Huh...with such a serious effort chassis, I would've figured drag car...but since you're installing an IRS, that isn't the case...did you say earlier that you intended track duty for this car?
The good things heard can be from people that sell parts for IRS and the bad things (long list) about IRS can be heard from people that DON'T sell IRS products (like Griggs). I've read up on FTBR about how great IRS is when it's weak points are addressed and how predictable they are in the turns especially when hitting the curb. I am still debating doing the hard tail conversion myself. Maybe next winterYeah, my original intention for this car is being able to open track/road race it once in awhile. It will see the drag course probably just for the occasional grudge night, but my true passion is in corner carving. I believe a stiff chassis is just as important, if not more, in road racing. Plus, I'm trying to build as much safety into the car without a full cage since I believe a full cage can cause more damage than not to a person on the street. You don't normally wear a helmet and fully suit up for a sunday drive. Smacking your head on a padded bar with a helmet on hurts enough as it is in an accident, I couldn't imagine what would happen without a helmet.
I don't want to hit anything obviously, but if I do, at least it won't be on a stock, spot welded sheet metal chassis. I see the potential to be hitting close to 170+ on some of the straights I race on with my motor goals. I'm already touching 125 at NJMP with our stock ~160HP engine, stock suspension E30. I used to hit 145+ with my 95' N/A 302 cobra.
The IRS just kind of happened. I was originally planning on a watts link/TA SRA setup, but decided to try this instead. I've heard some good things.
The hard tail conversion is the way to go. When people first started modifying them on cobras they would flatten the rear cradle tubes and weld a flat plate that allowed it to be directly bolted to the side of the rear frame rails.
That didn't work out well because that single plate wasn't enough support. " They then changed it to an angle that would allow bolting from the side and bottom.
The issue has been documented that IRS lower control arms flex with hard acceleration....and has been attributed to cause wheel hop. ( there was a video a few years ago that showed it ). Kenny Brown used to make tubular lower control arms that helped the issue. ( haven't seen them in years ). I've never seen the lower control arms break. My buddy runs consistent 10s with his cobra IRS.
Just FYI....the mid 90s Thunderbird V8 came with a factory cast iron center section just like the cobras aluminum one.
It also is an upgrade to the aluminum one found in the cobra. Under power the whole case can flex....the thunder bird still had an aluminum front cover.. So, a brace is still needed.
The debate is still out over the full Ford Racing cover vs. the metal brace. I chose the brace because the full cover has been noted to have fitment problems.
I researched a lot over the years and still do installs for local people. Its good seeing people doing this swap.
I love taking on and off ramps with IRS. The handling on the street is really nice compared to an SLA. On the road course the IRS tends to snap coming out of turns. That has given it unpredictable status. Our rears are sensitive to the geometry of the body of the car...meaning, as the body rolls and pitches it affects the direction of the rear tire ( bump steer ). That is true even when loaded and unloaded...like tire spin. The rear feels like its loose and most people try to correct steering....resulting in over or under steer. People tend to over come this by toeing the rear wheels out a tad. ( when the suspension compresses it pulls the toe back in )
There are drawbacks....but if you are a skilled driver....they can be overcome.
Stick that in your M5 and smoke it.
I'll add that some of the "rear steer" is attributed to weak tie rods and tie rod ends. Upgrading these to a stronger piece and getting a MM rear steer kit helps eliminate/reduce the amount of rear steer that is the result of hard cornering (tires tow in/out) and hard acceleration (tires tow out). The IRS is very versatile and adjustable and being able to add camber to the rear helps a ton too. Being able to keep one tire planted on the pavement while the other tire hits the curb in a turn helps a lot.The hard tail conversion is the way to go. When people first started modifying them on cobras they would flatten the rear cradle tubes and weld a flat plate that allowed it to be directly bolted to the side of the rear frame rails.
That didn't work out well because that single plate wasn't enough support. " They then changed it to an angle that would allow bolting from the side and bottom.
The issue has been documented that IRS lower control arms flex with hard acceleration....and has been attributed to cause wheel hop. ( there was a video a few years ago that showed it ). Kenny Brown used to make tubular lower control arms that helped the issue. ( haven't seen them in years ). I've never seen the lower control arms break. My buddy runs consistent 10s with his cobra IRS.
