[78 Trans Am]

I am new to this site, and would like some suggestions for my stock 78 TA. I am under a fairly tight budget, possibly 1-2k, whatever I can get my wife to let me spend. I can get a set of disassembled #62 heads for 50 bucks, and that should help me some, but I need some suggestions on what to do with these heads. This car is going to be driven on the street regularly, so please keep in mind street performance. I also have a set of jet coated Flow tech headers waiting to go on the car, but will wait until I pull the heads. Any ideas on cam, intake, rear gears, also a stall converter? Specifics of the car at present are in my bio. Thanks.

[78 Trans Am]

I am new to this site, and would like some suggestions for my stock 78 TA. I am under a fairly tight budget, possibly 1-2k, whatever I can get my wife to let me spend. I can get a set of disassembled #62 heads for 50 bucks, and that should help me some, but I need some suggestions on what to do with these heads. This car is going to be driven on the street regularly, so please keep in mind street performance. I also have a set of jet coated Flow tech headers waiting to go on the car, but will wait until I pull the heads. Any ideas on cam, intake, rear gears, also a stall converter? Specifics of the car at present are in my bio. Thanks.

[WDCreech]

78 TA,
Unless you're going to install dish pistons avoid using those #62 heads. Too much compression for pump gas and they don't have hardened seats. There are better heads out there.

------------------

Bill

[KS circutguy]

You should be able to purchase a set of 6X heads from Butler,Rock@Roll,or Jim Tayler Engine Service complete and ready to bolt on for less than $1000,my opinion is that would be the way to go..

These guys are pontiac experts and do the job right the 1'st time.

Too many machine shops think a pontiac motor is a chevy and what works in a shuvet motor does not work in a pontiac...Also check with TFX for a solid lifter cam and their lifters... And go with a Solid Lifter cam..

Just my opinion, [img]/infopop/emoticons/icon_biggrin.gif[/img] Good luck,Steve.

[Brian Baker]

Here's my .02 on the subject:

The 62 heads, although a good choice for performance, are not a good choice for a pump gas 400 as they would give you between 10.0:1 and 10.5:1 CR. I'd just redo the heads you have on the car (they should be 6X). They'll will probably come in around 98cc, you can have them milled .030" which will reduce the chamber size to about 92cc, which will produce just about 9.0:1 CR. Mill them .060" and this will defiantely bump you over 9.0:1 but not so much that you won't be able to run 92-94 octane pump gas. Just be sure to have the same amount of metal milled from the intake manifold mating surface of the head, otherwise you'll run into intake manifold alignment/mating problems. Mill the head, not the intake manifold, this way you'll be able to use any manifold on these heads.

I strongly recommend not installing a solid lifter cam. They can produce more power as compared to an "identical" grind hydraulic, but unless you enjoy constantly adjusting the lash on them, they're a pain in the ass. I mean, this is a street car that you plan to drive alot, right? I'd go with a hydraulic having 215-220 degrees of duration @ .050" (intake). I've had good luck with Comp-Cams.

Nix that stock intake manifold as well as it has restrictive secondary openings. You can go with an earlier Pontiac cast-iron intake (made before '74) but be careful as some of the early ones don't seal very well against 6X heads in the heat crossover area. My choice would be to just install an Edelbrock Performer (not the RPM as it will cause interference between the shaker and the hood) or a Holley Street Dominator (if you can find one at a swap meet, they're out of production).

I'd also freshen up the tranny with a shift improver kit and a new filter (and fluid). Get a set of 3.23 or 3.42 gears for the rear (3.55's not available with the 8.5" 10-bolt, 3.73's may be too steep if this will be driven frequently on the freeway).

A set of exhaust headers and a good 2.5" dual exhaust will help as well.

No need for expensive head porting. For a budget of $2K, you should have trouble aquiring the folowing and installing them:

cam w/lifters
intake manifold
double roller timing chain set
valve job on 6X heads
headers and exhaust
tranny shift kit
rear gears and installation

Keep the Q-Jet, just have it cleaned and rebuilt, it'll work fine for the street. With the above mods you should have little difficulty getting it into the 13's in the quarter mile.

