[Lee]

SUMMARY: Tri-Y headers 1.75" gained 45hp and 35tq on a very mild 455, compared to standard log exhaust manifolds

I just tested a set of 1.75" primary Tribal Tubes on my low-budget, ultra-low CR (7.8:1) 455. The results were better than I had expected.

I initially tested the motor with the stock log exhaust manifolds and head pipes. The exhaust system necked up to 2.5" pipe off the headpipes, after they turned horizontal, then to 3" Flowmasters, and finally out 2.25" tailpipes. After playing with timing and metering rods, I got 225hp and 310tq at the wheels.

I have since installed the tri-y's. I spliced into the 2.5" pipes to connect the headers, but the rest of the exhaust remained the same. With the carb and timing the same as on the best previous run, it put 265hp to the wheels. I played around with different metering rods, and richened it with some CV's and got 270hp and 345tq. Going even richer caused the HP to drop, but TQ remained the same.

I will next replace the entire exhaust system past the collectors. I'll post results once I have them.

455, .030" over bore, iron intake, Q-jet, stock "66" heads, 222/242 @ .050 low-lift cam.

[Lee]

Too late to edit my initial post, but:

Peak to peak TQ gain was 35 ft-lb., but notice at 4500 there was a gain of 55ft-lb. The headers improved power everywhere, but the improvement increased as RPM increased.

[steve25]

I am not surprised in the least!

As you get into motors who's stroke is equa to or greater the there Bore like the 455 there piston speed creates much more Exh velocity which makes them far more sensitive to to restrictions and sharp bends in the Exh system that are in place right off of the Exh ports!

455 SD motors of 73 & 74 lost 90 hp thru the cars stock traverse muffler system even with nice round port Exh Manifolds bolted to the heads and 2.1/4" head pipes!

People who state that they have bolted up headers to 455 motors and not found a big power gain have a motor that's way out of proper tune to begin with!

[Dave M]

Great info. I can't tell you how many people have told me over the years that I won't see much difference in power by adding headers to a mild Pontiac. I wonder if the results would have been similar on a 400


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[goatless]

Not surprised, BUT...
I'd really love to see one of these log comparison tests that uses a better down pipe. Every one I've ever seen is the same thing- unmodified logs and crappy compression bent 2" head pipes.
I would really love to see info on a set of logs that have had the outlet opened up (can be done at home by someone with basic tools in less than half hour) and some mandrel bent head pipes. I bet the difference would be much smaller. Shoot, I'd be curious to see what just using some better head pipes would do!

Lee, also curious what the LSA was on the cam. We always hear that wider LSA works better with manifolds.

[Half-Inch Stud]

Data like this convinces me that the need for Headers is related to compression lowliness.

[goatless]

Originally Posted by Half-Inch Stud

Data like this convinces me that the need for Headers is related to compression lowliness.

So you're suggesting that the difference would be less with more compression?

[Lee]

Originally Posted by goatless

Not surprised, BUT...
I'd really love to see one of these log comparison tests that uses a better down pipe. Every one I've ever seen is the same thing- unmodified logs and crappy compression bent 2" head pipes.
I would really love to see info on a set of logs that have had the outlet opened up (can be done at home by someone with basic tools in less than half hour) and some mandrel bent head pipes. I bet the difference would be much smaller. Shoot, I'd be curious to see what just using some better head pipes would do!

Lee, also curious what the LSA was on the cam. We always hear that wider LSA works better with manifolds.

The head pipes were pretty smoothly bent. But I'm sure that larger WOULD have helped. I'm sure these are probably original and have lost O.D. due to corrosion, but they measured LESS than 2.0" in most places.

The LSA of the cam is 116.

[mgarblik]

It's great to have actual numbers to compare those log manifolds to good headers. I am a bit surprised by the amount of the improvement, but it's a happy surprise for you. The Pontiac engineers were well aware of the terrible exhaust manifolds that were on most of the OE engines. That's why they put so much effort into making some of the best HO iron manifolds/headers ever put on a production engine. Looking forward to seeing the rest of your results.

[b-man]

You can go from the stock 1.850" opening which is same basic size as the inside diameter of a 2" exhaust pipe, to 2.150" which pretty much matches the I.D. of a 2-1/4" exhaust pipe.

Shown below are a pair of right side 4-bolt 1969 log manifolds, casting # 9796992-1 date coded E129 and J078. The upper manifold in the picture has been opened up to 2.150", the lower manifold has the stock 1.850" opening:



The early-style right side manifolds have a larger outlet opening than the left side ones, the right side was bored out to around 2.050" to accomodate the thermostatic flapper valve that diverts exhaust flow through the intake manifold crossover to activate the choke during engine warmup. In the 1968 model year the flapper valve was eliminated from the right side manifold if I'm not mistaken, but the manifold outlet was still bored out and was larger than the left side manifold outlet. By 1969 the right side manifold no longer had the provison for the flapper valve, the outlet casting was shortened and the opening size matched the smaller left side outlet.

