new missing at upper rpms issue

[grumpyvette]

"Grumpy? having an issue with my bbc. before i put it into my camaro it would rev to 6500rpms with no prob. that was with a edelbrock dual plain intake. now I'im running a team g (that I've run before) single plain.
now I've tried my Holley 750 and my edelbrock 800. no change. I've tried fuel press adj. Ive tried my hei dist that was ran on the motor before also a whole new ignition system from summit. i just cant figure out y it wont go over 6000rpms now.. any suggestions would be very help full.

its like a rev limiter at 6k but there is no limiter lol. when i use the ignition box limiter is set at 6500.


a logical step by step approach is best,, a worn cam, weak valve springs , the new ignition, ignition timing issues or lack of fuel volume could be the cause, but you stated ...

"before i put it into my camaro it would rev to 6500rpms with no prob. that was with a edelbrock dual plain intake."
so my first suggestion would be to drop back to the former known to be working combo to test if that still works, verify your carb float levels and fuel pressure at the carb inlet during acceleration, as it only takes some time, you might want to swap back to the older intake,with new intake gaskets to test, so,if it does, help you temporarily solved the issue, its most likely a tuning issue related to the new intakes fuel distribution, if its not still working you know for sure its not intake related and you can proceed on isolating what it is., if your running less than 3/8" fuel lines or a different fuel pump those may be the cause. think back to any changes you may have made,if the fuel pumps not supplying enough fuel volume at a minimum of 5 psi, that could easily be the problem, have you checked the valve train for busted & worn parts ? a logical step by step approach is best, isolate and test, you'll quickly find the problem
since this is a new car, the engines installed in, I suspect its a fuel delivery issue, it could be fuel filter or fuel line size related very easily, if you fuel pumps working against a different fuel supply lines tank etc. I'd suggest looking that over carefully a big block could easily have significantly greater flow requirements than the previous engines fuel system parameters required.
does the new ignition advance curve operate smoothly, have you verified that or only assumed it works because it used to in the old car?
what do your spark plugs indicate? they can usually provide valid info on upper rpm lean conditions, or other problems.
have you tried adjusting the valves to 1/4 turn in from clicking at idle minimum pre-load on the lifters, too much lifter pre-load tends to lower the rpm lifters pump up and cause valve float??
about twice a month I get some guy driving a early corvette or muscle car thats badly out of tune or one that needs minor repairs because the engine runs like crap, now in many cases the owner is CLUELESS as to how to locate the cause OR he assumes its just in need of a tune up, which can of course be true, but its surprising the number of mechanical issues like busted valve springs or leaking vacuum hoses, or badly adjusted coils, etc. that come up, so learning to isolate and test is a critical skill.
I know some guys would rather be boiled in oil than read links, and SUB LINKS but for those that would rather get the car running correctly, heres a few very useful links
now keep in mind missing can be from 3 general areas in your engine , and yes ITS THE SUB LINKS WITH 90% OF THE INFO YOU NEED TO READ
mechanical,
like badly adjusted valves, broken rings, busted valve springs ,leaking gaskets, leaking vacuum lines etc.
electrical
badly adjusted timing, cracked insulators, defective connections, wires or ignotion, defective plugs or wires or bad grounds defective coils, bad battery, bad grounds
fuel/induction
low fuel pressure, badly adjusted floats, defective injectors or fuel pressure regulators, clogged filters,etc. youll need to isolate and correct the source but without knowing how to test your screwed

http://www.dragstuff.com/techarticles/MSDchipvalues.html
yes you'll want too open and read the links and quotes

Volt/Ohm Meter measured values of Automer RPM Pills
rpm
3000 = 1880 Ohms
5000 = 3590 Ohms
5200 = 3790 Ohms
5400 = 3980 Ohms

From Darell
3000 = 1900 Ohms
5800 = 4400 Ohms
6000 = 4600 Ohms
7000 = 5680 Ohms
8000 = 6860 Ohms

To use round numbers (and only be off by 10-20 rpm), I determined the approximate formula in the 5000-6500 range to be:
RPM - 1400 = Resistance
or
RPM = 1400 Ohms + Resistance

So
5000 rpm = 1400 + 3600, so I need 3600 ohms of resistance for 5000 rpm
5500 rpm = 1400 + 4100, so I need 4100 ohms of resistance for 5000 rpm
etc.

