Starting A 331 Stroker The First Time

ajoyce76 · Mar 5, 2016

Hi folks, okay I have a 331 stroker engine that is just about done. It's a weird combination because i've had to change direction a couple of times. Okay I have a 96 Explorer engine that has had a 331 stroker kit installed. Gt40 heads and intake and a Comp cams xe270 cam along with supporting valve train components. It's going in a 94 Mustang GT convertible. If I try to start it the first time with stock injectors and tune will it run super lean and destroy itself? Should I install 30lb or 40lb injectors with a corresponding MAF? Will that get me to where I can get it tuned better somewhere else (i'm in North Dakota now but i'm headed home to Indiana in a couple of weeks)? Any suggestions? Thanks.

90sickfox · Mar 5, 2016

The 94s are a little picky. A friend of mine runs 30lb injectors in a 331 with a calibrated pro M MAF but he's also in a 91. I was going to run 30lbs in my 331 but now I'm going for that turbo/jackstand look. I wouldn't run 19lb injectors on your set up but I'm no where close to the smartest guy here.

Gearbanger 101 · Mar 6, 2016

Starting, running and driving it with the stock injectors will be fine. Your combination isn't that wild that it's going to instantly self destruct the engine. If anything is going to make the engine run a little "loopy", it might be the cam.....but the comp 270 should pull plenty of vacuum to keep the computer happy.

To answer your questing "no" the stock 19's aren't enough injector to feed your new engine, but as long as you aren't pulling any prolonged WOT pulls, they'll get you by until you can get a new set in there. They might run just a tad lean down low, but that's nothing a $75 adjustable fuel pressure regulator and an additional 5psi or so of fuel pressure won't fix. Don't just guess though. Spend $200 on a decent wide band like an innovate, or PLX (like I run) and know for sure.

I'll assume you plan on keeping it n/a? When you finally do get around to having it tuned and changing injectors, go with a set of 30lb/hr and call it a day. Anything less is a waste of money and a thing more, while it won't hurt anything is unnecessary.

Do not, I repeat DO NOT waste your time with calibrated MAF meters. They only "fool" the ECU into thinking it's running the correct injector in there during WOT pulls but are still innaccurate and irratic the rest of the time. You'll never get it to idle as smoothly, or drive as nicely with a calibrated meter, as you would had you just pony' up fur a proper tune. Spend the money and have your ECU reprogrammed. Your stock 70mm MAF unit will flow more than enough air for that engine combination, so take whatever you planned on spending on an aftermarket meter and put it towards your tune.

FWIW, I run a similar (all be it slightly more aggressive) set up in my fox body with 30lb injectors and calibrated meter and it ran like crap. I finally wised up and installed a moates quarterhorse to tune this thing properly and it's already running better.

jozsefsz · Mar 6, 2016

Bumping your fuel pressure as a temporary measure is a good suggestion. Plus it's cheap, certainly if you already have an AFPR. Going from 302->331 I used this calculator (https://www.rceng.com/technical.aspx) and determine you'd want to bump about 8psi (from 39 to 47) for the car to run with about the same AFR's on the 19's you have now.

As to the calibrated MAF, if you're already planning to upgrade the MAF and injectors (the injectors you should, though the stock MAF is tough to peg with a naturally aspirated combo), picking a calibrated one is just fine. Whether it's calibrated or not is meaningless when you have it tuned -- at that point only the MAF's transfer function is important, and provided it can handle the flow rates you want, it will work fine. Don't know why Gearbanger hates on the calibrated MAF's so much. I understand that a calibrated MAF (WITHOUT A TUNE) is a trick on the ECU, and it leaves power on the table, but the hardware itself is perfectly fine. It's an easy and effective way to get the car running with the hardware you want, at least to get to the tuner. You really don't have anything to lose by giving it a try, if it runs good then you can confidently drive it to have it tuned. If it doesn't, those are parts you'd want to upgrade anyways and then have the tune. I agree with Gearbanger, a Wideband is a nice add, though not entirely necessary if you don't plan to tune yourself.

But, you will want to get tuned at some point, certainly before you do any real romping. The calibrated MAF may or may not give you a decent idle or good top-end performance. There are other parameters that need to be adjusted in the tune when you increase injector size that the calibrated MAF cannot trick it into adjusting -- things that will cause hot-start problems and a decrease in overall power.

EDIT: Note, even if you upgrade to a calibrated MAF, you'll want to do the fuel-pressure trick. It's going to be calibrated to your new injectors running on a 302. You'd be just as lean as if you left the 19's and didn't bump the fuel pressure.

