W-72 Performance improvement
 

I am looking to make my 1979 TATA run a little better. I just had a new dual exhaust system installed with 2 1/4 inch pipes all the way back through Dynomax turbo mufflers with an H pipe. The engine is otherwise stock with about 50k miles on it. Plugs, wires, cap and rotor are all reasonably new. The carb has been overhauled and the heads were also cleaned up. What have any of you done to get your W-72's to run harder? I am looking mostly for just changing the distributor timing curve and carb rejetting. I do not want to change cams or anything else, just want to maximize what the factory gave me.
The butt dyno tells me that the new dual exhaust did not seem to make much difference in performance, I am actually disappointed so far......

i loaned my manual out, but if you can find an old HO Racing catalog, they sell tech flyers. all kinds of neat articles, but one was where they took a stock 77-or 78 and did a super tune on it. they detailed how they redid the carb, distributer, and added 1.65 rockers and the difference it made.
myself, i had a 78 that i worked on. we rejetted the carb, recurved the distributer, added the 1.65 rockers, gutted the converter, added a 3,000 stall converter, and the car felt like it went from a 350 2bbl to a true 400 4bbl. this was too long ago to remember the the exact changes, but there is a big change done right, if i can find the link i will post it for you.

If 71 bird was realy true he'd have said it made SOME difference but no matter what you do to the car without changeing partd i.e. heads, headers, intake, rear gears, torque converter, or add to it i.e. supercharger, turbo, You will only get minor changes, that engine was built with just so much hp that you can't make any vast improvements without makeing big changes. It will respond to the fine tuneing a little but it may be as big as 2 10th's or as little 1 10th in the quarter mile but don't expect any huge amounts. Hopefully you will understand this & not exoect to much & then be disappointed with the results , plus be mad at the person who tried to help.

While I'd agree not to expect miracles from tuning, that doesn't mean there isn't a lot to be gained. Look at engines like GM's 8100 Vortech. With the same internal parts, it was sold as everything from a 325 hp to a 550 hp engine - all it took was a calibration change to wake it up.

When you installed the exhaust did you change the exhaust manifolds too?
Change the manifolds to Ram Air or headders, to really open up the exhaust.

No change to the exhaust manifolds. I want the car to look stock yet.

I guess I need to be a bit more clear about what I am looking for. I am not expecting to add 100 horsepower, just better throttle response and slightly stronger feel throughout the entire range. I used to have a '76 455 4-speed car that was bone stock with 76k miles when I bought it. It still had the factory cat on it. I pulled the heads to repair some broken exhaust bolts. While the heads were off, I hot tanked them and did a valve job. The car then got true dual exhaust. I replaced the plugs, cap, rotor and wires. I also overhauled the carb and changed the springs for the centrifigal advance. The engine was entirely stock but it felt like I added 50 hp after just those items. It ran so much better and had incredible throttle response. I have already done those same things to my W72 and I can't tell any difference. So, there either has to be something else wrong yet or the carb needs some jetting changes. It runs as if something is holding it back under part throttle.

can't give exact beginning numbers, but after the changes it ran several 15.0's in the quarter spinning thru 1st gear. if i had known how to drive back then would have been mid to upper 14's easy, which isn't too bad for a 180 hp rated 400 that still had the original exhaust with only the converter gutted.

adding the 1.65 rockers is like doing a small cam change. while they say you need to open up the push rod holes before installing the rockers, i have done it several times on the stock cammed 77-78's. i would never do it on one that has an aftermarket cam already added without doing the mod first.

Leave your stock exhaust manifolds on........the Ram Air manifolds look COOL but really don't add much,if ANY performance....There are guys running 12's through the log style manifolds.

Beyond carb tuning & dist. recurve for MAX performance,I'd toss in a 068 factory grind cam. (455 HO) It will support an A/C compressor at idle & will wake that engine RIGHT UP.

In reguards to mzb & the reference to the chevy engine your talking about it's not just a computer upgrade to make them run better or have more hp. You have to look at the cam change , the injector change , the intake change & the throttle body change to get that extra hp. A comp. upgrade will not give you a change from 325hp to 550 hp. If you did every one would be doing it & there wouldn't be any use for any aftermarket support for them. A comp. upgrade will give some increase but will NEVER gain 225hp from it by itself.

