j9fd3s

iTrader: (3)

yeah, i've done about 200 yards of street driving on this tank of gas, i did do 2 track days though, and my FC buddy took 4 tanks to do the same, so on track its 10-12mpg, which is good.

i might get a moving permit and just drive it to an auto-x in the next couple of weeks, so we may find out.

i think your 24mpg will be higher than mine, although my friends carbed 13B BP Rx3 would do 26 on the freeway....

peejay

Running at 100% is the easy part. Drivability is where good tuners make their money, carb or EFI.

Siraniko

iTrader: (13)

Exactly and thats why my cars have no issues being daily driven in which i do on weekends and twice on weekdays but rotary and lead foot equates to poor gas mileage. The only change i have done recently was the switched to 3.7 gears for freeway driving but coming out of dead stop and corners suck. However, i believe i averaged +/-25 mpg when i drove my RX-3 from LA to WHIV in las vegas last May. If i cruised it at 75mph, im sure it would have been higher but im not a cruiser.

peejay

Heh... 4.78s in mine...

Siraniko

iTrader: (13)

I have a 4.78, boring on the freeway

rx7freak13v

that pp with the ida sounded raw as Fawk! however the pp on efi was so tame. it didn't even brap at idle!!!! i bet that thing drives nicely. but i wants some brap

im planning to run 4.78's....just throwing that out there.

i must have misread Peejay, i thought you were saying that the 2nd trans was a shorter ratio then the 1st gen trans.

im not expecting drive ability to be the best, it's a bridge port. it's going to be wild to an extent. however i do actually want to be able to drive it.

Siriniko: i thought the stock 4.10 was too long of a final gear, but yea highway driving isn't the best on it. more less a 4.78. why do you say the 4.78 is boring on the highway? obviously lower top speed but is that the only reason why you say that?

j9fd3s: for the record, i have heard that pp engines are easier to drive on both efi and carb compared to a bridgey. can you explain why that is?

j9fd3s

iTrader: (3)

why do i get the boring question? i've heard that too, my friends bridge would buck unless you were accelerating/decelerating under 4500rpm. mine has an area between 1000-2500rpm where it doesn't buck at constant throttle.

i think if you reduced intake manifold vacuum on the bridge it would probably equal the PP.

if you misadjust the TPS in an FC, that's close to what the bp/pp is like...

peejay

4.78s plus FC trans plus 205/70-15 tires = less RPM in 5th than a stock FB.

I took a quick video while driving but it's not really useful. You can't hear anything but differential and transmission.

rx7freak13v

j9fd3s: lol i didn't think it was a boring question lol. it was more, educational, which i guess in most cases = boring, but not this time. i have had my tps get far out of wack and it would buck, all the time. but not anything that i couldn't handle while delivering pizza haha.

my buddy bought an fc with a holley on it and 30* advanced timing with low compression. it would brap away. the PO said it had a bp but needed to be tuned. once i fingered the intake port i found no porting at all. just really advanced timing and 75psi max compression on both rotors. thing bucks like crazy when not on accel or decel. still tolerable though.

Peejay: i missed the fact that your running 70 tall tires. that's why the rpm in 5th is lower. i was planning to run a 1st gen trans, but i think i will test out the set up on the 2nd gen trans first. then swap it if i feel like it's needed. with the 4.78 rear end, it shouldn't have any trouble spinning up to the power band. i wish your video would have turned out better. i always enjoy good vids with na engines . im assuming that you tuned with alphaN due to a weak vacuum signal. are you using ms2 or ms3? how hard was it to tune with the efi holley?

i appreciate you guys educating me. it's hard to ask questions some times when it isn't all laid out in a thread like this.

peejay

Speed-density, just like every other engine I've run (including the peripheral port). Vacuum signal is plenty strong enough, idles at 60kpa @1100, 50ish KPA @ 1700, cruise at 50-70kpa. MS1, B&G firmware.

