t_g_farrell

iTrader: (1)

Thanks for the answers. Now I have more questions.

I don't have an MSD to drive the coils. Right now I have a 2G coil for the leading directly connected and the stock trailing coil going through the cap both driven by the stock 105 igniters. I'm thinking I could adjust the trailing timing back until its within a few degrees of leading. Will this buy me anythng? What the pitfalls of doing this?

peejay

On the Megasquirt site, they noted no or extremely minor difference between running stock split, no split, or no trailing at all.

I noted some difference in fuel economy when juggling vacuum advance, but I wasn't keeping very good notes and my memory is sieve-like, so I don't remember what worked best.

On my current engine, I will be running standard split and a 6AL with two-step on the leading. This way if the rev limiter hits at high RPM, or when the two step is engaged(*), it won't be a hard ignition cut, just a dramatic loss in power because the trailing, while still active, is severely retarded relative to leading.

(*) I *may* have problems with blowing right past the staging limiter. In which case, I'll work something out. I am still debugging/wiring/sorting.

But, in my experience, and my opinion, the MSD is worth every penny. There's no reason to not be running one. Find the money. It's about 10 times better than the stock ignition system, while the 2nd-gen-coil bodge is about 1.5x better, on the subjective scale.

peejay

Okay... it blows right past the staging limiter unless the trailing ignition is disabled, even at stock timing and split levels.

Well, that's about what I was expecting, anyway.

Looks like I'm going to go to zero split again. I think, for the trailing to still run the tach, I should be able to put a ballast resistor into the circuit to take the place of the coil. Not the most elegant solution, but time is short, and when time is short, elegance is trumped by expedience.

2Lucky2tha7

iTrader: (3)

I'm using the rev limiter in the ms settings with my mallory hyfire and it works great. I don't think I'd have the patience for trying to use the ignition amplifier's built in rev limiter and making it work, when my ms can already do it for me.

peejay

Sure, if you have ignition control...

shm21284

I did, you can see the dyno here:

https://www.rx7club.com/attachment.p...8&d=1201567457

And the mods done to it are in this thread, further down from the dyno graph:

https://www.rx7club.com/naturally-aspirated-performance-forum-220/highest-power-challenge-2-rotor-13b-non-bridge-non-peri-712131/page4/

peejay

You list spec for five different engines.

Roen

iTrader: (2)

Form what I've heard, 0 and low split is used to give better low end torque, but as you get into the high-end, a split of around 10 degrees produces better power up to (and power doesn't drop off as fast.)

ultimatejay

iTrader: (1)

Running zero split or close split the engine is very susceptable to pre detonation so be very careful if you do it.

Roen

iTrader: (2)

you mean, pre-ignition, right?

peejay

It is extremely difficult to get a N/A to detonate. It can be done but it requires absurd amounts of timing (I did it with trailing 196 degrees BTDC...)

I still don't know what "pre-detonation" is. A lot of people on this forum seem to think it exists.

Pre-ignition is when the air/fuel mixture ignites before the spark.

Detonation is when the air/fuel mixture doesn't burn controllably, but *detonates* all at once.

Pre-ignition can lead to detonation, detonation can create hot spots that can cause pre-ignition, but they are still two separate things.

Pre-detonation implies that it's detonating before it is supposed to. It is *never* supposed to detonate...

A good, common visual way of picturing the way it is *supposed* to work is by turning on a gas stove. The gas comes out of all of the jets but the flame starts in only one spot. And *fwoom* the flame propagates smoothly around the burner. In a combustion chamber, of course, there is a fixed amount of fuel.

Detonation is more like a trash can full of acetylene that you shoot with a 50-cal. BOOM!

shm21284

There's only 1 dyno graph, and the explanation of that dyno graph is there.

peejay

Found the problem... you linked to "page 4". Thread is only three pages long if you have your posts per page maxed out, which I do. The forum software was giving me page 3 by default which is page 5 for standard layout...

A FYI for smoother linking in the future, you can link directly to an individual post by grabbing the URL from the number at the top right of every post. That way, URLs are valid no mater how someone has their forum settings.

It seems that 4 ports are the way to decent power. Certainly the manifolds look a bunch better, if you're sticking with stock manifolding.