3tas4me , you may want to change the cam if you don't want to change the basic look of the car. as it won't show then, but by just changeing to 1.65 rockers you need to do nothing to the push rod area as it doesn't affect the area at all. If you change the push rods you will have to open up the guides because they are a different diameter. The difference in the rockers is in the placement of the hole in the rocker where the push rod sits, it closer to the piviot point of the rocker so it doesn't affect the push rod area. The reason you would affect the push rod guide is the RA IV push rods are bigger around & longer then the stock push rods ou have at present. You can also add some lift by installing some of the new melling HD (raceing) push rods that are 9.130 long & that will increase the lift without affecting the duration which will give you the extra you might be looking for. That along with the o68 cam will really wake up the car. Don't forget you have to change the lifters with ANY cam change or you will wipe out the cam & lifter in a very short time, & don't forget to use the ZZDP additive when you do this because with out it the cam will go away while your trying to break it in, our new oil is JUNK.

I appreciate the replies, but as I stated originally, I do not want to get into changing the cam at this time. I am looking to maximize what the factory gave me with simple timing and jetting changes. HO Racing used to offer a kit for these cars that consisted of carb jets and distributor weights/springs. As Warbird said, if someone could find the HO article and post it that would help.

Jeff,
have you tried changing out the secondary metering rods on the carb (to richer ones)? That is a quick, easy change I've done to wake up the car ('74 455/auto T/A). I'm sure you'll want to change the jets & primary rods, too, but this is an easy one to start with.
I have a couple of good Q-jet books if you want to borrow them.

What is the timing set at now on your motor? If it's around 8* intial it's going feel like a pig. I usually start at 10 and go up from there but also check your total advanced. What springs are in the distributor? The factory use heavy ones that didn't fully advance until 3000+ rpms. In my T/A 6.6 motor,i used 1.65 rocker on the exhaust side.
And your fuel pump,what type is it. It might be losing fuel pressure at higher rpms,buy a good fuel pump. A decent running T/A 6.6 Trans Am should be in the mid to low 14's if it's tuned right.

I am going off of memory, but I believe initial timing on a W72 is 16 degrees BTDC.

I thought I read where HO Racing published a diagram that changed the vacuum hose routing. That is something I would also like to see if someone has it.

I essentially built an engine just like this. 400, 6X-4 heads, 068 cam (Melling SPC-7) well tuned distributor advance and carb. Engine is great fun to drive and will flat out fly.

W-72 upgrade
 

I owned a 1978 TA with that engine combo: I put true duals(2.5 pipes with turbo mufflers) and opened the hood scoop. I then recurved the distributor with an over the counter weight kit, used the middle (gold) springs and brass limiter bushing(got an approximate 22 degree curve at the crank), which worked out to 11 degrees in the distributor and moved the timing around to where the engine liked it (generally 12-16 degrees initial running premium gas), all centrifical timing in by 3000 rpm (at the crank). Ign total timing ran between 34 to 36 degrees, remember these heads were an open chamber design and if I had used 39-42 degrees I would have caved the pistons in- That would have ruined my day. Used all new Accel ignition components as well as a hipo coil. Then richened up the carburator primary jets 2-3/000ths, did NOT change primary metering rods, used a set of pontiac over the counter secondary metering rods-I believe 031 short tip ram air 4 variety- allowing for headers in the future. Also, ground off 1/8th of an inch off the top of the accelerator pump rod so it will sit higher and give you a richer pump shot when you nail it. The 79 w-72 cam, part#10003402 only has .374 lift on the intake side vice the more normal .406 lift which reduces the breathing at midrange and top end so you need to use 1.65 rockers on the intakes to balance out the breathing. installed poly locks and ran the engine, backed off each till it clattered loudly, turned it in till noise went away, then turned it down another 1/4 of a turn and tightened the adjustment, this allowed me 6000rpm when I needed it and kept the engine stable under load at lower speeds. installed 160 degree thermostat, carter hipo mechical fuel pump and Hurst linkage. Car had 3:42 gears so I did't screw with those, rear was posi. Performance improved significantly, could easily light tires up in first, bark second and third. Also installed 65-68 full windage tray and ram air oil pump, H.D. pump driveshaft and was able to cobble 79 L-82 chev clutch fan hub(noticeably looser-alot of milling/ drilling on that one to make it fit). Oh, one final item, No air conditioning and manual windows-who ever ordered this TA wanted a machine-the car was quick from jump street-I just tweeked it!!

RE: exhaust. Have to disagree with 2ManyTAs. Log manifolds are a definite hindrance in the midrange+. I hate headers myself, and the RAREs with 2.5" outlets work well! Would love to have long-branches.

