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Pontiac of the Month

360Rocket's 1970 GTO

2019 March
of the Month

Last Indian

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Last Indian last won the day on March 13

Last Indian had the most liked content!

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About Last Indian

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    Century Club
  • Birthday 11/08/1951

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    Northeast Ohio
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    Pretty much anything in motion, architectural design & work, sports, space & and why humans fail to learn from clear & obviously results of past generations!

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    Grand Prix
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    Dark Navy Blue

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  1. You don’t mention, in the other post, changing the vacuum secondary's of the carbs to port vacuum! Did you? If those are connected to manifold vacuum that’s a problem. In the picture you’ve taken I see more questions than answers. It doesn’t look like the secondary’s are connected to port vacuum. Also wow, all the adaptors connecting the carbs to the tunnel ram present a challenge! Are there vacuum leaks? Quite possible, that needs check at each gasket interface with ether. Any leaks at those will cause precisely what you describe. Are the gaskets at each interface the correct ones? If not that can change vacuum! I assume the car came with that setup on it and you did not install it?
  2. Ringo’s going to move this any time now! That said, you don’t mention changing the vacuum secondary's of the carbs to port vacuum! Did you? If those are connected to manifold vacuum that’s a problem. Take a picture of the carb setup and post it over on the maintenance garage part of this forum.
  3. Wrongway, if it was mine I would use 304 SS 2 ½ all the way to the mufflers, all welded, no clamps, no balance cross pipe. The super 44s are a good muffler choice. After set in the right orientation I would weld them to the 304 pipe. When the time comes to replace the mufflers you just grind the weld till the muffler is released. The area of a single 3” pipe, working diameter 2.9”, is 7.18 sq in for 8 cylinders. The area of single 2 ½ pipe, working diameter 2.4” is 4.5” sq in for 4 cylinders. This mean that the laminar flow is much more stable with less inverted flow in the 2 ½ pipes. Think of it this way, a flowing river with no curves, no rocks flows smooth, but add some large rocks and a lot of smaller ones and you have inverted flow, disturbance, rapids! Because the volume of fluid verses flow rate has been reduced. The other thing that happens is that the sound gets louder! If you increase the width of the river at the area of rocks, but the rock disturbance area stays the same the water disturbance decreases as does the inverted flow & noise. The noise at the rapids is higher pitched and a racket type. Now think of Niagara Falls! Very loud, but deep toned. No invert flow, until after the falls. I could continue, but I hope this helps? Does that explain it a little better?
  4. What material are the headers made from, 409, 304, are they coated, are you keeping those as part of the system? Can you tig or mig weld or know someone who does? The super 44s would be a good choice as a muffler, it’s 409 though, but on a 304 pipe it will last a long time. Plus when they need replaced they’ll come right off the 304. Summit Racing sells, as do others, 304 pieces for making your own system. That would be my input. Buy 304 pipe, bends and flanges, Tig weld them together using 304 rod. Use the super 44s, but don’t clamp the 44s weld them to the 304 pipe.
  5. Did you or can you disconnect that line at the hose connection of the fuel pump and see what happens? Does it pump out gas, does it suck, is it vapor? It might help diagnose that’s going on!
  6. In general I usually don’t comment much on exhaust stuff. Everybody usually has their own thoughts on what they think works, what they like too hear, etc. Still something you might want too consider is, what you want? Power, performance, sound, what? Attached is a link to an in depth article about exhaust, JustA headers, not really even getting into downstream. I’ve built systems for 45 years and two things I learned early on was louder wasn’t better, neither was quite, and bigger was better! http://www.epi-eng.com/piston_engine_technology/exhaust_system_technology.htm Most of the systems that you’re going to look at are 400 series stainless. It’s better than steel, but as it ages it starts to perform like steel. It slows down the laminar exhaust flow because of the resistance at the wall. You will see in this article how they talk about exhaust waves & pulses and how, depending on tube diameter, material selection and pipe transitions, a negative invert flow can be created that is counterproductive. A simple example, a V8 running headers into 3” collectors than into 2” duel pipes has a area of 6.28 sq. In. But the same engine could run the same headers into 3” collectors an than into one single 3” pipe. This delivers over 7” sq. In. Creates less shock waves that send inverted waves back at the valves, gives a deep rich tone. Also by slowing down the flow due to a larger pipe size you hear more of the throaty sound. Always see if you can get at least 304 stainless. So as my buddy JustA would say, I’m JustA saying!
  7. I’m not familiar with them either, but keep in mind that a loud raucous exhaust doesn’t always equate to power! I don’t know your engine, but type of engine design, hp, torque, compression, etc all play a role in how much or how little back pressure you need for optimum performance. I have seem guys loose more than a second in the quarter just because of exhaust. As I said, bigger and louder don’t necessarily mean better! I would hate to see you spend good money and be disappointed. All you’re running are headers right!
  8. Here’s a couple pics of Hodges I found
  9. Well you’re going to need a OBD ll scan tool. It appears the traction control is coming on which reduces power output. This would kill acceleration. Which component it is would be a crap shoot without using a scan tool. Could be a wheel sensor, throttle switch, wiring etc...
  10. I think there’s some confusion here! The PCV isn’t the problem, or at least it should’nt be. I can’t see your engine, but the hose to the PCV should be coming from a fitting on the manifold or large nipple coming out of one of the throttle plates. This means when the engine is running, just a idle you have high vacuum. By connecting the vacuum advance secondarys to that vacuum the secondary’s are opening at idle. When you step on the gas they close. That’s backwards! Port vacuum is taken from above the ventures, which means as you increase throttle, vacuum increases and starts to open the secondary’s. Timing, with the vacuum connected put a timing light on the harmonic. Increase the rpm’s until the timing stops increasing. This is the total timing of the engine. If it’s more than 36 degrees it’s to much. Check initial timing, remove and plug the vac line. Check the timing. So for instance say you have 40 total timing and 16 initial you need to set the initial at 12, not 16.
  11. Well a couple things. First you need to know the total vacuum your pulling. For a Pontiac 400, 36 degrees is about it. So whatever the total is with the vacuum you deduct the initial from that. The carb should be port vacuum not manifold. PCV is manifold vacuum. So that may be your biggest problem, your dropping vacuum just when you need it!
  12. Hey, cool! I’ll have to visit there the next time we go to Boston! Thanks!
  13. Yes Welcome! I would agree! Either timing or a vacuum issue from the carbs. I.E. secondarys coming on to some, leak at the base gasket, etc. I don’t think it’s to much carb because of how you say it acts when you take your foot of the gas. I would check timing first, and not just the initial, but how it advances when you rev it. You may be getting a bad advance curve.
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