Engine Bog

[Screaming Metal]

Do as 2O2F said...also, get yourself a centri. Advance kit from Summit or where-ever, comes with weights new buttons for weights, new springs. Install this kit to get all you mech. advance in by 2000-2400. You should be able to find this at any decent speed shop. Will help tremendously.

 

[Screaming Metal]

Do what 2O2F said......
One thing wrong with TunnelRams is with a 2x4 setup, when you have both dumping at the same time, you have so much under the curve, so-to-speak, all that air and the vacuum drop, its like balance-ing a penny on the edge of a razor blade. You have to get it rich enough to overcome the rush of air into the intake. You want it just so-so, too lean and you'll have a hesitation or a lean pop, too much and you'll have a bog, or a backfire.
When you get right on that edge of getting it perfect, one, or the other usually happens, then, usually, you have to go to a progressive throttle setup. You have to remember, these things were made to idle at 1500+ rpms, with alot more cam and carb than you are running.

What I would try to do is bump your timing up just a hair, one one of your carbs, move your accelerator pump cam to the #2 hole, and on the other carb, leave it in the #1 position, put a heavier pump cam on that one and try it. Your having such a big drop in vacuum, what you want to do is try and have a longer 'Spray shot' which will usually help.
With the mild cam, which is what you want with the tunnelram, its all in your tuning. Remember what I said about balancing on a razerblade, or a narrow fence....theres a narrow window where the motor will run clean and not load up, off in either direction, you'll have your bog.
It can be done, just adjust slowly....

 

[Screaming Metal]

Also, go by any good speed shop locally and pick up a performance cent. advance kit, put your new plastic buttons, weights and light springs in....you want all your advance in by 2000-2400 rpm, this will help tremendously!

 

[sstock]

Noticed you have your vacuum advance hooked to ported, I found on my tunnelram tuning a real benefit to having it hooked direct. Found that the tunnel because of its plenum volume needed the extra timing at idle and off idle. On my 301 small chevy , I run 14* initial, 21* mechanical, vacuum hooked direct. Mechanical is all in by 3000rpm

 

[Wild Mango]

Check the advance works. Measure the circumfrence of the damper from the TDC mark. Divide this number by ten. Measure this against rotation from the TDC mark, make another mark. This is 36degrees advanced. Warm it up. Take the springs off the weights, disconnect the vacuum advance. Fire it up, it may buck a bit but take it up to 2000rpm or so should be smooth enough. Set 36deg advance with timing light. When you pop the cap off to replace the springs, the weights should be all the way out. Replace the springs carefully. Fire it up again and note the idle timing. If it's for instance 12deg that means you have some 22deg of advance weight timing which is about right. Replace the vacuum line. I like to see all the advance in by 3000rpm latest

 

[Screaming Metal]

Sorry for the double post on the centr. advance....my other laptop is supposed to be back the next few days, I'm going Ubuntu, I've had it with windows.
Most smallblocks with TR's like between 11 to 16 degrees, I'd try 14 if your at 12 now. But, the centr. advance kit will help out. Is that a dual point distr.?

 

[Bennett]

I'm trying to order a new HEI ignition system but to be totally honest I don't know enough to make an educated purchase. Too many choices and I'm not well versed. So frustrating! How much is enough and where do I stop? You can spend anything you want. I don't mind spending money but I absolutely hate spending it for the wrong reasons. It's giving me brain cramps. &

 

[RPM]

Will an HEI fit with a tunnel ram?

 

[sstock]

Will an HEI fit with a tunnel ram?

No not the factory gm wont

 

[2old2fast]

Most aftermarket ign. co.'s make a small-cap electronic ign. . As to who's best , that's kinda of an "ask 10 people, get 10 answers" The relucter/pickup [like GM HEI is probably the most bulletproof , that being said , I've been running a mallory unilte [photo cell] for 11 years /35K miles w/no trouble. Pertronix used to be good , jacob's was well respected, some swear by MSD, but I feel you're paying a high premium for a so-so product. Really what you need to look at is features that you want or need & base your decision on that.
dave

 

[Screaming Metal]

Will an HEI fit with a tunnel ram?

