Horsepower?

[Festus E. Simkins]

Just wondering. Does anyone have an idea about the horsepower an ITA 12A motor should make. Just wondering have never really heard anyone quote numbers. RWHP and @ Flywheel.

Drive well.

120 RWHP leaned and timed at 26 deg dangerously, dont do that. settle for 112-115 to live and let live.

[This message has been edited by 7'sRracing (edited September 05, 2002).]

[ddewhurst]

Festus, do a search (I think it was) under this page "Mazda Race Cars". This was a topic some time back.

Have Fun

David

[Quickshoe]

Festus,

The old discussion was about 13b's (I think).

A decent 12A ought to put out 135hp at the flywheel.

I've only had one 12A on a chassis dyno. It had a rejetted carb and a street port. The street port was the first time I'd ever attempted any port work on anything! I bought templates to give me a 2-D shape and location. I was on my own with the depth and shape of the port. I tried to error on the conservative side as I figured I would lose some if I didn't go big enough and lose a ton if I went too big. That motor put out 143HP at the rear wheels. We stopped tuning on the dyno then because 1 more HP would have bumped us up to the next class. No fancy apex seals or light rotors.

[bcarter]

Cool, if you got 143. I have a streetport, with stock carb, header, no jetting, and got 135 at the wheels. Works for me.

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G. Brooke Carter
# 10 Challenge Car
Calgary, Alberta

[Quickshoe]

BCarter,

Spend some money for time on a dyno with someone familiar with rotaries. You can try to build them all the same, jet and time them the same and they won't all be optimized. I wasn't at 135 before we started messing with timing and jets. We only ended up changing the jets once, as the A/F mixture was off and the "educated guess" of the dyno guy put us really close, the rest of the hp was found in L and T timing and their split.

[Skid]

So, those of you who have experimented with timing on the dyno, how closely does your end result compare to the ubiquitous 24*L/16*T recommended by Paul Yaw?

[Quickshoe]

too many variables to say that that's optimum for your set up.

According to some rotary guru's there is not much HP to found in the timing on a rotary. That may be the case if everything is in great shape. However, any adverse condition may require more timing. Going too far can cause some serious problems, so don't go out there and dial in a bunch of lead. If the last 5-10hp are worth $100 bucks or so to you find out what works for your carb, rotor, housing and seal conditions. Pay attention to the oil/water temps when you start advancing timing to the point of diminishing returns. If you find out that messing with the timing doesn't change things for the better then you were right on to begin with!

[This message has been edited by Quickshoe (edited September 06, 2002).]

[bcarter]

Hey Quickshoe...

We did chassis dyno the motor, and 135hp at the wheels is what we came up with. I am in a class that forbids any carb work, so we run them absolutely stock, which is costing us some power up here in Calgary, at 3500 feet above sea level. We run these streetports, with headers, but nothing else can be touched, except removal of all emissions junk. The motors in the class come from several builders, and we are all pretty close in power. Mine is new this season, and I might have a slight edge in power/torque, as I can pull quite well on the rolling starts.

We found the sweet spot on the timing, and found that even small changes either way dropped the HP quite dramatically. We also found that the HP starts top drop off after about 7500 rpm. Also found it is best not to go below about 4500 either.

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G. Brooke Carter
# 10 Challenge Car
Calgary, Alberta

[This message has been edited by bcarter (edited September 07, 2002).]

my new motor sounds very good, cant wait to take it out to buttonwillow and for chassis dynotune and testing on track. its been seven months since it went pow, nah nah nah naaaaaaaaah clunk clunk, silence...

[rlekun]

7's,

On another thread, you mentioned you had a source to get me a pro-built motor for less than $2K. Is that the same build as your new motor?
Can you get me more info (spec sheet,etc.)? Is sevensonly the source? Let me know. email me if possible
My JY motor had its first session this weekend at M-O. It blew out clouds of smoke at every lift and couldn't maintain oil pressure....started getting noisy above 6K Revs

[This message has been edited by rlekun (edited February 24, 2003).]

[Tak]

rlekun-
Beware a pro motor for $2000.
I build my own motors, and the parts/machinework adds up to $2k.
Here is my list of parts and machine work:
New from mazda comp:
rotor housings,
complete motor seal kit
(includes all apex, side, oil seals and springs) Does NOT include new bearings.
New clutch, pressure plate, throwout bearing.
And, if you don't have one already, a new mazda water pump (aftermarket ones are junk).
Machinework:
lap side housings,
balance entire rotating assembly

Like I said, the components alone are about $1500. Machinework tips it over 2k. If someone builds you a motor for less than this, you are getting USED PARTS.

Tak
SFR # 29 ITA

[lateapex911]

This is all good news to me...I'm down on power! Whooo Hooo! Now I just need to go get that 14 Hp....

Once I spend the $ and get myself a new motor, how do I break it in? I wonder if the Hp. is all there right away, or does the motor need some use? Follow MazdaSpeeds advice?

And, how long do you get to keep the power once you've got it? 10 weekends? 20? And does the drop of happen gradually?

How high do you guys rev it? I try to keep it under 8200 or so, as it doesn't pull too well up there....I just do it to save a shift.