Gearbanger 101 · Mar 6, 2016

jozsefsz said:
Don't know why Gearbanger hates on the calibrated MAF's so much. I understand that a calibrated MAF (WITHOUT A TUNE) is a trick on the ECU, and it leaves power on the table, but the hardware itself is perfectly fine. It's an easy and effective way to get the car running with the hardware you want, at least to get to the tuner. You really don't have anything to lose by giving it a try, if it runs good then you can confidently drive it to have it tuned. If it doesn't, those are parts you'd want to upgrade anyways and then have the tune.

I hate on calibrated MAF meters because they're a half asses solution. They've always been advertised to give the buyer the false impression that regardless of the engine modifications, all that is needed to do for the car to run ideal after an injector swap is just match it to a "magically calibrated" MAF meter and you can call it a day.

On a very basic bolt on car, with minimal changes this might be the case, but when you start adding decent cylinder heads, displacement, a healthy camshaft profile along with a free flowing inlet and outlet, that calibrated meter becomes a paper weight. While the car might technically be drviable with one, all out performance and drivabilty suffers greatly. Inputting the correct transfer functions, injector slopes, injector break point, dashpot settings, ISC, spark, dialing in your idle, etc all need to be addressed at the ECU end. And even this can only be done with a meter that's electronically calibrated like a Pro-M or the like. You'll be in even worse shape with something that uses sample tubes to calibrate the meter.

I just see them as kind of a waste on an OBD 1 car. I don't know how many guys have modded their cars over the years, then added calibrated meters to try to tie everything together, only to end up with sub bar drivabilty and performance. Quite honestly, it can down right turn a person off to even wanting to drive the car (I know it did for me). I would never consider a build, if I hadn't budgeted for a proper ECU tune to go along with it.

Heck, if it were a cheaper option and knowing what I know now, I'd do away with MAF altogether if I could. With today's tuning hardware/software, you can tune a speed density every bit as well, or better than a MAF car. For the life of me, I don't know why '86-'88 guys ever bother with the conversion. The money would be better spend on a Moates or Anderson PMS or for those with more exotic combinations, a PiMP, Megasquirt or AEM set up IMO.

90sickfox · Mar 6, 2016

+1 for moates quarter horse. Pro M has a good reputation for MAF sensors. If you get one from them pay the extra for the transfer function sheet. It helps with tuning. The guy to answer about all of this is willy lynch at dirtydirtyracing.com. great folks to deal with. People here have tons of experience, too. Its solid advice to tell you to get the car tuned or at least purchase a base tune from someone reputable, like willy lynch .

madspeed · Mar 6, 2016

Willie did the tuning via email on my old turbo'd 89 using a Moates Quarterhorse, highly recommended

jozsefsz · Mar 6, 2016

Gearbanger 101 said:
I hate on calibrated MAF meters because they're a half asses solution.

I agree that in-and-of itself, a calibrated MAF is not equivalent to a tune, and in my experience also doesn't get you far enough to have good driveability and performance -- I like you imagine this depends on the extent of your modifications. I likewise tuned my '95 turbo with a Quarterhorse and Binary Editor. I'm simply suggesting it's not the fault of the meter -- a good quality meter like a PRO-M is a high-flow meter (mine pegs 5V at over double the flow rate of the stock meter) that just so happens to be calibrated to your injector size.

Why is this a good idea? It's nice to have the car run to some degree without a tune applied -- especially if you have to get it to a tuner and don't plan on doing it yourself. Also, when that battery in the Quarterhorse drops dead 5 years from now (mine did in 5 years after a few winters), or if the board itself eventually dies like all electronics do (mine did after about 7 years losing the tune every few weeks), I like the idea of being able to drive home without having to run 15psi of fuel pressure. To that end, I actually wrote my 'final' tune to a non-battery-backed chip. This isn't a scenario you encounter every day, but if you're picking up a meter, may as well have it 'calibrated' to your injectors for this reason. As long as it's a good meter (like PRO-M) and has a transfer sheet with it. But yes, be prepared to tune in some fashion.

Personally I've never tuned speed density, so I can't say anything there. There are areas in my tune (like idle) where I command open loop because it runs better than the MAF tried to tell it to via fuel trims. For some really exotic combos, I've known a few guys to tune the whole thing open loop, effectively killing the MAF and learning altogether. The partial, strategic disablement may be a good compromise to chucking the MAF altogether.

Starting A 331 Stroker The First Time

ajoyce76

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90sickfox

Wasn't a pretty sight...and I've got big hands

Gearbanger 101

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jozsefsz

Gearbanger 101

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90sickfox

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madspeed

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jozsefsz

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