Newbie with injector question....42# injector with 40 psi of fuel pressure on a v8 running pump 93 octane will support what HP? with what headroom or safety margin? I know there is a formula some were?

 

google is a wonderful thing.....

http://www.gtsparkplugs.com/InjectorSizeCalc.html

 

I had around 350-375 at the wheels and they were pretty much perfectly within the duty cycle

 

Around 475-490rwhp is what i've seen with a turbo @ (.65 BSFC & 90% duty cycle)
500-525rwhp with a centrifigal supercharger @ (.60BSFC & 90% duty cycle)

Higher HP rating's can been achieved by using a higher base fuel pressure. Increasing the static fuel pressure flow over the injector would ultimately raise the power potential. 550rwhp is not uncommon to see with 42lb/hr injectors on a turbo car.

 

There is something wrong with this post. A centrifigal should make less power with a given amount of fuel than a turbo.

 

It really doesn't matter which it is, its the BSFC that matters. However, I have seen some very good BSFC numbers from a centrifugal supercharger before. I could see a D1SC at low boost on an efficient LS motor have a better BSFC than a tiny TC76 on a similar sized motor. (not sure on the exact BSFC, but purely by going on RWHP numbers).

 

BSFC #'s in "most" cases are always less with a centrifigal set-up vs. the same set-up with a turbo combination. This is just what I've seen from being in the forced induction game for alot of years testing & tuning different combo's. I'm not gunna point any fingers saying who's right and who's wrong. Just giving my 2 cents from experience.

 

made just over 500whp with my 42s but at 100% duty between 5700-6000rpm. 43psi base.

 

If your injectors are seeing 100% duty cycle before 5,500rpm with roughly 500rwhp your MAF is most likely pegged... you may want to look at the flow range of your MAF meter because In most cases your MAF will MAX out before your injectors will with 42's @ 500rwhp. I ran into the same issue but corrected the problem using a larger cal. MAF and still stuck with 42lb injectors... I needed to run either larger 60lb injectors with a 60l/b cal. MAF or I could continue to use 42lb injectors with a 55lb cal. MAF that would provide an extended flow range over my exsisting MAF. At 5,300rpm my MAF was "pegged" after I looked at my data logger sheets and would "hense" shoot the injectors to 100%. I changed the MAF and with a little tuning down lower in the rpm range got the car to around 90% duty cycle on 42lb'ers with atleast 575rwhp on a single turbo 306. Injector's could still support more if the static fuel presssure was raised or I switched to pump gas only which would also cut down on the flow rate (mabey would see 85% duty cycle instead of 90%)

 

Had the car on a mustang dyno on friday. the results was 14 plus psi boost, 357 hp @ 5321 rpm (c4 w/3500 stall converter on 26 x 11.5-15 hoosies quick time's w/ 20 psi) arf #'s were good, @ 11.6, until about 5300 rpm mark...then it was going lean...i think 12.3 - 8? arf, and the hp/torque droped like a rock. the injectors were at 100%, the fuel pressure held at 40 psi.

so, the numbers/results don't seen to add up. the HP seems a little low...the web site i found shows 42# will support 450-500 hp. i thought 14 psi would be more HP...also, folks here are talking the same (450-500) hp #'s for the 42# injectors...confused newbie

 

Perhaps the difference between flywheel and rear wheel HP.

Jess

 

At 14 psi I would think you'd see more rwhp....

 

Also remember dyno is a tool, you've got an auto with decent stall.....run the car at the track and see what you've got before you get fixated on dyno hp #'s.

 

You never have said what motor this is besides a V8 is it a 302 based pushrod or modular ? but i agree the numbers for that boost don't ad up. Maybe a boost leak or converter slipping bad , somethings going on some where .

I run the ford green top 42s in my D/D with a roots supercharger and make around 385 390 and they are in range.

 

Check you MAF voltage during a dyno pull or a pull on the street!!! I'm telling you I bet it's seeing 5 volts right when it goes into a lean spike/ static injector flow situation. Exact same thing happened to me. I was wondering the same thing why my injectors were static (100% DC) and this was happening aroung 500hp at 5,200rpm. Turned out my 3.5 blowthru MAF cal. for 42's could not support the volume of air that was needed. Changed to a 50lb cal. MAF still using 42's and with a little "tweaking" using a PMS-IV... no more lean spike from 5,200-6,000 and duty cycle held steady @ 85% HP numbers are prolly somewhere around 575rwhp still using 42lb'ers.

 

it's a 302 push rod, f303 cam, iron gt 40 heads, 70mm .70 ar turbo...the converter is 3500 stall.

 

my injectors are 100% way before 5000 rpm....i think around 3000. this, I'm told is a Pro M MAF...is this good? need more info on it? what should the voltage look like on the MAF?

 

Your MAF voltage with your set-up should hang around 4.75 vlts max from 5,000 - 6,000rpm. Never should your MAF reach 5 vlts. A 42lb cal. MAF flow sheet is provided below so you can calculate how much lb/min airflow your set-up requires using GARRETT TURBO'S FORMULA ON THERE WEBSITE (your Pro-m flow number's are prolly very close to the flow number's of my MAF) My 306c.i. h/c/i single 70mm @ 10psi requires around 60lb/min of airflow currently... well beyond what my MAF was calibrated for. At 4.65 vlts on the sheet, 51lb/min of air is required & beyond that is when my MAF will "peg" and the car will have a massive lean spike to around 12.5-13.0 AFR from 5,200 - 6,000rpm. What you can do is split a voltage signal wire off your MAF and run it to a volt meter during a little pull on the street. This is a ****** rig way of looking at your MAF's voltage without a datalogger, but would still do the job and it would def. let you know if a MAF recalibration is needed.

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Talked with my dyno guy....the MAF was not pegged, it climbed with rpm's and was 4.5 at 5200 rpm's. he said the tune in the eec which has a mote's chip...it was tuned this way?

he also stated that...at 39 psi, 42# will only support 410 HP.

Thanks all

 

What is the rest of the fuel system ? pump, lines, etc