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Jake Gulick
ITA 57 RX-7
New England Region
[email protected]

[ITSRX7]

Jake,

Time to take your car to a chassis dyno. Use the power curve for YOUR motor and pick your shift points for the tracks you run.

This is elementary but: You want to shift before your power falls off too much while at the same time your resultant RPM range is still in the meat of the power or torque curve.

On my chart, it looks like I should be shifting at about 8200 and that should place me back in the power.

Too early of a shift nets me not enough power at the top and below the power in the next geat. To late of a shift keeps me too long on the back side of my power band and unneccesary stress on the engine.

You gotta have a dyno chart for your engine. Maybe they can do a little carb and timing tweaking while you are strapped on!

AB

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Andy Bettencourt
06 ITS RX-7
FlatOut Motorsports
New England Region
[email protected]

[C. Ludwig]

In Carrol Smith's Tune To Win he actually advocates revving the motor past the HP peak under certain situations. You'd have to read it for yourself as I don't recall the details. Just playing devil's advocate.

Chris

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Chris Ludwig
08 ITS RX7 CenDiv

[Greg Gauper]

Carrol Smith's idea is to maximize the area under the horsepower curve between the shift points.

It really depends on the shape of the horsepower curve but the general idea is to look at the curve at the upper shift point, and where the engine revs drop off to immediately after the upshift.

Draw a set of uniformly spaced narrow vertical bars, starting at the 'zero' horizontal axis and ending just at the curve. The narrower, the better.

Each vertical bar will have some area that is easy to calculate (height * width). You don't really car about the width if it is narrow AND you use the same width consistantly in your comparison. Just add up the all the length 'units'.

Now repeat the test and move your upper shift point. The lower point will move an equal amount. Recalculate the area. The larger the area 'units' the faster the car will accelerate.

Another non-horsepower reason for not shifting...If you reach your shift point but only have a short distance until you have to brake for a corner i.e. 50-100ft, you can sometimes save time (not speed!) by not upshifting. An upshift take finite amount of time no matter how good you are. (this is why F1 cars have automatic gearboxes that can shift in 25msec or less!)

Keep in mind, the issue of a 'shift point' and a 'red line' are two different things. The red line is the maximum engine speed you can turn before something breaks. Your shift point is where you maximize the area under the curve.

Some engines have a conservative red line (i.e. 1st gen CRX/Civics, Rotaries, etc.) and can be over-revved briefly, within reason.

Some engines will blow up if you exceed the red line by 1 rpm.

Some engines actually produce peak power BELOW the redline. I understand some VW's have this characteristic if properly tuned.

Carrol Smith also cautioned that he discussed the issue in depth with his engine builder and received permission from him before using this technique. The respected engine builder saw now problem in a very brief overrev, IN THE LOWER GEARS!!!

[This message has been edited by Greg Gauper (edited October 18, 2002).]

[Allen Brown]

Jake.

Re; Engine breakin....I broke my 85 GSLSE 13b in 3 years ago by following what Racing Beat published. I don't remember the details, but I think it was somewhere along 500 miles below 4500, mild acceleration, next 500 miles start building rpm up to 5500.

My car was street legal...sort of..at that time. I took 2 days off work to break the motor in before my first school. Engine still pulls quite well (except I wish it was a 90 13b) and it is shifted at 7500 to 8000. Depends on whether I'm running a sprint race or an enduro. I've seen many rotaries die sooner, I will be in my 4th season with the engine (rebuild with some used components) next year...I could be wrong, but I feel alot of my engines life comes from taking the time to break the motor in before going to the track.

Bye for now.



------------------
Allen Brown
#36 IT1
[email protected]

[ITSRX7]

Chris,

I am with you. That is what I was trying to say when I wrote about slightly past the peak power if that brings you back into the power curve.

AB

------------------
Andy Bettencourt
06 ITS RX-7
FlatOut Motorsports
New England Region
[email protected]

[BrianB]

Along with A dyno chart showing horsepower and torque at different rpm's, you need to know your overall gear ratio for each gear your in.Its road speed for the gear you're in at shift rpm that determines whether you'll be in the peak torque range in the next gear. This is why reving past peak hp is done. The increase in road speed in that gear,placing the engine rpm's in the optimum range in the next gear.

Road speed= rpm X tc/gr X 1050
tc=tire circumference in inches
gr= overall gear ratio

Example; For a wheel diameter of 24 inches, a 3rd gear of 1.366,4th 1.00 and a rear ratio of 4.88.

RS=8200rpm x (24x3.14)/ (1.366x4.88)x 1050
RS= 88.28 MPH in 3rd gear

A shift to 4th at 88.28 mph will drop rpms to
rpms= 88.28x (1.00x 4.88)x 1050/ 24x 3.14
Rpm= 6000
You can then check your dyno chart to see how this places you in the power range

hope this helps,
BB

[Crack Monkey]

120 RWHP leaned and timed at 26 deg dangerously, dont do that. settle for 112-115 to live and let live.

The Spec RX-7s in DC are making 105rwhp w/ stock exhaust manifold, no carb work, stock intake filter housing, and full emmissions gear.

That is dynoed with <2psi fuel and timed somewhere near 24*.