I once had a dual exhaust made/put on by a "reputable shop," and I specified 2.5" all the way and even provided the straight pipe. Later, upon inspection, they had used some pathetically restricted bends, especially toward the front of the car: maybe as small as 1 3/4". By the time I went back, they were out of business. So you might want to have a look at yours on a lift.

tryconcom , all the Pontiac heads from 1967 were & are open chamber heads. The only heads that were closed chamber heads were the 670's in 1967 for the RA III engine. All the heads after that are open chamber heads. Unless you go back farther with some of the 389 heads. But again all 400 heads are open chamber heads.

FIRST things FIRST........you didn't say what GEARS you are running.

3: 23 is stock 70 W72...have they been changed out,because that will really affect your BUTT DYNO readings....

The car is stock, so it has the 3.23 gears. I am not looking to set the world on fire here, just want to make it run the best it can for what it has, which is definetly not the case right now. The dual exhaust alone should have woke the car up to some extent. It is the mid-throttle where the car seems to not run good. Light throttle seems fine as well as heavy throttle.

Is your car an automatic?
A higher stall converter would wake it up also.

:)

Rex RAIII heads were #12s not 670 heads 400 HO.

The stick is "the given" in this equation....

ALL 79 W72's were sticks. :D

I have several 78 W72 4 speed T/A's that are reasonably low mileage & basically STOCK,other than true dual exhaust (2 1/4") with set up carbs & HEI's and am VERY happy with MY butt dyno readings.....(78 W72 sticks came with 3:42's)

They DO pull pretty HARD & run GOOD but obviously the stock camshaft is holding them back.

You can probably bump your initial to 19.

Did you check for timing chain slop?

Is your stock EFE valve in place still? (and working?)

Ok, here is what I did. I pulled the stock 17059263 carb off and replaced it with a 17056263 that I have that is in good condition. I opened it up first and set the float level to 5/16 per HO Racing specs in the "Supertuning the Quadrajet" article. I checked the jets and metering rods and recorded what they are. The jets are 70 and the primary rods are 42K. When I removed the original carb, I noticed that the bolts were loose. Since the car acted like it was lean, this was a good indication that it probable was. I bolted the 17056263 carb on after cleaning and blowing it out. The car now runs like it should. Burned rubber as long as I wanted to in 1st gear when stomping on it after taking off. Pulled all the way to redline without a hint of pinging or any flat spots. I am now going to take the top off the 17059263 and record the jets and metering rods. I am also going to set the float level to 5/16, factory spec is 17/32 which is much lower! It is clear now that the car was having some carburetor issues. I will get the carburetor sorted out and then want to play with the timing advance.

W72 is fast.
 

I swapped out a set of RAIII Manifolds on a 73 455 automatic and gained a tenth of a second! Not statistically significant. You can get more of a power boost (up to three tenths) by cooler ambient air.
In box stock form breathing through the single catalytic converter, a W72 should, seat of the pants, feel no more than a tic slower than a RAIII. Check out the first car, a box stock Martinique Blue 78 W72 in my Movie This car has the original pellet style single cat:

http://www.youtube.com/watch?v=aLf5a5gejUI

Here is what I found with the original carburetor. When I pulled it off the engine, I found a pile of small black pieces. Figured out they came from the charcoal canister. The picture attached shows some of the pieces on the cardboard. Cleaned out the carburetor, reinstalled and tuned it. Runs much better now. I still think there is more to be had however. I set the float to 5/16, which is a much higher setting than the 17/32 that the service manual calls for.

Enjoyed your vid... The 78 does pull pretty strong,what RPM were you shifting at?
(sound like you might have short shifted into 3rd a few times}

Generally speaking I don't rev these cars past 4k. Most shifts were in the 3.5k range. Definitely had a few gears left on the martinique blue/black custom 78. Lots of things that sound good on paper (headers) don't necessarily work on these cars.
75 has stock 3.08 rear gears with close ratio t-10 and 2.43 first gear. Sounds terrible on paper, but this is a great combo on the street/road. Plenty of low end torque. Running only 2k at highway speeds.

Still looking for that HO Racing information if someone has it.

HO article
 

Here is the data from the mods. Car was a 1977 Trans Am TA/6.6 Automatic, most luxury options (cruise, a/c, etc.). 3.23 rear gear. Data is for 0-50 mph in sec.

