Autocross and a 904 transmission

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Tuesday

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Hey FolkS,

I’ll be at Moparty next month, autocrossing my 1973 Scamp - this will be my first time at an autocross event and am fully prepared to be making a fool of myself.

Am looking for tips - am a year away from installing a Tremec 5-speed, so for 2024 it’s the 904 with the stock torque converter and a Quick Performance 3.50 rear end.

What tips can you offer for set-up, laying down a respectable time (do I leave it in 2nd or let auto do its thing etc.?). Any driving tips too, to get the best out of car, generally under its current set-up. The chassis is torsion bars set up with lots of goodies to the spec of abody chassis set-up warriors including @BergmanAutoCraft and @72bluNblu etc. Hoping I don’t need to do too much, as driving in and out of the event - touching wood and crossing everything!

Look forward to meeting a few of the folks from A Bodies too!!

Cheers, and best, Tom

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Hey FolkS,

I’ll be at Moparty next month, autocrossing my 1973 Scamp - this will be my first time at an autocross event and am fully prepared to be making a fool of myself.

Am looking for tips - am a year away from installing a Tremec 5-speed, so for 2024 it’s the 904 with the stock torque converter and a Quick Performance 3.50 rear end.

What tips can you offer for set-up, laying down a respectable time (do I leave it in 2nd or let auto do its thing etc.?). Any driving tips too, to get the best out of car, generally under its current set-up. The chassis is torsion bars set up with lots of goodies to the spec of abody chassis set-up warriors including @BergmanAutoCraft and @72bluNblu etc. Hoping I don’t need to do too much, as driving in and out of the event - touching wood and crossing everything!

Look forward to meeting a few of the folks from A Bodies too!!

Cheers, and best, Tom

View attachment 1716292161
Where's the rest of the car ??
 
What’s the basic rundown on your set up?

-wheels and tires
-torsion bar diameter/rear spring rate
-sway bars
-shocks

I would mostly just make sure to do a thorough pre-check on everything before going, especially since you’re not going to be changing parts or anything. If you have adjustable shocks you might want to consider changing the adjustment. Tire pressures are important too, but with street tires you don’t want to get too extreme with the changes. You can ask other folks that are running what they’re doing for tire pressures, as it will depend on the temperatures that day, the tire manufacturer, etc. When I did track days with my motorcycle some of the track day providers would post basic tire pressure recommendations based on track temps and sometimes even break it down by major tire manufacturer, not sure if they do anything like that at MoParty.

For the auto, especially if it doesn’t have a shift kit or anything I would probably pick a gear and stay in it. It will depend on the track though. What shifter do you have? My Challenger with its 904 had a slap stick shifter, which would make it easy. With that I’d just put it in first, “slap” it to second when I got the speed up and then probably just leave it there unless there was some really slow corners. But an A-body shifter wouldn’t be quite that easy.

If it’s your first time or close to it though I wouldn’t get too crazy with car set up changes, just have fun, try to pick the brains of some of the more experienced guys. If you make any changes at the track, make sure to only change one thing at a time. But most of your improvement will come from you, not your car, especially early on.
 
Agree. Depending on the course might do like blu posted, but typically put in 2 and and let it do 1-2 2-1 automatically. If you have kit that holds it in 2 no matter what, then start in 1 and upshift.

Most important thing is to practice. You can try a local event - usually SCCA affiliated these days. Moparty probaboly runs theirs a little differently. With SCCA autocrosses, the morning walk is an important part of the game.

Second most important thing for many is to enter the corner smooth, and get the speed down early enough for the tires to bite and turn. Super easy to go in too hot and then complain the car understeers. No. The driver induced the understeer. <embarressed>

Slow is smooth and smooth is fast ;)
Not too slow! Slow enough to be smooth and keep on course. On an SCCA autocross - knowing the course and thinking ahead is critical and also challenging. I expect the Moparty course may be easier to follow (less visual tricks and traps) but the priciples will remain the same.
Stay as close to the critical cones as possible - the shorter distance traveled the less time it takes to finish the course.

 
What’s the basic rundown on your set up?

