PaulFitzwarryne

There have been many threads about the best way to get power and the cost-effectiveness of individual improvements such as air filters.

What has been missing is data on what performance you can expect from improvements in power. Also there is a lack of what it will cost to acheive that power. Whether its worth while is another question!

I have collected as much data as possible from road tests and attempted to build a mathematical model which provides useful information. The performance results do have a degree of error according to eather and state of tune when the road tests were conducted. It would be great to have a week on a dyno continually adding improvements to the same car along with an addding machine to ssee how far the budget had gone!

Thus for a gen 1 12a engined RX-7 car

power bhp 0-60 secs 1/4 mile secs stage

100 9.5 17.0 0
125 8.6 16.3 1
150 7.8 15.7 2
175 7.1 15.2 3
200 6.5 14.8 4
225 5.9 14.4 5
250 5.5 14.0 6

From 200bhp upwards the cars are no longer stock with major changes to weight, tyres and suspension which make comparison difficult

Now what are requirements and order of magnitude in costs to achieve these. The stages are my arbitary choice to explain the levels of improvements and the associated costs.

stage improvements cost $ per bhp

1 +25 header and exhaust system 500-800 25

2 +50 carb modified/high performance 300-600
free flow air filter 50-100
fuel pump 7 regulator 125-150
Total 475-850 30

These two stages can be done on an existing car where the engine/gearbox is in good condition, plus minor improvements such as cold air box and flowed inlet manifold. Thus total cost of bringing up to 150 bhp is $900 to $1600
plus the cost of suspension modifications which could be another $1,000. See Mike Ancas book on RX-7 performance in particular lessons 1-6 before you go any further!

If you decide further performance is needed and your credit card is available the necessary step is an engine build costing up to $3,000.
If your engine is on its last revolution then you would have to pay any way!
3 +75 street port 300-500
tyres and wheels 1,000-2000
Total 1.300-2500 70

4 +100 large steet or bridge port 400-600
body work 1,000- 1,500
suspension 600- 700
Total 2,000--2,800 90

Thus to get a streetworthy 12a with a reliable 200 bhp you are looking at $5,000 to $8,000.

5 +125 fuel injection 1,500-4,000

6 +150 turbo 1,500-2,500

From here your performance is a matter of budget with lighrt rotors, dowelling etc. Plus remember its not only the cost of improvement but you are loosing reliability with a much reduced engine life.

In summary I think the data up to about 180 bhp is reasonable to make an informed decision. if you are at the $30 a bhp level, is that $400 gimmick the best way to go. Of course their are people who value appearance before performance so if you want to go for the upmarket and spoiler earlier at least it will make the car look faster to the girls. After all a hole in the muffler adds at least 20mph to its appearance!

I would be grateful for any comment, as this area is one of subjective opinion and I have learnt from previous comment from RX-7 owners.

I own a 1984 convertible, its impractical but when the sun is out, the flowers are growing, and there is no traffic, who cares.

peejay

I think your power to 1/4mi estimates are a little off.

My Series 1 did 15.1 at 90, and would have been in the 14's with a better launch (excuses excuses ) but it only made about 130 flywheel HP. Of course the car itself only weighed 2210lb (about 1000kg). I suspect you're assuming a later 1st-gen with all the luxury options.

I calculated that it would take 250hp to make a mildly lightened Series 3 go enough into the 12's to justifiably call it a 12-second car. (I don't count 12.999 as in the 12's) This was assuming a weight of 2300lb without driver, 2500 with.

rx7passion

i think your turbo numbers are off. a stock turbo around stock psi will get you into 13s and its not going to cost 1500-2500. the only way its going to cost to you that is the nessescary pieces to make it work which i can understand, but if your talking just about the turbo itself a 1500 turbo is going to make you car alot faster an 14.0. i base this off the fact that steve84gs on mazspeed ran 13's with a bone stock 13bt and 88 turbo with 12a drivetrain setup for california emmisions.

PaulFitzwarryne

PEEJAY thanks for your comment. Your time of 15.1 on 130 bhp is better than I predicted. I have a lot of stock GSL-SE runs with a quoted 135 bhp in the range 15.9-16.5 seconds. They are approximately 300 lb than your 12a. On reflection I agree that the 250 bhp prediction is slow. A R2 with 255bhp goes through the 1/4 mile in 14.0-14.3 seconds. It is around 500 lbs heavier but a better CD. Thus a lightened Series 3 could have a target of about 13.5 seconds not 14.0 as I gave.

