cicch95

What ideas do you guys have to upgrade the performance of an 81 while still meeting emissions requirements? This is the first year of computer control, correct?

-Rick

Riceater

first year for total production. The 80's that were sold in Cali had the computer coupled to a 305

BSeery

In my opinion any car can be tuned to meet emissions. It's a mater of getting the mixture right.

My generic answer for how to get some HP out of a L-48 engine is the following.
Install the L-98 Aluminum 58 CC heads. That will bump up the compression, get you better flow and aluminum heads for better cooling.
You can use the stock intake and carb with a little tuning. If you want you can step up to an aftermarket intake, but if I remember right the stock is already an aluminum dual plane.
Headers and with a larger 2-1-2 system is cheap, or you can convert to full on dual exhaust with 2 converters, but that can get pricey.
Step up the cam to a 266 version. Some say that the 268 is good, but many complain that there is no "umph" down low. With a lock-up automatic tranny and low gears you are going to want some torque.

UKPaul

See sig for what I've done. It's far better than when I got it & I'm expecting to get the full benefits of my mods once I can afford a set of decent heads. The computer does limit the choice of aftermarket cam that can be fitted (Crane do computer "friendly" cams) but, as far as I know, all the computer needs from a cam is a decent manifold vacuum at idle to work correctly. With a low vacuum it'll think the throttle is open so will richen the mixture. This extra fuel will "puddle" in the manifold & will bog the motor when the throttle is opened (and cause major emission problems).
By far the biggest bang for the buck I got was from dual 2 1/2" pipes. The cat had been replaced with a straight pipe when I got the car, but duals really woke it up (I dread to think how gutless it must have been with a cat in the system). I'm expecting that upping the CR & improving gas flow by fitting some decent heads will get me considerably more power than a stock L81.
:cheers:

Gator81

See this for exactly what I've done with my '81:
http://www.rogerscorvette.com/free/morris.htm

I'm required to have an inspection every year at registration, so meeting the emissions requirements is a "must" for me. However, there are some "shades of gray" here that you might want to consider. It all boils down to exactly what you are required to do for emissions.

First, it's important to understand that there are two basically different kinds of emissions requirements: 1) equipment, and 2) performance (that is, actual quantities of pollutants emitted).

I am concerned about air quality, and I want my car to meet the standards. But I couldn't care less if it has a particular piece of emissions equipment on it or not. Fortunately for me, the State of Utah sees it the same way. As long as my car passes the "tailpipe sniffer" test (IM240), they never look to see whether I have cats, EGR, EFE, PCV, etc., etc.

As it sits right now, my car does have all that stuff except for the EFE. As UKPaul noted above, the greatest single (no pun intended!) impediment to performance in the L81 is the exhaust. The tubular exhaust manifolds are just plain awful. Way too small, probably only 1 and 3/8 inches in the bends. My plan is to replace those with headers (as UKPaul did), keeping the O2 sensor, and adding true duals (like Paul's). However, without the cat, I don't know if it will pass the emissions test or not. It would be close. My plan would be to install the headers and true duals, take the test and find out. If it won't pass, I'll cut the pipes just behind the headers and weld in the smallest cats I can find, one on each side, to keep true duals.

UKPaul

Hi Gator,
I'm trying to get my Vette put on a mate's sniffer to analyse the exhaust gasses in an attempt to find out if it's running weak after having Headers fitted. Assuming that it's running OK I'll get the results to you to give you an idea if you can get away with no cats. I should be able to get readings for nitrogen oxides, CO, CO2 & unburnt hydrocarbons. Is that all you need, or should I try to get any other readings?
I'm guessing that most things should be fairly equal, or in the same ballpark, but the nitrogen oxides may be different as you've got a higher CR (envious? Me?!)
:cheers: :thumbs:

Gator81

Hey, Paul,
Thanks! That's info I'd like to have. The numbers I'm required to show are ppm CO and ppm HC at 1000 rpm and at 2500 rpm, each speed held 60 seconds. [edit] Of course, in both of those situations, the engine should be running on primaries only, in closed loop mode on the computer. It tells nothing about how things run when anywhere near WOT.

