Gator81

:iagree:
This is how I understand the Hypertech chip to work. First, it does nothing, zip, nada, for the carb. As I understand it, the Hypertech is a 100% copy of the GM chip in regards to the fuel control. There's not really a fuel map. It's a simple closed loop controller, no different from the thermostat on my aquarium heater. A low reading from the O2 sensor triggers the chip to apply voltage to the M/C solenoid, which pulses the needles against their springs, down into their jets, thereby leaning the mix and, shortly thereafter, causing the O2 sensor's reading to rise. That's it, that's all. No fuel map.

But there is a spark map. A table, really, that lets the computer find the proper spark advance for a given combination of rpm, vacuum (as a proxy for load), throttle position, and intake manifold temperature. The Hypertech chip simply provides a more aggressive spark advance curve, allowing more total advance at WOT when compared to the GM chip, given the same number of degrees of base timing. The tradeoff is that it is assuming that you are willing to upgrade to higher octane fuel. On the stock engine, the premium fuel wouldn't do you any good without the extra spark advance, and the extra spark advance would cause knocking without the premium fuel.

Clearly, as Paul points out, other engine mods like more cam, better exhaust, and more compression will allow the extra spark advance and premium fuel to be used to greatest advantage. All by itself, as a stand-alone modification, I think you be hard pressed to identify a performance improvement after just clicking that chip into the computer.

At a minimum, if I were doing the chip (which I did, and recommend) I would bump up the base timing and fill the tank with premium fuel. Then, maybe, you could tell a difference at WOT. But you'll still be held back on the L81 engine by the stock exhaust, more than anything. IMO, somewhere around 4500 rpm, those manifolds and that single cat reach an effective conspiracy to choke off the flow.
:seeya

Gator81

:iagree: :cheers:

Dalannex

Disconnect the 4 wire flat connector from the distributor to set the timing.

On the mods to the L81 take a look at my sig. So far the mods are real simple and basic, but the power that I am getting is really amazing. The stock ignition and fuel systems (yes, I'm talking computer controlled carb and all) will work just fine with some performance mods. As Paul said above your cam selection needs to be something that will have a good amount of vacuum at idle, I would say no less than 10 hg. and a cam swap along with an exhaust switchout to 2 1/2" true duals will cause a drastic seat of the pants power improvement. The cam and vacuum thing I can attest to since I rebuilt the motor with way too much cam and the car ran just like any other car with no vacuum will. You have to richen it to get it to run at low idle since there isn't any vacuum to suck the gas into the engine. Then it puddles in the intake, you step on the throttle and the sudden vacuum increase sucks the gas in and floods the motor out. I went to the comp 260H and it is money well spent as far as HP per dollar. My other cam had 1 or 2 inches of vacuum at idle, and it wouldn't run below 2000 RPM. I put the Comp in and now I have 15 inches, car runs real nice, plus I don't have emissions testing so my duals with no cats and no crossover sound real nice too. :cool: The next thing I want to do (motor wise that is) is go with the Hypertech chip and 160 thermostat. Now on to assembly of my new 4 post lift, work on the NCRS 69' 427 vert project, 68' trans rebuild, etc. etc. :D


-Justin

UKPaul

Same here :iagree:
The only reason I could see for junking a good, working computer system is if you were after some serious HP. The system, if set up correctly, can work very well & also give good economy (especially needed now that the price of crude oil is going up again - and we've got the added bonus of our government increasing tax on fuel :mad ).
Clutchdust,
I think if we gave our true opinion of the stock exhaust system we'd lose all our %age points & go the way of George (the place still isn't the same without him!!) :D
:cheers:

UKPaul

Hi Justin :thumbs:
I'd be interested in how you get on with the 160stat. I think it was Gator who tried one & found that the system kept going into open loop as it wasn't quite warm enough?
Well, that's Saturday taken care of, what have you got lined up for Sunday? :jester :lol:
:cheers:

Gator81

Yes, the 160 stat and the L81 computer, even with the Hypertech "Thermomaster" chip which calls for a 160 stat, just would not work together. The computer could not convince itself that things were ever warm enough to go closed loop, the high idle was cycling on/off, other general confusion. Went back to a 180 and all is well.

Dalannex

I agree about not scrapping the computer. You wouldn't believe how many people have told me that the computer controlled q-jet is a piece of junk, and these are all people who have never owned one, and certainly never worked on one and don't know how it operates. :mad I'm okay with people having their own opinion, but at least have some basis for that opinion.

The reason I was thinking 160 thermo was that the hypertech chip recommends it, but I guess I'll just skip that part. I'm in no hurry, but would like to get the hypertech chip before next summer. I'm seriously thinking 383 for the 81' right now, along with 200R4.