Brian

[GTO Karl]

What Brian said:

Only exception, in my opinion, is the cam. In my experience, you can run at least 10 degrees larger than he is suggesting without any effect on idle quality. My 4000# 70 Goat ran 13 ohs to 12.90's year after year with a 228 int, 234 exh at .480 lift. 3.31 gears, 2000 stall, 3 tube headers w/2.5 inch through tailpipes...I did run slicks at the track however. I drove this car everyday, had good economy, lopey, but consistent good idle in gear, best shift points of about 5600 rpm. Stock intake and Qjet.

I now run solid lifter or roller in all my cars, more power and ability to tune with lash...good poly locks solve adjusting problems that everyone always worrys about. Stories of constant adjustment, are leftover from the days of pinch nuts from the factory,that work loose regularly. Also, you can adjust while car is cool and not running, hyd. need adjust while engine is idling and flinging oil all over. And no matter what cam chosen, make sure and degree it, installing at an intake centerline of 104-106 degrees because of your lower compression. And always install 2 deg. extra advance to make up for timing chain stretch, which from my actually checking this, is about 2 deg in the first 5k miles, then , 1 deg each 5k miles afterward. This may not be as bad with a low rpm non roller cam setup like I have been running lately, but it is still enough to plan for with a little extra advance.

Otherwise, everything Brian had to say is what I would say as well.

Good luck

Karl

[Brian Baker]

Karl,

Perhaps we are both thinking "old school" (me in regards to solid lifters, you in regards to hydraulic). The method of adjusting hydraulic lifters while the engine is running is really not neccessary anymore when using quality locking rocker nuts. To function correctly, the lifter only needs .020" to .060" of preload, which is easily accomplished while the engine is cold and not running. I adjust mine by rolling the pushrod between my thumb and forefinger with a light touch as I tighten the rocker nut. Once I can no longer rotate the pushrod without tightening my grip, I take the nut another 1/2 turn and lock it down.

An important note when locking down a rocker nut with a set screw in the center (like those used on most roller rockers) is to NOT lock it down after achieving the desired position of the nut. Turn the nut until you get to within 1/8 turn of where you want it set and locked, then turn the set screw until it "bottoms out" against the stud. From here, turn both the set screw AND the rocker nut the additional 1/8 turn simultaneously. Locking the set screw AFTER you tighten the rocker to wher you want it will not ensure that it stays locked in that position.

Karl, was that 228 cam in a 400 or 455? Additionally, did you have to be concerned about emissions testing?

[GTO Karl]

Brian:

It was a 400 motor, .060 overbore with #13 heads. It went through emissions testing last in 1987, (before our laws changed to allow for older cars). In Oregon, we have always had to drive through state operated emissions testing since the mid 70's. At the time, it went through emissions passing 1987 standards, which amazed the guys at DEQ(slang for the Department of Environmental Quality that runs the testing stations). However, two things are of note, my tuning skills are excellent, and at the time I was running my own carb and distributor shop. And also, most all important emissions controls are for dealing with the engine while it is under choke conditions, this is when most pollutants are spewed out, since most all testing is done on warm engines at cruise and idle, it is fairly easy to get an older engine to pass emmisions even for modern standards. I have done it many a time for customers. In fact, my friend has a mid 10 second car that just passed emissions testing. Another thing of note is a little trick, Platinum spark plugs will simulate the effect of a Catalytic converter, but to a lessor degree. The platinum electrode will cause the same reaction in the combustion chamber as the platinum in the Cat., but less so. Sometimes, this can make the difference at the testing station.

As per adjusting valves, you are correct, and I have used that method before. Fact is I have more reasons for using solid lift cams.

In a hyd., you never actually know what your running duration is...it is affected by too many variables, such as: oil viscosity, oil temp., lifter bore clearance, oil pressure, lifter bleed hole diameter(.0001 makes a significant effect, I have used a bleed rate tester to check this),and ramp design of the cam. None of this means hyd cams don't work great for many applications, as we all know. However, after blueprinting and measuring every important thing I can think of in my engine, I want a cam in which I can accurately describe exactly when the valve events are happening, this is especially important when calculating effective(or dynamic,as I've seen it reffered to on the board) compression. Also, you can get more lift for any given duration with a solid, which means more area under the curve, which means more top end with no give away of bottom end.

