I haven't posted here in a while, relocated to WV for work and have been really busy. My car is mostly a weekender for car shows but I'm planning to bump the ins. to cover me for drives to work when it's nice out this summer. Thanks in advance if anyone has advice or a past experience that helps me out here. I'm not sure what I'm missing in my tuning, but my firebird doesn't seem to be performing at it's best.

I'm set as follows:
1) stock 400 rotating assembly (68k miles), rebuilt heads w/hardened seats
2) rebuilt quadrajet
3) pertronix(points & condenser replacement), new cap and wires
4) rebuilt stock M40 auto
5) original torque converter
6) 3.08 posi
7) The pontiac blueprinted "068" cam

I'm running a mix of 92 octane and 115 leaded. About 70/30, the timing is set 6 or 8 degrees advanced past 6 degrees BTDC.

The car doesn't bog or hesitate, launches strong with no tire spin & will chirp the gears on occasion. Back tires are P245/60/R14. Seems to me that tire spin should be an issue at WOT from a stop (not that I'm planning on melting them), the transmission also seems to me like it shifts out of first way to early, & under WOT it shifts into 3rd at 4k rpm. Am I expecting too much from this combination or does something stand out as a potential problemm, maybe the torque converter or mechanical advance in the distributor?

Don't know about your early shifting (might be the modulator), but my guess is that you need a higher stall convertor to help with those launches.

You may be right, the original cam was 325 HP at 4,800 and 445 torque at 2,900.

The new cam is 360 HP at 5,100 and 445 torque at 3,600.

I'm not sure how to calculate the best stall speed, rough guess from the numbers seems like I should bump it up 300 to 700 from the stock converter(?). I've seen 2700 rpm mentioned on some of the drag race books but I don't want to ruin the streetability.

Modulator sounds like a safe bet, I hadn't really considered it since the trans was rebuilt but don't know what else it could be. I'm researching these two items...

Where areyou getting the hp and torque numbers from? Dyno? Engine or chassis?

I think they are the factory cam specs, I'm sure the actual numbers are less, I'm just looking at them in relative terms.

http://www.dapa.org/jhpages/jhand5.htm

Cams can't be rated for HP and torque. Such a figure is meaningless out of context. That said, it sounds like the 068 cam, which is a nice grind that has been made in many close variations by many makers over the years and is well suited to 400 street engines.

Continental has the best converters on the market. Lots of Pontiac guys love them. I can tell you first hand, they work like a tighter converter when part throttle accelerating and cruising, but allow more stall when you really put foot into it. Can't say the same for other brands.

If you call them with your specs, they can custom build for you. http://www.ctconverters.com/

Hey thanks Mike, I was looking at that as well. Here's an interesting look at governers.

http://members.optusnet.com.au/iroc-z/mods/TH-400%20Governor/governor.htm

Vikki,

Yet, that is exactly what pontiac did, rate the camshafts with horsepower and torque. They were listed in the link you responded to, cam specs that relate to horsepower and torque. And as I said, they are relative.

I think you need to read Jim Hands article a little more close. I believe he used several different cams in his 455 engine in a 4100# car with a 3.55 ratio. Quite different than a 400 engine...and still we do not know head codes.

Cams are related based on other factors and are based on which heads and car they were installed in. Cams can be rated for HP and torque only with other known parameters such as head CC, carb, exhaust, rocker ratio and compression.

For instance, a 400 GTO with the same heads and cam as a 400 Firebird the same year would show 360 HP in a GTO because the GTO was heavier. The 068 in a GTO was rated at 360 HP and in a Firebird 335. HP numbers also depend on the carburetor and exhaust manifolds.

What head codes are you running? That could be an issue. As well, the carb linkage could be binding up, not tuned or you may have a vacuum leak. What are you seeing for vacuum at the port?