-wheels and tires
-torsion bar diameter/rear spring rate
-sway bars
-shocks

I would mostly just make sure to do a thorough pre-check on everything before going, especially since you’re not going to be changing parts or anything. If you have adjustable shocks you might want to consider changing the adjustment. Tire pressures are important too, but with street tires you don’t want to get too extreme with the changes. You can ask other folks that are running what they’re doing for tire pressures, as it will depend on the temperatures that day, the tire manufacturer, etc. When I did track days with my motorcycle some of the track day providers would post basic tire pressure recommendations based on track temps and sometimes even break it down by major tire manufacturer, not sure if they do anything like that at MoParty.

For the auto, especially if it doesn’t have a shift kit or anything I would probably pick a gear and stay in it. It will depend on the track though. What shifter do you have? My Challenger with its 904 had a slap stick shifter, which would make it easy. With that I’d just put it in first, “slap” it to second when I got the speed up and then probably just leave it there unless there was some really slow corners. But an A-body shifter wouldn’t be quite that easy.

If it’s your first time or close to it though I wouldn’t get too crazy with car set up changes, just have fun, try to pick the brains of some of the more experienced guys. If you make any changes at the track, make sure to only change one thing at a time. But most of your improvement will come from you, not your car, especially early on.

Good advice - as always!!!

This is my set-up - have it saved :

***SUSPENSION***
  • Bilstein Shocks - A Body - Front and rear - non-adjustable
  • Sway-A-Way Torsion Bars - A Body Mopar - 1.08
  • Bumpstop - Round - 11/16
  • Mopar Lower Control Arm, stiffened with a BAC welded plate
  • Hellwig Sway Bars - front and rear
  • SPC/BAC Upper Control Arms, W/ Ball Joints
  • Dynamic Strut Rods - A Body
  • Delrin Bushings

***WHEELS and TIRES***
  • Cosmis XT-206R 17-inch (front: 17x8 and rear: 17x9)
  • Tires: Continental ExtremeContact DWS06 PLUS - 235/45ZR17 front and 255/45ZR17 rear.
  • The car is my daily driver - tires were not chosen for track, but for driving 365 days a year in NC.
100% there for the fun and am in alignment with everything you have written. Frustratingly, it’s a column shifter, but I’m not too bad on manual column shifting but it’s not 100% guaranteed !!
 
Agree. Depending on the course might do like blu posted, but typically put in 2 and and let it do 1-2 2-1 automatically. If you have kit that holds it in 2 no matter what, then start in 1 and upshift.

Most important thing is to practice. You can try a local event - usually SCCA affiliated these days. Moparty probaboly runs theirs a little differently. With SCCA autocrosses, the morning walk is an important part of the game.

Second most important thing for many is to enter the corner smooth, and get the speed down early enough for the tires to bite and turn. Super easy to go in too hot and then complain the car understeers. No. The driver induced the understeer. <embarressed>

Slow is smooth and smooth is fast ;)
Not too slow! Slow enough to be smooth and keep on course. On an SCCA autocross - knowing the course and thinking ahead is critical and also challenging. I expect the Moparty course may be easier to follow (less visual tricks and traps) but the priciples will remain the same.
Stay as close to the critical cones as possible - the shorter distance traveled the less time it takes to finish the course.

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Solid advice - think I’m a reasonable, quick and smooth driver - but I’ve only driven against myself!! Practice might be tough but am going to join my local AX club soon - an abody amongst the Miatas and Ford STs ! In any matter, going to practice the hard starts from 1 to 2 on the column shifter over next couple of weeks - shame my Tremec budget only kicks in next year but going to make sure I keep smiling, push that engine and 904 transmission hard and most crucially, don’t embarrass my teenage boy!!
 
