Aurora40

The computer will constantly adjust the fuel trims when in open loop regardless. There's nothing wrong or bad about that. It's not like the ECM will burn out sooner due to overuse.

To me the AFPR is like the cheap/simple way of tuning. The better way of course would be to burn a chip, but an AFPR lets you tune the fueling to some degree without a lot of complicated tools.

GREGGPENN

This is not my quote. Someone else might have posted it... Not sure how you got it, Aurora40... did you combine text that I was responding to with my UserID? (In fact, with what I know about the ECM, I would agree with your statement!)

Gregg

UPDATE: I went back and found the quote. I did include it in one of my posts (on the first page of this thread), but it is advice from Nathan Plemon's website. Those are his words! Sorry if my quoting of him was not clearly indicated.

Now that I re-read it, I think Nathan's point was more about doing something that the computer will counteract anyway -- creating unwanted side affects.

JAKE

That ". . . fire in banks" applies to Batch Fire systems. Some of ours are Sequential Fire systems.

Jake

CFI-EFI

If you didn't want to hear from me, why did you quote a post of mine, twice, unprovoked? It is past time you did some reading. I hope that doesn't put YOU out.

RACE ON!!!

aboatguy

redrose

none of the ''tuned port'' engines/ecm's are sequential, all are ''batch fire'' injection...late lt1 engines do have sequential/mass flow sensors for ''emissions'', not for power.

GREGGPENN

Thanks for the feedback. BTW: Wouldn't creating less emissions imply better burns and result in better mileage/power anyway? Maybe the intent of the change was targeted to emissions but....

gp

Aurora40

It's better all around. Spraying the fuel for the cylinder and having it sit there waiting for the intake stroke isn't doing anything positive.

It was an electronic limitation of the time. A cost-effective, etc, ECM just couldn't control each injector independently.

Also I believe on L98's that it wasn't each bank, but rather the whole motor. They only have one O2 sensor in the Y which is used to monitor/adjust the whole motors fueling.

The LT5, and I believe the LT1, had an O2 on each side so the feedback was per bank, almost like controlling two 4-bangers. The LT5 was sequential fire from the get-go, and I think the LT1 picked it up in '94? Prior to the '94 MY, the LT1 would have been batch per bank.

As a more general comment, it seems you are saying that based on rather simple math, there is no gain from different intakes to be had.

If people reply with "I used X intake and got Y gain", you say you don't care, you want to understand the concepts. Yet when people suggest you read some specific books on concepts, you say you aren't interested.

An an aside from that, to some degree what does it even matter? If you want to increase power, it's a lot more useful to know what kind of power increases various other intakes have made for real. What some different flawed math will tell you doesn't matter much. And even if you read and read and read and understood all of it, I doubt you have the equipment to cast your own intake. So you are choosing from the same pool as everyone else. Having their feedback on what worked and what didn't seems fairly invaluable if you ask me.

Aurora40

(I mistakenly said "open loop" being controlled by feedback in my previous post. I always do this, swap the terms. I will correct it.)


I'm hardly advocating you run out and get an AFPR. But this is not an unwanted side effect.

You adjust the fuel pressure up or down (within reason). In closed-loop mode, neither your drivability nor fuel economy will suffer. This is because the ECM is smart enough to make adjustments so that the fueling is still spot on. This is hardly unwanted.

In open-loop, if you adjust the fuel pressure higher, the car will get more fuel across the board. If you adjust it lower, the car will get less fuel across the board.

If you have made some smallish modifications, and do not wish to dyno test, wideband, and burn a new chip with the correct fueling, an option is to simply up the fuel pressure a little to provide more fuel at WOT. Some tweaking at the track, etc can help guide you making the right adjustments.

Again, to me burning a chip would be the right way to do this, but an AFPR isn't expensive, and is easy to adjust without any expensive tools. It works for what it is. I don't think anyone is stroking their motor out to a 383, and then just bumping the fuel pressure up to save on a tune.

JAKE

Interesting observation, except for this: I have a 1986 and a 1996 and both are referred to as "Tuned Port" engines. The 86 is L98 based and the 96 is LT1 based. Even the little placard I bought to attach to the ash tray door on my 96 which has on it some of the stock LT1 engine specs, like CID, CR, etc., and it says the engine a "Tuned Port" engine.

I know that my LT1 is Sequential Fire, and my 86 is Batch Fire, but the question is "When is a Tuned Port engine NOT a Tuned Port engine?" If both are, in fact, Tuned Port engines, then we can't use the term "Tuned Port" to distinguish between Batch and Sequential fire.

Jake

JAKE

TPIS, for one, claims it does. Says higher pressure gives a better spray pattern. I believe that would occur in all modes and loops, although the ECM/PCM will correct for it in Closed Loop operation.

