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Jason Merritt's 2014 Street Mod Build...

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  • Jason Merritt's 2014 Street Mod Build...

    After 3 full years of development, and limited success in the NWR SCCA, campaigning my 1989 Nissan 240sx in the Street Mod class, I'm changing up my philosophy a little.

    Originally the game plan was a 4-5 year process, of FULLY developing the chassis, suspension, and engine on the smaller 275/35/15 Hoosier A6 tires, and if the car was not competitive, I would just simply add ballast, and switch to a larger wheel and tire package. The added ballast would of been positioned to balance out the chassis.

    I have decided to move on from my smaller 275's, and develop the chassis around a 315mm Hoosier A6, with inexpensive, and fairly light weight 18x12" wheels. It's unfortunate that I will never be able to realize the full potential of the 275mm tire package, as I know there was still lots of improvement left.

    For a wealth of SM and S chassis information, click here a quick link to my old build thread,

    A couple pics of my old setup...

    I have experimented quite a bit over the last 3 years, many times trying to run an "out of the box" setup, and many times ending up right back into the same box that everyone else runs in. However those experiments have taught me a lot.

    If I could go back in time, there are a couple things I would do differently...

    Number one, I would not of tried to develop the S13 subframe. The high levels of anti-squat which is not something that is proven to work with multilink suspensions. High levels of anti-squat is not optimal for putting the power down with a multi link suspension. When acceleratingwith the S13 subframe much of the weight is transferred to tire through the suspension links, instead of though the coil spring/damper assembly.

    Number two, I would not of experimented with my low SAI setup (12-14 deg's), as all that did was lower my roll center, and remove all camber gain, and in fact add positive camber gain during the second inch of suspension travel. In my ignorance, I neglected the fact that the Strut tube defines the slider axis, which defines the roll center & the camber curb of the mc strut suspension.

    Number three, moving the strut inward with longer "strut ears", in order to fit wider wheels and tires, was also a huge mistake, as this changes the slider axis of the strut in a negative way.

    Number four, I would like to go back in time and focus in on more important aspects of the car, that actually have a large effect on handling. That's easier said the done though, as when I first got into this build, and admittedly even now, I'm unsure on the most important and most efficient bang for the buck mods.

    I think the most important thing (besides tires), is actually a good "high end" set of dampers. Setting up a car around sub par damper can have you spending thousands of dollars trying to overcome certain issues that could possibly of been resolved by simply having a proper set of dampers right off the bat.

    Besides all of the obvious mods, like installing adjustable arms, spherical bearings in the rear knuckles, and installing lightweight parts, I would recommend purchasing a software program to analyze and understand your suspension, measure and correct the front roll center and camber curve, measure and correct the rear roll center and camber curve, install good high end dampers, fit the largest wheel and tires you possibly can, If auto crossing, choose an engine that has the widest power band, and the most area under the curve, SR20VET, Ka24de-t, LS1...

    Ok, enough with the rambling about the past, and what I think I've learned...
    I have not posted anything in a long time, so it's probably going to take a couple posts to get caught back up.

    Unlike most "must Read" race car books this book is current and up to date, as it was recently published. IMO, it contains a wealth of knowledge and makes it easy to get a look into the world of dampers. i'm hooked! Whether you have an interest in dampers or have little to no knowledge of dampers, this book is a must read!

    Performance Trends suspension analyzer was another investment that I recently made, that I would recommend. It has taught me quite a bit in a short amount of time. I wish I would of invested into it at the beginning of this build.

    I wrote back to them, thanking them for working with me after arguing with them for a week, but once I realized I was wrong, it's the least I could do... They posted a pic of my car, and quoted me, in their "what our customers say" section. I'm just happy to get a pic of my car on their website!

    Sneak peak of the next post...
    Last edited by Jason M; 11-03-2013, 07:24 PM.

  • #2
    Inspired by my purple Hoosier decals, I've decided to accent the car in "Hoosier purple"... S14 subframe with custom made "J Spec" solid subframe bushings

    Solid mounting the subframe without "offset" subframe bushings, which are against the rules in SM. I'm a little worried about putting the studs in bending because of loading the threaded area, as opposed to the large diameter shank.

