I have been hearing people regurgitate this 3 mod rule for years. Some who legitimately believe it, and those who have just heard it and disseminated the info to others. But is it true?

Before someone posts to ask what it is, it generally says: You should not make any more than two of the initial bolt-on mods (intake, dowpipe, midpipe, catback) without upgrading your ecu. This is to ensure that you don't run lean with the addition of extra air, and not enough fuel do to the stock ecu's limitations.

I currently am running a 3inch downpipe, resonated midpipe, HKS CF/Ti Hiper catback, Pettit intake, street-ported motor w/3mm seals and a STOCK ecu. I am using simple needle valves to keep boost at 10psi.

Watching my Autometer Air/Fuel ratio monitor, at WOT it is always deep into the green. Now there are those who are going to say that Autometer makes horribly inaccurate gauges, and there will be some that say that the A/F ratio monitor's inability to show enough detail is not enough to ensure you are not leaning-out up top. I'll agree that the gauge does not show enough detail to distinguish between sufficiently rich, and barely rich enough. So let's not pay any attention to the gauge.

How about the rearview mirror? At WOT in 1st, 2nd, 3rd and 4th gear runs there is "cloud" of unburned fuel pouring out of the exhaust, with no hint of let-up until you shift at 8000 rpms. This would suggest there is PLENTY of fuel to avoid a potentially hazardous lean condition.

If anyone can find fault with this, please post. And I apologize for the length of this, but I'd like to give another view on this whole 3 Mod rule, which seems to have become gospel around here.

 

We've seen too many posts on this forum about blown engines not to be wary about pushing our luck. Even though your engine may be running rich today, the margin of safety can sometimes narrow suddenly.....it's a 45 degree day, you unknowningly got some bad gas and now your fuel filter is partially clogged, and suddenly you've got detonation and a big engine bill.

 

luck. thats all that is. you would be the only foo who can do that. I did not do all my mods in the right order and I cooked a motor.

its up to you...risk it if you want...its your six thousand dollars for a rebuild...if its working then its working...who knows if you are getting minor detonation that would add up to a lot of heat damage on the seals or not....write us again in six months.

99 percent of the cars out there wont handle that mod setup without doing the ecu. the stock ecu is a piece of crap. Even the stock upgrades have their weaknesses in my opinion. I wont run anything but the power fc or the haltech now that i paid my dues. (two motors in two years)

from my personal minimal experience Id say to do the basic mods in the below order... (only had the car as a daily driver and track rocket for the past three years...I know some of the boys been doin this a lot longer)

1 reliability mods...hoses...AST...ties....turbo timer...boost guage..etc..
2cooling system. (heat killed two motors of mine)
3 dp and catback and intake
4 ecu and boost control and fuel system
5intercooler etc...
6great tires as those crap kumhos that have been getting you by just wont cut it at this point.
7 keep going..haha..as your car will never be fast enough...if you are at all like me.

my mistake was doing the cooling system last...Ive done everything up to this point but need to go with the upgraded radiator and intercooler by the time my motor is broken in next month. Im not getting on it til I do.

just say no to lawn ornaments.


jason

 

Unfortunately, I believe that a majority of the blown engines we hear about are due to poor tuning or just plain carelessness. As far as ambient temperature goes, if you don't adjust your boost accordingly, that falls within the careless category. And as far as bad gas goes, it would affect a car with a richly tuned PFC or chip no less than a car with a sufficiently rich stock ECU.

I'm just saying that if people are responsible and careful with what they do, a stand-alone ECU is not required for such basic mods.

 

i have MP,DP,intake,catback,smIC,boost controller to keep the spikes to 10 psi. ran the car with that setup for a year. i recently just got the pettit ecu and the ast when i found out about this forum.
when i look back, i think i was really lucky my engine didnt blow, it has 60000 miles and the compression is still good.

 

On a side note, you can tell if you got a bad tank of gas with the PFC in that your knock numbers would be higher than what you're used to seeing. Then you can go in and retard the timing, or go buy some octane booster to add to the fuel to bring it up some and again watch the knock sensor reading to see if its to high. With the stock ecu, you can't do that.

Tim Benton

 

I'd refer you to MAx Cooper's website and his fuel computations. The stock ecu is set up for about 11 psi, with corresponding fuel and timing curves with the stock setting of roughly 10 psi. As Max clearly points out, our cars are set up with the speed/density system which can't tell that the flow through the system has been greatly improved with the porting, dp, mp, catback, intake, IC, etc. So the car sucking in and flowing a lot more air, but the ecu thinks its still 10 psi and uses the stock maps and timing. Eventually your engines going to go POOF with the stock ecu in there and all your mods, I'd even wager less than 6 months of normal driving and some high speed sprints. Its just not smart to keep running your car that way. Take out the plugs and check them to see what they look like, creamy brown color? half white/brown, black. Post that info and its also another way to tell if your running rich or lean.

Tim Benton
8 plus years of owning my FD, 6+ modified with various power adding items.