VETJET

I am planning my winter performance project on my 1981 and I would like your input. I want to be careful not to screw up anything with the computer control and so far the only performance modifications that I have made is swapping out the 350 tranny to a 700R4.

Here is my plan and any constructive input would be greatly appreciated.

Gears / change to 3.73, and does it make sense to change only the gears or should I do a complete pumpkine rebuild? the car has 46K miles

Carb / maintain the factory electronic Q jet

Intake manifold / use the stock aluminum intake

Heads / some sort of aftermarket, any suggestions?

Cam / some sort of aftermarket, any suggestions?

Exhaust / factory exhaust manifold with dual exhaust with dual cats. I am concerned if I goto headers that I will have to disable the pollution control which could mess up the computer, is that a concern?


Finally where should I be at as far as HP and torque after these modifications?


Thanks!!!
:cheers:

phxraptor

Go to the Edelbrock website,there you can choose an intake,head and cam combo that has egr ports and will not mess with your puter. The Performer line is what you will be looking for.The Performer RPM line does NOT allow for the egr passages in the heads or on the intake. You can also get AIR headers for your smog setup,I believe Hedman makes this type. And get ceramic coated headers if the wallet is thick enough. Horsepower? My guess would be 300 or close to it. :cheers: :seeya You do know that your 81 trans is also computer controlled for the lockup don't you? It's a 350C. :seeya


[Modified by phxraptor, 9:34 PM 10/13/2003]

macx

We're about on the same page. I'm taking a similar approach. I have a 65k mile stock engine. About settled on upgraded Vortecs (available on ebay quite reasonable) with ss valves, springs good to .510" lift. Thinking GMPP EGR Vortec intake that will take the stock carb (dual pattern intake) that should be an improvement over stock but still retain EGR and clear the hood. You can check it out on Sallee Chev site. That changes the cr from about 8.1 to about 9.5 using .015 compressed head gaskets as the heads are 64cc versus the stock 76. I'm thinking Comp Cams XE262 hydr flat tappet although the relatively early intake closing will likely give me high enuf running cr to have to go 91 octane. Using the XE268 you can likely get by with 87 or mid grade, although the 268 reportedly runs a little rougher. See these 2 articles.
http://www.corvettefaq.com/c3/goodwr...20part%201.htm http://www.chevyhiperformance.com/ (go to tech articles, about 3 pages in, see the series of articles on the Quest - very similar to our plans, and it does fine on 87 octane)

Then check out some of these dyno articles, surprisingly our basic setup with the flat tappet 262 or 268 does as well as similar engines with roughly comparable hydr roller setups, and obviously lots cheaper!
http://ryanscarpage.50megs.com/combos2.html http://www.geocities.com/MotorCity/7610/dyno.htm

Last, I'm thinking Hedman 68301 (adding a -6 gives you coated) headers which are 1-5/8 and have the AIR fittings. For exhaust, either a true dual setup or going a larger pipe in the single section.

The only computer upgrade I've seen is on Corvette Central, it's a hypertech chip - you can also find it on hypertech's web site. However, the info says it's for basically stock motors (not a bigger cam or heads), and I've read some posts where even mild hops like ours won't run properly with the stock computer.

So we might have to end up getting an HEI with standard advance mechanism and a non-electric carb - don't know if it would be worth trying that hypertech chip first, or best then to go to a 625 Road Demon or 650 Holley. I think the EGR and AIR system could still be retained with that. Might be worthwhile getting ahold of Lars (on this website or do an archive search) who's an expert with the stock TQ, he might be able to suggest carb mods that would allow it to function with the computer with the better cam & heads. For a good auto math calculator, check this out (for everything from comp ratio to rpms with diff trans & gears). I'm thinking beefed 2004R and 3:55's. http://www.smokemup.com/auto_math/index.php

Have fun, good luck, and let me know how yours turns out.