    Playing around with mounting the front subframe pins in double shear utilizing the factory subframe moutning bracket holes. I don't know how legal it is though... I know that longitudinal subframe connectors are legal, but two of the oem connections are transverse.

    Solid diff bushing's.

    Two for me, two for Logr...

    Slightly lighter then the oem bushings. 1/8 lb lighter each = 1/4 lb!


    • #3
      JM Spec V2 RLCA's...

      V2 has an improved manufacturing process for better consistency, modified the front strut of the A-arm for increased wheel clearance, and utilizes a proper billet low friction ball joint, with replaceable studs, of multiple lengths. Weighs only a couple ounces more then V1.

      I have some lighter weight ones in the work, that use a weld on ball joint housing, from Coleman racing. Anyone interested? 300zx ball joint inserts reamed for the 772 Chrylser, or GM taper could be included for the conversion. I'm not looking to mass produce these, but it would be fun to fab up a couple custom ordered A-arms.

      I still need to finalize the sway bar mounting attachment. I would really like to design a cockpit adjustable sway bar setup, to set my RLCA's apart from the rest. any ideas? I've seen the blade type sway bar arms, and that seams like a good system, but expensive. I was thinking more along the lines of a sliding attachment. I suppose I could also come up a variable stiffness sway bar arm...

      Picture story!

      Notice the small holes drilled to relieve the hot air trapped in the tubes while welding.

      Tack weld

      Notice the dowel pins on the Jig plate. CNC located within .0001"...

      Getting ready to notch out both strut tubes of the A-arm, at the same time...


      • #4
        Also, the jig plate manufacturing process... I've been working on this plate, off and on, for the last 3+ years. I still need to machine up an adapter that bolts onto the jig plate to locate the ball joint housing. Its one thing to notch both tubes perfectly for the BJ housing it's another to weld it on, and maintain a target angle and location!!!


        • #5
          Yay new thread!!!

          I'd be up for some arms depending on pricing. I was toying around with learning to actually use my TIG and make some out of aluminum, but it's definitely a learning process when fabbing stuff up, so I don't mind profiting from your earlier mistakes and observation.
          '18 Chevrolet Volt - Electric fun hatch for DD duty!

          DefSport Koni Sleeve and Spring Perch Buy!!!


          • #6
            Prices should be $400 or less depending on options. Ball joint options are abundant. I can custom fab ball joint housings for the (possibly) ultimate lightweight setup, utilizing a high misalignment Qa1 spherical bearing and 5/8" shanked ball joint pins, or one could choose to use a weld on ball joint housing, like these

            The threaded ball joint bungs that I used in the protoypes for V2, would give the end user the option to use a oem factory style Chrysler ball joint, with oem quality dust/grease boot, for longevity on street driven cars. The option I choose is a Coleman Racing (rebuildable and pre-load adjustable) billet screw in style low friction ball joint. I'm not happy with the Qa-1 ball joints, they are heavy (over 2lbs), and have a loose thread fit in the Coleman racing weld in ball joint bungs. All Chrysler ball joint options have multiple pin lengths available.

            QA1 ball joint.

            OEM BJ weight.

            Custom made ball joint housing...

            Extra long 772 pin.

            Standard 772 pin.

            High misalignment spherical.

            V1, with bolts.

            I use quality, 1" .070" DOM tubing. The metal does not have heat affected zones around the welds during fabrication like 4130 does, and should bend and not break, incase of an impact with a curb or a collision.

            If someone does want, 4130, I will accommodate them, but looking at material specs, 4130 in the annealed condition, is not that much stronger then DOM tubing. I'm not sure if 4130 is more rigid then mild steel 1020/1018 tubing that is seem welded, cold rolled and drawn over a mandrel to give it properties that make it, considered to be "seamless" tubing.
            Last edited by Jason M; 11-03-2013, 07:55 PM.


            • #7
              I'd probably be game for a set of lower control arms, depending on when you're planning to have them done (i.e I can't pay for them right this second ).

              So stoked you started a new thread!


              • #8
                Thanks for starting the new thread and thanks for making these arms available to us.


                • #9
                  Bah... typed out a response and the internets carpped out and I lost it.

                  I was saying I can maybe look into helping you save a few bucks on the Coleman stuff - I get a slight discount on their stuff I think. Might be worth it... might not.

