When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
So I got the exhaust replaced. Modified the existing RB short collected header to 2.5" outlet followed by 2.5" RB presilencer, 2.5" - 4" x 10" long Jones resonator, then over the axle w/ 2.5" mandrel bend to 2.5" oval muffler.
Before I made the change, I measured the system backpressure at the outlet of the header collector. You can see it at the beginning of the video. At 7800 rpm and WOT, the backpressure was 3 psi (you can see it on the left gauge, the right one was pegged at 60 inwc = 2 psi). Under the same conditions (but on the dyno, not the track) with the new exhaust, the backpressure was 0.6 psi. The horsepower measurements were not completely conclusive, since the more open exhaust resulted in the AFR increasing significantly. I wasn't expecting that so didn't have enough carb jets to dial it in. Based on previous testing and the results from the most recent dyno test, it looks like there was about a 5 HP increase from 150 to 155. Not a huge difference, but.... I needed a new exhaust system anyway. Interestingly, the torque seemed a bit less below 3500 rpm. Will finish dialing in the AFR at the track tomorrow.
Hopefully will see Kurt at Willow Springs this weekend. I am just hoping he doesn't lap me in EP. ;-)
Oops! Guess I won't add the video, since it is in an unacceptable format. It was probably too big anyway and not really that interesting. Just watching the needles bouncing around on some large pressure gauges.
Thanks for doing the research. 5HP is nothing to sneeze at and it might make the difference at the end of a long straight against an otherwise "equal" race car.
I saw this set up last weekend and it looks and sounds great. For sure am going to copy this on my ITA car...someday.
Scott, How's the progress on the tranny?
I'm still a dude.....oh wait that wasn't what you were asking!
The transmission is back together. Based on what I am seeing I think the issue was largely with the tail shaft roller bearings. I also corrected an issue with the placement of a shim so now the rear torrington bearing is supported correctly. I'm becoming way to proficient at working on this thing.
Now working on the engine. I completed modifications to an S4 water pump housing so it will work on my S3 engine. Next I will add some trap door baffles to the oil pan and check the oil pump and front stationary bearing. After that it is reassembly. Looking to make the Majors Race at Heartland Mortorsports Park in late May. I should have the car ready by then but that may get side tracked by work as we have major Production deployment that will kill a weekend this Spring I just don't know which one yet.
Also working on my street Mustang for Autocross purposes because I plan on going to Solo Nationals this year. My neighbor asked me what I was doing and I told him I am making it ride like crap on the street so it will be faster when I race it. Which is pretty much the truth.
Hey Scott, can I ask you about your ignition? You're running direct fire on the leading via MSD 6al with the trailing using the ignitor/cap and rotor correct? I saw only two wires connected to the distributor but didn't see where the coils were mounted so I assume there are three coils? We are having a hell of a time trying to get the 6al to function. We've been trying to run 2 boxes, one for each system running through the distributor with no ignitors. Our precedent is a teammates RX3 sp Autocross car that has been running great that way for 25 years. When we try it on the 7 both coils fire together even though both boxes are completely separate. We did try the three coil method once last year and it worked for a while until the trailing ignitor failed. That's why are trying to eliminate ignitors all together. Any suggestions?
Leading
The Purple and Green wires from the MSD 6A are wired directly to the magnetic pickup on the Leading side of the distributor. The Orange and Black wires from the MSD 6A are connected to the MSD 8224 coil. I located the MSD 8224 coil on the roll cage ahead of the left shock tower. Note that i used shielded wires from the distributor to the MSD and from the MSD to the 8224 coil. The shielding on the wire is grounded to the chassis in the interior of the car by the MSD 6A. Because the MSD 6A does not have a rev limiter I did not clip any of the cylinder count wires.
Trailing
Is wired like it was from the factory. The tach is connected to the negative side of the trailing coil. The trailing coil is mounted to the left shock tower.
The weights in the distributor are welded.
Last edited by mustanghammer; 04-05-22 at 09:02 PM.
First Qualifying Session - Not my new splitter!!! First Qualifying Session - The splitter is toast! First Qualifying Session - Splitters provide no traction when they are under your tires The Race - Showing them my nose at Turn 1
So is the leading set up as direct fire off the two pole coil?
Yes. In the GM application the batch fire the coils for a wasted spark on one of the cylinders just like on a rotary. So these coils are designed for this type of work and are affordable. Al alternative would be a Harley Davidson dual pole motorcycle coil, Or, two separate coils.
Thank you Scott. I'm hoping we can get our issues figured out. We were running an MSD for the leading and an MSD for the trailing all running through the distributor with ignitors removed. No matter what we checked and rerouted, if everything was plugged in then both coils fired together. If either side was disconnected, than the side that was connected would fire only when triggered by it's corresponding pick up. We then went back to ignitors and everything works fine...
Thank you Scott. I'm hoping we can get our issues figured out. We were running an MSD for the leading and an MSD for the trailing all running through the distributor with ignitors removed. No matter what we checked and rerouted, if everything was plugged in then both coils fired together. If either side was disconnected, than the side that was connected would fire only when triggered by it's corresponding pick up. We then went back to ignitors and everything works fine...