You do have to be a little careful when choosing a solid, cams of 280-290 degree seat to seat have idle charactaristics of hyd cams well over 300 duration, which only goes to show that much of the advertised duration of the hyd. cam is used up by the time the valve actually leaves the seat, but how much, almost impossible to tell without very specialized equipment. So a solid for a street driver should have 260-270 duration at .020" lift for decent idle, but the same .050 specs listed above, a cam can be found from many sources that will have these specs and .480-.500 net lift(after lash) as opposed to .450-.480 typical of hyd cams of equivilent idle and low end charactaristics. This will give an across the board increase in power, especially in the top end performance. Not a ton, but perhaps an extra 1/4 sec at the drags, and in my opinion, it is worth doing, since it only means a different purchase, not a bunch more work. And, its not very comforting for me to be able to quote a books worth of accurate data about my important engine specifications, and not know exactly when my valves are opening and closing. It would not surprise me at all, to find that a hyd. cam could vary +/- 5 degrees of seat duration from engine to engine, just because of different lifter clearance, or brand, or oil. The difference between the bleed holes from a stock lifter to a Rhodes type, is only a couple 10 thousandths. So, any quality control problems can cause your cam timing to be variable from cyl to cyl, and since most lifters are scooped from a barrel into a bag for delivery to the end user, I'll stick with solid lifter.

As a side note, I can't prove this but have been told, that at the factory in the 60's, each lifter was checked with a bleed rate tester and then sorted, so that engines would get closely matched sets, the looser ones going to the high perf cars with bigger cams, the engineers were well aware of the drawbacks to high production of hyd. lifters.

Still, hyd. cams work well for most people, I've just never had a problem with a solid, or had to adjust them much, which isn't hard anyway. So the peace of mind and extra HP is worth it to me. And you don't need to restrict the block, as I'm sure some still believe...non of my engines are.

And I like the sound of valvetrain clatter!

Later

Karl

[Will]

For those wanting to run the Performer RPM intake in their '70 - '81 TAs, there is now a special aircleaner base available specifically for that application.

Check it out at:
http://www.blockersperformance.com/

Now, if they'd just make one for the '70 - '74 Formula ram air systems...

-Will

[Brian Baker]

I just purchased one of these from Bryan, good quality! Haven't installed it yet, however.

Karl, maybe you can give me some tips on getting mine to pass emissions. 79 T/A, 455 with 238/243 - 112ls cam using Rhoades lifters, Q-Jet, headers with dual exhaust (no cats). I've tried leaning it out, retarding timing, installing a 195 degree 'stat and it still blows too much HC. Our state requires no more than 400ppm on the HC and it typically blows more than 1200. I even converted this thing over to methanol by installing a Holley 750-DP setup for it. This combined with a 195 'stat and timing reset to where I normally run it still blew more HC than required. What pissed me off was that my HC was way higher on methanol than it was on gas (2800ppm vs. 1250ppm). If a byproduct of burning methanol (alcohol) is oxygen, how the hell can my HC numbers be greater than on gas?! The rep. at the emissions station advised it was due to a rich mixture. I say that's bull****, even if the carb were rich, how could the HC's be nearly triple what they are on gasoline?

[GTO Karl]

Brian:

You did not say if your problem was at idle, cruise, or both.

Couple quick things:

Excessive HC is often misdiagnosed as a rich condition. Unburned Hydrocarbons are just as easily created through poor mixture burning from being lean as from just having to much fuel.

Also, to much timing at idle or cruise will cause the HC's to skyrocket. Make sure vacuum advance is at a ported source on the carb, so no additional timing is provided at idle above your initial timing setting(which for the purposes of emissions, should be held at or below 12 degrees).

What carb are you using?

I can give suggestions for different carbs.

Also, if your vacuum advance canister has a large amount of advance built in, it can lead to too much timing at cruise and aggrevate the HC problem, especially if on the lean side.

