Dyno Results w hard data (On a known Dynojet)
09-18-2003, 09:23 PM
#276
Forum Vendor
Boosting an RX-8
I have been looking at boost options for the RX-8.
Turbo or compressor, it seems that there is not a lot of room for boost.
The RX-8 Renesis uses a 10:1 compression ratio.
This is quite a bit higher than earlier RX-7's with Turbos start with.
On the turbo models they typically started with a compression ratio that is down from the naturally aspirated models by about .7 to .9.
See:
http://www.atkinsrotary.com/enginepart.htm
Rotor Weight & Compression Ratio
Year Engine Compression Ratio
79-82 12A 9.4
83-85 12A 9.4
84-85 13B 9.4
86-88 13B 9.4
87-88 13B Turbo 8.5
89-91 13B 9.7
89-91 13B Turbo 9.0
93-95 13B Turbo 9.0
Turbo or compressor, it seems that there is not a lot of room for boost.
The RX-8 Renesis uses a 10:1 compression ratio.
This is quite a bit higher than earlier RX-7's with Turbos start with.
On the turbo models they typically started with a compression ratio that is down from the naturally aspirated models by about .7 to .9.
See:
http://www.atkinsrotary.com/enginepart.htm
Rotor Weight & Compression Ratio
Year Engine Compression Ratio
79-82 12A 9.4
83-85 12A 9.4
84-85 13B 9.4
86-88 13B 9.4
87-88 13B Turbo 8.5
89-91 13B 9.7
89-91 13B Turbo 9.0
93-95 13B Turbo 9.0
09-18-2003, 09:25 PM
#277
Forum Vendor
Re: Re: Re: Off my chest!
Originally posted by bern
They are not per se' in risk of melting down, but I do bet they don't have to last the US federal emissions mandated 100K miles. I think Mazda was forced to play it safe with RX-8 here.
Longevity is the key thought here.
-Bern
They are not per se' in risk of melting down, but I do bet they don't have to last the US federal emissions mandated 100K miles. I think Mazda was forced to play it safe with RX-8 here.
Longevity is the key thought here.
-Bern
09-18-2003, 09:27 PM
#278
Registered
Join Date: Jul 2002
Location: So-Cali
Posts: 809
Likes: 0
Received 0 Likes
on
0 Posts
Off my chest!
Originally posted by canzoomer
Maybe. I doubt we can add much boost to the Renesis.
It is what, 10:1 compression ratio?
Add too much boost and you create a knock condition.
The earlier turbo'ed RX-7's use a much lower compression ratio.
Maybe. I doubt we can add much boost to the Renesis.
It is what, 10:1 compression ratio?
Add too much boost and you create a knock condition.
The earlier turbo'ed RX-7's use a much lower compression ratio.
I happen to run a 13B 9.4:1 turbo motor in my 1st gen. I can safely boost 11lbs or so on pump gas. I love my ride with race gas and more boost.
. I run a Electromotive TEC-2 ECU.BTW, on my prior comments, I wasn't addressing the merits of turbo'ing a RENESIS, just addressing the "heat and emissions issue" associated with a turbo on RENESIS and it's exisiting cat set-up.
-Bern
Last edited by bern; 09-18-2003 at 09:39 PM.
09-18-2003, 10:14 PM
#279
Registered User
Join Date: Sep 2002
Posts: 95
Likes: 0
Received 0 Likes
on
0 Posts
Re: Off my chest!
Please, now explain why does the car show the same low results when dynoed with GTech Competition? The car is at speed so the problems with safe mode because of standing on dyno machine should be missing.
Why does the RX8 show lower hp and tq results compared to other cars of similar horsepower?
Why does the RX8 show lower hp and tq results compared to other cars of similar horsepower?
Originally posted by rotarynews.com
Since thigs are out in the open now, I won't have to explain this to a thousand people at SevenStock. I guess we should have just play the 20 questions game from the start.
To reiterate: 3 know faults on the Dyno cause the car to go into Safe Mode. This is not a guess, it is a fact, and can be verified by someone with a code reader (how's that project coming along, anyhow?). You can also verify this by seeing the upper end of the dyno "spazz out" ... and look at the AF readings.
Now as to the why on the power reduction: Cat Core temp... By federal law, emmission equipment has to last for 100,000 miles. At the rotary's high exhaust temperature, the cat will destroy itself. (any previous RX-7 owner can tell you cheap cats will be destroyed by the rotary's hot-hot-hot exhaust in a matter of months... causing a neato flaming/shooting of little peices of converter material out the tail pipes... Happend on both my 1st gen (12a) and 2nd gen (13b) )
So there is hope: The engine is able to produce the orig promised HP, at the cost of cat longevity. Or, if anyone know a good chemical engineer with specialization in thermal calalistic reactions, have them see if there is anything they can recommed for a long-life, high-flow cat that can last under the extreme heat of a rotary's exhaust.
