popping through the exhaust at 4500 rpm or so.. HELP!

[beermanpete]

WEll I agree Beerman, but how many of us on here are running headers on a stock L24 with absolutely zero issues what so ever. On many cars I have worked on installing headers (many SBC) was a great power adder by itself. Yes, you could get more from rejetting, but it was not night and day. And certainly NOT the difference between running like crap, and running well. The E31 exhaust is very restrictive (Rebellos words) and the stock manifold is darn near as good as a header. Nobody is making crazy power with just a header on an L24.

I have checked the valves already as well. I checked them warm, not hot or cold. I can certainly check them again. I will also check the block ground, and make some more grounds just for kicks.

I imagine a lot of people have put on headers, do not "re-jet" and get decent results. My point is not that it is a necessity, simply that it should not a surprise. Since the round-top SU carbs have an adjustment for the jet height it seems a safe assumption that many of those same people simply adjust the mixture richer to get good drivability and live with a fat idle.

I always check the valves cold. I think it is better because the engine temperature is not changing during the process.

[Zedyone_kenobi]

I agree 100% with you on the cold adjustment, I may do mine again tomorrow stone cold, so at least I know they are even!

[Captain Obvious]

I believe much more in setting the valves hot than I used to. I'm no expert, but as I understand it...

Why are there valve clearances at all? Because the valve stem grows in length as it gets hot. Exhaust valves operate much hotter than intakes, and that's why the exhaust valve clearances are always larger than intakes.

If a valve lengthens so much that the clearance is reduced to zero, not only will you lose compression, but you may burn a valve. Why? Because the valve conducts a lot of it's heat to the head while the valve is closed, and if it never closes, it never gets the chance to lose that heat.

That's probably a simple layman's understanding, but it works for me, and because of that, I put much more importance on the hot settings than the cold. :classic:

[Captain Obvious]

Everybody has something they would like to see you try, and mine is trying a points distributor and maybe even a stock coil. I know it shouldn't matter, but it's just another variable that you could eliminate.

[beermanpete]

I believe much more in setting the valves hot than I used to. I'm no expert, but as I understand it...

Why are there valve clearances at all? Because the valve stem grows in length as it gets hot. Exhaust valves operate much hotter than intakes, and that's why the exhaust valve clearances are always larger than intakes.

If a valve lengthens so much that the clearance is reduced to zero, not only will you lose compression, but you may burn a valve. Why? Because the valve conducts a lot of it's heat to the head while the valve is closed, and if it never closes, it never gets the chance to lose that heat.

That's probably a simple layman's understanding, but it works for me, and because of that, I put much more importance on the hot settings than the cold. :classic:

This sounds right except that the cam towers also grow which increases the valve clearence. The gap actually gets wider as the engine heats up. The cold spec is 0.008"/0.010" cold and 0.010"/0.012" hot (in/ex). I have set the valves cold (using the factory specs for a cold engine) and then checked them hot and they are pretty close the the hot spec.

I would set the valves with engine hot if I could do it with the engine running but that is not possilbe due to the design.

Edited March 17, 2012 by beermanpete

[Travel'n Man]

Have you set your timing while maintaining a 3000 rpm and what NGK plug numbers are you running on?

[Zedyone_kenobi]

Well sort of.

I Use the NGK BPR6ES that is listed on here, both the regular type (NGK BP6ES) and the resistor type (NGK BPR6ES). I have tried both of those at .035 and .045 gaps.

I set my static timing at whatever I am going to run, depending on which distributor I have in the car at the time. One of them likes 11 deg BTDC initial, the other likes 17 deg BTDC. Then I slowly raise the rpm until the timing mark stops moving on the balancer. Then I use the lights adjustment buttons to see the rpm AND the advance at that point. Last time I did that I was fully advanced at 3100 rpm with 35 deg total advance. Yes, the vacuum advance was plugged.

[Zedyone_kenobi]

I think I am at a point were I want to pull the cylinder head off. I may do that today after I attempt a leak down test. I finally got a new compressor.

[Zedyone_kenobi]

Everybody has something they would like to see you try, and mine is trying a points distributor and maybe even a stock coil. I know it shouldn't matter, but it's just another variable that you could eliminate.

And I whole heartedly swear to all of you who have been with me here for 16 pages that I SINCERELY APPRECIATE ALL OF YOUR HELP! I HAVE NEVER met a bunch of people on an automotive forum as classy as friendly and helpful as you all have been with me. I am truly blessed to have discovered this forum.

I consider myself a pretty handy wrench. I really do understand the workings of engines for the most part. I have my areas where I am weak on, but for the most part, I get what everybody here is trying to help me with.

But Captain, no offense, while I appreciate the advice, the 'experiments' have been going on for almost a year now, 4 months of it was in this THREAD!

I am ready to change the game up a bit. I am still going to attack the problem, because I never quit. But instead of the surgical strikes I have been performing, I am going to go more with carpet bombing from a B-52.

I will keep reporting back to you with what I find with my leak down test. If I had another set of SU's I would try them. If I had a points dizzy on hand I would probably try it. But I do not.

[Captain Obvious]

The gap actually gets wider as the engine heats up. The cold spec is 0.008"/0.010" cold and 0.010"/0.012" hot.

Haha! Good point... I didn't even check the delta between warm and hot before I posted that. In my defense, the last engine I worked on in that depth was my lawnmower, and it behaved exactly as would support my understanding.

But Captain, no offense, while I appreciate the advice, the 'experiments' have been going on for almost a year now, 4 months of it was in this THREAD! If I had another set of SU's I would try them. If I had a points dizzy on hand I would probably try it. But I do not.

No worries bud. No offense at my end at all. I understand that it would take even more money to invest in parts that may or may not fix the problem. We're all at the point of long shots here, right? All of the easy stuff has been taken care of pages ago!

[LeonV]

A good thing to do while you're testing leakdown is check your plugs. Check gap and closely examine them for electrode wear. Poor running will cause spark plug electrodes to wear prematurely, so see if there is any degradation or erosion on the ends.

[Zedyone_kenobi]

Good advice, I will certainly look in to it!