8x8 fuel-only map all the way

It will idle at 1100 but that is about the lower limit of the alternator. If I turn the headlights or fan on it pulls the engine down and voltage drops to 12v. Most of the problem is the 3" crank pulley.

j9fd3s

iTrader: (3)

see its fine, its good to be worried, but that car is probably worse.

rx7freak13v

Peejay that's amazing. people i've spoken with have stated that when tuning a bridge port that alhpaN tuning is needed (because of the low vacuum signal the bridgey has) and to up to a ms3 or at least an ms3 board so can tune with a 13x13 fuel and timing maps (which is necessary when tuning with alphaN.) is vacuum strong enough because your using an efi holley or do you think a pair of 50mm itb's would offer a good enough vacuum signal to tune with speed density? did you tap you vacuum port from an intake runner or are you running a plenum on top of that hollley and run you vacuum hose from the plenum?

im planning to run a gilmer pulley set, which i have read on some sites that it will under drive the alt but others say it doesn't. i dunno. i was thinking about upping to a fd alt or even a torus alt but i am not for sure how to prevent over charging. still more research to do on that topic.

i have driven some cars that buck pretty badly. but im okay with it. if i wanted power and no bucking then i would turn towards forced induction and boost lag. but it just isn't what i "WANT". i have a very high tolerance of what im willing to deal with.

i've always wanted to efi a Holley but i havn't figured out the tps yet Peejay beat me to that solution. im still working on it though. if i can figure it out i might go that route. but then again, twin 50mm itb's are proven and other then Peejay i havn't seen anyone else use a efi holley set up

Siraniko

iTrader: (13)

Rx7freak,
With 4.78, like what Peejay said, too much noise from whinning trans and rear end. Its boring as 80mph is pushing it big time and its not a nice sight when toyota corollas are passing you and theres nothing you can do. btw, i was running Fb trans housing with early-90s miata 5speed internals.

j9fd3s

iTrader: (3)

its a little hard to convey how the big port engines can be mechanical chaos AND tame at the same time. once you get over the noise and blowing rags around the shop 20 feet behind the car at idle, it really acts like a stock engine.

one of my friends summed up the tuning part pretty well, the hardware; ports, intake, and exhaust dictate the airflow thru the engine, and all you need to do is supply the fuel. HOW you supply the fuel (alpha-n vs speed density or carb vs EFI) isn't the important part.

peejay

I've never heard that.

rx7freak13v

Peejay, are you really topping out at 80mph on the highways with the 4.78's? (maybe not 80mph but how fast will it push to?) i've "heard" of people still pushing 125+ with 4.78's. 5.29's on the other hand won't do much more than 85mph in a toyota 4x4 pickup with a 4.3 vortech with bolt ons (my buddy has this set up). maybe i should stick with like a 4.44?

the blowing things around the shop 20 ft away will really be funny, but im most interested in the nice flat tq curve that it's going to have. and every one agrees that brap brap brap is the best noise in the world (might be just a little opinionated) .

by what i've been explained, tuning with speed density is liking tuning off load, where tuning with alphaN is tuning off the tps. this way the engine doesn't have to be under load to have the same amount of fuel that's needed. however throttle input decides fuel. so when going up hill where with speed density it would mostly correct itself, with alphaN it doesn't. more pedal is required, much like driving a carb. tuning with speed density typically gives a nicer streetable tune where alphaN isn't comfortable in traffic. not sure why. again all of this is what i've read online and have been told with no personal experience.

thoughts on this guys?

j9fd3s

iTrader: (3)

with a 24" tall tire and .825 5th (i'm being lazy)

my 3.90 does 170mph @8000rpm and 60 is @2700rpm

putting a 4.30 in there makes 8000rpm 160mph and 60mph is 3000rpm

going 4.44 is 157mph@8000 and 3050@60

4.78 is 145mph@8000 and 60mph is 3350.

a stock 04-08 Rx8 turns 3000rpm@60...

i should have picked 80mph, but whatever

the brap brap IS the coolest thing, i got mine to idle without the brap brap, and it sucks, might as well be stock....

peejay

No. All stock 12A parts except for the gearing, 5th gear with 4.78 is the same as a stock 4th gear. All 12A cars had top speed in 4th gear. You do the math. (And not all 1st-gens even had 5-speed transmissions, some were 4-speed which is the same trans with a blanking sleeve where 5th goes)

The only problem you run into is that the ~80mph driveshaft resonance happens at around 60-65mph.