IMO, you will NOT see 360 HP with a blend of 70/30 in a 400. If you had the CR to attain 360 true flywheel HP, the 3.08 rear would be a detriment as Firebirds in the HO or RA realm were advertised at 335-340 (under rated) yet were optioned with 3.55, 3.90 and 4.33 rears. If you had true 360 HP, you would be hard pressed to see the benefit as 3.08 would not allow the engine to dig in early and hit your HP/RPM band as the cam/head/carb/exhaust package would allow.

You are running 98.9 octane. If you have a motor built that is at 9.5 or below, too much octane will reduce engine performance. I used to run a blend of 70% 94 Sunoco and 30% 110 unleaded in a 428 with #48 heads 0 decked at 11.2 to 1 and ran awesome to low 12's in a 67 Firebird with 3.55 gears.

If you are running a stock 400 with 72 cc heads with no milling to block, piston CC or motor, you will be right at 10.6 with a .030 overbore. Then yes, the blend would be appropriate.

Tom, more octane than needed usually has little or no effect on power output; there is only a slight variation in the energy content of the fuel.

Could you elaborate specifically? Perhaps I did not elaborate on something that perhaps you could have better elaborated upon.

I am not at all inferring that if you use 110 octane in a 9.5 to 1 motor that you will see a performance increase. That is asenine. So if you use 110 octane in a motor that is 9 to 1 compression that there will be no degredation in performance?

Too much octane will have a negative effect on an engine not needing higher octane. Too little octane will have a negative impact in an engine requiring same.

Excellent point on octane. I think my cars' compression is 10.75 to 1, since the block and rotating assembly are as-is from the pontiac assembly line with 68k miles on it(excpet for a new oil pump and roller timing chain), and the rocker ratio is still 1.5:1, if I am reading the AMA literature correctly.

And, Thanks.

I realize I don't have the most ideal combination, my goal is to have the car perform it's best this summer without throwing a lot of money at it.

In retrospect the cam seems like maybe a poor choice to me now.

I'm having a hard time finding the stall speed for the stock converter. In the AMA they list a Max ratio for stall of 2.3:1 for all firebird with the 400.

With the same drivetrain, isn't heavier simply slower?

1) The heads are stock 670, rebuilt with hardened valve seats. Rocker ratio and compression is what came from pontiac for the firebird 400 in 1967.
2) Exhaust is stock cast iron.
3) The carb is a Service replacement quadrajet made in the 1970's (rebuilt ~2 years ago, doesn't bog, leak or hesitate). The code on the carb is 7037263, which translates to a MT-AIR for a 67 full size pontiac or GTO with a 400 or 428.
4)with the vehicle warmed up and running at 600 rpm idle, vacumn is 10. Not using rhoads lifters.
5) Linkage and tune appear good to me, I just changed the spark plugs, set the timing and adjusted the carb.

No garage anywhere near where I live has a dyno or expertise working on old pontiacs. If there was I'd have the car tuned on a chassis dyno and take out any guesswork.

I'm not expecting the car to run the advertised numbers from the original specs., especially since I'm not running the ideal combination.

Changing the shift points looks inexpensive, any reason not to change these? I may just focus on the shift points and keep my eyes open for a complete 3.55 rear, unless there's some way 3.55's work with my differential housing. I have a date coded matching numbers carb which I haven't had rebuilt yet as well.

You are looking at a 400 with 670 heads which relates to 360 GTO HP.

Pontiac did not install 068 grinds in Firebirds opting for small 066 and 067 to keep the HP to weight ratio.

Could you see 360 HP by just swapping out the cam? Yes and no. All Firebird 400's came with 1.5 except RA II and IV.

Hey Vikki,
Point taken on context, the numbers are only good for the car they were published for, and even those appear suspect really.

Correct. Octane rating is essentially a measure of resistance to auto-ignition, not burn speed or burn temperature as some think.