Where's the rest of the car ??
Here are a few more shots of ‘Fiona’ - it’s now a fuel injection 360 Magnum - here’s my engine build specs - again a daily driver, so made some compromises:

· 5.9 block Magnum 360 block from a 2001 Dodge Dakota
o Bore and Stroke: 4.030 in. and 3.580 in.
· Stock OE crankshaft externally balanced
· Stock Rods with ARP Rod Bolts
· Clevite P-Series Rod Bearings
· Speed-Pro Hypereutectic Pistons
o H116CP bored .030 over
o Compression ratio: 9.72
· Liberty Performance Premium Moly Series Rings
· Clevite P-Series main bearings
· COMP Cams Custom Grind Camshaft (Grind # Camshaft-3714B/37616B HR 110 + 0)
o Hydraulic Roller Tappet
o Duration: 275/279
o Lift .533/.536
· Dura-Bond Cam Bearings
· Melling Freeze Plug Kit
· Morel 5321 Hydraulic Roller Lifters
· Liberty Performance pushrods - Overall Length 6.800″ Wall Thickness .080″
· Scorpion Racing SCP3302 Rocker Arms
o 1.6 Small Block Chrysler
o 5/16 Adjustable Pedestal Endurance Rocker
· PBM 7985 Performance timing set
· Kevko M302 5 Quarts Capacity Oil Pan
· Kevko M301-1 Mid Sump Oil Pickup
· Melling M72HV High-Volume oil pump
· Stock Oil Pump Drive Shaft
· ARP Mopar Tube Stud
· FlowKooler Hi-Flow Mechanical Water Pump
· Fel-Pro gaskets throughout
· Performance Injection Equipment (PIE) SuperTune EngineQuest Magnum Cylinder Heads
o 2.02" stainless intake and 1.625" stainless exhaust valves
o COMP Cams Valve Springs 26995-16
o Liberty Performance Valve Spring Retainers
o Valve spring 150# seat 295# open @ .536 lift max
o 8mm valve stems
o 172 cc intake runners and 72 cc exhaust runner
o 62cc combustion chamber
o Ductile iron exhaust seat to reduce cracking
o Manganese bronze valve guides
· ARP Head Bolts
· Mopar Magnum NOS Valve Covers
· Edelbrock Pro-Flo 4 EFI System (35900)
o 4150-Style single plane intake manifold and 35 Lb/Hr injectors capable of 550 HP with 58 p.s.i. fuel pressure
o ECU
o Fully assembled intake manifold with air valve, fuel rails, and injectors
o E-Tuner application for setup and engine monitoring
o Edelbrock EFI Pro-Flo 4 Distributor
· PIE CNC machined brackets and drilling to convert LA intake to fit Magnum heads
Patriot Full Length Coated Long-tube Headers

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That's one sexy looking car!

Also I thought those lifters are meant to sit the other way?
 
I autocrossed from '89 to '21 with some years off due to grad school, work etc. Most of those with my '67 Barracuda.
I wouldn't spend time practicing the 1-2 shift, unless your entering th edrag race.
First run autocross run, put it 2 and forget about it.
Study everything you can about a understanding a cone course and driving them well.
Some things you can practice on the street.
A lot of things you can't. The car will move in ways it can't (and shouldn't) on the street.
Get a feel for the course, then pick one or two things to improve or try out.
If you mess up big, give it up, stop the car. You can't make up the time lost in a fishtail or a spin. But if you can get back on course without a flag thrown, then use the time to practice the remaining course.

 
Good advice - as always!!!

This is my set-up - have it saved :

***SUSPENSION***
  • Bilstein Shocks - A Body - Front and rear - non-adjustable
  • Sway-A-Way Torsion Bars - A Body Mopar - 1.08
  • Bumpstop - Round - 11/16
  • Mopar Lower Control Arm, stiffened with a BAC welded plate
  • Hellwig Sway Bars - front and rear
  • SPC/BAC Upper Control Arms, W/ Ball Joints
  • Dynamic Strut Rods - A Body
  • Delrin Bushings

***WHEELS and TIRES***
  • Cosmis XT-206R 17-inch (front: 17x8 and rear: 17x9)
  • Tires: Continental ExtremeContact DWS06 PLUS - 235/45ZR17 front and 255/45ZR17 rear.
  • The car is my daily driver - tires were not chosen for track, but for driving 365 days a year in NC.
100% there for the fun and am in alignment with everything you have written. Frustratingly, it’s a column shifter, but I’m not too bad on manual column shifting but it’s not 100% guaranteed !!