Currently, I think my valve that controls air pump output is malfunctioning, and I'm not getting any air pumped into the exhaust manifolds or the cat. If that's true, then the cat is probably not doing as much as it could to oxidize the CO and HC. Never the less, my current numbers are all below the 50% mark for both measurements at both speeds. That means I've got 50% or more "overhead" in the standards, which is why I think I might be able to slip by without the cats. And if all of that is true, it appears that I can do without the air pump, too. :D Ahhhh, visions of horsepower... :D


[Modified by Gator81, 10:49 AM 9/24/2003]

UKPaul

Hi Gator :)
I'll get those figures. It could take a while as I'm relying on my mate being at work late one evening, or on a Sunday (since selling his Mopar he doesn't do many "Homers").
If your air pump isn't working, and as you're got some "slack" in your emissions, then it'd be a simple job to swap out your cat for a length of pipe & then get your emissions tested. If getting a "cat replacement" pipe is tricky, I've still got the one that came off mine that I could post over to you? I wouldn't mind betting a pint (or 40 ;) ) that you'll find that at least the HC's would be acceptable. I figure that our computer controlled beasties might have very good HC values due to the camshaft design?
It's worth checking as junking the stock exhaust system is a grin factor 10 modification :D
:cheers:

cicch95

Thanks for the great info supplied so far guys!

-Rick

Gator81

um... no, sadly. :( Way back when I first got the car, the stock mufflers were the first thing to go. Of course, for grins, I fired the motor with no mufflers at all on the car, just to enjoy the unfettered sound of a V8. Only problem was, it sounded exactly the same! WTF! :confused: A quick look at the exhaust system revealed the obvious: the stock original cat was so clogged, the mufflers were unnecessary! So, I fitted the new hi-perf mufflers and drove immediatley to an exhaust shop, where I requested a new, hi-perf cat. They said "OK", and about an hour later, I had a "Products For Power" (PFP) cat installed. Problem? I had managed to find Bubba's Muffler Shop, and that sorry SOB welded the new cat in place. That's right, the original cat, with its bolt-on flanges, was cut off with a torch. Including the flanges on the original stainless steel front and rear Y pipes. $400 worth of exhaust pipes, ruined in 60 seconds with a torch. I could've killed him. So, ever since then, I've had a one-piece welded exhaust system, from the manifolds to the mufflers... and bypassing the cat with a "test pipe" can only be done with another torch... :(

UKPaul

Gator,
I hear what you're saying :( That muffler shop must have a franchise local to me ("Bodgit & Scarper Tyre & Exhaust Ltd"), who did an exceptional piece of work on our MG. Their exhaust system is now laying in my back yard awaiting use as reinforcement in my new garage's concrete floor. I'm convinced that a major part of classic cars unreliabilty reputation stem directly from work done by so called professionals.
I forget, have you advanced your base timing?
:cheers:

Gator81

Yes, I'm running around 10 degrees as compared to the standard 6 degrees, if I remember right. Makes a substantial improvement in off-idle throttle response. It feels like it would be better yet at 12, but I'm fearful of detonation. Don't forget, though, that this beast lives and runs at 5000 feet or higher all the time. That translates into lower actual cylinder pressure, so it needs the extra advance to take advantage of the higher octane fuel that the Hypertech chip assumes I'll be using. On the other hand, the 9:1 compression of my Trick Flow heads would argue for a little less advance. I suppose the higher compression somewhat balances out the higher altitude, but in the end, it still runs better at around 10 degrees, and I don't get any detonation. :crazy:


[Modified by Gator81, 9:53 AM 9/25/2003]

UKPaul

Gator :seeya
Yup, a real simple & free performance enhancer. I set mine to 12BTDC & also noticed a much improved off idle pick up. It didn't ping ever, but the exhaust note sounded like it might have been close to pinging (it's hard to describe, it just had a certain grating sound that I recognised) so I backed it off to 11BTDC. Definately a change worth doing, probably even on a stock motor :yesnod:

Warning: This part is so far off topic that's its for Gator only. In fact, it's beyond OT!!!
Knowing that you're into aircraft you'd probably appreciate this. BA management, in their wisdom(?), are withdrawing Concorde from service next month :( So, each evening I go outside & watch it fly over. Yesterday it was flying towards the setting sun (which is in a completely different direction to normal) & the entire underside was bright red with the reflected sunset. Looked fantastic. As it flew over the reflections faded until only the underside of the engines were reflecting the sunset. One of the coolest things that I've ever seen: the underside of Concorde bright silver, touched off by brilliant red engines, set in a pink sky - if only I'd had a decent camera with me. In all my years of watching it fly over I've never seen it look so darn :cool:
:cheers:

cicch95

UK Paul or GATOR............this may seem like a silly question...but, is there particular procedure for setting the timing on these comp controlled cars? I am used to setting it on good old big blocks!!! But, I know on Fox bodied Mustang you had to pull a plug first then set it. Etc.