RX PASSION thanks for the information, as given above I now think 13.5 seconds is nearer the average time for a modified 12a with 250 at the flywheel. You quote for a 13b which I think may be marginally quicker as the powercurve is better lower down. You did not give the output figures but a stock Turbo II goes through the 1/4 in 14.8-15.3. With high boost the engine will give better top end acceleration. As far as costs go, I used total costs. If you went to a tuning shop. Obviously do it yourself is much cheaper especially on the engine rebuild. At the top end I think they are low as I have heard horrifying dyno costs to get the last little bit of power. Pinaapple Racing gave good advice, use the road times as your dyno!

There is an American radio program we get in Australia called Prarie Companion. It always ends with, in out town all the children are above average intelligence. Sometimes I think our track times are like that, we only remember the rare fast times!

As comments comes in I will modify the performance data as necessary.
One problem I am finding is that many tuning shop dynos are somewhat optimistic.

rx7passion

well yes there stock time is 14.5 to 15.2 but that is in a 2800lb car a first gen weighs a good amount less. ok i agree with your costs then since you stated your talking about total cost not just initial cost.

PaulFitzwarryne

RX7 passion. Further data.

Other than one off modifications I have data on a range of Gen 2 turbos. depending on the model and country. Power varied from 182-200bhp, weight 2850-2990lbs and the 1/4 mile in 14.9-15.2. one Japehese source gives the Anfini III with 215bhp having a 1/4 time of 14.6 seconds.

What I am lacking are official statistics on the 12at performance other than 165bhp torque 166@4000rpm. I tried to get one recently but they are now a collectors item in Japan

As a matter of interest there was little difference in weight between the GSL SE and the lightest Gen 2 with the same !3b which was only 2662lbs. Its official performance was less perhaps because of lead in the Japenese test drivers shoe.

The UK model was the lightest Series 3 12a and put out 110 bhp due to the lower pollution controls. A series Turbo version of it produced 205bhp in street trim and it could do 0-60 in 6.2 seconds and the 1/4 mile in 14.7 seconds. From memory it did not have an intercooler.

PaulFitzwarryne

There was some concern that my estimates for a a Gen 1 car were too low, this particularily applied to the more modified cars. My prediction based on factual data was for example with 225hp the 0-60 time would be 5.9 seconds and the 1/4 mile time 14.4.

It was interesting that another thread posted yesterday gave similar data from the April 1982 issue of Motor Trend. The magazine conducted a full road test on a modified 1982 GSL which weighed 2455 lbs and whose engine produced 221hp@6500rpm and 197 torque at 4000.

The performance figures were 5.91 seconds to 60 mph, and 14.62 for the 1/4 mile, almost identical to my predictions based on other tests.

The magazine article had full comprehensive results for the dyno, speeds to 100 mph, passing speeds and braking times. The results are a good yardstick to measure your prtformance.

Out of interest the modifications which produced 221 hp included

transplanting in a 13b from an old RX4
adding a turbo with 12b boost
changing the carb to one with 400cfm
mild steet port
aluminum flywheel

The overall result was a great street car. light weight and powerful.
That was in 1982!

jr69187

what about a supercharged 12a Me and sterling are competing to see who will get this done first. But this may end up beign a real cheap add on. If you are a junk yard dog like me and him. I have yet to figure the bhp +++ but if some one here had a good street port 12 a i could tell you. I am waiting to street port my 12a in the next few months. when it is ported i will put the intake and charger on and then we will see some numbers. But expect to break over the 250 mark easily.

theNeanderthol

iTrader: (1)

Hey PeeJay thats an awesome time for 130hp! What did you do to lighten it? I have an '85 with a stockport 12A, RB header, 2 1/4 straight pipe from the header back (used only to race), cold air intake, and soon to have a carter 7psi pump with holley regulator, and a either a holley 650cfm carb, or a rebuilt slightly modified nikki. That should produce at least 130 hp, right? My friend has a 300zx turbo that is running low 15's and i want to beat him. Now I just need to lighten my car a little.

theNeanderthol

iTrader: (1)

any guesstimates on my horsepower/quarter mile time? ( see above post) any thoughts on how to lighten it?

theNeanderthol

iTrader: (1)

come on guys!