If using a Qjet...I definately have some helpful suggestions. Just let me know.

I'll post again with more specific suggestions if you provide answers to the questions.

Karl

[GTO Karl]

OK:

I reread and see that you are using a Qjet. Many Qjets lack the range of adjustment necessary for a rich enough idle mixture when running a big cam, this VERY often gets misdiagnost(sp?-osed)as rich condition. With a cam the size of yours, and a Qjet likely from a later model near the year of your car(?), this will be especially true.

First thing to try is enlarging the idle discharge holes where the mixture screws are located. The factory only allows for an adjustment range around the specs of the car produced. So, you can turn the screw out all you want, but it may never get rich enough because of the small discharge port. If you drill this out to .093(and larger for big roller and solid cams) you will simply increase the adjustment range, you can still lean it as far as you want by turning the screw in.

If this isn't enough, then you need to adjust the orifice size in the idle down tubes. This is effectively the idle jet. If you need more fuel than the idle circuit can deliver, it is because this tube has become the restriction. This is difficult to do, but I have posted some info on how to do it on my web site: http://www.ponchopower.com under carb specs. There are other tricks but I don't have time to write a book just now. If you decide to tackle this and need specific help making decisions or having questions answered: email direct at gearhead@ponchopower.com and I would be more than happy to help.

Last thing...if the butterflies are open to far because of the larger cam, the mixture will be rich at idle because it will be drawing fuel from the off idle transfer port(the vertical slot above the idle discharge port), this can be corrected by enlarging the idle air bypasses or drilling the butterflies or both. This is shown on my website as well.

Also, check to be sure that the venturi's are not dripping at idle, and that the well plugs under the float bowl are not leaking.

Good luck

Karl

[Brian Baker]

I'm not sure if I want to get too much farther into this (don't want to rehash old info) but here it goes.

My Q-Jet has a "stage-2" modification from Jones (JET). 74 jets, 41 rods on the primaries.

HEI is set for 14-16 degrees initial advance with 32-34 total, vacuum advance is disconnected.

Cam = 238/243 @ .050", 112-LS, installed at 108, using Rhoades lifters

Our emissions test in MD consists of an idle "sniff" and a higher rpm (like 2500 rpm) "sniff". Because my car was made prior to 1984, I do not have to subdue to the treadmill test (which is similar to the California IM-240). Basically I do the IM-240 without the treadmill. They don't show difference for idle or higher rpm, you get one number. In my case, I'm not tested for NOX, just HC and CO.

For now, I have a friend whose father owns a shop and he's willing to help me with obtaining a waiver (in MD, I have to show I spent $200 trying to improve the cars emissions before they give me a waiver). I'll still need to get it tested one more time though before its 25 years old (at which point I can get "street rod" tags and have the car exempted), so I'd rather not go through the waiver crap again.

[GTO Karl]

Hi Brian:

Only thing I see is you are running substantially richer mixture than I usually do in any of the cars I've built or tuned. My current car as listed on my web site, a roller cam 455, uses 74 jets and 46b rods. I experimented with 76 and 78 jets with the same rods and fuel economy dropped dramatically, from 14 to 9, with no improvement in ET at the track! In combinations I have owned similar to yours, I have usually run 72 or 73 jets with 43 to 46 metering rod. It doesn't particularly matter which jet you have, since it only effects full throttle performance, but the metering rod determines the metering area(area of jet minus area of rod). So for whichever jet you choose for max full throttle performance, you then choose a leaner and leaner metering rod until part throttle perf. suffers. This will net you the best emissions and fuel economy. So in your case, you are running the equivilent of five jet sizes richer than the richest combination I have ever had to run.

Once you lean the metering area, you will probably find that the idle circuit will need some work.

Also, you seem to like to run your cams less advanced than I, judging from comments in some of your other posts, 108 is fine, just not where I would put it, however, if you have any miles on your car, I can garauntee, it is not at 108 any more. I don't know how this will affect your emissions because I have never played with an engine(that I know of) with the cam that far back. Especially a cam as large as yours. But, it is likely your effective compression(comp. calculated at the intake valve closing point) is low, which will have a significant effect on cyl. pressure at idle and during low throttle position engine activity such as when at part throttle during emission testing.