With my car, 5th gear is actually taller than stock FB. I'm running through the traps in the 1/4mi at 100mph, and I'm at the top of 3rd. Just like when I used to run shorter tires and stock 3.91/4.08 gearing. (The difference between the two is so miniscule that it makes no difference)

It sounds like a zero sum game, but there are huge benefits to taller tires. For one, they have a lot more thrust grip on dirt compared to shorter tires. And for two, no matter where you are, a shorter final drive means there is less of a tendency to lift the right side tire, so acceleration is better and left and right corners are more similar. (And if you want to be a REAL weenie, like I am, when you install your 3-link, you install the chassis mount a little to the right of the axle mount, which REALLY eliminates axle torque-over. There's formulae to calculate the proper amount, I just went a little offset and figured it was better than making it straight)

rx7freak13v

j9fd3s thank you for that calculation of speed and rpm vs. final drive gear. i thought a 4.78 would do more than 120+ lol. i don't mind the higher rpm in cruising. it's ok. im curious, how tall is a 24" tire? (forgive my stupidity). 145mph at 8k isn't bad at all. i don't really mess around on the freeways or the streets at all really. sometimes when someone is trying to show off and failing at it, but i try not to. i don't think i will reach those speeds on any autocross course muahahahaha.

the important part about a race engine other than reliability and performance is the raw sound you get out of the exhaust. for us it's the almost echoing brap brap we get from high overlap. i would be pissed if my race engine didn't sound like it has high overlap, you should tune it back in man, it's a requirement lol.

Peejay it's interesting that the top speed cars were running 4th gear instead of 5th, which makes 5th more of an overdrive than a speed gear which also makes since.

i understand you use a taller tire since your rallycrossing, but a shorter tire with a shorter final drive should offer a faster trap speed. also, wouldn't the shorter final drive gear still cause you to rev out faster to get you into your power band, even with the larger tires?

and guys please forgive my ignorance, but what is "driveshaft resonance"? i've never heard that term before. and how does using a shorter gear change the effect or speed it occurs at (unless it's all based off rpm which it probably is)?

also, can you give a quick explanation of what axle tq over is? (never heard that phrase either). and now im going to go learn what a 3 link suspension is. i believe that's the full independent (like the fc has) but because im feeling like a total idiot after you guys using you fancy racecar lingo, im going to search it and find out so i can feel accomplished lol.

Sgt.Stinkfist

iTrader: (6)

^A 3/tri-link rear set up is a way to correct the problems brought up by the stock SA/FB rear axle design. Stock, the Rx-7 has a 4 link setup (2 upper and 2 lower control arms), with a watts link and usually a sway bar... putting all those moving/articulating parts together will eventually cause interference or binding under heavy movement/articulation. A 3/tri-link eliminate the the 2 upper arms, located on the far ends of the axle and replaces it with a single, center mounted arm


When it comes to the axle torque, that is an issue of solid drive axles. Think of the axle as a big T shaped tube. When torque is applied through the center "I" of the "T", the legs will twist in relation to the torque input of the the drive shaft, in our case causing the left rear wheel to be pressed more heavily to the ground, while at the same time lifting the right rear wheel off the ground. One of the main redeeming characteristics of a fully independent suspension is the elimination of this trait (one of many)

rx7freak13v

thank you for explaining that , i had tried searching but wasn't understand exactly what i was reading. you explanation is much easier for me to comprehend. so my fc, with full independent rear suspension doesn't have these problems? and it sounds a lot like when using an aggressive lsd such as a 1.5 or 2 way, am i correct?

j9fd3s

iTrader: (3)

the simple way to find out is to just look at the tire MFR's website. hmm i actually screwed up the 225/45/15 Toyo R888 i'm on is 22.8" diameter.

Proxes R888 | Toyo Tires

i'm running 225/45/15 because that way i can use take offs from the race car.

rx7freak13v

hmm i understand why you wen't with witht eh smaller 225/45/r15 tire size. makes a lot of since. i couldn't find a price on those r888 toyo tires. can you clue me in please?

j9fd3s

iTrader: (3)

i went with em cause they were free used, but <b>....TOYO TIRES: ((NEW)) >>> RR, (full slick) RS-1, R-888, RA-1 and R1R, plus the D.O.T. Proxes T.Q. DRAG tires

$177 each

its a good tire if you wanted to do track days, and some street driving, they do work well in the rain. on the track they are 2 seconds slower than the hoosiers, and on the street they will heat cycle out quickly

rx7freak13v

not a bad price. sucks they heat cycle out quickly out it is a competition tire not a normal street tire. so probably mount them on the race rims and keep something else for street use. have you used the R1R's? it says they were originally meant for autocross use but people have been using them for track days. im building for autocross so it might be a better choice for me? any experience?