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Old 01-27-2020, 09:59 AM   #1
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Default Mustang 3-link suspension

saw a comment on Facebook that Cobra Jet owners are adding 3-link suspensions to their cars, I thought they were 3-links? I;m curious why they are doing this and who "they" are. Are there any Copo's running this suspension?
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Old 01-27-2020, 06:08 PM   #2
Todd Gross
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Default Re: Mustang 3-link suspension

All the Cobra Jets I've seen are 3 link. The COPO's and Drag Paks are 4 link.
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Old 01-27-2020, 07:10 PM   #3
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Default Re: Mustang 3-link suspension

The newer Cobra Jets have a 4 link, 2015 and up Mustangs have a IRS rear axle. The 2008-2014 Cobra Jets are the 3 link.
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Old 01-28-2020, 09:19 AM   #4
Jesse Kershaw
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Default Re: Mustang 3-link suspension

I think the confusion is coming from the fact that Bo Butner’s 2019 CJ runs a 3-link. Drew Skillman is cutting out his factory 4-link and putting in the 3-link. Bill Skillman’s 2014 car with the 3-link was the faster car compared to Drew’s and at the end of the season to clinch the FS championship they put Drew in Bill’s car. At least one other 2019 CJ owner, Jack Hodge, is chopping out the factory 4-link for a 3-link. And when Drew beat Bo it was on holeshots, Bo’s 3-link car was the faster car, both with Holbrook engines.

Why would people do this?
Why is the 3-link an option?
Why didn’t Ford use the 3-link in the new Cobra Jets if arguably the teams that are currently most successful are using it?

I’ve had this question come up a few times in the last couple weeks, then a text yesterday “did you see the classracer post on 3-link?”

No one asking realizes the pandora’s box they were opening with these simple questions. The success of the 3-link cars in 2019 combined with Drew Skillman converting his car to a 3-link has people scratching their heads and the truth is that there was no good reason to put a 4-link in the cars to start with.

For drag racing Ford was lucky that up until 2015 the Mustang had a solid axle, but the S550 changed to an independent rear suspension and the Cobra Jet needed to have a solid axle added like the Copo or Challenger. As the program lead I wanted the 3-link from prior year Cobra Jets. It was uniquely Ford, it setup easy, there were lots of aftermarket companies familiar with it and we had been wildly successful. There was no reason to reinvent the wheel.

Development for the S550 based car started in 2013. The engineering team had assigned the design of the rear suspension to Andy Vrenko. Immediately he reported back that the 3-link couldn’t work and that it would be too much of a tear up to the car. He assured me that a 4-link would be easier and cheaper and work as well or better than the outgoing 3-link. He had the support of another engineer that I had a long working relationship with and trusted him at his word when in hindsight I should have demanded hard data.

At this time we were still calling the car a 2015 model and intended to debut it at the 50th anniversary of Mustang celebration in April 2014. I can’t recall exactly when this target was abandoned but it was a sigh of relief for our engineering team that had missed several targets already. The engineering team had so far converted the 2014 test car to a 4-link that would never have been approved by NHRA tech for a Stocker and spent 10 days in Florida “testing” how 4-links work in February or March 2014.

Shortly after this I made sure that whatever we worked on was NHRA approved before any more money was wasted. The initial rendering and drawings for the Vrenko 4-link were shared with NHRA in the spring or early summer 2014. Their first question was “why can’t you use the suspension you already have?”, the 3-link, and I explained to them that the 3-link was a non-starter and required far too much work, as I had been told. Nhra agreed to a 4-link design pending final approval of the suspension in car. I think it was August 2014 we scheduled them to visit and the car wasn’t ready. Bumped back a month and not ready, bumped another month and not ready. Finally NHRA tech said to just send pics when we were finally done. We did eventually send the pics and got approval around the end of 2014. The Vrenko 4-link was a major tearup to the car. It cuts out the entire rear seat, incorporates a complex multipiece frame rail (I wish I had a pic, it’s unbelievably complex) and uses a jig to locate the assembly in the car.

Starting 2015 there still wasn’t a running car. My recollection is that they the first track trip was around March or April 2015 and things weren’t good. The car was only getting down the track about 20-25% of the time. In short order it got the nickname “mulligan” because it always needed a do-over. Vrenko was the only driver unlike prior years so there was no second opinion as to what was wrong. Our group had a new business manager named Doug White and my role in the Cobra Jet program was changing. I was told to leave the engineers alone and they would deliver. This was the most hands off I had been in a CJ program. Vrenko rarely came into the office so it wasn’t convenient or easy to talk to him anyway. I had my marching orders, let them do their job.

John Calvert was a sounding board for ideas and he knew we had a 4-link approved for Stock. In April 2015 John reached out and asked why we didn’t use the 3-link, so of course I told him because it didn’t fit. He responded with a photo of his 3-link axle from his 2014 car in an S550 body. 3 days later he sent me a rough CAD drawing of the minimal changes it would take to put it in the car. It was a fraction of the work required for the Vrenko 4-link, my recollection is that it required only about 1.5 sq/ft of material removed vs removing the entire rear seat which was like 6sq/ft. Seeking further data I reached out to some friends on the Mustang engineering team and they gave me CAD that showed clearly the 3-link would fit with minimal modifications, in fact at one point they considered making body mods to offer a solid axle 3-link as a factory option.

Armed with this information I confronted Vrenko and he denied having ever said the 3-link wouldn’t fit. I was shocked. I think I said something like “you’re seriously telling me that?” I turned to his fellow engineer who was there when I was told explicitly the 3-link wouldn’t fit and his response was “I don’t recall”.