And to the Mazda folks who we promised not to reveal the causes( that read this forum), we are simply restating what someone else on the forum has mentioned.
Since thigs are out in the open now, I won't have to explain this to a thousand people at SevenStock. I guess we should have just play the 20 questions game from the start.
To reiterate: 3 know faults on the Dyno cause the car to go into Safe Mode. This is not a guess, it is a fact, and can be verified by someone with a code reader (how's that project coming along, anyhow?). You can also verify this by seeing the upper end of the dyno "spazz out" ... and look at the AF readings.
Now as to the why on the power reduction: Cat Core temp... By federal law, emmission equipment has to last for 100,000 miles. At the rotary's high exhaust temperature, the cat will destroy itself. (any previous RX-7 owner can tell you cheap cats will be destroyed by the rotary's hot-hot-hot exhaust in a matter of months... causing a neato flaming/shooting of little peices of converter material out the tail pipes... Happend on both my 1st gen (12a) and 2nd gen (13b) )
So there is hope: The engine is able to produce the orig promised HP, at the cost of cat longevity. Or, if anyone know a good chemical engineer with specialization in thermal calalistic reactions, have them see if there is anything they can recommed for a long-life, high-flow cat that can last under the extreme heat of a rotary's exhaust.
And to the Mazda folks who we promised not to reveal the causes( that read this forum), we are simply restating what someone else on the forum has mentioned.
09-19-2003, 12:40 AM
#280
Banned
Thread Starter
Join Date: Jun 2002
Location: Auburn, CA
Posts: 360
Likes: 0
Received 0 Likes
on
0 Posts
RotaryNews/Bern/Mazda:
The HP data from multiple sources seem to coincide with the dyno runs that some of us have done.
What HP are we really putting to the wheels ITRW according to your sources?
Vince
The HP data from multiple sources seem to coincide with the dyno runs that some of us have done.
What HP are we really putting to the wheels ITRW according to your sources?
Vince
09-19-2003, 02:25 AM
#281
Registered
Join Date: Jul 2002
Location: So-Cali
Posts: 809
Likes: 0
Received 0 Likes
on
0 Posts
Re: Re: Off my chest!
Originally posted by jmanolov
Please, now explain why does the car show the same low results when dynoed with GTech Competition? The car is at speed so the problems with safe mode because of standing on dyno machine should be missing.
Please, now explain why does the car show the same low results when dynoed with GTech Competition? The car is at speed so the problems with safe mode because of standing on dyno machine should be missing.
Please read his post at:
SPEED RACER POST
Originally posted by jmanolov
Why does the RX8 show lower hp and tq results compared to other cars of similar horsepower?
Why does the RX8 show lower hp and tq results compared to other cars of similar horsepower?
-Bern
09-19-2003, 09:55 AM
#282
Registered User
Join Date: Aug 2003
Location: Spring
Posts: 42
Likes: 0
Received 0 Likes
on
0 Posts
Since we have a number of experts on this forum, I would like to get an explanation on the Peter Yaw article.
It makes sense to me that you can 'increase' the torque by gearing (half torque with 2x gear is the same). SO, how come the measured torque on the RX8 is so low. If it is being multiplied should it not be higher.
This is a serious question, I do not know the answer, so please don't give me a flame answer.
Thanks
It makes sense to me that you can 'increase' the torque by gearing (half torque with 2x gear is the same). SO, how come the measured torque on the RX8 is so low. If it is being multiplied should it not be higher.
This is a serious question, I do not know the answer, so please don't give me a flame answer.
Thanks
09-19-2003, 02:25 PM
#283
Forum Vendor
You can not "increase torque"
You CAN increase mechanical advantage.
Look at it this way:
With a rope and a 1000 lb weight you can not lift the weight off the ground.
Add 2 pulleys ( called a block and tackle), and when you get a 3:1 mechanical advantage and you CAN lift it. Much more slowly.
If you pull the rope faster you lift it ifaster.
So, strong man who can lift the weight on rope by pulling rope at 1 foot per sec. Lots of "torque"
Wekaer man who pulls rope, thriough two pulleys, with a 2:1 mechanical advantage.
Lifts weight at half speed if pulling same amount of rope.
Double the rate you pull rope, and you keep up with the "strong man"
In both cases the same amount of WORK is done.
Both are making the same HORSEPOWER.
On big V8 we use less pullies, as it is "stronger" ( has more torque) and needs less revs to do the job.
The total job is "horsepower".
Basically revs ( of feet of rope) x torque (strength).
You CAN increase mechanical advantage.
Look at it this way:
With a rope and a 1000 lb weight you can not lift the weight off the ground.
Add 2 pulleys ( called a block and tackle), and when you get a 3:1 mechanical advantage and you CAN lift it. Much more slowly.
If you pull the rope faster you lift it ifaster.