Here's a look at the center manifold inlets at the head flange on a 1969 9796992-1 (at the right) and a 1964 545467 equipped with a thermostatic valve. Note the wider casting and longer bolt bosses on the earlier manifold coming off of the head flange:



A look at the inside, note the smoother inlet on the early manifold and the slightly more restrictive opening on the later inlet with the bolt clearance notches cast in:



It looks like using some of the earlier log manifolds might offer a little better exhaust flow. Removing the flap and shaft and plugging the shaft holes on the earlier manifolds would be the way to go.



After you have done the work to enlarge the outlets you now need some larger headpipes (or downpipes) to take advantage of that modification.





These headpipes were fabricated using a stub of 2-1/4" exhaust tubing that was flared on both ends. The 2-bolt flange is an original factory piece that's been opened up a little using a half-round file. It's always a good idea to make sure you put the 2-bolt flange on the pipe stub before making the second flare on the pipe.

The bottom flare on the stub makes for a pretty decent transition from 2-1/4" to 2-1/2" tubing. The 2-1/2" 90-degree pieces were cut from some bare mild steel 180-degree mandrel bends that I bought from a parts house many years ago, today I'd make sure to use aluminized tubing instead.





As you can clearly see the old factory 2" crush-bent pipes can't even come close to flowing as well as the new bigger headpipes, the 2" pipe shown here is a rusty original from the right side on '69 Grand Prix.



Anyone running log manifolds looking for the least amount of restriction after the manifolds can simply purchase PYPES mandrel bent 2-1/2" stainless steel headpipes (p/n DGA10S-1 & DGA10S-2).



I measured the inside diameter of the pipe at the flare and came up with 2.100".

[tom s]

Would have been interesting to compare to a set of long branch.Tom

[Larry Navarro]

I don't know if y'all are aware of my undertaking in production of Tri-Y's. I am in the process of having a jig built to produce headers and if the cost is sustainable, meaning I can make a buck or two from the effort, I will be offering "D" and "O" port configurations. I realize that most everyone would rather spend $300 on a cheap set of headers but there is NO way I could offer such a "bargain". It will be a while before I can get a cost analysis if my efforts are feasible but I wanted to give some "hope" that there will be another option in header choices. Do it once, do it right. "The bitterness of poor quality lingers long after the sweetness of low price is forgotten."

Hey Lee, I need to speak with you about fuel injection. PM you number please, thanks!

[n2ogpsj462]

455 with 66 heads was rated at 325 so I'd say you've optimized your tune. Only know this because they're the factory heads from my 71sj I have sitting in my attic. 7.8 cr seems low. Without looking it up weren't they around 8.2?

[Lee]

Originally Posted by n2ogpsj462

455 with 66 heads was rated at 325 so I'd say you've optimized your tune. Only know this because they're the factory heads from my 71sj I have sitting in my attic. 7.8 cr seems low. Without looking it up weren't they around 8.2?

This motor has the pistons with the chamfer around the pistons, and I'm using an .041" head gasket. I don't have all the numbers right by me, but the heads cc'ed at either 114cc or 118cc. With non-chamfer pistons and a thin steel-shim head gasket, 8.2 would probably be about right.

Larry, my phone got destroyed about an hour ago. I'll be in touch though :-)

[n2ogpsj462]

Ok I've never CC'd my original heads but was considering using them to lower my compression. First time I've ever seen 66s mentioned on someone's motor. 7.8 would be far to low! Although I remember when I first bought this car and firing it up after sitting 15+ yrs and it ran like a raped ape. Would shred the tires until you got out of it while blowing chunks of rust out of the tailpipes!

[1968GTO421]

My Thanks to B-Man for some interesting info regarding improvements to "logs"........Appreciate it!

[Skip Fix]

Good info Lee. had a set of those for the 81 TA until I decided to use a set of my Round Port E heads for it's next motor-they are still in the box.

I have a header test planned when I dyno my E head Stump Puller 455. Have some Tribal Tubes 1 3/4Ys, Hedman Step 1 3/4-1 7/8 4 tube I had built years ago for the 400, and my standby 2" Hooker round ports. If Ron would ship me some 2" Ys I'd add them to the list.

I finally found an associate to start in Jan so I may have some time off to do car stuff! Been just me for awhile.

Larry keep us all posted on the project.

[Cliff R]

Despite how "pathetic" log manifolds can be for power production they do respond very well to modifications. We've been involved with a few "max effort" vehicles that had to use them, and have obtained some very astonishing results, dyno, chassis dyno, and at the track.

Another thing we continue to see with the big CID engines is that they will absolutely LOVE big head pipes and an X or "H" ahead of the mufflers. Even with log manifolds and smaller exit size, immediately opening them up for larger heads pipes is always a good things for them, at least from what we've seen here.......Cliff

[Kevspontiacs@aol.com]

The tribal tubes that I put on my 76 4-speed TA fit like a champ. Glad to hear that they work as good as they fit

[Formulas]

Its my belief that its important with lower compressions that you optimize scavaging because if your going to have a huge chamber at least try to get it as full as possible with a fresh highly combustable mixture. .. alot of people think high RPM flow is a trigger to go with headers but tri'y,s are reported to have excellent scavaging and if your going 4 tube go small diameter primary