safe hp level on rb26/good aftermarket injectors to get there??

[drftnrps13]

ok im getting rid of my stock rb26 injectors and looking for a bigger set! im running a stock rb26 with a single turbo conversion power fc d-jetro and a upgraded fuel system. now i wanna make 500hp to the wheels. can this be possiable with a mods listed above? and what injector size should i go with to get there? thanks,paul

[mello88]

720cc to 850cc injectors for <=500whp.

Search my posts and read my reply in the recent thread about fuel pressure. I put some info on injector sizing in there. Or hit up the RC Engineering website, they have a little calculator that should help you out and give you a guideline...

http://www.rceng.com/technical.aspx

[drftnrps13]

yeah i checkd that calculator, im just wondering what company to get the from. i wantd to here what others use?

reguards to the hp level-ive researched and found-400hp - to- 500hp. i just want to make sure the headgasket will be good! i check SAU and they said they get headgaskets from there local auto parts store. slap them on and make 500hp no problem. i hope this oem on holds up!!!!

[WhatsADSM]

RC likes to sell big injectors so their calculator is largely based in theory.. I'll be honest. In real world terms you can easily get away with a smaller injector like a 600cc or something, if that is all you can find.

However since you have the PFC anyways I would say get something in the 700-900 range just to give yourself a bit of head room.

And yes, PROPERLY TUNED, there shouldn't be an issue with the headgasket.

[mello88]

RC likes to sell big injectors so their calculator is largely based in theory.. I'll be honest. In real world terms you can easily get away with a smaller injector like a 600cc or something, if that is all you can find.

Hi, I'd like to know what you base that on? Their math is about the same as I've seen everywhere else I've researched injector sizing... I'm curious how you calculate your BSFC?

Here's another calculator which will give almost identical results.http://www.z31.com/software/injector.pl

[WhatsADSM]

All of the calculators should be about the same. They are calculating fuel pressure and sizing to give an fuel volume then factoring in the BSFC.

I am simply based it on running cars on the dyno and the track. Real world results. If you would like to back calculate the BSFC then it can be done.

Not that I would suggest doing this but case in point was that I had an old RB20 that made like 260some whp on the stock injectors (270cc), before I got some 440s.

[mello88]

I'm sure you can get close to 500whp on 600cc injectors, but what duty cycle will you be at then? Also do you have a link or any info on calculating BSFC... Assuming you know all/most the engine variables AFR, power, injector rate, compressor map, PR, etc. BTW is the .60 to .65 RCEng suggests for a turbo car very accurate? Thanks

[WhatsADSM]

You are correct the IDCs will be very high likely around 90-95% or something, again it depends on the fuel pressure you chose as well.

So really what BSFC is a generic, lumped coefficent that specifies how much fuel you need per horsepower, and in general there are no set numbers but more of a rule of thumb. If you want to calculate the BSFC you plan to run then as mentioned you can use engine specs, VE, and compressor maps, and IC efficiencies to get an idea of your AIR FLOW. Then once you have that you can get an idea of horsepower and depending on your fuel volume (calculated through duty cycle, pressure, size, and # of injectors) then you will get your BSFC. Thats why I am saying in a way it is a very theoretical number, and in most cases you are best off using it as a rule of thumb but tuning to your specific engine.

In general if you are on 93 octane you will want to hang around .65 for an easy safe tune (this is why RC specs it), more aggressive (i.e. if knock and EGT look good) .6 will also work. In fact this is where many of the well tuned turbo cars will run on 93 octane. I have even seen well setup turbo engines go below this on regular pump.

However, if one plans on running a high octane fuel such as C16, lower BSFC can be used due to the knock suppression, slow cool burn, and higher BTUs per volume. Hence you can get even bigger (yet still safe) numbers with the same injectors but very high octane fuel.

So to the OP:Make no mistake, I am NOT condoning get injectors that are very small. I agree you should probably look to get something in the 700ish range just to give yourself a little extra head room.

However to those that are searching and find this thread and are wondering:If you have everything you need to safely monitor your engine you CAN safety get away with 500whp on injectors smaller than 700s, again each setup is different.

[drftnrps13]

ok thanks. i going to run 1000cc injectors since the price is the same as he 750cc. also im adding another fuel pump to the setup. im now running two walbro 255 fuel pumps. also will run the car on c16!!! i wanna make 500wrhp no questions, no problems! more info is greatly appreciated!!! thanks

[mello88]

You are correct the IDCs will be very high likely around 90-95% or something, again it depends on the fuel pressure you chose as well.