Ah! Yeah with a column shifter I would do as @Mattax said and just put it in 2 and leave it alone.

With your setup you don’t have a ton of adjustments to make at the track, the rear sway bar is adjustable but you probably don’t want to change that at the event. That would probably be something to note and make adjustments later if needed, kind of like any alignment changes. You can see how the car handles over the course of the event and then make changes for the next one.

How do you like the Edelbrock Pro-Flo?
 
Yes. By 'pick one thing to change or try' I was refering to a section of the course and your driving, not a mechanical adjustment.
I still usually shoe polish my tire sidewalls as a crude way to judge air pressure. But these marks can get messed up as an indicator when overdriving any corner.
 
I autocrossed from '89 to '21 with some years off due to grad school, work etc. Most of those with my '67 Barracuda.
I wouldn't spend time practicing the 1-2 shift, unless your entering th edrag race.
First run autocross run, put it 2 and forget about it.
Study everything you can about a understanding a cone course and driving them well.
Some things you can practice on the street.
A lot of things you can't. The car will move in ways it can't (and shouldn't) on the street.
Get a feel for the course, then pick one or two things to improve or try out.
If you mess up big, give it up, stop the car. You can't make up the time lost in a fishtail or a spin. But if you can get back on course without a flag thrown, then use the time to practice the remaining course.
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Perfect - turning my girl into an oversized go cart - 2nd gear all the way it is (for these pre tremec days!) - my engine was built for lower end torque, so hope this helps (will be getting it Dynoed at Moparty too, so be interesting to see the stats from that too). Yep, this is all sound advice. Hoping for multiple runs and getting better each time. Fingers crossed all the chassis goodies i have underneath and new wheels etc. will keep me nice and tight on the track - we'll find out! Will check out your links too!
 
Ah! Yeah with a column shifter I would do as @Mattax said and just put it in 2 and leave it alone.

With your setup you don’t have a ton of adjustments to make at the track, the rear sway bar is adjustable but you probably don’t want to change that at the event. That would probably be something to note and make adjustments later if needed, kind of like any alignment changes. You can see how the car handles over the course of the event and then make changes for the next one.

How do you like the Edelbrock Pro-Flo?
Yep - looks like i'm going to have fun in my oversized go kart! I'm going to rock up, look at tire pressures but that will probably be about it - this is for fun in any matter, so not planning on loosing site of that!

The Pro-flo 4 has stood by Edelbrock's promises so far - be that I went straight to it when I swapped my 318 carb LA to 360 Magnum - it starts up like a charm (even when cold), idle and acceleration feels much much smoother. Have used the tuning app a little but more so on the self-learning mode and playing with the idle for the moment. Love how the overall package feels so easy compared to the carb and as I drive it daily, that easiness and modern feel has, in my eyes, made the upgrade more worth it - even my neighbors like me more now, at least in the small hours of winter!! Looking forward to having Tremec, to round off the full powertrain set-up but even with the 904, I have no regrets.
 
@Mattax they do a morning walk of the course. It typically has one tricky corner (end closes to the drag strip) and it's very easy to miss one cone and trash the whole run. @Tuesday you can watch some videos from previous years on YouTube, layout hardly changes much if any.
 
If yur gonna run in Second gear with 3.55s; realize that the car is geared about 16 mph per 1000 rpm @zero slip.
at WOT, that makes about 14.4mph, and so
2000rpm = 28.8mph, 3000= 43.2, 4000= 57.6 and 5000=72
And you have a "stock stall".
Ima thinking; SOMETHING has to go.
Either the 3.55s, or
Second gear; or
the stock convertor.
But I'm not an organized event, auto-crosser, lol.
 
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He's probably making 380-400 lbs-ft at 3000 rpm, lets say 390 lbs-ft, and probably peaks 450 lbs-ft probably around 4000 rpms, 390 x 57% = 222 hp & 450 x 76% = 342 hp.

So probably makes around 222 hp @ 3,000 rpm and 342 hp @ 4,000.

