do I need a tune if...
 

Will I need a tune if I install a tpis intake manifold and 24lbs injectors to a stock 91 L98?

Probably wouldn't run perfect. I'd wait till I have headers and just do a dyno tune. Depends on how finicky you are. If you are like me, I'd do it all at once, get the tune and go with it. I'd find the facility to dyno tune instead of "guess a tune" unless they do fine tune with datalogs.

My thoughts as well

I want to know if I'll run into big problems? Or until I can get it to a tuner.

Probably won't run perfectly smooth. Might trip a code or two. I know my Superram and Headers on the F-body tripped a code till I got it down to LPE and then the throttle response was better too.

Mini ram or big mouth TPI? The ECM maybe able to deal with it. If you other mods planned in the immediate future you may be able to wait. If it's all you are doing its worth considering a tune to optimize what you have.

To maximize your ability to run w/o a tune for any given period of time, install injectors the same size and as close to the same characteristics as stock. I don't know what stock 91 injector size is. However, I do know that my 89 batch fire ECM has the ability to deliver fuel at much greater rates (than injector size would imply) via double-fire mode. If this feature remained until sequential fire started in 1996, you don't need larger injectors. And, a change in injector size creates the much bigger percentage chance of needing a tune.

That said, many would argue stock engines could benefit from a tune. IDK. What I DO know is most people overthink the need for more fuel and more air when making minor mods...(i.e., injectors, air box, and/or throttle body requirements). It's NOT overthinking it, to assume you need new injectors -- if they are still stock. AND, that OEM replacements may gouge you....meaning I'd rather buy aftermarket -- with a tune -- vs $100 per injector! LOL

Full disclosure: I'm unaware of current injector costs but would still assume FIC is the top referral for C4 fueling needs.

https://cimg5.ibsrv.net/gimg/www.cor...1daaf709c8.jpg

This is what I bought. just a tpis manifold too fit my stock runners. And 24 lbs injectors.
Stock is 22lbs injectors. I didn't think that would make a big problem.
I have original stock injectors. 27 years old now.
I will get a tune. It takes time. I was just curious on opinions about the hit in performance I will take until I get a tune.

I don't think you will need a tune yet, since your still running TPI

Ran some Bosch 24 lbs on a stock 89 with catback and ported intake with no tune it behaved just fine & passed emissions.
http://www.wongsperformance.com/

TJ is a member here hes done a few for me came out great, honest guy who knows his craft.
There are a few old timers here that have been doing it forever that may chime in. Its like learning another language, never had patience for it.

Is he fine tuning the program with data logs or just "this is my guess at what it needs"?

You probably can get away without a tune, A 24 lb injector is 9% larger then stock and assuming your car was running with little fuel correction the ECM has the ability to correct up to 15% before it can not correct for the additional fueling at cruise. At WOT it may be too rich but it should work, A tune would maximize your combination but is probably not required.

Doesn't look like a TPIS Big Mouth base, so not sure what you really have there. A polished stock base maybe?

Before changing anything, log some data on your current combination to see the fuel trim behavior under various conditions, idle, part throttle cruising and WOT.

You may already benefit from a tune as-is due to today's fuel differences (Likely E10) and your actual fuel pressure. Also wouldn't hurt to positively ID those injectors since modern injectors may have significantly different offsets and may be undersized (rated at 4 bar instead of 3 bar?). Hard to predict how they will really behave.

I would plan on some tuning to be safe, but try and figure out what you have first.

I'm with you tequilaboy. Doesn't look like an aftermarket intake....though nicely polished. Just because it's got a TPIS EGR plate, doesn't mean the lower intake isn't stock. Aftermarket bases look a bit different. Let's see the tubes.

Also, measure the diameter of the openings. Obviously, it could be ported OEM, but stock tubing I.D. runs about 1.45", IIRC. TPIS tubes (including the base openings) are in the 1.65"-1.7" range.

For my edification (and possibly the OP's), is the [15%] ability to correct the same for MAF and SD cars? I always thought MAF cars have more flexibility for modification than 90-91 SD cars. Since MAF provides the 15% mentioned, what were posters talking about when referring to less flexibility on SD (e.g., 90-91) engines?

Copy that thank you

A MAF car actually measures the amount of air entering the engine and then bases the 15% fuel correction on that information. So it is capable of handling more modifications since it is measuring the actual amount of air the engine is using. The SD car has its fuel correction based on the base tune programmed in the chip if the engine is modified enough to require more then a 15% change in fueling the computer will not be able to adjust for the changes.

https://cimg2.ibsrv.net/gimg/www.cor...cbcc434503.jpg
https://cimg0.ibsrv.net/gimg/www.cor...4905b98dd2.jpg
https://cimg4.ibsrv.net/gimg/www.cor...e1a88ae7a8.jpg

Opinions?
These look ported to me.

Here is what a TPIS "Big Mouth" intake looks like:
https://www.thirdgen.org/forums/atta...p-p1010895.jpg



Notice, how the top is flat where yours has "tube humps". On TPIS (and other large-tube) TPI intakes, the top contour is the same as the TPIS pic shown above. Back in the day, it was proposed that the aftermarket LOWER bases may have all been made by Accel or Edelbrock. Even if not, the OEM intake is the ONLY lower base with the appearance of the one you pictured.....meaning it's the only one where the tube humps are visible from the top. Hopefully, others will confirm to provide you some level of confidence in my feedback.

There is very mild porting visible on the head side of your polished intake. It's definitely not "professional", nor is it significant. By that, I mean it's not enough to affect overall performance. Unless there's more that visible in your pics, you won't feel any difference compared to your current OEM intake. It will just look better.

For a bit of comparison, I'll show you how I ported my Edelbrock (basically the same as TPIS) for my 383.....
https://cimg8.ibsrv.net/gimg/www.cor...eeb5847709.jpg


Here is the bottom where you can see I ground so far I actuallly broke into one of the injector bungs (luckily I didn't break through anywhere else! :D) See if you can tell how thoroughly this porting extends throughout the base tubes (compared to what you see in yours). Look at the space between the tube openings.

Keep in mind I'm not a pro, I was just shooting for the max I could get w/o getting extrude honing. Large UPPER tubes and an extruded OEM base were shown to create about the same increase as a Big Mouth base...so you could consider that. Or...have it professionally ported. Here's the bottom of my lower intake...
https://cimg6.ibsrv.net/gimg/www.cor...e2db893870.jpg


I never took a pic next to a ruler so I can't provide that level of reference. But, I'm sure I got the round (upper) holes out to 1.75". The lower openings were gasket matched to a FelPro 1205 gasket which measures 2.09x1.28". If your porting extends more than an inch or so into the tubes, it might be pretty good....though it looks somewhat "superficial" extending only an inch or so into the tubes. Your pics don't expose the inner tubes well enough. What upper tubes do you have?

Thanks for the information.
I agree it does appear that I have a ported stock intake base. I bought this intake hoping it was ported decently, but also I can do whatever I want to it. I'm not going extreme or radical with my l98 build. I'm just using slightly larger 24 pound injectors and a decent porting on the intake. I have stock Runners and stock plenum.
What are the feelings out there? Should I go more extreme porting to feel a difference in the car? Or can the mild improvements I'm doing give me a slight bump and performance?
I like the way the car drives now stock.
my personal feelings is I don't want to go too Extreme with Frankenstein builds.

How much do you want to spend?