how much boost and what fuel mods?
 

Hi guys recently had my car mapped again after fixing a turbo problem (stock twins). Car came back from mapping at 292rwhp at 6100rpm (0.8 bar boost,, alll bolt on mods). Tunner said that injector duty is reaching 90% and i shouldnt puch car over 6000rpm. He said i need to look at fuel upgrades and there should easy be another 30/40 hp in there.
Right fuel upgrades i need a walpro 255lt pump, but what else i didnt want to get a crap idle by putting some secondary 850cc in the primary slot. So i need some bigger secondaries ,what are my options??

Also i wanted to know what boost can be run on stock twins theres many opinions my tunner said i wouldnt run over 0.9 bar but i reallyi wanted to run 1 bar (tunner said turbos really dont last long at 1 bar). Can people chime in with any info,, i cant beleive im reaching 90% injector rate with 0.8 bar boost and bolt ons???

Here's a thread that had a similar discussion a few years ago:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/what-situation-do-you-have-259912/

you can run 1 bar on the stock turbos, it's pushing it tho, I personally wouldn't run higher than 13 lbs, which is about .9 bar (1 bar = 14.7 lbs)
rewire the fuel pump first, 850s in the primary rail, then retune it and see where you're at.

i ran 14psi.. 356whp... 255 walbro fp and stock inj but @ 100% inj duty tho......... from my understanding its okay to run it that high its just you're running the risk if one gets stuck then pop..

inj wise ur options are...
550/850
850x4
550/1300
850/1300
550/1600 (what i decide to get)
850/1600
every option besides stock will be enough for you to support atleast 400whp

If you push the stock turbos that far they will fail. Its not if it will fail it is how much time can you get out of them. This usually leads to an upgrade when they fail ( 99 spec, BNR, or Single). If you are going to upgrade you fuel system, why not do it with future upgrades in mind? It will cost a little more but it will be cheaper than doing it twice. I run 550/1680 on a gt35r, at 16psi I see around 75% injector duty.

Not sure what your AFRs are but I'd imagine they're on the rich side to be hitting 90% duties before 6k RPM. FWIW, I use 91 octane fuel, I run stock primaries, 1300 cc secondaries at stock fuel pressure with an upgraded fuel pump. I'm around 300 whp on dynojet (tuned at about 12 psi almost 2 years ago, I've done quite a bit of street tuning since then, haven't dynoed again... but have 112 mph trap speed on 1/4 mile track to hint at the power level) and my duty cycle at 8k RPM is around 80% @ AFR of 10.8-11. Boost is around 93 kPa/ 0.93 Bar (about 13.5 psi). I've been running my car like this for the last year and a half, about 15,000 miles... some track days/autocross at 11 psi and some street boosting. Ask anyone I know I don't baby this thing after the motor is warmed up!

mdpalmer comparing your car with 1300cc's to his car on the stock injectors isn't a fair comparison, I would hope you're only at 80%.

Like I said, rewire the fuel pump (there's a ton of write-ups in the club about this) and add 850 primaries (cheapest route, I picked up a pair of stock secondaries for about 50 bux). There's write-ups on this too.

i didnt really want to go with the 4 x 850cc because i heard you can get a bad idle so i really want to get a walbro 255 and hopefully 1300cc secondaries. Does anyone know where to get these 1300cc secondaries?

Also if i run 1 bar boost on stock twins how long will they last are we talking months or years? im planning going with the knightsports rf420 within the next year.

i have 850 primaries and 1300 secondaries.. my idle is smooooth... :) Thanks to Nelson..

completely hit and miss, your turbos may last through some dyno pulls, or they may function fine for years to come, but the more boost you run, the more likely your turbos are to break, but it won't mater if your motor blows an apex seal.

seriously, don't waste money going with the 1300 secondaries just yet, mill out the stock primary rail, and run 850s. I've also heard of problems with the stock secondaries that have been enlarged, I'm looking for the thread now.

this is what I found about the milled secondaries:
bad spray patterns/atomization or reliability,

buuuut I don't feel like digging around more, you might be able to find another thread about this.

i'm running the stock turbos still. pretty much maxed them out though. pushing 1bar.