What 2O2F said...
The small units will....like....
http://www.davessmallbodyheis.com/

Proform makes a small hei, too.

 

[Screaming Metal]

The Mallory Unilite is hard to beat, for the price, you get a damn good quality unit. one of my favorites....

 

[Screaming Metal]

More or less you want is a Electronic unit or HEI the size of a std. dist., nothing fancy. A good, dependable, quality unit. 2O2F and I have given you some good names....Accel, MSD, Mallory, Jacobsen, Pertronix, I could go on.
Give Daves a call and tell him your motor and the tunnelram, he'll fix you up. Or Summit, and see what a Mallory Unilite will run. With the Daves unit or the Mallory, you'll have to mount yourself a Hi-Perf. coil on your firewall.

Hell, if Pertonix has a drop in unit that will work with your std. dist., go with that. That'd give you some extra $ for a Monster coil....

With Daves, just go pick up a used distr. for your motor and send it to him and he'll work his magic....that way you can continue work on your car and it'll be running. Then, you'll always have a backup. You don't miss those until you don't have one.

 

[railroad]

I am going to differ on the vacuum gauge diagnosis. When bog occurs and you look at the manifold vac reading, if it is above your power valve rating, it means the pv is not open and the engine is probably lean.
ie you are at 2200rpm cruising, you press the gas to increase speed, the vac falls to 8.0, the engine goes flat, this is where you need the pv to open. If this example was the actual readings I would put in 8.5 pv. On the dist, it may need attention, but I like get one thing right before adding more medicines to the illness.

 

[Dirt-T]

I am going to differ on the vacuum gauge diagnosis. When bog occurs and you look at the manifold vac reading, if it is above your power valve rating, it means the pv is not open and the engine is probably lean.
ie you are at 2200rpm cruising, you press the gas to increase speed, the vac falls to 8.0, the engine goes flat, this is where you need the pv to open. If this example was the actual readings I would put in 8.5 pv. On the dist, it may need attention, but I like get one thing right before adding more medicines to the illness.[/quote
I could not agree more. One thing at a time.

 

[2old2fast]

Yep, my apology , sometimes my finger doesn't keep pace w/my brain [of course that could be in reverse also ] railroad's right!!!
FWIW , the 450 mechg sec carbs come w 8.5 PV & are marketed as "tunnel ram" carbs . However , I've yet to see my vacuum reading fall below about 10" h.g. under any thing but wide open operation.

dave

 

[Screaming Metal]

On the dist, it may need attention, but I like get one thing right before adding more medicine....

He's talking about upgrading his distributor....he isn't electronic.

 

[Screaming Metal]

On the dist, it may need attention, but I like get one thing right before adding more medicines to the illness.


I'm not gonna get into the mix here, too many people telling you what to do is bad, I'll be on the sidelines listening. Its best to do as you are doing....one thing at a time, systematically, when you find it, it'll be sweet! The inside of those carb throats are Dirty!

 

[Screaming Metal]

This morning I checked to make sure that everything under the distributor cap was moving freely. Everything was free however the centrifugal weights looked like they were dragging a bit (rubbing and scraping debris evident). I gave them a small squirt of WD40 to test the theory. It definitely made an improvement. The bog became less. Earlier some of the other guys on this site had suggested that I replace my ignition system with a HEI distributor. I'm an Engineer by trade so I like controlled experiments but the evidence is mounting and I guess it's time to take their advice. The new ignition may not totally fix the issue but the bog is becoming less with most every improvement I make.

Sounds like the man is going about this correctly....
I tell ya'll what, you guys just get the mans stuff straightened out, never mind me....I got better shit to be doing than sitting here holding folks hands that try to sling crap at the walls and see whats sticks....

 

[railroad]

He's talking about upgrading his distributor....he isn't electronic.

Just trying to keep from putting another unknown in the mix. I tried to be delicate.
By his description of how it would accel with some gas pedal modulation, I do not think the dist is bog related. I know the tag ons, of I knew a guy who had a carb on his car and it, blah blah blah, and he said to blah blah blah are confusing the tuner, but that is their right and the tuner will just have to filter through it.