So, I think you might want to try a one or two smaller size jet, a one or two size larger metering rod at the same time, then correct for any idle problems found as per above discussion.

I also run more total timing than most, but thats a topic for a different discussion, even though it might have some bearing on your emission test.

Good luck

Karl

[Brian Baker]

Thanks Karl,

I was shooting for the recommended 106 installed centerline, but with Rhoades lifters I was told the cam would react more like it was installed at 104 if I put it in at 106, hence the reason for retarding it to 108.

[KS circutguy]

Hey Brian,if ya think we (Karl @ Me)installed my thumper tooo advanced.

Karl has his at 100..

A cam too advanced will affect HC too,and I dont think tuning will get it threw.
But ya never know till ya try.

Also if mine wont pass the sniff test I'm just going to install 2 aftermarket high flow cats.
You can get em for around $89.00 a piece..And just connect them at the header flange,and add another flange to the other end.Then you can leave um' on or take um' off when ya need to ...Why hand over $200.00 to someone just to get it threw the emissions testing when the cats will do the trick..And the money is for parts that will get the job done!!

Then you can tune her right as per Karls instructions.

Just remember to get the thing up to temp. and stable,so the cats fire off...


[img]/infopop/emoticons/icon_biggrin.gif[/img] Good Luck,Steve.






[This message has been edited by KS circutguy (edited 11-27-2000).]

[This message has been edited by KS circutguy (edited 11-27-2000).]

[78 Trans Am]

Thanks for the posts guys, I appreciate the suggestions. After X-mas, I will start investing some money into the engine, and this has been a big help in determining the route I want to go. GTO Karl, I see you have a business in building Pontiacs, especially for the street, so if it would be possible, I would like to send you my carb for a rebuild. I live in Ga, and the car does have to pass emissions, so along with the 2.5 exhuast, I have to go with cats because they do a visual inspection. I will try to go as close to your post as possible, so I might be emailing you sometime soon for more specs. Thanks all.

[GTO Karl]

Steve is correct that I have my cam set currently to 100 ATDC, this is a recent change(mid July), and is not where the car runs best. I have experimented with different settings, and, in my particular combo, the cam works best at 103. This is after long term track testing. I have had the cam from 106-100 at various times and have checked timing chain stretch each time. The car has best 60fts with the cam at 104 or lower. No topend change when above 104, however when moving from 103 to 100, my idle quality improved in gear(stayed same out of gear), 60ft did not change, but I gave up .05 in et and 1/2-1 mph trap speed(best at 103=117.95 consistently above 117 even in heat of summer, best at 100=117.45 but this was in kill conditions, usually mid to high 116 range. I'll be changing it back this winter. Although my et improved throughout the season as my launch technique improved for street radials(in other words, 60fts dropped considerably)my split times (60-1/8, 1/8-1/4, and 60-1/4) all showed about .04-.05 consistantly slower with the cam advanced past 103.

All this is just to say, that, there is no right or wrong cam advance, only what works best in your combo. I always build low compression engines, with the lowest being 7.8:1 and running 12.30's at 109 mph. My current "high compression engine" is 9.02:1. The choices I make are relative to the type of engine and cam combos I am typically around. I wrote a program, that allows me to choose the cam advance, setting my effective compression with the intake valve closing point. I know how much effective I can get away with and have no trouble with detonation. So, I choose the biggest cam that will work with the rpm range I plan on running when advanced to give appropriate effective compression. This method has worked very well for me in building street strip type cars that are driven more than occasionally and have to have compromises made to deliver best perf. for buck with least hassle for driving ie, av gas, race gas, bad drivability. Of course there are more factors I consider, this is just the most critical and all I can fit in a paragragh.

78 Trans Am:

I would be glad to help with your carb, but I don't like using the board for advertising, just trying to help out when I can, and try to stimulate scientific and methodical thinking when approaching making the choices that affect the performance goals of other Poncho lovers. So email me direct, and I will deal with you on a personal business level separate from goings on of this wonderful tech board.