currently i'm running the following fuel setup:
* rx7store.net Extreme Fuel System (stock primary injectors, 1600cc secondary injectors)
* Nippondenso "Supra TT" Fuel Pump
* Re-wired fuel pump (10g wires, aftermarket relay)

unfortunately my primary rail is leaking and needs to be replaced. if you're gonna get one of the kits from rx7store, don't bother with the Extreme kit, just go for the Ultimate kit.

anyway, with that fuel setup i dyno'd 380hp on the stock twins (non-seq), but with a ported motor and all the bolt-ons.

sounds about right, that's in line what most people are making on all bolt ons with enough fuel maxing out the stock turbos

Another check point.

I run AFR 11.0 or below at 12-13 psi
Stock (unported) motor, stock twins, and stock injectors
catless, N1 dual, RP modified Denso pump wired directly to the battery

I only hit 100% duty (as logged) at higher boost and very high rpm (like 8,000)

If you have the PFC and access to your map, you can compare your cell values to the calculated available injector on time (rpm dependent). Provided that your cell values do not exceed those limits, you will have no problem.

Available Injector on time [msec/revolution] = 1,000/(rpm/60)
Max injection - not to be exceeded in the map [in msec] = Available Inj on time (as calculated above) divided by the ratio between primary and primary+secondary [exhaustive explanation is in Chuck's notes]

Only if you can't keep your AFR to your target value or feel uncomfortable maxing out the injectors occasionally, then you may want to upgrade injectors, otherwise is not necessary.

- Sandro

I agree, but I wasn't comparing my car to his per se, just providing a data point to help him make a decision, hence the "FWIW" in my prose. Some people have pointed out that going too far over 80% inj duty is *generally* a bad thing and on that basis I set up my car not to go past that limit. I must admit that I've read about some people who run their cars above 80% (some very frequently to 100% if the 'net posts prove truthful) and have not had any problems. My point was to say that I have not had any fuel related problems so far based on my setup and boost level, that's all :)

Fair enough. I know with a full intake, 3" exhaust, FMIC, and efini y-pipe on the stock port with stock injectors and a PFC I see upper 80s on stock boost with very aggressive timing.

I plan on rewiring my fuel pump, getting a walbro, going to 4x850s, and adding meth before I up the boost. I'm also non-sequential, and I dynoed 260 before I worked out the tune, and my timing map was all over the place.

just my $.02 here, but I have heard you want to continue running 550 Primaries to keep your idle smooth with a PFC (others supposedly give you more options to tune this out, but from what I have heard from some local tuners leave the primary rail at 550). Goto the 1600s on the secondary and that will cover you pretty much to a mid single. Fuel pump is a must and KKM states.

Personally I have a Cosmo fuel Pump (a lil better than stock) with the old bored out 850s at 1200cc on my secondary rail. Primaries are still 550s(bought the car that way). I am pushing 13.5 PSI on the stock twins with a 73% duty cycle on average. Under WOT in cool temps I have seen as high as 76 but normally no more than 73%. PFC dyno tuned by Steve Kan @ just above 300 RWHP. I need to retune an can probably get another 25HP out of it.

it's more than possible to smooth out your idle with 850s, a friend of mine is running 850/1600s and his car is EXTREMELY smooth, and besides, a rotary with a lumpy idle just sounds good. :)

Anything past 12psi your going to need a bigger fuel pump, I wouldn't take the twins past a bar (14.7psi) but if you dont mind the short life span they will more then likely have turn the boost up even more. I'm running the Supra TT pump and it works great. As far as injectors go, again after 12psi you will need more fuel (bigger injectors).. I am personally going to go with either 1300cc's or 1600cc's secondary and keep the 550 primary before I re-tune my FD on 14-15 psi, but I will also be running Water/Meth to play it safe. You should maybe look into aux. injection section on the forum if your wanting to max out the twins. Just my 2 cents... Good luck!

Get the supra pump don't bother with the walbro cause a the end, you wil need more power and go with the supra pump any way.
850cc primaries is the cheapest route. No need for fuel rails. I managed 429whp with these injectors. Idle is fine. Just get someone who knows what they are doing.