macx

Just to whet your appetite - the 1st of the 2 above articles cracks the 400hp and 425 torque barrier with an RPM style intake and the 268 cam. The GMPP intake and the 262 cam should be very close - check out the dyno sheets on Comp cams website - the 262 and 268 have very nearly identical hp and torque figures and curves throughout most of the useble rpm range. The engine in the Quest series of articles also uses Vortec heads, I believe an RPM style intake, and the 268 and gets like 390hp and 420+ torque on 87 octane (the 268 bleeds a little more of the compression off which combined with the good comb chamber in the Vortecs is what lets it use 87 octane). That's quite a step up over the Ebock combo. That's having your cake and eating it, too!

macx

Here's the 87 octane 390 hp series of articles:
http://www.chevyhiperformance.com/howto/47075/

Steve81

Modifing the 81 can be trickly because the computer controls the carb and timing adv. If you plan on keeping the CC you have to be careful with your cam selection, if i remember correctly, the cam has to make enough vacuum (15hg?) for the ECM to work right at idle. If not the elec. Q-jet will run too rich and you will have emission problems. As for the timing, you will have to change the chip in the ECM to get the timing curve to match the new cam.
You could just switch to a standard Rochester or Edelbrock q-jet and dist. (more $$$$) and, as long as it's tuned properly and your other mods are smog legal, not have any problems.
Hope this helps.

Dalannex

As long as you have enough vacuum to pull the fuel into the cylinder the car will run just fine on the stock equipment. E4ME's are the same idea as any other q-jet, just more accurate fuel metering. There's no reason heads, cam and exhaust should cause any major problems with the computer control.


-Justin

UKPaul

I agree with most of the above. See sig for my mods. Changing to true duals (esp. with "X" or "H") is an excellent mod but the stock manifolds then become a restriction. I junked them & fitted Headers last winter & can feel that there is an improvement at higher rpms (Dynomax ceramic coated with stock O2 sensor mounted in the reducer). I can't see that there would be any computer problems if Headers with provision for AIR were used.
Cam selection is crucial as you'll need to ensure a decent vacuum at idle. This seems to be the major "drawback" with the computer. With a low vacuum it will think that there's some throttle so will richen the mixture. I fitted a Crane Compucam but other cams may be used.
The Hypertech chip made an improvement when I fitted it & increasing the base timing also helped. I think the chip just modifies the timing curve. If it's not the curve you want then a custom chip can be blown.
The TCC lockup isn't a problem to modify. On mine I bypassed the computer for lockup so that my 200-4r locks up whenever in OD, although it can be left to the computer to decide when to lockup.
The computer controls the mixture on the primaries & the secondaries work like previous Q-jets (ie. change rods/hangers to adjust mixture - once you find somewhere that can supply Q-jet rods :rolleyes: ).
Heads: Not sure! It's something I'm trying to save some cash for, but I'm looking at a set of AFR180s. The way I figure it is that I need to choose heads with the smallest intakes port volumes that will flow OK at the valve lift I'm using. eg. with .45" lift then, given a choice of heads that flow the same at that lift, use the ones with the smallest volume as they'll give the highest gas velocity, giving improved torque. It's something that I'm still looking at but whatever I use I'm going to bump up the CR as the stock CR isn't going to help performance.
With the mods I've done the power has improved noticeably (but I'm convinced that the Headers have caused the secondaries to run weak, so there could be a bit more HP hidden away) & the computer has no problems with it. The only emissions systems still in place are the charcoal cannister & the thermac in the air filter, although I'm convinced that if the EGR, AIR, etc were still there then the computer would still work OK.
:cheers:
edit: If your only worry about disabling the pollution controls is the effect on the computer then you have no worries :) I got mine with the AIR, EGR & EFE already removed & it ran OK (once I'd found the ported vaccum pipe that was open to the atmosphere!!!!). As a lot of these systems have common wiring/componants eg the EGR & TCC lockup, then once they'd been removed it was lot easier to see how the computer system works - it's pretty basic!!



