turbo-minivan

sorry this is a bit long of a question, but please read....

so i have a street ported, 6 port motor with a custom intake, and a 500cfm edelbrock carburetor, T2 5 speed trany, in a 1250 lb car. hard to describe... see pics below.






i have a wideband o2 sensor and have the carb tuned in very well. as far as i read, a stock 86 rx7 was rated to be capable of doing around 125MPH.
in theory, this ported motor (170hp??) in this weight of car, should be in the realm of a mid 11 to low 12 second 1/4 mile car, and should easily be able to exceed that 125mph top speed.
so heres my issue... its fun and peppy from light to light, but when i get it on the highway, it has a hard time getting past 75mph in 4th, and will NOT go faster than about 83mph in 5th gear. it accelerates gradually in 4th, but as soon as i shift to 5th, it feels like driving a toyota echo. just completely falls on its face for power, and will in fact LOOSE speed slowly in 5th gear.
in 4th gear (1:1 ratio), at 60mph, my tach is showing me about 6000rpm, when in theory, it should be showing around 3000rpm. (right?)
-my rear end gears are 3.78:1
-my tires are 28" tall
-my air/fuel ratios are a very nice and consistent at 12-12.5 all the way through the entire RPM range
-the clutch is not old or slipping
-my tach is set to a 2 pulse pick up, reading off the - wire of the trailing coil (as a 2 rotor should be in theory), and i have compared its readings to a digital timing light off the #1 leading plug (as well as all other plug wires), and both the tach and timing light read the exact same RPM.
-distributor timing off the L1 plug is set right on the yellow timing mark on the front pulley
-the 2 vacuum timing advances on the distributor are hooked up to the same vacuum hose and run to the carb from throttle vacuum (not constant vacuum).

i am STUMPED!!!

my theory's have been,
-a lack of air or fuel at WOT, but even at wide open throttle as the power peaks/dies off, the wide-band reads a flawless 12 to 12.5 A/F ratio, so this tells me that its not choking for air or fuel (otherwise it would show very rich, needing more air, or very lean needing more fuel). ive run it with, and without the air cleaner to see if the restriction made a difference. it did not.
-im wondering if my tach is right. my thinking is, if the tach is reading double the actual rpm, then im basically short shifting every gear which is constantly keeping me BELOW the power band and thus its not able to accelerate past 80-83mph. (example, my tach is telling me the motor is revving at 7000rpm, so i shift, when maybe its only at 3500rpm). but yet the tach set to a 2 pulse pick up setting, perfectly matches the reading off a digital timing light on the #1L plug. so how can that plug pulse lie, unless its pulsing twice per revolution for some reason?? but how could it? as far as the tach readings go, it doesn't even feel like its making power until the tach is showing 7000. so is that actually 3500???

if it is revving only half as high as the tach is telling me, and im basically always driving it well under the power curve, its hard for me to tell by the sound of the revs, because i have no other concept of what a rotary should sound like at different RPM levels as this is my first rotary.

i stopped at an RX7 specialty shop the other day to ask about it and he noticed that my distributor is turned 180*. in my thinking though (and theirs), this shouldn't matter as long as all my timing marks are lines up properly (which they are). this simply just puts the vacuum diaphragms facing forward rather than back. the internal workings should still be in time and advance properly..... OR DOES THIS HAVE ME FIRING MY TRAILING PLUS WHERE IT SHOULD BE FIRING MY LEADING??
they did say though that a good ignition is key to making top end power. he also said to get some nicer MSD coils, but there's no way one coil over another is going to suddenly gain me my missing 50MPH.

so does my issue lie some where in my ignition and my seemingly high tach readings???


ill start i guess by doubtfully turning my distributor around on Monday, but what are your thoughts on this lack of power?? iv owned cars in this kind of power/speed capable range before (11 and 12 second cars) and this feels only about 1/2 of what those could do, even from light to light, not to mention my highway speed issues. help me make this the death rocket that it should be!