In Closed Loop operation, the spray pattern would remain better - due to the higher pressure - but the ECM/PCM would trim the pulse width to address the info the 02(s) sends. I've actually watched the ECM do that using Diacom running on my laptop.

In Power Enrichment - PE (WOT) mode, Limp Home mode and Open Loop mode the higher pressure will cause the mixture will be richer since in those modes, the ECM/PCM ignores 02 feedback and uses tables.

I've seen tables showing how higher pressure results in an injector flowing fuel comparable to what a larger injector would flow at the stock pressure setting. Of course, this wouldn't happen in Closed Loop since the ECM/PCM would trim the pulse width.

I've forgotten the exact numbers, but say - just to illustrate - you have a 22 lb injector and increase the stock pressure by five psi. That injector would then flow fuel comparable to what a 26 lb injector would flow at the stock pressure setting. Those numbers are just for illustration purposes.

But, don't forget, you'd have to factor in Duty Cycle when going the higher pressure route.

Jake

GREGGPENN

I've seen several conflicting theorys about the value/waste of different mods. Removing the MAF screens is a perfect example. Flow numbers for manifolds/runners I found never showed a correlation between what was needed and how results were acheived. I merely found flow numbers.

OTOH, the benefit of a larger TB seemed consistently slammed with formulas to support it's uselessness on a 350 (see "footnote" note below). The math I derived from TB discussion did no account for the periodic filling of cylinders (vs. the constant flowing of a TB). Now, I get it. I see why more than 200cfm flow is required! And, it would appear that a different intake should help. Times on 65Z01's website (republished from CF support it). But, the gains aren't as impressive as I'd expect. (The post implies 8HP vs the 20HP I'd guess).

I got busy at work that day and feel the pressure to get the injectors (manifold and runner) issue resolved. I lost patience. FYI: I've been looking thru the net and forum since Aug. I'm always open to learn more. Sorry for the confusion.

I agree. I agree. I agree. But most people who've changed intake, change other things. The few who don't typically talk about SOP results. They don't even time their car on a set distance to see what really happened. 65Z01's website was the first instance of info that segregated an intake swap with specific results.

Thanks for your feedback!!!!!!!
gp

(footnote: corvetteplenum offers a service which seemed close to creating a psuedo superram. By mega porting a plenum and SLP runners, the intake is opened up and the runner length is effectively shortened. On "gotcha" is he WANTS to do 58mm TBs. The alternative is 52mm. I would have guessed there'd be no problem with installing a smaller TB on the mega ported plenum -- but the site says 52mm can be done by special request???

Nathan Plemon's site (link from Tech FAQs) explains why a bigger TB is a BAD idea. So, the less-expensive psuedo SR seemed a lot less attractive. Then, I found formulas which led me to believe gains were'nt very likely -- at least not significant ones. That's how this thread got started!!!!)

GREGGPENN

I'll buy that. Got any idea if mpg is improved (in addition to HP)?

Huh? Was this supposed to repeat the first point?

-----
On a side note: another poster said the stock fuel lines were designed to handle 60psi (if I recall correctly). By pushing things from 43.5 to 50psi, a higher risk of leakage/rupture is present. This was one reason he thought using the ECM to affect changes was better -- because higher FP was not constant.

gp

redrose

while ''every'' intake tract will ''tune'' at ''some'' rpm, the 85-91 system with its ''nest of snakes'' is known as a ''tuned port''...the 84 crossfire and 92-96 LT1 intakes are ''not'' generally referred to as ''tuned port'' ...btw, the 92 Lt1 is batch fired (don't know abt 93) and 94-96 is seq, so an additional category may be req'd

JAKE

If you really want to see the quantifiable effect of a single change, you should subcribe to some of the magazines that do back to back testing, like Vette, Corvette Fever, Hot Rod, Chevy High Performance, GM High Tech, etc.

For example, one of them ran a series of tests to show exactly how much power was achieved when the compression ratio was changed. They started at, I believe, 8.0:1 and worked their way up to 12.0:1. I'm going from memory on this, but I believe they made three dyno pulls at each CR and averaged the three.

Another mage article showed the dyno results when different CFM carburetors were bolted on. That article put the "formula" to the test.

Another series of tests was published recently in Engine Masters Summer issue where different LS1/LS2 cylinder heads from different companies were tested. They flowed each set of heads, then installed them on their "mule" engine and dynoed the engine. From those tests you can see how flow effects power - how much and where it's made.

If you want to see intake manifold dyno results, both before and after porting, take a look at some of the other Forums, ThirdGen.org comes to mine. MadMax posted several dyno graphs showing the results he got by siamesing his TPI setup. Others have followed suit.

Quite a few guys on ThirdGen have setup websites and posted the dyno results from the mods they made. Many of them post both the objective and subjective results.