What I did was put a variable potentiometer (10K) in and set it to 3600 ohms (5000 rpm).
From then on, each ohm of resistance = 1 rpm added to 5000 rpm. Units are now interchangeable.
The output from the pot goes to 3 of teh DIP switches. They are 0, 500, and 100, so if one is selected, that output would then be 5000, 5500, or 6000 rpm. That value goes into the other 5 DIP switches which have values of 100, 200, 300, 400, and 500.

The outut is then 5000 rpm (3600 ohms) PLUS 0, 500, or 1000 PLUS 100, 200, 300, 400, or 500. That gives the opportunity for any 100 rpm increment from 5100 (switches 6 and 1) to 6500 rpm (switches 8 and 5).
5100 rpm = 6 and 1 (5000+0+100)
5800 rpm = 7 and 3 (5000+500+300)
6500 rpm = 8 and 5 (5000+1000+500)

To get the resitance values, I used a number of resistors (they add in series and divide in parallel) on a circuit board. I put the whole thing in a small (~1.5"x3") box and cut the switch box out and a hole for the pot. I then spliced into the two wires in teh shift light that go to the place where the pill plugs in. I used copper phone line. I ran the wires down the A pillar and out underneath the seat and place the box there.

Realistically, you could use 7 adjustable pots for the resistance values instead of resistors, or just use one pot and no switches or resistors, but you need a VOM to read the resistance everytime you want to set it. I like being able to flip a switch at any time and change the light value.

A while back someone talked about making their own MSD chips using a Radio Shack adjustable resistor.

Since an MSD rpm chip is nothing more than a resistor in a fancy plastic case with two prongs, all you would need to know is the resistance value for each rpm level.

I just bought two adjustable chips. Not the Radio Shack type, ones already in a case. There are made by Shiftnoid (electric shifter company) and are sold by Jegs. they have a small screw in one end and adjust all the way from 0-12,000 rpm. Problem is that the screw has no scale on it. It comes set at 6000 and for every 1/4 turn of the screw it moves the rpm level by 100. Would be easy to get lost if you didn't know what the chip was set at. Also would be easy to lose count of the 1/4 turns if making a large adjustment.

I figured it would be easier and more accurate to set it by measuring the resistance. Borrowed a friend's chips and measured both his and mine. Used my digital multimeter set on the 20K ohm scale. Feel free to copy the list and I would appreciate it if anyone has any numbers to add. Would really appreciate those numbers below 4000. I use the lower chips in my MSD two step to control starting line rpm in my drag car.

RPM Resistance
3000 1.91
3400 2.21
4000 2.70
4600 3.21
5000 3.58
5200 3.77
5400 3.95
5600 4.16
5800 4.35
6000 4.57
6300 4.88
6500 5.10
6600 5.20
6700 5.32
6800 5.43
6900 5.55
7000 5.65
7400 6.12
7600 6.38
7800 6.63
8000 6.89
8600 7.69
8800 7.97
9000 8.27

It appears the scale is .10-.11 for every 100 rpm for most of the range, but is closer together below 4000 and wider apart at the top end of the range. Also may be some variance in the chips themselves. Example: I checked 3 different 6600 rpm chips . Resistance of 5.19, 5.20, 5.21.

Here's a list of resistance values for anyone interested in making their own MSD chips. 1/4 watt resisters work just fine.



RPM Kilo-OHMS
1400 = .491
1500 = .639
1600 = .819
1800 = .947
2000 = 1.161
2200 = 1.364
2400 = 1.50
2500 = 1.58
2600 = 1.70
2800 = 1.78
3000 = 1.906
3200 = 2.062
3400 = 2.222
3600 = 2.385
RPM Kilo-OHMS

3800 = 2.551
5000 = 3.63
5200 = 3.82
5400 = 4.02
5600 = 4.20
5800 = 4.41
6000 = 4.62
6200 = 4.82
6400 = 5.04
6600 = 5.26
6800 = 5.46
7000 = 5.72
8000 = 6.96


To make an adjustable RPM switch get a 6 position rotory switch with detents from an electronics store. Then solder in the resistors for the desired RPM levels. Use it in conjuction with a two step to control launch RPM. It works great. I found that when you launch the car 1,000 RPM below converter stall the car hits real hard as you take advatage of the flashing.

Below is the resistance ratings for Autometer chips for their shift lights.

• RPM kohms
• 3000 = 1.897
• 5600 = 4.22
• 5800 = 4.44
• 6000 = 4.64
• 6200 = 4.85
• 6400 = 5.08

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