So really what BSFC is a generic, lumped coefficent that specifies how much fuel you need per horsepower, and in general there are no set numbers but more of a rule of thumb. If you want to calculate the BSFC you plan to run then as mentioned you can use engine specs, VE, and compressor maps, and IC efficiencies to get an idea of your AIR FLOW. Then once you have that you can get an idea of horsepower and depending on your fuel volume (calculated through duty cycle, pressure, size, and # of injectors) then you will get your BSFC. Thats why I am saying in a way it is a very theoretical number, and in most cases you are best off using it as a rule of thumb but tuning to your specific engine.

In general if you are on 93 octane you will want to hang around .65 for an easy safe tune (this is why RC specs it), more aggressive (i.e. if knock and EGT look good) .6 will also work. In fact this is where many of the well tuned turbo cars will run on 93 octane. I have even seen well setup turbo engines go below this on regular pump.

However, if one plans on running a high octane fuel such as C16, lower BSFC can be used due to the knock suppression, slow cool burn, and higher BTUs per volume. Hence you can get even bigger (yet still safe) numbers with the same injectors but very high octane fuel.

So to the OP:Make no mistake, I am NOT condoning get injectors that are very small. I agree you should probably look to get something in the 700ish range just to give yourself a little extra head room.

However to those that are searching and find this thread and are wondering:If you have everything you need to safely monitor your engine you CAN safety get away with 500whp on injectors smaller than 700s, again each setup is different.

Awesome post, thank you. I kind of knew what brake specific fuel consumption was before but wasn't sure how it was calculated. Sounds like it's largely dependent on AFR and airflow, especially the way you refer to tuning to run a certain BSFC... Could one assume a BSFC of .65 is equivalent to a tuned/12.5 AFR on an RB? And perhaps a stock RB running pig rich 9-10ish AFR would be around .7 BSFC? Thanks again for your info, I wasn't trying to argue with you or anything like that, just interested in BSFC and how it's calculated/relates to injector sizing equation...

[mello88]

ok thanks. i going to run 1000cc injectors since the price is the same as he 750cc. also im adding another fuel pump to the setup. im now running two walbro 255 fuel pumps. also will run the car on c16!!! i wanna make 500wrhp no questions, no problems! more info is greatly appreciated!!! thanks

From what I've read other places you might want to consider running the smaller size due to the atomization at idle and lower speeds being poorer on the larger injectors than the smaller ones. And if you're only going for 500whp and not interested in pushing much past that, I would expect the 7xx's would be a better choice for idle, fuel consumption and tunability/drivability..

I guess I equated it to MAF sizing, running a "too large MAF" with little airflow gets you less granularity/tuning ability than running the next size smaller MAF.... IE if you have to pick between two upgrade MAFs, one you would pull 4v at WOT/8000rpm and the other MAF you'd pull 3.25v from at the same load, the smaller MAF would be a better choice for tuning and driveability since it would report a more accurate # for a given airflow.

WhatsADSM what are your thoughts on going "too large" on injectors or MAF?

[WhatsADSM]

From what I've read other places you might want to consider running the smaller size due to the atomization at idle and lower speeds being poorer on the larger injectors than the smaller ones. And if you're only going for 500whp and not interested in pushing much past that, I would expect the 7xx's would be a better choice for idle, fuel consumption and tunability/drivability..

I guess I equated it to MAF sizing, running a "too large MAF" with little airflow gets you less granularity/tuning ability than running the next size smaller MAF.... IE if you have to pick between two upgrade MAFs, one you would pull 4v at WOT/8000rpm and the other MAF you'd pull 3.25v from at the same load, the smaller MAF would be a better choice for tuning and driveability since it would report a more accurate # for a given airflow.

WhatsADSM what are your thoughts on going "too large" on injectors or MAF?

You are 100% correct.

In general the larger the injectors the more difficult it will be to control... especially at low loads such as off idle or a low speed cruise (Imagine using a fire hose to fill up a 5 gallon bucket).. and just as you mentioned, you will be loosing effective resolution. Also as you mentioned they will typically atomize a little worse than their smaller counterparts... so you likely will experience a little worse fuel economy.

To the OP, unless you plan on eventually making like 800ish whp you may want to just run with a smaller injector in the 700-800 range. That way you have a little extra head room without sacrificing the resolution and daily drivability (sp?) more than you need to.

Mello, as for the other question, AFRs and BSFC are not the same but they are loosely tied to each other. AFR is strictly mixture related, while BSFC also includes variables that effect with the efficiency of the engine and setup. But yes you are correct in that if you say have a 12.0 AFR your particular engine may be running with a BSFC of .65 and if you have a 12.5 AFR with all another variables the same your BSFC will be lower maybe in the .6 range (just made up numbers but the concept is true).