GtoRx7

iTrader: (5)

4-ports for life!

dbragg

iTrader: (7)

wait, peejay. you piggy back your leading and trailing coils? like many do with piggy backing two coils for a direct fire leading set up?

i have two MSD boxes on my SA. with a 2nd gen coil on the leading and a MSD blaster on trailing. i am currently havinf some issues, detonation or something, with my leading on, so i had to pull the fuse to the trailing MSD box to get my car to run better. i think my carb needs a rebuild.

i may try this after i get her running right.

this wouldnt work with keeping the 2nd gen coil would it?

peejay

Exactly so. This of course requires running through the distributor.

Not sure but one MSD should be able to fire *three* coils...

I think the FC coils suck. Plus the MSD coils are wound to work with the MSD.

I've heard of people running GM dual-post coils with an MSD and going through the distributor, as well as people running one GM dual post coil per rotor and one MSD per unit. This requires custom mounted pickups to ensure they are exactly 90 degrees (180deg crank) apart, though.

dbragg

iTrader: (7)

MSD makes a DIS coil like the 2nd gen coil, and i plan on picking one up later. just too broke right now.

if what youre saying works then wouldnt you be able to:

disengage the trailing ignitor and coil
run one MSD box through a 2nd gen(or any DIS) coil and run the wires from the coil to the leading and trailing inputs on the dizzy
then run the wires from the dizzy to the spark lugs

or do as you say and piggy back 3 coils from one MSD box and all being signalled with the leading output on the dizzy. then run a direct fire set up with leading and the trailing normally.

one question peejay, do you keep or ditch the metal dust shield in the dizzy?

also, with this set up is it while youre running stock timing or are you still running full advance? vacuum advance?

peejay

That's the setup I have.

You cannot disable the trailing ignition entirely. The MSD's tach-out will run the tach, or it will run the MS, but it will not run both.

I haven't done the wiring yet but I have a little doodad that will replace the coil in the tach circuit with a 470 ohm resistor. The trailing ignitor is still required, but all it is doing is working as a tach drive. The 470 ohm resistor takes the place of the coil as the resistance in the ignition circuit. Should be pretty slick, if it works. (Pics still on the camera, car is literally buried under many feet of snow right now)

Given that it is necessary for spacing the cap away from the distributor...

I am currently running a stock 12A distributor and no vacuum advance, but I only drove it 70 miles the day I got it running/tuned, and 350-odd miles to the rallycross and back. And then it got buried in snow I need to find a source of ported vacuum but I do not think one exists on the GSL-SE intake manifold. Fuel economy can best be described as "sucks". Doing the math vs. average pulsewidths, it's around 15-17mpg.

Whizbang

really? The mileage turned out to be that bad? maybe it will improve with the vacuum controlled timing working.

that or get an EGT gauge and lean it out more?

rotarygod

iTrader: (1)

Are you serious? The FC coils are the most under appreciated over achieving coils out there. They are fantastically strong. The GM coils by comparison plain suck. That's a downgrade. I have no idea why anyone who is serious about power would use them. On my 1st gen I got rid of my MSD coils and am using a custom setup with VB921's for ignitors and am using 4 FC trailing coils. Awesome setup. I see no reason to ever replace stock FC coils with any aftermarket pieces.

peejay

Bumping on minimum pulsewidths on the highway. Need smaller injectors. I can't seem to get duty cycle below the 11% range.

Also... and it hurts to say this... it appears that taller gearing would work better, since PW's go up for a given duty cycle, when RPM drops.

Or I could just run smaller injectors

Here's the pic of the doodad.



$2.29 junction block and one $.20 470 ohm 1/2 watt resistor (.99 for pack of five). The resistor has a loop wound on each end and is screwed down, and for strain relief it is also superglued to the side of the junction, and because I'm paranoid, I painted it with liquid electrical tape. The spade terminal came with my fuel pump.

The plan is the green/yellow wire that normally went on the coil negative plugs right on. The old coil positive wire will go on the other side of the junction next to it.

This seemed like the best way to put the resistor into the circuit without stressing the resistor in any way. In addition, now I can use this block to connect other things under the hood that get switched power (MSD small-red, fan control box, a couple other things I am forgetting at the moment) without using the "bolt through ring terminals and wadded over with electrical tape" method that I have been using.