Assuming that there is no way that the MSD boxes are wired incorrectly then I would look at the routing of the Orange and Black wires and the Purple and Green wires from each of the MSD boxes These wires from the two MSD boxes should not be close to each other or share the same looms.
For example, if you have the Orange and Black wires routed side by side from both MSD boxes there may be enough cross talk between the wires to cause both coils to fire. Likewise with the trigger wires (the Purple and Green wires) if they are routed together it could trigger the MSDs in correctly. Using shielded wire is beneficial and I highly recommend it but even then I would keep input and out put wires from the two MSD boxes completely separated.
I would also recommend going to wasted spark on the leading side. I removes the variable of the distributor cap/rotor for the most important part of the ignition.
We did have both sets of pick up wires and both sets of coil wires bundled together to go through a bulkhead connector so hopefully that was it. We'll be rewiring this Sunday so I'll update afterwards.
Okay, so we did some investigating and testing on Sunday. We verified our theory. So a little back story first, we had the ignition system wired with two MSD boxes with one each for leading and trailing but still through the distributors. Basically just replacing the ignitors with the MSD boxes. We were following the way one team member's AutoCross RX3 SP has been wired and functioning great for the last 30 years. The differences were, his was wired with shielded cable for the pickup wires and for the 7 we used the wires the boxes come with plus some standard Tefzel wire. We then routed both leading and trailing pickup sets of wires and both leading and trailing coil signal wires together through a Duetsch bulkhead connector in the center of the firewall back to the boxes mounted on the passenger foot well area. As I stated above, both coils were firing together. We verified this by running the coil leads to engine and running a screw driver across the magnetic pickups (with the ignition powered up) and watching the spark jump. We de-loomed everything and ran each pair of wire separately over the cowl to the boxes and redid the test. In this configuration each coil fired individually. We then grabbed a set of the coil signal wires and gradually moved it closer to the opposing set of signal wires. At about the 6" mark the other coil began firing as well. So our issue was definitely crosstalk between coil signal and pick up wires. The next step was re-routing with coil wires through the bulkhead connector and replacing the pick up wires with a shielded twisted pair and running them through the passenger side of the firewall and to the boxes. We configured the leading as direct fire and the trailing through the distributor but still using the second MSD box in place of the trailing ignitor. We also switched from poorly fitting male spade connectors plugged into the distributor to hollowed out ignitors as plugs for a more reliable connection. For testing we used three new OEM style coils and ignition wires but the MSD coil and 8mm wire set you listed are on the way (delivered today hopefully). Engine now lights right up idles pretty evenly and runs up through the revs clean. I know using an MSD box for the trailing is a bit overkill but we already have the box, it's mounted and wired and no confirmed to be functioning correctly so we figured why depend on an ignitor...
Our first race of the year is in a week and a half so we'll see how it goes then. Fingers crossed for good weather but since we just got a few inches of snow two days ago (the first ever snowfall this late in the year around here) I'm not holding my breath...
Hey Scott,
Another ignition question. So the two tower GM coil just showed up and the instructions show a 4 wire coil interface module PN8870 required to connect the coil. Are you using this? How did you connect the coil with or without the module? Thank you again.
EDIT: Nevermind, I see you just plug spade terminal connectors into the bottom. Now to make a bracket for it...
Last edited by Conekiller13; 04-13-22 at 04:28 PM.
Reason: New info
Hey Scott,
Another ignition question. So the two tower GM coil just showed up and the instructions show a 4 wire coil interface module PN8870 required to connect the coil. Are you using this? How did you connect the coil with or without the module? Thank you again.
EDIT: Nevermind, I see you just plug spade terminal connectors into the bottom. Now to make a bracket for it...
I used the prongs out of a male 110V plug - the kind they make for repairing a bad plugs - because it gave me a way to use the ring terminals on the wiring I already had. But basically the same idea. The MSD base for the coil pack was too expensive
So, update: The car ran absolutely great last weekend. Felt like we found some missing horsepower. Our best lap at the Ridge was a 1:56 and change. For reference the EP lap record is a 1:52 and change. We ended up 7th both days. Saturday we spent some time in first place but training and new driver and some ill timed pit stops pushed us back to around 12th. Sunday we got hit pushing us back from second into 16th. So getting back up to 7th both days was good progress. We had a friend with a YouTube channel come hang out with us Sunday so here's his video:
Quick question. Do you remember anything about setting float levels in a Nikki with Grose jets? I finally found a pair (Mike Haag) and installed them. The floats are set dead on 16mm. Fuel level in bowls wants to hang around 1/2 way up sight glass, but with pump running and engine not, the level slowly creeps up until fuel overflows. Maybe that is just a characteristic/problem with some of the Grose jets? These appear to be from the original manufacturer (D&G or something like that). I may end up going back to the stock style if I can't get this sorted.
03-10-22, 04:04 PM