                  On the 4130 vs. DOM A-513 - the rigidity is exactly the same (as it is in all steels, regardless of strength). 4130 needs a PWHT to be any stronger in the welds than DOM tubing, and the only reason car guys get away with not PWHT 4130 weldments is that they build stuff that is so lightly loaded they would have been fine making it out of A36 (i.e. crappiest steel known to man).

                  If you've got a solid model of it, or even some basic dimensions you want to shoot over, I don't mind doing some FEA. It might be interesting to see what the utilization of the material is (i.e. can you bump down the wall thickness on one or more members?), and maybe a way to get a nice bump in rigidity with just a little added weight by adding extra members. LMK
                  '18 Chevrolet Volt - Electric fun hatch for DD duty!

                  DefSport Koni Sleeve and Spring Perch Buy!!!


                  • #10
                    Interested in how you are mounting the subframe... I have no experience with sm rules, so this might be an easy answer: are you allowed to move the mounting studs on the body?

                    Is your approach to use bushings that are drilled oversize to fit the narrower mounting points of the chassis and a large plate/washer? This being what you mean by putting the load on the threads of the stud rather than the shank?
                    If so, could/did you weld the plates to the studs?
                    Anything in the rules about adding add'l mounting points to the subframe?


                    • #11
                      Good to see a 2014 thread.

                      In for updates, and possibly arms.
                      1990 240sx - Aristo 2JZGTE, R154, GT37, Defsport Wilwood kit, KTS coilovers - daily driver
                      1991 civic si - B18C5 / toda / ATS / hytech - autox
                      2001 integra type R - Greddy td05-18g - garage queen


                      • #12
                        Originally posted by Jason M View Post
                        Number three, moving the strut inward with longer "strut ears", in order to fit wider wheels and tires, was also a huge mistake, as this changes the slider axis of the strut in a negative way.
                        Well damn... I'm in the middle of redoing my front struts again and was going to push them further in to get the 18x12s to fit a bit better on the FC (current offset is -10 )... what is your strut angle with your new crazy upper mount?

                        Originally posted by Jason M View Post
                        I think the most important thing (besides tires), is actually a good "high end" set of dampers.
                        So when do the triple adjustable penkes arrive?
                        '89 RX-7 TurboII - SSM - Widebody - Ford 8.8 IRS - giant wing - Megasquirt3
                        '89 Corolla SR5 - SMF - 4A-GE 20 Valve 6 speed swap - Megasquirt-2
                        '01 Impreza 2.5RS - Rallycross Stock AWD / Daily
                        '81 BMW R65


                        • #13
                          Originally posted by eage8 View Post
                          Well damn... I'm in the middle of redoing my front struts again and was going to push them further in to get the 18x12s to fit a bit better on the FC (current offset is -10 )... what is your strut angle with your new crazy upper mount?

                          So when do the triple adjustable penkes arrive?

                          The front Sai is about 20-21 deg's, from my calculations. The strut angle is 13*. I'm also using a 6" spring to help clear the wheels. I still have not finalized the front end setup...

                          Josh McCall's old FC/XP build had 21-24 deg's SAI up front and turned in better then my car. He had 285's up front and 315's rear. The front end really seamed to work well.

                          The angle of the strut is important. It has a huge effect on camber gain and roll center height. Even if you have to mount the strut top/camber plate underneath the fender well, just move the strut top all the way in until the spring almost hits the inside bodywork.

                          As for high end dampers... I'm day dreaming about JRZ's double adjustables. Remote reservoirs with adjustable gas pressure, and the compression adjusting orifices inside the reservoir.

                          I'm also looking into double adjustable AST's, which are a little more affordable. I'm just not sure about their construction. Not sure how their valving works compared to a JRZ. I need to do more research...


                          • #14
                            Do you do stuff like this for your day job or do you just happen to have a lathe and mad fab skills? Color me jealous!
                            ~1992 240SX, SR20/Koni track day car
                            ~2016 M3, daily driver


                            • #15
                              Originally posted by turtl631 View Post
                              Do you do stuff like this for your day job or do you just happen to have a lathe and mad fab skills? Color me jealous!
                              I'm just a Toyota tech... I think I'm just driven, obsessed, and challenged. I've also be very fortunate to have guidance from a couple individuals who have the same passion for motorsports, fabrication, and machining as I do.

                              I still have much to learn!