Brian:

I don't know what compression you're running, but cam degree changes are not super critical, as you can see from my own experience, however, the closer you get to the killer tune-up that makes your car fly, the greater the effect will be in having your cam in the most appropriate location. If I was running 11:1 "actual measured" compression, or even 10:1, I could not advance my cam as far as I have without encountering low end detonation problems. On the other hand, if I retarded my cam, I would have to rev past my shortblocks limits to achieve max performance. (when it was at 106, it labored shifting at 62-6400, advance the cam, and it hits nice and hard when you shift). So, the point would be, that many factors need to be considered for each desired end result. I probably have to big a cam if my car was only driven on weekends and I used slicks at the track, I went extra big to kill the bottom end for traction, advanced the cam for more mid range and lower shift points, and it paid off with a killer daily driver that runs high elevens, with a killer top end charge, but has the manners of a 13 sec car. And it even hooks "pretty good" on the street.

If I ran more converter, or less gear, or slicks, or even sticky street tires, or any number of other parameters, the choices I made would be different.

Last thing, I'm a test and tune fanatic, and document everything I can, making very careful changes with the patience to follow through on timing loops, jetting loops, and even shift point and driving style changes with virtually every change I make, this takes along time, and many trips to the track. But it always pays off in dividends!

But no matter how I try, I always have to run 38-44 degrees total in every car I've had my hands on, at 30-36, they always run slower if jetted correctly, (at 32 degrees, my car is a dog, over 1/4 sec slower at the track), at least for street strip, I'm not talking about 10 and 9 sec cars with very efficient combos. I don't want to turn this post in to an argument about total timing, but if you are in fact running a lower compressin motor, don't be afraid to richen your secondarys, and bump your total to 40 degrees, and see what happens. I'll bet you'll be pleasantly surprised. Our engine designs are just not efficient enough to support the lower timing figures, those kinds of numbers aren't normally productive until you start using high dollar cnc ported, heavily engineered, modern technology head designs. The flame speed in our old cyl heads, at least with street strip level mods, are not fast enough for the timing to be as low as what is seen on 700HP dyno tuned race engines with efficient combustion chamber designs, and all other factors optimized.

Anyway, I hope some of this was helpful!

Karl [img]/infopop/emoticons/icon_smile.gif[/img]

[TinInjun]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Brian Baker:
I even converted this thing over to methanol by installing a Holley 750-DP setup for it. This combined with a 195 'stat and timing reset to where I normally run it still blew more HC than required. What pissed me off was that my HC was way higher on methanol than it was on gas (2800ppm vs. 1250ppm). If a byproduct of burning methanol (alcohol) is oxygen, how the hell can my HC numbers be greater than on gas?! The rep. at the emissions station advised it was due to a rich mixture. I say that's bull****, even if the carb were rich, how could the HC's be nearly triple what they are on gasoline?[/B]<HR></BLOCKQUOTE>

Brain:
Thats a good question, seeing how alcohol is not a complex hydrocarbon as is its fossil fuel cousin. Hydrocarbons should have been nill if you were running a 100% mixture of alcohol. I use a 10% mixture of alcohol/gas when I do my emmisions check. This works like a champ. The other thing to consider when running alcohol is that it has half the btu's per gallon than of gas. You need to richen the running mixture by double to get the proper mixture. One more problem when running more than a 10% mix of alcohol/gas, it will eat any rubber fuel system parts, such as lines and fuel pump diaphragm's.
BTW adding a catalitic converter may help some with hydrocarbons but not much. Its main function is to reduce CO by changing it to SO2(sulfer dioxide). By the time the exhaust has reached the cat, there is not enough O2 left to burn the unburnt fuel. GTO Karl has sent you on the right path. Follow him and you shall make it to the promised land, or at least pass emmisions. [img]/infopop/emoticons/icon_smile.gif[/img]


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"Run wild with an Indian, not with the crowd in a Chevy"
Check out my restoration at http://members.aol.com/jetmech15/gto