This weekend I won't get nearly what I want done. Tonight is a local high school homecoming football game, this afternoon was the parade (my son's class marched) tommorrow my wife and I are going out to dinner, some mini golf and go cart racing with friends, Sunday is church in the morning, departmental "stress relief" meeting at the golf course with the rest of the guys in my department at work. That leaves Monday as the day to get the lift installed. The 69' 427 is a local guy who quit driving the car in 72 and it has sat ever since. I get to get it running and roadworthy again, but it is 100% original, so I get to worry about NCRS standards. Should be fun.


-Justin

BTW, we have had the 80' and 81' out quite a bit today. :steering: :cool: :cheers:

cicch95

UKPaul or Gator...or whoever!! I see two wires attached to the distributor. One is labeled TACH and the other is BATT. Is one of these the one you are talking about unplugging to set the timing?

Thanks,
-Rick

bertmeister

The four wire connector is just inside of the tach and batt connector. Check out the sticker on the hood for setting the timing. It gives you all the needed info.:cheers:

cicch95

Thanks Todd! One of these days you and my buddy with his 81 will have to meet up. He is in East Greenwich!

-Rick

VegasJen

whoa! wait a minute. the plug behind the tach/bat connectors is something totally different. there is a 4 wire plug that comes out of the distributor at the base, around the back. it's a plastic weatherpack plug with a clip that will probably break off the first time you touch it. it's at the very bottom and if you have trouble finding it, or determining for sure that's the one, you could just pull the cap loose. slide it to one side and you'll see the spark control module bolted down on the bottom of the base. it has five pins on one end and two on the other. follow the connectors on the 5 pin side and they will go to something else (don't remember what right now) and those wires will all go out of the distributor. it will be four wires at that point, those are the ones you need to unplug. your unpluging that spark control module to set the base timing.
as long as your in there, it's not a bad idea to pull that module out and recoat the bottom with some dielectric grease. those modules run pretty warm and if one goes out on you, you'll limp home with that base timing all the way. the grease helps it dissipate the heat into the distributor base. it's good practice and i recommend it become part of your annual maintenance.

Dalannex

GOOD ADVICE!!! New grease on the module should be listed in all the manuals as part of the routine maintenance procedure.

And I second the motion on the 4 wire connector. It is not one of the ones that goes up to the top of the cap. It comes off of the bottom of the distributor and is 4 wires, running to a 4 pin flat weatherpack connector that is probably a couple of inches wide, maybe a quarter to half inch thick. (going from memory here)


-Justin

cicch95

Thanks guys! Appreciate the advice and help. One more question.....at what RPM should I set the timing? I know I rev it to 3,500 on my big block.

Thanks again,
-Rick

VegasJen

trying to remember without actually popping the hood, but i believe that 4-speed cars are at 750 in neutral and autos are at 700 in drive. something to that effect. is your smog sticker still under the hood? that will give you the specs. if your engine is original and has alot of miles on it, i recommend adding about 2* to the base timing. these cars came with those super cheezy nylon gears and single roller chain so they get really slack after 50-75k miles on them. just my opinion, maybe it's a little superstition. i'm sure others will jump in and make their own recommendations. who knows who's right?

UKPaul

Good question! Just try different settings until you're happy with it.
I set mine (with the wires disconnected) to 11BTDC (stock=6BTDC) with an idle speed of 600rpm. The stock idle speed (on the under hood sticker) was set to the correct 700rpm (can't remember if that was in D or not). Disconnecting the wires dropped the idle to 600. Setting it at the wrong idle speed will have the effect of slightly altering the base timing (which is what you're trying to do!).
For max effect you should do the old favorite of advancing the timing in 2deg increments until you detect pinging when driving & then back it off 2deg for the final setting. Somebody told me that you could safely run at 13BTDC on an L81, so I figured that I'd set mine at 11 to give me a greater safety margin (sometimes some fuel seems to be really bad). To do it correctly & get every last horse out of it I should have found the advance that would have just started it to ping under heavy load when hot, but I just went for a nice safe setting as I figured there was no point trying to get every last fraction of HP out of it when still running stock heads.
What you're trying to do is alter the base timing, which is the advance at low rpms. As the rpms increase, the computer does all the advance curve adjustments that bob-weights, springs, vacuums, whatever used to do. The computer doesn't "know" what the position of the crank is, all it does is says "I'm at xrpm so I'll advance the timing y degrees from the base setting". It's a pretty dumb system - but I like that in computers :)
:cheers:

bertmeister

Hey Rick,
My mistake, :confused: The correct four wire connector is out the back of the distributor and is located on the left side of the distributor shield.