MAP adjuster

If I stroke my 4.0 will the MAP adjuster that Turbo City sells allow me to adjust it out enough to not knock? Or will I definitely have to run premium gas? I'm trying to save some dough here in the long run.

Well.. I don't know about this since you're trying to save money, but this wizzmo will definitely fix your problem.

www.advancedinjectiontechnologies.com

It's a wideband tuner that can do a lot of things.. one of them is interfacing with your MAP signal to the stock computer and adjusting for optimum air/fuel ratio.

Running high-octane fuel is not so much a matter of fuel metering, it's a matter of compression and quench. Higher octane is a higher resistance to ignition - which means that the fuel is less likely to "pre-ignite" due to the higher compression/higher heat in the chamber. Quench mitigates this somewhat - by setting up a "swirl" in the chamber, and keeping the fuel/air mix from getting "hot spots."

Most stroker recipes seem to be somewhat quench-compliant, but it would take some experimentation on your part to be sure.

While it's true that you could reduce the potential for knocking slightly by running rich, you'll have to run quite a bit rich to effectively bump your fuel up a couple octane points on the scale. This would work by adding more heat capacity to the system (in the form of liquid fuel, which would require additional heat to vapourise.)

Short form - you will probably end up needing some sort of MAP adjuster anyhow, to get your fuel mix right, but I'd want to start with running 89 octane fuel instead of 87, and monitor for knock/ping. If 89 isn't working, then it's time to go with 91. Your MAP adjuster will have minimal effect on knock due to a too-low octane fuel.

5-90

GoliathJeeper said:

If I stroke my 4.0 will the MAP adjuster that Turbo City sells allow me to adjust it out enough to not knock? Or will I definitely have to run premium gas? I'm trying to save some dough here in the long run.

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It'll help a lot if you have the correct injectors to begin with and for '87-'95 based strokers, Ford 24lb'ers are the way to go. You can use the MAP adjuster to fine tune the fuel curve.
You could save a bundle of $$$$ by making your own MAP adjuster instead of buying Turbo City's. All you need is $10 worth of Radio Shack parts and a soldering iron (Turbo City's MAP adjuster costs $95). Making one is easier than you might think:

http://www.angelfire.com/my/fan/MAP_adjuster.html

Making the engine run rich or using colder plugs is not the way to go to reduce knock. All you're going to do is waste gas and you'll fail the emissions test. Build the stroker right the first time and you can run 87 or 89 octane without any knock. Make sure you have a real cold air intake and make sure the cooling system is up to scratch. Insulating the underside of the intake manifold will keep the heat radiated by the exhaust manifold out of the intake and reduce the risk of detonation. Take a look at the pages on my site for some ideas:

http://www.angelfire.com/my/fan/

Just be glad you dont have to run on 85 octane gas like myself.
Detonation isnt really a problem up here at 5800 feet, but I would prefer to run 89 all the time .

Thanks for the info. I knew about how higher octane "works" since my ASE Auto-Tech teacher is constantly harping that into his students (along with other info lol) But I was just looking for a way around using higher octane fuel. Around here emissions is not a problem (yet) and the difference between lower octane fuel and the highest premium is quite a jump. I don't know how it ijs for all you other guys though. Another question I had that I didn't have time to ask earlier (teacher was coming) was is there a computer based program that I can download on my PC that will allow me to manually tune my engine? There are a few guys I have noticed around my town that have this system installed in their tuner cars but I have yet to get ahold of any of them to ask them what company they are using. One of these guys is driving a Neon so at least I know there is one out there for at least ONE Chrysler based vehicle. Thanks again.

Those guys have a stand alone fuel system, it's not just a program they downloaded and than plugged there laptop into the car. That's rediculous to have that on a neon anyways (unless it was an SRT-4, than I could see it). Any money you would save drowning your pistons in fuel in order to stop pinging because you aren't running high enough octane would be negated by your sh!ty gas milage. Just make sure you build your stroker with the proper quench so this whole thing isn't an issue.

I keep hearing about quench, but didn't know what it was, so I looked it up and found this informative article:

http://www.chevyhiperformance.com/techarticles/94138/

So now, I have a new question... what shape is our piston & combustion chamber in the 4.0?

That's not a bad article - I'm saving it for future reference.

The piston chamber (stock) for us is "D" shaped, with the "D" being under the combustion chamber in the head. As I recall, the AMC242 is very nearly "quench-compliant" as it is - the difference will be, as mentioned in the article, the production tolerances. This can be reduced somewhat when building an individual engine, instead of knocking them out by the thousand.

Do remember that quench isn't just a function of piston dish/head shape, it also has to do with compressed gasket thickness (the largest element of the piston-head clearance formula) and with the shape of the piston relative to the combustion chamber in the head. If you reverse the piston, you'll screw up your quench - for instance.

The idea of "quench" is to prevent "stale" areas in the chamber airflow, and to create a "reversion effect" as the piston approaches TDC - which effectively increases the heat capacity of the system and allows the use of lower-octane fuel (sorry, I lapsed into thermodynamics. I'm an "engineer-in-training...") We are very nearly quench compliant - the principal issue is that the addition of compressed gasket thickness and piston/deck clearance ends up with rather too large a number for true "quench compliance" - .040-.050" being close to ideal.

Another idea I'm working on for fuel mapping/metering would be the adaptation of the GM V6 HEI/DIS control system to the AMC242 - which would really open up ideas. I'd also like to play with the MegaSquirt by Bowling & Grippo - but that would require two dedicated run-stand engines, and I don't have the space for that right now. Maybe later...

5-90

XJHummerRescue said:

Just be glad you dont have to run on 85 octane gas like myself.
Detonation isnt really a problem up here at 5800 feet, but I would prefer to run 89 all the time .

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At high elevations, 85 octane isn't a problem because cylinder pressures are much lower and detonation is unlikely. You won't find that grade of gas in the USA at sea level though.