The kind of horsepower you'll have to play with even if 370 lbs-ft @ 2,500 rpm would equal 176 hp.

So obviously deeper gear more hp to the ground.
 
He's probably making 380-400 lbs-ft at 3000 rpm, lets say 390 lbs-ft, and probably peaks 450 lbs-ft probably around 4000 rpms, 390 x 57% = 222 hp & 450 x 76% = 342 hp.

So probably makes around 222 hp @ 3,000 rpm and 342 hp @ 4,000.

The kind of horsepower you'll have to play with even if 370 lbs-ft @ 2,500 rpm would equal 176 hp.

So obviously deeper gear more hp to the ground.
You and @AJ/FormS have got me worried ! I need to drive home afterwards! Appreciate the 904 isn’t an AX gearbox, but took that it’s pretty robust. My engine parts are all pretty high-end - only things that are stock are crank and connecting rods. Diff and rear end is brand new Quick Performance 3.50. How high is chance of failure? Should I be concerned?
 
You and @AJ/FormS have got me worried ! I need to drive home afterwards! Appreciate the 904 isn’t an AX gearbox, but took that it’s pretty robust. My engine parts are all pretty high-end - only things that are stock are crank and connecting rods. Diff and rear end is brand new Quick Performance 3.50. How high is chance of failure? Should I be concerned?
I wasn't implying the trans and rear end ain't strong enough, or even if you need deeper gears, guess a few races will tell. Was just guesstimating your hp at those rpms you'll spend most of your time at.
 
Ok. So those who have never driven an autocross - or driven one with a v-8, whether a 'vette or Pony car, or a Griffith...
Kegan has driven at Moparty, so he can offer more insight on this particular event.
In my experience, with a 4 spd the right pedal should never be a switch, and very rarely if at all will you get to floor it and make good use of it. Sometimes maybe a 1/2 second or so. With an automatic, there is a little more built-in cushion accelerating and maybe with engine braking but if so its not enough to prevent upsetting the car. My car has 3.23 gears and shorter tires. Even on a tight course that never exceeds 60 mph I find it very difficult to take advantage of leaving it 1st gear. Maybe a better driver, with a better seat could, but that's my experience.

@Mattax they do a morning walk of the course. It typically has one tricky corner (end closes to the drag strip) and it's very easy to miss one cone and trash the whole run. @Tuesday you can watch some videos from previous years on YouTube, layout hardly changes much if any.
That's very interesting.
Missing a cone and getting a DNF is major disappointment.
When I had opportunities to influence course design (event chair, program chair, etc) my goal was no DNFs for anyone. Getting lost isn't fun and it is discouraging to have repeated incompletes.
Regardless - Knowing that - @Tuesday can be alert to the possibility of a hard to see cone.

What I was talking about was understanding how a 'gate type' cone course differs visually from a 'road type' cone course. Moparty looks to be the former. These are more common because they are easier to setup and maintain during the event. They also require the driver to come up with the true course and the best path(s) a car should take. Sometimes one has to imagine a cone that ought to be there, and frequently one has to ignore tricky cones that mislead the driver into making the couse tighter or more difficult than it is.

I'm going to steal an example from Roger H. Johnson (the Insane) Solo II Course Design.

A driver following the course cone to cone will follow the black line.
1724287015393.png

A driver who has planned the course will ignore the inside cones, and pick a couple critical cones to look for while driving.
And a really good autocrosser will be able to plan a tightish sweep that still maintains momentum and allows some throttle to be squeezed on as the steering wheel is returned toward center.

In this example I'd be looking for these 3 cones
1724287444706.png


Although 2 might be hard to pick out before the apex, its exact location is not critical, we start the sweep left as or after we pass it. Before then we're looking at cone 3 and the turn beyond.
 
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I wasn't implying the trans and rear end ain't strong enough, or even if you need deeper gears, guess a few races will tell. Was just guesstimating your hp at those rpms you'll spend most of your time at.
Thanks for clarifying.
Yes. In my experience, at least those with older more traditional transmissions (3 speed auto, 3 speed and 4 speed manual), dedicated autocrossers ran steep rear gears.
 