Just FYI....the mid 90s Thunderbird V8 came with a factory cast iron center section just like the cobras aluminum one.
It also is an upgrade to the aluminum one found in the cobra. Under power the whole case can flex....the thunder bird still had an aluminum front cover.. So, a brace is still needed.
The debate is still out over the full Ford Racing cover vs. the metal brace. I chose the brace because the full cover has been noted to have fitment problems.
I researched a lot over the years and still do installs for local people. Its good seeing people doing this swap.
I love taking on and off ramps with IRS. The handling on the street is really nice compared to an SLA. On the road course the IRS tends to snap coming out of turns. That has given it unpredictable status. Our rears are sensitive to the geometry of the body of the car...meaning, as the body rolls and pitches it affects the direction of the rear tire ( bump steer ). That is true even when loaded and unloaded...like tire spin. The rear feels like its loose and most people try to correct steering....resulting in over or under steer. People tend to over come this by toeing the rear wheels out a tad. ( when the suspension compresses it pulls the toe back in )
There are drawbacks....but if you are a skilled driver....they can be overcome.
They don't make M5's anymore,...(At least not until later this year)I like the picture you're painting here. A car that has a modern suspension, can handle well, but still needs a skilled driver as there is no fancy traction control. Sounds like a lot of fun.
Stick that in your M5 and smoke it.
They don't make M5's anymore,...(At least not until later this year)
Annnd...You take two drivers with a similar set of limited skills,....put one in a BMW "M anything", and put the other in a non-assisted something else..( No TC, No Stability control, No ABS,...) and have them hot lap a track.
The "smokin" is gonna come from the guy driving the M car.... that is if the other guy even makes it through a full lap w/o running off the track, running slow, or wadding it up against a wall.
It wouldn't have mattered...Technicalities.
Hence why I specified "skilled".
I knew I should have just typed "AMG" instead.
The hard tail conversion is the way to go. When people first started modifying them on cobras they would flatten the rear cradle tubes and weld a flat plate that allowed it to be directly bolted to the side of the rear frame rails.
That didn't work out well because that single plate wasn't enough support. " They then changed it to an angle that would allow bolting from the side and bottom.
The issue has been documented that IRS lower control arms flex with hard acceleration....and has been attributed to cause wheel hop. ( there was a video a few years ago that showed it ). Kenny Brown used to make tubular lower control arms that helped the issue. ( haven't seen them in years ). I've never seen the lower control arms break. My buddy runs consistent 10s with his cobra IRS.
Just FYI....the mid 90s Thunderbird V8 came with a factory cast iron center section just like the cobras aluminum one.
It also is an upgrade to the aluminum one found in the cobra. Under power the whole case can flex....the thunder bird still had an aluminum front cover.. So, a brace is still needed.
The debate is still out over the full Ford Racing cover vs. the metal brace. I chose the brace because the full cover has been noted to have fitment problems.
I researched a lot over the years and still do installs for local people. Its good seeing people doing this swap.
I love taking on and off ramps with IRS. The handling on the street is really nice compared to an SLA. On the road course the IRS tends to snap coming out of turns. That has given it unpredictable status. Our rears are sensitive to the geometry of the body of the car...meaning, as the body rolls and pitches it affects the direction of the rear tire ( bump steer ). That is true even when loaded and unloaded...like tire spin. The rear feels like its loose and most people try to correct steering....resulting in over or under steer. People tend to over come this by toeing the rear wheels out a tad. ( when the suspension compresses it pulls the toe back in )
There are drawbacks....but if you are a skilled driver....they can be overcome.
I'll add that some of the "rear steer" is attributed to weak tie rods and tie rod ends. Upgrading these to a stronger piece and getting a MM rear steer kit helps eliminate/reduce the amount of rear steer that is the result of hard cornering (tires tow in/out) and hard acceleration (tires tow out). The IRS is very versatile and adjustable and being able to add camber to the rear helps a ton too. Being able to keep one tire planted on the pavement while the other tire hits the curb in a turn helps a lot.
I will soon begin squirreling away IRS parts as I see them up for sale at a decent price. Since nobody makes replacement parts for the IRS the prices will only go up up up!
Soooo.... progress yet?
Same here. When I get a few free hours here and there, I'm hanging a door, or installing new molding/casings.
We want a deck, so once the ground thaws I gotta get some footings dug and poured.
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