Thanks,
-Rick

Gator81

Well, Paul, now that we've completely hijacked Richard's original thread... (Sorry, cicch95! :bb

I've never seen a Concorde in flight, although there was one on the ground where I was changing planes once... LAX, or maybe SF, can't remember. One very cool bird. I've read a lot about them. The engineering challenges of thermal expansion alone make it a marvel - the airframe can lengthen by more than 8 inches in flight! Mind boggling.

So now that BA is mothballing them, they fly over Surrey every evening??? What's that all about?

I suppose now that they're "surplus", they'll be up for sale... or maybe not. Don't they require a a crew of 3 or 4 just to fly? Plus ground crew? I suppose some filthy rich bastich will pick one up... maybe Richard Branson? Or that other Brit who's always trying to fly around the world while drinking champagne in a balloon or some such... :rolleyes: I'll tell you this, my friend, the rich life is wasted on the rich. You and I, now, after all these years of hard work and bloody knuckles, we would know how to wring every last ounce of fun out of a pile of money, eh?

Ah, well. To the Queen and all her Good Men! :cheers:

Gator81

No silly questions, Rick! Yes there is a wire by the distributor that must be disconnected, so that the computer allows the timing to drop to the "base" level at idle. Right now, I've forgotten the color of that wire... seems like it's gray, but I haven't looked at it in a long time. Perhaps Paul will chime in.


[Modified by Gator81, 12:48 PM 9/25/2003]

UKPaul

Rick,
I've also forgotten what one it is :lol: But it's easy to work out. There are 2 connectors on 2 separate bunches of wires going to the dist. One must be disconnected to set the base timing & it's easy to work out which it is.... if you disconnect it & the motor still runs then you've got the correct one. If you disconnect the wrong one then the motor will just cut out as there'll be no spark. Then just set the timing as you normally would (xBTDC @ 600rpm) & plug the connector back in. Hopefully you'll notice a better off idle response afterwards :)

Gator: I live under the flightpath to Heathrow. Concorde goes over twice a day and, when the pilot is giving it some "welly", it sounds great. If only I could get the Vette to sound the same :) Apparently they're withdrawing them as a cost saving exercise. Richard Branson apparently tried to buy them but BA refused to sell (so I heard). As countless millions of taxpayers money were spent developing it, I can't see how BA have got a say in what happens after they've finished making their money out of it :mad I blame the Queen! She should step in & give the BA management a good hefty kick up the butt with a hefty royal steel toecap! If they don't want it then Branson or whoever should be allowed to have it. It'll be a black day when it's withdrawn, heck, the only thing worse would be finding out that it's French :crazy: :lol:
:cheers:

cicch95

Thanks guys! You have been a BIG help!!

-Rick


[Modified by cicch95, 11:14 AM 9/26/2003]

UKPaul

BIB? :confused: What's that mean (hey, I'm foreign!!!)?
Rick, if you do advance the base timing could you post up the results, just out of interest?
One thing I should say is about the Hypertech chip. I've seen a lot of bad press about the chip, but most of it was from people with fairly stock engines. I fitted mine just after swapping the cam & fitting a Performer manifold (dual exhausts already in place) & immediately noticed that low down torque was improved. So, going by my experience & other people's opinions, I'd say don't waste your money on one unless/until you've done some engine mods :yesnod:
:cheers:

VegasJen

hey gator! hate to disagree with you but just plain awful is not nearly strong enough here. probably should be more like "gawdawful horrible" or "the biggest pieces of crap ever installed on a motorized vehicle since before the model T" or "a complete friggin disaster".
you know, something more fitting.
heck, if i was running my AIR, i'd probably rather have the old cast iron jobs over these POS headers.
like you guys have said though, it's really not that hard to get some decent HP numbers out of a relatively stock L81. you just have to realistic. and the last thing anyone should be recommending is junking the computer controls! :mad