Later as I was driving home the second engineer sent me a text that said something like “you’re right, Andy did say that”. I called him immediately and he told me that it was politics. He was sorry to sell me out but he knew if he didn’t back Vrenko there would be professional repercussions, he felt he had no choice but cover for Vrenko or face a hostile work place.

What I did next was no doubt a nail in my coffin at Ford. I compiled all the data that the 3-link would fit, would cost less, was easier to setup, and weighed less and took it to the group’s business manager Doug White. I knew this was a risky play because White and Vrenko had a personal relationship that I had seen put ahead of Ford many times. When White was suddenly “retired” I have no doubt this dynamic had something to do with it.

I brought the data from the Vrenko 4-link showing how much they were struggling to get down track. I told him I was bringing this to his attention because if I were in his shoes I would want to ensure I had all the facts to make decisions.. My recommendation was to scrap the 4-link and go to the 3-link ASAP. I brought the group’s marketing manager with me because I wanted a witness to what was going on. White passive aggressively thanked me for my input and never brought it up again. I believe as soon as I left the room my presentation went right in the recycle bin. If my stand did anything it made the engineers begin production sooner, they started chopping the back seats out of bodies in June or July even though the car wasn’t close to passing the testing requirements. By doing this it locked in the 4-link suspension.


Eventually Mike Pustelny was called in and he put them in the right direction to get down the track while walking on eggshells to not upset the egos in the performance parts engineering team. Mike did a great job of making his ideas their ideas. Without Pustelny’s help I’m not sure they would have ever gotten down the track successfully.

At the same time Calvert talked to me about the 3-link he talked with Pat Cvengros at NHRA to ask if it would be legal to put it in the new body. An innocent question, but he didn’t know that I told them it wouldn’t fit. They naturally asked for photos and immediately I was a liar. My next meeting with NHRA tech I had some backpedaling to do. I apologized and said I was using the data given to me but it was clear my credibility and the credibility of Ford had taken a hit. I asked if they planned to make the 3-link legal for the new car and Danny Gracia said something like, “how can we not? It looks way more OEM than what we approved for you.” There was a push from the Ford engineers to fight NHRA on this and make the 4-link the only legal suspension. I flatly refused. Not only did we have no leg to stand on and would look even more foolish I felt the 3-link would be the better choice for DIY builds as it’s easier to put in.

With Pustelny’s help the Ford engineering team got their required validation runs in October 2015, the car was shown at SEMA 2015 although we’d already started producing them (this was why it was 25 of each color instead of build to demand), and if memory serves me John’s car was run with the 3-link at the Pomona finals, making the first NHRA pass of a 2016 Cobra Jet a 3-link car.

Customers did struggle with the Vrenko 4-link and the teams that have gone fast with it made significant changes to do so. I applaud them because I know it wasn’t easy and there was a significant learning curve. Even at its best the factory 4-link is heavier and more costly than a 3-link would have been. And I think it’s fair to say that the Skillman’s aren’t changing to a 3-link to go slower so they must think there’s something there. In Ford’s development testing the 2016 car with the 4-link got down track a lower percentage, had a slower average 60’ time and a slower best 60’ time than the 2014 car with the 3-link and less power (to be fair the 2014 car had multiple test drivers who were vastly more qualified while the 2016 had only Vrenko, so while I can compare tracks and conditions driver likely played a role). So it doesn’t surprise me that people are going to the 3-link. The data supports it and if I was building a car it would be my choice. This isn’t to say that 4-links in general are bad and I’m not trying to start a war comparing the two, just that as Ford delivers the new CJ it needs work, is very costly, and could have been a 3-link for less .
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Old 01-31-2020, 08:33 AM   #5
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Default Re: Mustang 3-link suspension

Thanks for providing this information. I wondered what the "backstory" was with Calvert's car being an accepted modification.

Now I'm curious? Do they have to put the stock floor back in when converting to Calvert's design?
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Old 01-31-2020, 02:35 PM   #6
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Default Re: Mustang 3-link suspension

Quote:
Originally Posted by Tom Broome View Post
Now I'm curious? Do they have to put the stock floor back in when converting to Calvert's design?
I'm not sure. Calvert's car and Bo's car both had factory back seats.

The Skillman car and Hodge car both started as the Ford 4-link, but both are going to be Factory Showdown cars. I am betting NHRA let them put the upper pickup in the correct spot but allowed the modified seat pan for Showdown.

I almost forgot, Chris Holbrook's car that he won Indy Showdown with in 2016 was also a 3-link. That car probably should have been the first 7 second Stocker but it took a hp hit before he put down the number. He sold it to Joe Welsh and I'm not sure what's going on with it now.
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Old 01-31-2020, 03:08 PM   #7
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Default Re: Mustang 3-link suspension

Seriously Jesse, write a book. You are a wealth of knowledge on the whole Cobra Jet program. Thanks for sharing!
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Old 01-31-2020, 05:06 PM   #8
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Default Re: Mustang 3-link suspension

Quote:
Originally Posted by Jesse Kershaw View Post
I'm not sure. Calvert's car and Bo's car both had factory back seats.

The Skillman car and Hodge car both started as the Ford 4-link, but both are going to be Factory Showdown cars. I am betting NHRA let them put the upper pickup in the correct spot but allowed the modified seat pan for Showdown.

I almost forgot, Chris Holbrook's car that he won Indy Showdown with in 2016 was also a 3-link. That car probably should have been the first 7 second Stocker but it took a hp hit before he put down the number. He sold it to Joe Welsh and I'm not sure what's going on with it now.
Joe Welch was testing with it in Bradenton last weekend.
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