lduley

iTrader: (1)

when your at 60mph in 4th, does it sound like 6K? the sound should be obvious, if your at 6K at 60 in 4th, I think your rear gear isn't as low as you think it is

Cause in my 7, 60 in 4th is around 3-4K

that and what trans are you using?

turbo-minivan

the rear gears are absolutely 3.78:1. (for the issue to be in the rear gears, they would need to be crazy low like 6:1)
the trany is a typical 86 T2 trany, so the same gear ratios as most every rx7 ever made.

the sound of the RPM is what i dont know. ive never worked with a rotary or worked around rotarys, so i dont have an ear for what 3000rpm sounds like compared to 7000rpm. ive tried looking on youtube to compare the sounds, but the only videos i can find are quick blips to redline on cars with full exhaust. mine has wide open pipes 16" long... so its LOUD, and hard to compare to vids on youtube.
ill post a vid of the exhaust sound and you guys can listen and see what you think.

turbo-minivan

in this quick video, im in 5th gear and my tach was reading about 5000rpm, and i was going a speed of 65mph. obviously it blows the flames when i let off the throttle for a moment, but the majority of the vid was telling me 5000rpm. does it sound like 5000??

turbo-minivan

in this vid, the tach is reading 6000rpm from the 26 second mark, to about the 50 second mark.
this is in 4th gear doing about 55mph. does this sound like 6000rpm?

j9fd3s

iTrader: (3)

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with a 28" tall tire, 3.78 diff, it says 2770rpm @60mph in 4th...

with the distributor, the tach is just run from the negative side of one of the coils, like any other car, and the tach should be set to the same as a 4 cylinder.

turbo-minivan

^ exactly. ive done the calculators and come up with all the same info, and the tach is set up exactly as you stated. so why the huge misleading power/rpm?
my tach is reading around 6000rpm in 4th gear at 60mph. almost exactly double what it 'should' be.
im worried to push it super hard (past 8000rpm of what my tach reads) in case the tach IS right and i break apex seals. although it DOES seem to have more power to give past 7000-8000rpm. im just worried to push it further, just in case.
what is your opinion on my videos judging the rpm by ear??

anyone out there have a good video or sound clip? or willing to make one of what 60mph revs sound like in 4th gear? or even just film the tach and sound as you rev the car through each 1000rpm range? (preferably with a loud exhaust)

j9fd3s

iTrader: (3)

the first one sounds like 2500rpm or so.

turbo-minivan

and what would you say about my second vid? im assuming 7000rpm is out right SCREAMING and should be throwing constant glowing flames out my short pipes...?

j9fd3s

iTrader: (3)

second one is hard to say

turbo-minivan

i guess tonight ill put it on jacks and get the crank spinning in 4th gear and put a laser tach on it. that will be the only way to be sure of the RPM

turbo-minivan

ok, so i put it on jack stands and put a laser tack to the crank shaft in 4th gear. i was right. its ACTUAL RPM is exactly half of what the tach is saying. so im basically just under revving the car.... which is why its only acting half as fast as it should be. basically ive been driving it like a girl.
strangely though, when i put the digital timing light on it again though, even the timing lights tach reading is saying the RPM is double, same as the dash tach. so this must mean that the coils are pulsing twice as often as they should be. what would cause this????

i have a positive+ power signal to the coils, and the coils respective grounds go to the their respective Ignitor, and the tach signal wire is pulling its signal from the trailing coils ground wire.

could i maybe have my ignitors wired backwards?? or would it even run if i had them backwards?
the car runs fine, other than this tack and ignition signal that is being doubled for some reason

misterstyx69

iTrader: (142)

I read this real quick so I'll toss this out there.
set the tach to 6 Cylinder.

turbo-minivan

^ tried that. the tach goes all wacky.... as it would on a 3 pulse.

an easy solution would be to just live with the ignition pulsing twice as often as it needs to (as its doing now) and set the tack to V8 mode, but for some reason my tach is all messed up in the 4 pulse V8 mode. plus id rather fix the real issue rather than mask it with the tach setting.

any more thoughts as to why my ignition system is firing/pulsing twice as much as it should be??