RXcetera

Mid 15's. Low 15's with the Holley.

mar3

iTrader: (8)

If it's stockport, the Holley 650 is too big for the engine. It'll have to idle at 1500 RPM to stay running and the engine will never draw enough air to utilize that carb's potential. Back pedal to a Holley in the 400-500 CFM range. Even with that exhaust system, your stock ports are the flow killers, so 500 CFM may even be too high for your current application. Oh, lordey, another person going to try the Carter. Hopefully, your car will be a strip-only vehicle with that noisey curmudgeon...

RX7145

iTrader: (1)

Also understand that PeeJay is VERY good at Drag Racing. Not just any body could get that with his car.

theNeanderthol

iTrader: (1)

do you think if i jetted the holley correctly it could work? I a going to rebuild it anyway I could always do some modifications. I am also going to attempt to modify a Nikki. maybe that will work better. And i was also thinking of getting the holley blue fuel pump instead. is it just as noisey? I am hoping to do better than Fitzwarryne's predictions. I wanna beat that 300zx turbo.

REVHED

Hey Paul F, you might be interested to know that hp numbers quoted by the Americans are generally alot higher (about 20%) than ours because of the type of dyno they use. ie Dynojet. Over here we mainly use the Dyno Dynamics system which is a much more advanced dyno but also calculates torque/horsepower differently. Point is, don't start comparing power figures too much or you'll end confusing yourself.

FuLLsMoKe

While on the subject of horses... How do you breed yours--just kidding.

OK. This has been a mystery to me, I've heard too many different things... What the hell is HP a measure of?! I know that 550 ft-lbs/sec is 1 horse power. And torque is just ft-lbs. A friend of mine says that HP is the measure of the power of the explosion that pushes the rotor/piston. Someone else told me that HP is calculated after the torque is found... I have other explanations but those just sound wrong (I think they were trying to act smart...).

And another thing--WHP is the measure of HP from the wheels and BHP is braking horse power. What does BHP measure?

Thanx

REVHED

Fullsmoke, tell your friend that he's full of ****. Torque is the work or the twisting force being produced at the flywheel/wheels while horsepower is a calculation of the rate at which that work is being done. In other words it is a function of torque and rpm. The formula for horsepower is hp = torque x rpm / 5250 The number at the end is a conversion factor to bring it to the right units. BTW, when you put a car on the dyno it is actually measuring the torque being produced. It then uses that forumula to give you a horsepower figure.

Felix Wankel

This is why you see the hp and torque curves always cross at 5250 rpm.

Yes, peejay is very good at dragging. He would have been in the 14's had he not bogged the car a slight bit at the launch on the 15.1 run

Need more clutch slip man

FuLLsMoKe

I see... I see... My friend was full of ****
When he told me that it's the measure of the explosion, i thought "how the **** would they measure that? run the engine for one cycle and then drop it into a giant *** calorimeter? wtf?"
Hehe, now I know

PaulFitzwarryne

Thanks REVHED. I agree the American numbers are different from the traditional Australian. I use the US figores for hp and $s as most of the Forum thinks that way. To an Australian audience I would use Kw and Nm of torque.

Thus, the vehicle I just road tested did the 0-100kph in 4.85 secons and the 400 metres in 12.95 seconds with 230Kw and 395Nm in street trim.

The reason for quoting the 12a power was simple. Most people want to achieve a given performance, how much power will they need to get there subject to a few minor points, what are the modifications needed to do it at minimum cost? If the budget will not stand it now, what is the best way to stage it for later additional modification.

Some people just like tinkering with their car. For the amont of money they spend it would be better to buy a Gen 2 or 3. But for some people its the fun of doing it themselves. I bought a turbo Capri for my daughter to drive to high school. She knows how to put in the fuel, and thats all. The critical thing for her is its easy to park and blondes look better in open cars. I get my joy from an RX7, I can tune it but dont have time or skill to rebuild the engine. My pleasure is jumping in it and stirring the gears enjoyably for 10-12 hours. Its a great start to the week on a Monday morning!

SOLORX7

Don't know if it helps my 84 turns 13.5's with about 225 h.p. with a 1/2 bridge port holly setup on a 74 13-b 4 port, car weighs 2494 lbs. with me and 3/4 tank of gas onboard . Used 225/50/14 toyo proxes r coumpounds on the rear to get it to hook up.