Ok. So those who have never driven an autocross - or driven one with a v-8, whether a 'vette or Pony car, or a Griffith...
Kegan has driven at Moparty, so he can offer more insight on this particular event.
In my experience, with a 4 spd the right pedal should never be a switch, and very rarely if at all will you get to floor it and make good use of it. Sometimes maybe a 1/2 second or so. With an automatic, there is a little more built-in cushion accelerating and maybe with engine braking but if so its not enough to prevent upsetting the car. My car has 3.23 gears and shorter tires. Even on a tight course that never exceeds 60 mph I find it very difficult to take advantage of leaving it 1st gear. Maybe a better driver, with a better seat could, but that's my experience.


That's very interesting.
Missing a cone and getting a DNF is major disappointment.
When I had opportunities to influence course design (event chair, program chair, etc) my goal was no DNFs for anyone. Getting lost isn't fun and it is discouraging to have repeated incompletes.
Regardless - Knowing that - @Tuesday can be alert to the possibility of a hard to see cone.

What I was talking about was understanding how a 'gate type' cone course differs visually from a 'road type' cone course. Moparty looks to be the former. These are more common because they are easier to setup and maintain during the event. They also require the driver to come up with the true course and the best path(s) a car should take. Sometimes one has to imagine a cone that ought to be there, and frequently one has to ignore tricky cones that mislead the driver into making the couse tighter or more difficult than it is.

I'm going to steal an example from Roger H. Johnson (the Insane) Solo II Course Design.

A driver following the course cone to cone will follow the black line.
View attachment 1716292870
A driver who has planned the course will ignore the inside cones, and pick a couple critical cones to look for while driving.
And a really good autocrosser will be able to plan a tightish sweep that still maintains momentum and allows some throttle to be squeezed on as the steering wheel is returned toward center.

In this example I'd be looking for these 3 cones
View attachment 1716292871

Although 2 might be hard to pick out before the apex, its exact location is not critical, we start the sweep left as or after we pass it. Before then we're looking at cone 3 and the turn beyond.
Solid advice - it's almost like you have to draw the course curves in your mind and focus on a particular cone as a braking spot and/or turning in spot on the opposite side to your line, as effectively the apex isn't always going to be the cone. All about finding the smooth and faster line.
 
I have never autocrossed but I drive hard and fast on the street if you catch my, um, drift. Have you driven your car hard and fast? How does it feel going through a corner or curve? When you go hard through a right hander and the right side pops up and the left side drops do your sphincters loosen up? Or vise versa? The Max is one of the few vehicles that I have never done that with. It’s set up for a straight line! Everything else from the ’59 Plymouth Big Block wagon I learned to drive on to the ’92 Dodge 1 ton window van and the ’90 Subaru with the 4EAT I now drive I know what they will do or won’t. Yes my late wife and I would road race through Levittown, me in the wagon and her in the ’68 Corona. Can you drift it? I had a ’66 Valiant wagon, 225/904 and yes I could! And the ’59 wagon too! What happens when you brake hard? What happens when you brake hard in the middle of a corner? What happens when you punch it in the middle of a curve or corner or entering or exiting?

Much has been said about leaving it in second, but practice 1st to 2nd shifts you may want to drop it down either manually or with the kickdown. And know where your kickdown is. If you have a normal 904 it’s gonna kickdown. Be ready for it and use it. Kick it down then drop it into first and use the engine braking, then shift it up, that’s how you road race a ’59 Plymouth! 30 years ago I had a ’77 Newport 4 door with a 400/TQ and, yes, I drove that hard and fast and showed at least one Acura driver how to do it in a C body!
 
I’ve done it once. Walking the course was the most important aspect to planning your first successful smooth run.

After that your goal is to run a little faster. Every time.

Ask a veteran to ride along and critique. You probably won’t go solo first time anyway.

Ask a veteran to critique your solo runs from the sidelines….or your boy take a vid.

These inputs will give you information to push the car as far as it can be pushed.

Bring plenty of water and snacks. And a big hat. And sunscreen.

It’s an incredible time no matter what.
 
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