BLUE TII

iTrader: (9)

I know nothing about RX-7 distributors, so forgive me if I am way off the mark.

When I look at an RX-7 distributor's rotor I see two contacts on the bottom and four contacts on top.

This leads me to believe the Leading plugs are fired off the top circuit and are wasted spark and the trailing coils are fired off the bottom as I know they cannot fire off wasted spark.

Problem 1) RPM Discrepancy.
Sounds to me like you have your tach connected to the Leading coil instead of the Trailing coil.

Problem 2) Lack of power.
Your rotor cap is 180 degrees off.
Lack of Trailing spark as well as RPM discrepancy?
Looking at the distributor cap it looks to me like the Leading coil contact is in the center of the rotor like a standard distributor, but the Trailing coil contact is off to the side.
If you rotate the distributor cap 180 degrees does the Trailing coil contact line up with a contact for the Point Breaker? Can't see why the factory would put a contact 180 degrees out on the Points.

Basics-
L1 and T1 are the front rotor
L2 and T2 are the rear rotor
T(railing) = Top
L(eading)= Lower.

Oh god the new rotary will F with me on Trailing and Leading...

FührerTüner

iTrader: (5)

Yo,

Probably not your problem but ill give it a shot.

IF you are getting your tach signal from the Trailing coil,

AND you have the toggle wire and the trigger wire switched,

you WILL see double RPMS.

Just throwing that out there. Easy check.

turbo-minivan

^ explain "toggle" wire, and "trigger" wire. i AM getting my tach signal from the trailing coils negative terminal but not sure what you mean by toggle vs. trigger wire.


the lack of power is absolutely because i have a tach reading double what it should be and ive been driving and shifting it SUPER early.... acting like its a gutless POS.

now its a matter of getting the ignition signal right so the tack is working right.

a friend and i were tossing around the idea of the wires that lead from the coils to the ignitors needing to be shielded as not to mix signals or cause electrical 'noise' with one another. i separated these wires from each other as they were all loomed together and gave them a good amount of space from each other (6") hoping this could be the issue..... still the same double ignition/double RPM reading.

turbo-minivan

i have double checked that my wiring to the coils and to the ignitors is correct, and it all seems to be. im getting even more stumped!!!!!!!

here is exactly how my coils and ignitors are wired, with my tach signal spliced in from the trailing coils negative wire... image my wiring pulled from this link...
https://www.rx7club.com/1st-generati...wiring-935875/

Jeff20B

iTrader: (13)

Set tach to 4 cyl, and remove a little metal from your donkey door. A few ounces.

FührerTüner

iTrader: (5)

For the leading coil, L1 and L2 both fire at the same time. The trailing coil uses a toggle. It toggles back and forth from T1 to T2. There's four wires that go to the trailing coil. Two are hot, one is a "toggle" wire (which choses T1 or T2 to fire), and one is a "trigger" wire (the wire that actually fires the coil).

If you wire them backwards, the tach will see twice the amount of fires per revolution, causing rpms to double.

A tell tale sign of this, on the stock fc tach anyway, is a bouncy tach needle.

FührerTüner

iTrader: (5)

Wait what coils are you using?

Hey man I'm trippin. I didn't know you were using 12a ****. My bad.

turbo-minivan

^ yes, all my ignition is 12a stuff. very basic, thats why im so confused

FührerTüner

iTrader: (5)

Do you have the tach spliced in on both negative wires on the coils? Maybe try only connecting it to 1?

turbo-minivan

The tach signal is only being pulled from the trailing coil signal. It is 100% garenteed that Both coils are firing twice as often as they should be as my tach signal (set to 4 cyl mode) is picking up twice the pulses, and my didgital timing light that has tach readout, is telling me the same RPM as the tach. So the couls are firing twice as often as they should be, and mt plugs are all firing twice as often as they should be.

FührerTüner

iTrader: (5)

And youre using a distributer?

What are you using to control the ignition?