Specifically, high octane fuel does not burn slower or cooler. The energy content and flame speed of pump gas will not vary much regardless of octane rating, although some engines will produce slightly more power with a lower octane fuel. That is partially because the energy content can be slightly higher (different additives) but also because it can actually be beneficial to have a trace of detonation. I wouldn't recommend tuning for that though.


No; using fuel with more octane than the engine needs will have a negative effect on your wallet.

I think the gear ratio is hurting you the most on take off. I'm not sure on how well the stock exhaust flows but that could also be a little restrictive. I'm not sure how much it will help but I installed a 350 converter on the 400 tranny. It's suppose to have a little higher stall. I think B&M also sells a adjustable vacuum modulator.

10 inches of vacuum seems low. Could be late cam timing?

Well, I had a 400 with 5C heads and was running a blend which came to roughly 100 octane. I was at 8.8 to 1 compression. I did not know what heads were on car because they were ground off. When I switched to 87 octane, the car ran exceptionally better with no other modifications after I pulled heads and CC'd chambers. That was circa 1990 or so.

Anomoly?

I'd keep the 3.08 gears for highway driving and engine longevity. Also keep in mind, that depending on trap speed, you can actually run a faster 1/4 mile, if it allows you to avoid shifting into 3rd gear. Food for thought. And, even if you change to a deeper gear, you should still change to a torque converter with the proper stall.

Also with the factory compression ratio and assuming a factory ground (116 LSA) you should have no problem running super unleaded.

The vacuum does sound low with that cam even at 600rpm. It's not a large cam, and with a 116lsa, it should be pretty good. A tighter LSA might give you a little more low to mid-range torque to go with those 3.08 gears, but again, at the sacrifice of idle vacuum and octane tolerance.

First thing I'd do is properly set your dwell, and then check your initial timing and total timing (with vacuum port on the carb plugged). Also record when the max timing comes in. The 670 heads are closed camber, which tend to like up to 42° total timing. I'd try increasing it by 2° increments until you get to that point and see when you get the best performance. Don't bother with "light" aftermarket springs and weights. They can cause the distributor to hang up, and artifically starting the advance earlier can tend to cause irradic idle. Then verify with the engine warmed up, if you have excessive starter load. If you do, you might have to compromise and back off you timing. Once you get the timing set, readjust your idle mixture for highest rpm (you'll probably need to adjust it leaner than it was before. That's because more timing can cause enrichment. Then readjust your idle speed back to 600rpm. I think you'll find a significant vacuum increase. If you're not getting at least 14 Hg-in at that point, you should redegree your camshaft to make sure it's set properly. You might find you need to adjust your cruise mixture leaner than before as well.

Also keep in mind, too tight a torque converter can also cause low vacuum. So be sure to order the new torque converter once you have your timing and carb mixture reset.

Likely, but hard to say without testing both fuels. What were you using for ignition?

MSD 6AL box and HEI with a retard mod which was not adjusted.

change the carrier and gears to 3:55. swap out a higher stall convertor and let us know your results. somewhat unanimous among majority of board your asking. <<<< just making an observation!!

Again, I'd leave the gears (at least save it for last). They're fun for acceleration, but not so much for highway. Overdrive really spoils a person. I think with the proper stall, degreed camshaft, and tuning he can get where he wants to be and keep the gears. A set of rhoads lifters would be nice too, if he can handle the "solid lifter" sound.

Agree with Mike, no sense in changing out gears if you have drivability issues, won't make any difference.

What's total timing, and at what rpm?
For higher shift points, gon'a have work on the governor.

Tom, that should be fine so no reason for the difference there. Low octane fuel has the light ends that can be the difference between fire and no fire in a marginal case.

I'm going by my experience and dyno testing of pump gas and haven't come across a situation like yours personally. Not to say that it can't happen, obviously, but that I haven't seen it yet. I've seen a couple of cases that looked like an octane issue but turned out to be something else, usually ignition related.

Anyone else have input on this?

So any update on this? Has the OP gone through the tuning measures yet?