would like to use the rb streetport headers, but was wondering if anyone has put an O2 sensor bung in one?

Carl

iTrader: (2)

I actually did a couple more comparisons relative to the air cleaner side. The stock air cleaner with clean K&N was basically the same as wide-open intake, RB air cleaner with K&N and RB aircleaner bottom only without filter (trying to smooth the airflow into the carb). The RB air cleaner with filter actually showed a couple of HP less than the others, but as you say, that is most likely noise level.

I came away with the feeling (perhaps mistakenly) that the stock air cleaner with a 3" snorkel (largest allowed in PRO7 and ITA) out to a scoop at the bumper was probably the best racing solution.

What does the ISC airbox look like? Are you taking air from outside the engine compartment?

I did not have a fan blowing air at the front of the car, so I really only had what the electric fan (from a Taurus v6 and installed as a pusher) could move.

The street port exhaust (which doesn't merge until near the rear axle if at all) is supposed to be better for stock port 12A's. I'm sure your intake set-up moves a lot more fuel and air than my stock as well.

As far as the absolute numbers go, they were surprisingly low. Worst case (spec7 exhaust with hood closed) was 86HP. Best case (RB header w/ hood open) was 97HP. The absolute numbers have to be low, because the car is competitive with other Spec7 cars and slower Spec Miatas, which typically have +/-105HP. A couple of years ago, the same car made +/- 108HP and the motor shows no signs that it is any slower. Regardless of absolute numbers, the comparison seems valid.

Carl

Sir Timmy

iTrader: (2)

great info am planing a cold air intake and nikki mods & exhaust mite do exhaust 1st as think i mite have a restriction my little rx7 dusnt seem 2 have any were near the perfomance i here claimed for these. runs smooth but dusnt biuld power after bout 5500 rpm & cant hardly hit 80 mph tops, 0 to 60 i quit timing aft 20 sec, i to have bean trying to hit 10 post soz i can do more @ this site, have ben learning a lot.

thunkrd

iTrader: (1)

wow... sounds like you have no secondaries. buy the test pipe from racingbeat, or make one yourself. keep the cats. the test pipe from racingbeat will replace all 3. when you need to redo smog or w/e just put the cats back on.

i would look into whether its the cats or your carb's secondaries not opening, but the test pipe will add extra performance at a cheap price.

What year is the car?

vipernicus42

iTrader: (4)

It looks like this



Jon

Sir Timmy

iTrader: (2)

i didnt suspect secondarys as it will lean cough if i go wot b 4 choke pulls open but not after. i hafta check this.

Sir Timmy

iTrader: (2)

i didnt suspect secondarys as it will lean cough if i go wot b 4 choke pulls open but not after. i hafta check this.

evil_motors

iTrader: (3)

why not heat wrap your headers? is that allowed?

Super82

iTrader: (1)

Why are your HP levels so low? Thats lower than stock!

FirebirdSlayer666

iTrader: (3)

Stock hp is 101 at the flywheel. Estimating 20% drivetrain loss you have 80.8 hp at the rear wheels bone stock. His numbers are higher than stock. That ISC air box looks pretty nice, Looks like it flows better than the RB box does.

Super82

iTrader: (1)

Oh...I always thought it was 100 at the wheels. How is it possible that people are pushing 150 at the wheels with bolt ons then?

And better yet, how do our cars feel so fast? I know it comes down to power to weight ratio, but if what you say is true even our power to weight ratio isn't great. Yet my car bone stock had enough to put me back in my seat on a twisty road or break my tires loose in 2nd gear.

FirebirdSlayer666

iTrader: (3)

Alot of stock parts are restrictive like the exhaust and carb/intake. Opening these up can make good power. The reason 1st Gens feel quick is pretty much weight. It has nothing to do with power to weight ratio. 1st Gens are around 2400lbs, it doesn't take alot of power to move it quickly. Doing bolt ons and making more power makes more of a difference in our cars VS a Mustang which has 1000 more lbs to push around. My FB when it was stock with just an RB clutch could break 2nd gear loose and chirp 3rd

Super82

iTrader: (1)

Even so, it seems extreme that we can go from 80hp to 150 just by doing carb/exhaust/misc stuff. I mean, I know it is very hard to hit 150hp on the stock ports, but I've seen others get in the 120-140 range with the average FB power upgrades. Thats pretty cool to know that we can almost double our power that easily.

For instance, I know that dj55 (sorry, don't quite remeber your name) with his ITBs and other full mods was at like 140 something, and he's on the stock ports if I remember right.

FirebirdSlayer666

iTrader: (3)

Yeah. It all comes down to using properly designed parts and a good tune.

Carl

iTrader: (2)

A few weeks ago I was talking to a guy who tunes a lot of PRO7's and he said that with max tuning to the carb, the highest he has seen is about 120HP. That was without a header. If a header can add 10 HP (probably reasonable for a long primary RB header then that would be 130HP at best. I really don't think it is possible to get 150WHP with stock port 12A and otherwise bolt-ons.

I am not a dyno expert, so I don't know why my recent numbers were so low. Comparing to other spec RX7's and dyno reports for spec miatas, I think I have to be in the 105HP range (with the base spec7 exhaust). That's about what it was a couple of years ago. If I was really only 86HP, there is no way I could keep up with any spec7's or miatas. Especially since my car was >2480lbs w/ driver in spec7 form. Spec Miatas are 2300lbs. The good thing for the future is that my weight is now down to about 2390 w/ driver (still 90lbs heavy for PRO7) and I probably picked up 8 HP. Hopefully will make a noticeable difference in lap times. Learning to drive wouldn't hurt lap times either, I guess.

Not sure what this is worth, but ...

Carl

PercentSevenC

Not with a Racing Beat header, you couldn't.

Keeble

iTrader: (3)

would an old rotary engineering header and presilencer produce more power than an rb?

Super82

iTrader: (1)

I think he is making a smug remark against the RB header in favour of the SDJ headers, heh. SDJ headers were like $500 headers that aren't made anymore.

PercentSevenC

Not really. The RB header is the only decent bolt-on header still being made, at least over here. I'm just saying you're not going to hit 150 at the wheels with a stock port unless you put some effort into your intake and exhaust setup.

Carl

iTrader: (2)

Update to my original post. This weekend while at the track (Buttonwillow) I had the car re-dynoed with the RB collected header and presilencer. New results were 117HP which matches with the 108 2 years ago with a 2-1/4 exhaust and stock manifold. Both of these tests are with same emissions equipment and stock carb built to meet California emissions. I have no clue how my local guy came up with 90-97 HP. Wrong gear and high drivetrain loss? Wrong correction factor? ???

Conclusion (for me at least) is that the RB 2-into-one header gives 8-10HP increase of reasonably stock exhaust (without a cat in either case).

Noisy as hell though. Can't even think of getting in the car without earplugs.