Hey Avatar, how big injectors should one need if getting the 264 or 272 cams with the stock turbo? Is the Walbro 255lph pump also a necessity?

Thanks man.

 

Anyone doing the 264/272 cams here?

Chris

 

excuse the ignorance but what is a powerFC?

 

http://www.apexi-usa.com/electronics_fc.asp

 

If you're going to stick with the stock turbo, don't bother with 272's - get the 264's. They make almost the exact same power with the stock unit.

Most seem to like 660cc - 680cc for the stock turbo + 264 or 272 cams. I went with 780cc because i'm plainning on a 60mm turbo in the future, and maybe some nitrous if the money hasn't run out

Yes, get the pump - adequate fuel pressure is always a plus with turbo cars.

 

How does different injectors and different fuel pump prevent fuel cut? And with bigger injectors would duty cycles have to be updated on the ECU?
Sorry if these are dumb questions but this has me pretty confused. I find it odd that cams would need all these change to the fuel system.
Lastly, a question about the head bolts. Why? If I was planning on running stock boost can OEM bolts remain? Or is this just a preventional measurement.

 

I think that even with stock boost presures, bigger cams will give the turbo more time to push extra air/fuel into the cylinders. This means compressing a denser mix of air/fuel and raises the actual presure inside the cylinder.

To the head, it seems like you've increased the compression ratio, even though you haven't. (That's why you upgrade the head bolts) This is where the added power comes from.

One additional question here; would making a spark plug change be a good idea with the cam change?

 

OK. If extra air is being forced into the cyclinders shouldn't some sort of fuel management system be put in place to prevent a lean condition? Even with improved air flow into the cylinders the manifold pressure (what boost gauges measures) will remain the same correct?

I just really want to get a good grasp on all this. I don't like doing a 'mod' that I don't know exactly how it works. With NA cars a cam change was usually no big deal. Slap in the cams, maybe some new valve springs depending on the grind and go!

 

Upsizing the injectors itself doesn't fix the fuel cut issue - the cut occurs because the MAF indicates it is reading too much air. The way piggy backs work, such as the Emanage, when upsizing injectors is done by actually reducing the signal sent from the MAF to the computer. It reduces it to a number that will never trigger fuel cut. I hope this makes sense to you.

 

OK. So you're saying the piggy back says there's less air coming in, so therefore it sends less fuel BUT because it's a bigger injector there's actually more fuel and hopefully it all evens out.

Doesn't seem like a very accurate or efficient way to do it, but if it works, it works.
Can fuel injector size be accounted for in ECU mapping instead of using a piggyback, assuming a tuner takes this challenge on?
Also when fuel cut is issued, is it a decision because the ECU sees too much air or it's just more air than the MAF can handle and it errors out?

 

You're dead right about this! Getting well developed and tested generic maps for your configuration is one approach. The other is to strap your car onto a dyno and have an experienced tuner build a custom map for your car.

The generic maps can usually get you between 85% and 90% of the gain a custom map will; assuming you tune to the same saftey margins. If you' willing to cut the safety margin some, you'll find more power.

I've always found the power vs. performance issue can be really tricky. I've know quite a few street tuners who have blown up engines running what they thought, were told, or read somewhere was a safe tune. Personally, I opt for "positively safe" over the extra few HP - engines are expensive.

 

Oh - I would be hesitant to try to build my own maps for something like this; too many variables, and engies are expensive (wait - I already said that). I'm sure that's why "stage" kits are so popular; all the parts are matched to the tuning map (or settings) supplied with the kit.

 

ive noticed discussion on 264 cams and 272 cams setup , can a combination be used like what was common with dsm;s
264 intake 272 exhaust? or is there no benefit?

Kyle M.

 

You can, but the 264 set is sufficient for stock turbo. For big turbo, 272's will yield more gains and still remain driveable which is a problem on DSM's.
A few things to correct; if you have mods to make more power at the same boost level, the ECU already knows that because you had to suck more air past the MAF to do it even though it's the same boost pressure. The first level of understanding as to why this happens is your basic pV=nRT equation. The second level requires understanding of fluid dynamics and whatnot. Essentially, the boost pressure is nowhere near constant ANYTIME despite how smooth the boost gauge may say. (I hope that doesn't confuse anyone). Your basic understanding, however, is simply that colder air at the same pressure yields more power. The extra atoms of air had to be drawn past the MAF sensor (which is still ingesting air of the same density) so the ECU knows it is flowing more air despite the same manifold relative pressure level. The problem with using a tool that fools the MAF sensor is because the ECU will use additional timing when it sees less MAF at the same rpm and relative pressure level, etc. Thus, using an SAFC can be dangerous in extreme cases because you cannot retard the timing on the top end to reduce some of the unwanted advance associated with -12% fuel, etc.
Also, you cannot "clamp" the voltage of the MAF sensor because it is a Karman based sensor. It reads in cycles per second; not voltage unless I am missing something.
The method of using larger injectors and then reducing the fueling with a piggyback will yield zero change in fueling (if setup properly) and result in the ECU not hitting MAF cut. The byproduct of this is that the ECU is now using a lower part of the timing table (with MAF as a lookup) and yielding more advance (as said before). That is why you should only try big injectors (when simply fixing a MAF overrun problem) with an eManage or something that can control timing or at least offset it somewhat.
The eManage has a great tool to plug in an injector size change which automatically yields a reduction in MAF across the board. Just note that while most ppl say the stock injectors are 550, they are really 560's. Also, because different injectors take different amounts of time to actually open (based on battery voltage) this will come into play when changing injectors. The common piggybacks don't have any way to make a pulsewidth offset (since they are only changing MAF) and therefore your fueling may be a tad off when simply plugging in a change from, say, 560's to 660's. Larger and/or aftermarket injectors usually take longer to open (stock injectors are usually pretty nice design and quick to open) so the same amount of fuel; corrected for injector size) will give you a bit less actual fuel based on the delayed opening of the injectors. Normally this is in tenths of a millisecond but it can make a difference. There are different types of injectors designs as well and that will have as big or bigger effect on the "minimum injector on time" or minimum injector time; MIT. So, just so you know, not all injectors are the same. Some open faster; some spray a better pattern, etc. The stock injectors have four separate openings and I suspect they spray a rather larger pattern for better atomization and lower air flow levels.

Whew, hope that helps someone.... anyone...

Mark
www.Quantum-Racing.com

 

Mark, Excellent explanation. Thank you.