Sterling

I believe the more experienced tinkerers and race engine/sytem builders have the ability to look at a proposed set-up and say, "Well, that'll get you doing the quarter in 'x' seconds...". But rarely until proded do they volunteer HP guestimates.
And I don't think it's because of their experience in having seen most every concievable set-up before, but rather the experience they have - almost an intuition - for the ability to "match up" the engines they are familiar with to the appropriate intake mods and gearing to produce results for a specific application.
But the first questions home car modders and newbies alike share, is, "How many HP will this particular set-up make my car have?".
I myself ask this often...It's the need for us all to quantify the amount of money, time, and sweat we're proposing to put into our cars- in something other than dollars. But truth is, the best that even the best of us can ever do is "ball-park" the results of a pecific HP number combined with wieght, ect.
I'm willing to bet that if I track down 20 people on this forum, all with the same weight cars having the same HP number attached to their engines...all other conditions the same (gearing, tire diameter, ect), I would get only "ball-parkish" proximity for their quarter mile times.
Some would be way out there - on either end of the average.

See, there are so many variables involved, that there's just no way I'll be convinced that the same car...a daily driver, was dynoed @ 200 HP last week, with no changes in tuning made, will dyno @ exactly 200 next week!
The variables are too many to start listing. Just start with everything that makes your engine happy (or unhappy!)...air cleaner, fuel filter, fuel, plugs, oil temperature (and thus thickness) in the engine, transmission, and gearbox; did the fan turn on? Are your tires even one mm less in diameter due to pressure or worn tread? What's the temperature? What's the humidity? Are the wheel bearings warm?
When they dyno the car, is cool air being administered to your cold air intake box?
Yaddayaddayadda...

And out on the track...
Conditions have to be perfect every time for the driver and his car to pull off the same Q times on every run.
Anybody personally know anybody that routinely does that? Does anybody here do that? Out of the "Yes"es to that question, how many do not race regularly?
My point is that, whether top fulers, or first get Rx-7s, the pros are like golfers...Athletes of skill and repetition. They are driving cars that are not street cars, and so have not changed their characteristics since the last time they raced. And they react faster than the car reacts to them...They have to because they have to anticipate exactly how the car will behave in any given drag situation...cold, hot, humid, greasy track, ect.

My whole point here is that you can go ahead and build that 251 HP engine because you wanted to break the "250" mark (Like me...I would like to do that!), but don't expect your quarter mile times to reflect near what the guy on Speedvision is doing with his 250 HP 2300 pound car!

...There are too many variables, and the biggest one for most of us is ourselves!

This is certainly not to say, "Don't bother quantifying anticipated power.", or, "Don't bother with dynos and tracks."; but just to remind everybody that if you're tooling around in your daily driver, that car is gonna change with every condition you can think of when you start spliting seconds into hundredths.

Quantify, but don't bother pulling out your own hair in order to split one.

...Just a green penny I threw in the pot.

PaulFitzwarryne

STERLING has a very good point. There were over 800,000 RXs built of which 471,009 were Gen 1 cars. I would suggest around 450.000 of the Gen 1 cars, were never modified. Based on Forum members tjhey may be less than 2,000 which were seriously modified.

For the 10% of cars with some form of improvement the greater majority have never done a timed 1/4 mile and always think in terms of getting a higher hp and a feeling it goes faster. For the keen RX7 owner, improving the 1/4 time time becomes an addiction.

In sailing they have an expression, if you want to feel what offshore racing is like, go under a cold shower and rip up $100 notes! Car, racing can feel the same stuffing $100 notes into the air intake.

As the starter of this thread my intention was to get a simple table bringing together power, speed and cost, The reason was to meet the large number of requests from people, usually with their first RX7,
If I fit a header what will be the difference and what will it cost?
What is the cheapest way to get 25 hp?
What power will I get from a streetport and what will it cost?

I fully agree that 1/4 times will vary for a whole range of reasons, In the days I raced Lotus we ofteh got better results on the dyno for a tuning change, wheeled it out on the track and got slower lap times!

Many experts[?] do not like to give hp because it is relatively easy to check, slower than expected 1/4 times they usually claim are the fault of the driver, track or weather.{or any combination you like to pick]. Some experts such as Peter Yaw are totally committed to getting good dyno results. Those results can be out marginally, for example much tuning was done on a RX-7 for the Bathurst race in Australia. Unfortunately the Japanese tuners did not take account of the height of the track abovesea level.

In summary what I was trying to do was get realistic information to use as a starting point before making a decision. There will always be disagreements on which brand of carb to use, while certain drivers naturally have a very heavy foot!

theNeanderthol

iTrader: (1)

Thanks for gathering the info. I know it has helped me with a few decisions about my 7. Keep us updated!