Hope some of this helps.

Jake

JAKE

I guess given the two choices, re-programming the ECM/PCM is the better route to take. The downside is each time a mod is made, new programming would be called for, and to do it the BEST way, the car should hit the dyno. TPIS has advocated higher fuel pressures from as far back as when GM was recommending pressures a lot less. GM finally came on-board and raised their recommendation for later model cars. I know Vettes got the higher recommendation; probably 'F' body cars did too.

Another little point, the fuel pressure IS constant. As constant as it is when the pressure is at the stock setting. It increases in the modes I mentioned in a previous post, but remains constant in Closed Loop. The ECM/PCM doesn't and can't control Fuel Pressure, it only controls the injector pulse width. That is, how long the injectors fire, in Ms.

I wouldn't worry about the fuel lines bursting or leaking. There are guys running a lot more pressure than 50 using the stock lines. There are things to be concerned about and there are things NOT worth being concerned about - guess which catagory that falls in. LOL

Some create 'dooms-day' conditions just to add credence to what they believe. They feel it adds validity to their position. Others are just "worry warts".

As I wrote on a different Forum, whenever I decide to modify my engine to increase the power, all bets are off. I use the factory recommended settings ONLY as a starting point. I tweak from there. GM's recommended settings are for their engine as it came from the factory. As soon as changes are made some settings will still work and others won't be best. Take lifter preload, engine oil, etc., recommendations as examples.

Oh, it was a duplicate post; I deleted it a couple of days ago. Well, at least I see you're paying attention. LOL

Jake

GREGGPENN

I've looked to see what articles are in Vette/Corvette Fever the past few years (at the store). Only saw one issue worth buying. Good suggestion though.

Hadn't thought of that. I've always confined my searches to the C4 forums under the assumption that results (improvements) would be specific (for me) for this generation's setup. However, I understand the SBC preceeded C4's.

Thanks for the suggestion.

gp

GREGGPENN

BTW: Here's Mike GrayCar's response to my query on siamesing the base (suggested on 65Z01's website. Link earlier in this thread). Mike is the owner of the CorvettePlenum website and appears to the a member of the Corvette Forum.

Hi. Gregg, That whole thing, It's just a bad idea.

Good plan= Ported plenum, Aftermarket runners and an aftermarket base.

The siamese bottoms and base were born out of people trying to get the most out of the stock parts. There has been alot of fierce debate for more than a decade now on this topic. Bang around on thirdgen.org Look on the TPI boards. There were guys, back in the day who did this. At first it seemed good then a few guys burnt their motors up. then a few more. It seems that when you compromise the long runners buy forming a merge just before the valve it creates a lean condition between 2 of the rear cylinders as one steals from it's neighbor during high RPM's. The result: one very crisp piston. look around abit before you consider doing this. I decided it's just not worth it.-Mike

JAKE

VETTE and FEVER run very informative articles on how to check and repair certain parts of our cars; those that seem to fail a lot. Like how to diagnose the Anti-Lock brakes, Digital-Dash malfunctions, Cruise Control, etc. Sooner or later you'll need some of that info since most of us get bitten in time.

There's SO MUCH bad information being passed around that, at times, after reading it, I have to just get up and walk away from the computer. A good example is "burnt up motors". Guys are quick to post about their engine failures, but seldom do you see them later admit that it was caused by something they did or something they should have done but didn't. Big psychological self-esteem issues at work here; denial/guilt transference, etc.

Engines in 'F' body cars are not IDENTICAL, but very, very close to the L98, LT1, LSx engines found in our Vettes. Many of the parts are directly interchangable. For example, rather than spend $300+ for a MAF, hit the wrecking yard and grab one off a wrecked Trans AM for $50.

The guys on the 'F' body forums make the same type of changes that we do. There are separate boards based on the type of engine being discussed. There seems to be a lot more of them - owners - than us too. "F" bodies are VERY popular; I had five before I bought my first Vette.

If for example, you want to know which TB is and works best, take a look at their experience and factor that in to your decision making process. Does removing the MAF screens really work? - Check out their experiences.

Many of those guys are REALLY knowledgeable. I regularly visit ThirdGen.Org, Camaroz28.com, LS1.com and a few others.

Anyway, best I can do is try to point you in the direction where you can find the info. "Lead a Horse to Water" sorta thing.

Hope this helps.

Jake

italia29

I agree with GreggPenn. I have a 1988 and i blew the engin laste year. So the shop i brought it to did a stock rebuild on the car but for some reason added a larger cam to it. (not my choice) when they returned the car to me they had adjusted the fuel pressure to componsate for the stagered rpm jumps. To make a long story short the car ran like crap and i had to get the actual computer chip tuned and replaced and then have a new pressure gage put on. It was a pain in the ***!!!