So, strong man who can lift the weight on rope by pulling rope at 1 foot per sec. Lots of "torque"
Wekaer man who pulls rope, thriough two pulleys, with a 2:1 mechanical advantage.
Lifts weight at half speed if pulling same amount of rope.
Double the rate you pull rope, and you keep up with the "strong man"
In both cases the same amount of WORK is done.
Both are making the same HORSEPOWER.
On big V8 we use less pullies, as it is "stronger" ( has more torque) and needs less revs to do the job.
The total job is "horsepower".
Basically revs ( of feet of rope) x torque (strength).
09-19-2003, 05:29 PM
#284
Registered User
Join Date: Aug 2003
Location: Spring
Posts: 42
Likes: 0
Received 0 Likes
on
0 Posts
Below is a quote from Mr. Yaw's article. As you can see, he clearly states that the torque will be higher at the output shaft in first gear than in fourth gear.
So my question is still the same. What is the torque advantage with the RX8 gearing. Does it equal other higher torque cars, come close etc.
And why would the dyno NOT measure this increase. This is what I am trying to get my mind around.
But thanks for the reply Canzoomer.
"If the transmission is in 4th gear, one complete revolution of the input shaft will result in one complete revolution of the output shaft, just as if there were a solid shaft running all the way through. If we attach a 1-ft. lever to the input shaft with a 10-lb. weight on the end, the torque at the input shaft will equal 10 ft.-lbs. as we have already determined. Since we have a 1 to 1 ratio from input to output, we will also have 10 ft.-lbs. at the output shaft.
If we were to keep the same weight and lever on the input shaft, but switch the transmission to third gear, we would still have 10 ft.-lbs. at the input shaft, but we would now have 13.91 ft.-lbs. at the output shaft. This value is the product of the input torque and the gear ratio. (10-ft.-lbs. times 1.391 gear ratio equals 13.91 ft.-lbs.) If we were to switch the transmission into 1st gear, the result would be 34.83 ft.-lbs. at the output shaft.
As you can see, a gearbox gives us a simple way to vary the torque through leverage, and it is equivalent to changing the length of the lever. Thanks to gears, we can have any amount of torque that we want! In fact, a bone stock 12A making only 100 ft.-lbs. of torque could be geared to pull an 18-wheeler up a steep hill, as long as we are not in any big hurry to get the job done."
So my question is still the same. What is the torque advantage with the RX8 gearing. Does it equal other higher torque cars, come close etc.
And why would the dyno NOT measure this increase. This is what I am trying to get my mind around.
But thanks for the reply Canzoomer.
"If the transmission is in 4th gear, one complete revolution of the input shaft will result in one complete revolution of the output shaft, just as if there were a solid shaft running all the way through. If we attach a 1-ft. lever to the input shaft with a 10-lb. weight on the end, the torque at the input shaft will equal 10 ft.-lbs. as we have already determined. Since we have a 1 to 1 ratio from input to output, we will also have 10 ft.-lbs. at the output shaft.
If we were to keep the same weight and lever on the input shaft, but switch the transmission to third gear, we would still have 10 ft.-lbs. at the input shaft, but we would now have 13.91 ft.-lbs. at the output shaft. This value is the product of the input torque and the gear ratio. (10-ft.-lbs. times 1.391 gear ratio equals 13.91 ft.-lbs.) If we were to switch the transmission into 1st gear, the result would be 34.83 ft.-lbs. at the output shaft.
As you can see, a gearbox gives us a simple way to vary the torque through leverage, and it is equivalent to changing the length of the lever. Thanks to gears, we can have any amount of torque that we want! In fact, a bone stock 12A making only 100 ft.-lbs. of torque could be geared to pull an 18-wheeler up a steep hill, as long as we are not in any big hurry to get the job done."
09-20-2003, 12:33 AM
#285
Forum Vendor
The dyno measures torque TIMES rpm.
This is power.
Torque, times motion, equals work performed.
You can reduce gear the output to make more torque.
The input speed in rpm is the same, but the output speed is REDUCED.
Again, speed times torque equals work performed.
There is no such thing as a free lunch.
You can pull more , but more slowly, through gear reduction, or pull less, but faster with less reduction, and even less more quickly, by gear multiplication.
In the case of your car, in 1st gear it reduces the ratio, and in 6th it actually increses it, so is basically an overdrive gear.
This is power.
Torque, times motion, equals work performed.
You can reduce gear the output to make more torque.
The input speed in rpm is the same, but the output speed is REDUCED.
Again, speed times torque equals work performed.
There is no such thing as a free lunch.
You can pull more , but more slowly, through gear reduction, or pull less, but faster with less reduction, and even less more quickly, by gear multiplication.
In the case of your car, in 1st gear it reduces the ratio, and in 6th it actually increses it, so is basically an overdrive gear.
Thread
Thread Starter
Forum
Replies
Last Post
Jst4fun
RX-8 Parts For Sale/Wanted
18
04-17-2021 07:43 AM