[Modified by UKPaul, 5:54 AM 10/14/2003]

Fast81

Hey Paul -- how loud is your 81 with headers/true duals/monza mufflers?? I've already got the Dynomax headers and the monza mufflers -- going true dual when I'm emissions exempt in 1 yr. Bye,bye cat conv!!!!

The AFR180's are awesome. Their tech line recommended the 180's over the 190's since I'm not running a 383 or dragging my 81.
See my sig

UKPaul

Dean,
Thanks for the info on the AFR's :thumbs: :) For the valve lift I'm using the 180's flow as well as the 190's/195's, but everybody is fitting 195's so I thought I was missing something. Good one!

Noise? With duals & Monzas there will be lots of it!!!! With duals it was fairly quiet at idle & cruising was OK, but there was one speed where it droned a bit. At WOT it was deafening. The 1st time I went to WOT with my new duals & Monzas I immediately backed off in shock (& I'm used to loud vehicles)! :eek: Last winter I made up my own dual system & fitted an "H" pipe in it. That "H" pipe has really been worthwhile. The engine feels "smoother", the popping in the exhausts on deceleration has nearly stopped & the sound is much more mellow & isn't as harsh. It's also not as loud as before but the idle sounds better & at cruising speeds there's no drone & I can hear my passengers again. WOT is still loud, but not quite as loud as it was, so I'd recommend an "H" pipe. Somehow I think you're really gonna like dual pipes :D
:cheers:

macx

Good info on the computer, esp. with regards to how much vacuum it takes to run it, and on the Hypertech chip thanks!

I see Hypertech has a "street stock" chip that runs with the stock 190 tstat, then another that is probably more aggressive in timing that works with either 180 or 160 tstats. I would pick the 180 setting and tstat as I understand that the oil doesn't warm up enuf with the 160 thereby causing more rapid cylinderwall & ring wear, etc. I also understand that 180 is the ideal temp for best combustion in normal driving (although you can get more mileage with a higher temp).

I would think the CC XE262 would make enuf vacuum, but would doubt the 268 would. (Per the info in the articles linked above). Can anyone say for
sure if the computer has anything directly to do with controlling the EGR and AIR sytstems, or do they run mostly off of vacuum, temp, etc type signals?

I would imagine Lars would know how to modify carb tuning to cope with the
better heads and cam and still retain the computer function?

Fast81

So you're saying going from the "2-1-2" (with no cat - your original setup) to duals was a BIG boost????

please say yes, please say yes, please say yes

Master Ho

Yes. But don't expect wheelies ;)

UKPaul

YES! YES! YES! :D
The seat of the pants increase from swaping out the stock system (without cat) & replacing with a MA system connected to stock tubular manifolds & mufflers was far greater than anything I've done since, including fitting Monza mufflers & then fitting Headers & an "H" pipe (the jury is still out on the Headers as I haven't got the carburation sorted yet). I was told on this forum that duals were the way to go, I wouldn't regret it, great bang for the buck, etc.... & were they right!! I was very impressed, if only all mods gave such a performance boost. And they sound good :yesnod:
:cheers:

UKPaul

Trying to remember all this. The stat temp rating is a compromise between efficient combustion (lower temps?) & efficient lubrication (higher temps?). Manufacturers tend to veer towards reliability rather than performance so fit the 190 stat (giving good lubrication).
Personally I wouldn't use a 160 stat as I don't think that the power gained is worth the risk of running the motor cooler (more condensation, maybe less contaminants being burnt off, risk off less effective lubrication). Additionally, Gator81 ran a 160 stat & had problems where the computer wouldn't go into closed loop as it thought that the motor hadn't warmed up enough.
I wouldn't bother with the milder Hypertech chip. The more aggresive one is running OK in mine even with more base timing dialled in. After fiting it I did notice an improvement in low end grunt, so it was worth buying. I'm not sure that it would have much effect in a stock engine though...
:cheers: