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"It doesn't make 200lb-ft of torque until 3,600rpm"
it is interesting to me that you look at that. when i want to get an initial understanding about the "curve" i look at the RPM where the motor first makes 200 rwhp.
i also have an excel file of 87 dyno runs corrected to SAE with power between 5000 and 7500 at 500 intervals. each of the 5 power prints is totaled and the highest total wins the race.
I calculate the total thrust of a vehicle by taking the torque at 500rpm increments and multiply it by the gear ratios, final drive ratio, tire size, and then plot the total thrust for each gear over speed. This essentially gives you a scaled torque curve for each gear, which makes for a great visual to easily see the area under the curve and determine ideal shift points for various Dyno sheets, gear ratios, final drive ratios, tire sizes, etc...
Over the years I've gravitated towards using 200lb-ft of torque as a threshold for 3.0L and smaller engines, especially when it comes to turbo response for the street and track. Knowing what rpm a setup makes 200lb-ft gives me a good idea of the transient response of a turbo and what rpm there will be minimal transient lag, usually somewhere around 750-1,000rpm higher than that crossover point.
I probably have just as many if not more Dyno runs and calculations, but mostly for NSXs. I'm now starting to play with RX7 calculations since I got an FD and am building it.
However, it was too laggy on the street ported FC due to the less exhaust volume from the engine turning a larger and heavier turbine wheel.
Youtube...
You cant judge a turbo by a travesty of a set-up.
A turbo engine performance is regulated by the whole system/engine peripherals.
Think of the pressure ratio at the compressor outlet (not post IC intake manifold) the poor turbo is trying to push. That is the cause of most the lag.
if one were to have pre and post turbo pressures on the compressor AND turbine side, it basically tells you what you need to do for more power or less lag or whatever the goal is
Met up with a mate to get the rx7 weighed/corner weights checked.
Mazda HQ?!
Full fat wet weight at 1231 kgs, this settled to 1230 kgs after a few mins! The BWG was off but i had a 7kgs pc680 battery put in the boot in addition to my optima red top to make up. Not that the wings weighs 7kgs!
With me in the drivers seat and a full tank of fuel it weighed in at 1312 kgs. The weight distribution was fairly good as it was. If i was doing serious track days I would change the balance and get the front left tweaked a touch. However, for the dragy runs im happy with a full tank of fuel a little big of weight is on the rear wheels which helps the dragy times and overall traction. Plus accelerating will push weight further backwards and keep it there. Overall happy with this.
I tried testing recently at high boost (18psi+) and there is way too much salt on the roads, meaning no traction as i found out the hard way. 2nd gear foot flat and the rear snapped instantly around 30*. I'll need to wait a bit longer before conditions are safe enough to test.
Floors are never level and can vary by over 1%. When measuring cross weights you need to have adjustable pads and level them with a laser.
Based on the unknown flatness of your floor, you have 1.2% cross. If this is accurate, you should lower the RF & LR or raise the LF & RR about half a turn each to make it more even.
I used stacks of sheetmetal under the scales, a long piece of rectangle stock and a level when I set my scales up.
You should also put ziplock bags with a bit of dish soap in them on top of each scale so the side to side tire stiction doesnt cause suspension binding (like how they unlock the floating pads for an alignment).
I used stacks of sheetmetal under the scales, a long piece of rectangle stock and a level when I set my scales up.
You should also put ziplock bags with a bit of dish soap in them on top of each scale so the side to side tire stiction doesnt cause suspension binding (like how they unlock the floating pads for an alignment).
Nice idea on the ziplock bags. However, sheetmetal does not balance and flatten out each individual scale pad like pad levelers. While using a level is better than nothing, it's not helpful when you are trying to get cross weight numbers below 1%. For road racing, a 0.2% difference can be felt by advanced drivers and 0.5% can often be felt by many experienced drivers. A laser level is cheap; but the scale pad levelers are pricey but worth it if you are working on getting the last seconds out of a car. But for OP's drag racing use, he's probably fine on the ground unless the car is pulling a little to the right, in which case he can just lower the LR or RF a little until it stops.
The correct tool for the job is always the best option.
I have enough mechanical, tire and driving issues I can work on for the $2,800 that a set of scale leveling pads cost that I will continue to settle for closer to level than my garage floor and free.
If one has access to a shop with the equipment and a technician with the skills, knowledge and the will to use the equipment correctly it can be worth it to pay to get your car dialed in.
Good thing i got mine weighed and corner weights checked for free then . The garage floor was flat or as flat as can be, 1231kgs weighed before and settled at 1230kgs a variation of 0.08% ~ 0.1%. Besides this exercise was to show this isnt a lightweight sub 1000kg or 1100kgs fd stripped/caged rx7.....its a full fat rx7.
Will post some 100-200kph runs soon. Weather is getting better slowly!
Yup that's really how expensive fuel is over here. Can take upto 120usd for a full tank and it's not even E85! Got the fd topped up on 99 octane with zero ethanol content. Increased boost to 18psi and noticed something wasn't right. Took a closer look at the engine bay and found the intake pipe had failed! Turbo was being choked! Luckily caught it early and all is well. Need to get a new intake pipe and filter made up then back to the grind.
Trying to reacquaint myself with the rx7 and getting up to speed with doing 100-200kph runs again. The first thing i noticed was the fear factor...i was letting off too early!
Managed to get 1 run in before it all went pear shaped with the intake pipe failure.
it is great to see you are back in business. it will be interesting when you turn up the boost on your turbo. hwen i first saw the pic of your intake tubing i thought that it was going to collapse, then i looked closer and realised i was a bit late on the thought.
here's my air inlet:
i am road limited so am doing 72 to 100 in 3rd. i look at the log times and am accelerating about 11 mph per second. around 500 hp. for your runs to 200 kph/124 mph... do you finish in 3rd?.
it is great to see you are back in business. it will be interesting when you turn up the boost on your turbo. hwen i first saw the pic of your intake tubing i thought that it was going to collapse, then i looked closer and realised i was a bit late on the thought.
here's my air inlet:
i am road limited so am doing 72 to 100 in 3rd. i look at the log times and am accelerating about 11 mph per second. around 500 hp. for your runs to 200 kph/124 mph... do you finish in 3rd?.
Yup that inlet and filter setup was not great, shocking it managed the 100-200 times its done. I'm looking to get a 4" aluminium or titanium intake pipe made asap and a 10" by 7" kn filter.
Ahh very nice, I like your inlet setup and lim shielding too.
I’d expect low 3rd to high 4th gear with the FD transmission. Starting pretty low in the powerband in 3rd for an open scroll, but probably aids traction over a twin scroll.
Had to go back and look to see what the previous times were, it having been so long. What boost pressure was that run?
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I’d expect low 3rd to high 4th gear with the FD transmission. Starting pretty low in the powerband in 3rd for an open scroll, but probably aids traction over a twin scroll.
Had to go back and look to see what the previous times were, it having been so long. What boost pressure was that run?
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17psi on that run to get used to 100-200 again.
I increased to 18psi for the next run but had the intake pipe failure.
The weathers improving slowly and I've been getting back to testing slowly but surely! A lot warmer which is great for traction but not to great for max power.
I got up to 20psi but the ambient conditions are much warmer than when i tested in the winter so I went no faster than my previous optimized run at less boost. So I'm working on optimizing this tune and will report back. If you're being pedantic dragy verified it went 0.01s faster than my pb for the 100-200 which is inconsequential in the grand scheme of things! Hoping to get up to 22-25psi this/next weekend weather dependent and see what it does in the 100-200. All runs on pump fuel and wi. Not sure what its gonna run but i'll post up results on the dragy be it good or no improvement!
For me the missing piece of data is the lack of egts...so i'm likely gonna have to retire the HKS cast mani and get another more modern mani. I've already for a new 4 barrel intake mani....but also picked up an excessive lim just cus i could. Also got a G40 - 1150 inbound. Not entirely sure of next steps but will get the G35 1050 to max out on the dragy before any setup changes are done.
20psi - 100-200 in 6.57s
The 15psi runs below done just as a base line to get used to the conditions. Still loads of fun and exhilarating in both settings.
Last edited by rx7srbad; May 16, 2023 at 06:20 PM.
please post your fuel injector sizes. i assume since you aren't running the Excessive manifold you are running 2 secondary injectors, correct? i want to calculate your power.
oil pressure only 40 at 7554? seems low to me. should be around 70.
are you running a thermocouple or thermistor for IAT?
the G40-1150 has a 4 inch hotside flange. i have numerous pulls from 72 to 100 (road limited) at 2650 altitude and it is making 530 rwhp off my spring at 15.9 psi.
the turbo manifold is quite important to get right. the HKS is a significant discount due to the mismatched runners. there are no good turbo manifolds on the market and i suggest you make your own.
please post your fuel injector sizes. i assume since you aren't running the Excessive manifold you are running 2 secondary injectors, correct? i want to calculate your power.
oil pressure only 40 at 7554? seems low to me. should be around 70.
are you running a thermocouple or thermistor for IAT?
the G40-1150 has a 4 inch hotside flange. i have numerous pulls from 72 to 100 (road limited) at 2650 altitude and it is making 530 rwhp off my spring at 15.9 psi.
the turbo manifold is quite important to get right. the HKS is a significant discount due to the mismatched runners. there are no good turbo manifolds on the market and i suggest you make your own.
. The garage floor was flat or as flat as can be, 1231kgs weighed before and settled at 1230kgs a variation of 0.08% ~ 0.1%. Besides this exercise was to show this isnt a lightweight sub 1000kg or 1100kgs fd stripped/caged rx7.....its a full fat rx7. 