I managed 350whp @15psi with stock twins. (Streetported) Then made them non-seq and managed to squeenze 361@17psi. Turbos didn't last more than a few months. My recomendation don't pass them from 15psi. There isn't much more hp after that any way,

I would think all you need is an aftermarket fuel pump.

You made 429whp with 4 850's?!

The walbro is good enough for what he needs/wants right now, no reason to spend double on a supra pump.

Yes 429whp with 4x850cc, a supra pump and rewired job. Duty cycle 90 percent. Stock fuel lines and pressure.

Interesting because i was under the impression that the walbro was better than the supra pump. I made a stupid mistake a few months back of buying a supra pump but when it arrived it was different from the standard mazda one i think i got it from a 1997 twin turbo, is there a certain year of car that the supra pump must come off. Can i ask is there any side feed injectors 1300cc or 1600cc that fit straight into the standard rail and where can i get them?

Thinki im gonna stick with the primary 550, tunner said getting car to idle with bigger primarys is a bit of luck, he told me some cars do idle and some dont? strange?

Who is doing your mapping? I'm surprised that the person writing your maps says it's not safe to run your car over 6krpms... seems a bit off to me.

Where about in the UK are you?


iirc 1300cc injectors are really just 850cc injectors which have been bored out, so they will still fit in the stock secondary fuel rail. I'm running 4x 850cc injectors and made 340rwhp at 1.2 bar on a DynoDynamics brand dyno.

fwiw I had my mapping done by Max and Geff at Re:worx in Portsmouth, I'm quiet happy with my results (even though the power figures look smaller then my American brothers..). The pull at that level is just mental, I've easily smoked every TVR which wanted to play on the dual carriageways, walked away from a Ferarri 456M and run even with the 911s..

hi, im in leeds up north .The car was tunned by Pip Gardner at WGT developments. His words were , the car is hitting 90% injector duty at just over 6000rpm your going to need some fuel mods. He said i wouldnt go over 6000 rpm to be on the safe side.

ive read that the bored out 1300cc injectors arent safe and many a engine has been blown with them sticking???

Personally I wouldn't go for 1200 or 1300 bored out injectors. They are expensive for what you get, eventually you will need more fuel and end up selling them, they have a higher failure rate especially if using the 15 year old injectors originally on the car. I've personally had a primary injector just stop working for no known reason, I can't imagine the hassle of that happening to a bored out secondary.

Really for your current goals an aftermarket fuel pump and a rewire will get you where you need to be fuel wise. If you need a little more then get an aftermarket regulator and turn the base pressure up a bit. 550/850 @ 50 PSI base pressure will flow 100cc more then 850/850 @40 psi base.

For my power levels I should be running 850/1680's, but because I'm running dual pumps, 550/1680 and slightly higher base pressure the highest duty cycle I've seen is 80 running 23 psi with a t70 and ported engine.

Ok, if Pip's got you then you're in good hands. I was worried that perhaps you'd run into a boy-racer who claimed to tune... I find it odd that Pip would limit your rpms, vice just turning down the boost a bit in order to make use of your full rpm range.

Have you re-wired your fuel pump? If I remember correctly I was able to run my car at about .85 bar with the stock fuel system, I was hitting HIGH duty cycles though. I only did that for a short time before swapping out the whole fuel system (Bosch 044, Aeromotive FPR, 4x 850's) along with uprated turbos (BNRs), uprated clutch, all kinds of other goodies and upping the boost. I wouldn't want to go much over .85 bar while using the stock fueling..

1300s are generally side feeds that have been modified by rc engineering. side feed 850s can fit into the primary if the rail is milled down (I think 1/8th - search this to double check).


http://www.rceng.com/


the supra pump is from the MKIV. Denso. You should have the correct one if it's from a 1997.


It's about even in my book. supra vs walb. 255lph. I run a walboro but a lot of others run the supra. by the time either of them run out of flow, you'll have to double them both ~ 500whp. There's a special math formula to determine it.

found it.


http://www.banzai-racing.com/how_to/...sion_chart.jpg

there was a calculator somewhere (maybe in the FAQ) that if you inputed your injector sizes and wheel horsepower it would tell you approximate injector duty cycle at base fuel pressure, this also assumed you rewired the stock fuel pump.