Stock baseline 7.0
H-O Power Kit (basically carb rejet) 6.6
H-O Accuracy Kit (dist recurve) 6.5
H-O High Lift Kit (1.65 rockers) 6.2
Tri Y Headers & CrossFire Muffler 5.4
Raise 1-2 shift 4.6k to 5.0k 5.2

To get an idea how your car should run (maybe a tick slower since this is a RAIII) please view my latest test drive video:
http://www.youtube.com/watch?v=8aBrM...hannel&list=UL

Zirconia that is a bad azz RAIII T/A.

In my opinion the only thing that's gonna wake up that car is another point in compression. Compression is directly proportional to acceleration. Maybe a set of 62's so as comp is not too high but still large valve. Don't forget those pistons are chamfered as well as a large chamber head.
I know you said you didn't want to change anything, but if want to make an omelette, you have to break some eggs! JMO

I think what he is doing is just fine.

Car is running really good now that the carburetor is sorted out. If nothing else, it is at least performing as well as when it was new and I would bet slightly better with the dual exhaust. If I get a chance, maybe I will hook up my Gtech and run it.

Thank you. Not mine, a fellow TA enthusiast stopped by and showed it to me. He scared me. And pushed me back in the seat. Point is, properly runnning TA6.6 should be almost as fast.

I would actually disagree, stock for stock, a W72 should be about .7 -1 second slower in the quarter than a Ram Air III if you believe the period road tests.

More compression would help..have the heads been milled?

We are actually in agreement. As I mentioned previously, W72 is about "a tick" slower or 1 sec. slower.

Ok, got it. Too tired to think today....

Engine is stock. I am trying to maximize what I have without pulling the engine apart or getting into expensive mods.

When you had your heads off would have been the time...for the price of some gaskets something to consider.

I know with my stock 400 T/A's I have had,opening the hood scoop,installing the medium moroso advance kit springs to have timing all in by 3000,installing decent headers,dual exhaust and maximizing the total timing until pinging and back down a few degrees made a big difference.The low compression engines will take alot of timing.This was back twenty years ago in my younger days,I actually have an old book "Supertuning Your Firebird Trans Am" by Joe Oldham..which actually got me into tuning Pontiacs.

Get the air in and get the exhaust out.

Back in 79, my 78 Y88 WS6/W72 TA, auto, stock ran 15 teens.
I added stock 74 head pipes into the factory resonators and tailpipes. A flex fan replaced the factory clutch fan, I opened the hood scoop and installed LR 60 radials. The car ran 14.20's in the fall of 79.

A friend had a bone stock RAIII 70 TA, 3.73 automatic, no options. We ran many times and I always pulled him by a car or more. (man it drove him crazy)

I installed a 455 right after that, but had I continued an HO or RAIII cam would have been next with a set of headers and an earlier factory intake.

The motor is an air pump, the easier you get it in and out the more power it will make.

My W72 Can Am has run a best of 15.1@91. Mods include timing, slightly fatter mixture, open scoop, and 2" dual exhaust. Race weight is 4300. No changes to the long block at all as delivered from PMD.

A couple of years ago my friend's 78 w72 4-speed ran 14.8@95 with just true duels best of 5 runs,I posted this on another t/a site and was pretty much called a liar,nice to see people aknowledge these cars made good power and could post OK times considering the relatively small cam,and low compression.

I too own a 78 w72 4-speed in '92 the PO installed a comp 268H and headers to me it pulls pretty hard,in '04 I ran it, after a couple of runs, I couldn't get it to hook, I've never ran it since.

I can only imagine what 10-1 400 must feel like.

My friend liked the way my car went so much that we just installed the same cam in his with a recurve and heddman 28150 headers,the cam REALY wakes up these engines.

Don't mean to put you all to :sleep: with my rambling :focus:

3tas just leave that factory cam in it. With this post you got me wanting a bone stock 79 400 So i can do the same mods.

agree, logs are the worst, you will not get the full benefit of duals if you keep stock logs on

Some of the FAST guys are running as quick with logs as RA manifolds. If you look at a cross section one hole is pretty small on the RA. RARE has soem cut up at one PSN and when they all join together one hole is really small.

Liek others said air in air out. Open the scoop, get a wide band and use it to dial in carb jetting, quicker advance curve and check timing it wants at the track or a chassis dyno.

Without tearing down the motor 1.65s might or might not rub, you could use offset trunnion Crowers to get more ratio/more lift without grinding on the heads.

Rear gears will make the biggest change you can feel.