12:05 Garage- ’70 Duster build

[JBrian]

Where did you get those pictures???

 

[racerjoe]

Where did you get those pictures???

From Benjamin, @bjkadron

 

[mopowers]

It’s the most fun you can ever have with your car. I love bringing people for rides who don’t know what to expect. Even my friend that has gone to Moparty with me the last 4 years seemed a little spooked the first few runs. The 3S heading straight to the wall at 70MPH really had him hitting the passenger side brake! LOL!

I'm curious- what spring rate do you run on up front?

 

[racerjoe]

I'm curious- what spring rate do you run on up front?

450lb, which is irrelevant unless you have an HDK since motion ratios are specific to the application.

 

[racerjoe]

Hit the autocross at Cruisin the Coast twice this week, driving back and forth both days. That equals about 350ish miles of interstate driving and I likely did about 30 autocross runs total. I only stopped because tires aren't cheap! As usual, Finch Performance was there with his "Share the Ride" program and his bad *** C10 trucks. If you don't know what those are, look them up. I was running within a second of these trucks and their hand picked seasoned drivers. Granted, they are bringing people for rides and likely not trying to put down fast times. However, whatever I was doing caught the eyes of many people. Several came over to look at the car and comment on how fast it looked out there. I even had a few random people ask for rides, which is always awesome. Oh, one of the share the ride drivers even gave me a thumbs up. I'll take that as a win! The car ran great with the AC on cruising at 75-80MPH. One more day of CtC but this one will be relaxed and just hanging out. Time to turn it back into a street car, i.e.; change wheels and driver seat. Have I ever said how awesome it is to have a car that can pretty much do whatever you want it to do and be comfortable doing it?
Oh, I also scored a set of 6.1 hemi heads. Time for more HP!

 

[JBrian]

The versatility of the GEN III Hemi. Street manners, any 93 octane pump gas, doesn't care about heat or lateral Gs, cruise all day at 2500RPM getting 18MPG and run 115MPH in the 1/4 mile. And that's just the engine! The stiff chassis, and autocross friendly suspension also pay dividends on the street. These are simply outstanding muscle cars to enjoy.

 

[75slant6]

Hit the autocross at Cruisin the Coast twice this week, driving back and forth both days. That equals about 350ish miles of interstate driving and I likely did about 30 autocross runs total. I only stopped because tires aren't cheap! As usual, Finch Performance was there with his "Share the Ride" program and his bad *** C10 trucks. If you don't know what those are, look them up. I was running within a second of these trucks and their hand picked seasoned drivers. Granted, they are bringing people for rides and likely not trying to put down fast times. However, whatever I was doing caught the eyes of many people. Several came over to look at the car and comment on how fast it looked out there. I even had a few random people ask for rides, which is always awesome. Oh, one of the share the ride drivers even gave me a thumbs up. I'll take that as a win! The car ran great with the AC on cruising at 75-80MPH. One more day of CtC but this one will be relaxed and just hanging out. Time to turn it back into a street car, i.e.; change wheels and driver seat. Have I ever said how awesome it is to have a car that can pretty much do whatever you want it to do and be comfortable doing it?
Oh, I also scored a set of 6.1 hemi heads. Time for more HP!

What’s the benefit of using the 6.1 heads versus eagle 5.7 heads?

 

[72bluNblu]

I'm curious- what spring rate do you run on up front?

450lb, which is irrelevant unless you have an HDK since motion ratios are specific to the application.

With the HDK motion ratio a 450 lb/in spring works out to about ~293 lb/in at the wheel. Basically about the same as a 1.12” torsion bar at 300 lb/in

 

[mopowers]

With the HDK motion ratio a 450 lb/in spring works out to about ~293 lb/in at the wheel. Basically about the same as a 1.12” torsion bar at 300 lb/in

Do you know if there's a table with all of the torsion bar diameters out there and their associated spring rates (at the wheel). I'd imagine the relationship isn't linear since it's probably based on cross-sectional area?

 

[72bluNblu]

Do you know if there's a table with all of the torsion bar diameters out there and their associated spring rates (at the wheel). I'd imagine the relationship isn't linear since it's probably based on cross-sectional area?

There are a few, there’s a list for factory bars with their associated wheel rates and I know Firm Feel lists the wheel rates for all of theirs on their website. There’s a slight difference in the calculations based on the LCA measurement, I know there was a table in one of the magazines back in the day that was a little different because they used a slightly different LCA measurement.

It’s a pretty straightforward equation that’s based on the diameter of the torsion bar, the length of the torsion bar, length of the LCA and the spring constant for the material used. The same kind of steel is typically used so the spring constant is basically all the same (unless you actually measure the specific steel used).

This one covers most of the factory bars, there’s a table in the kitchen car/circuit car manual that has additional torsion bar offerings that went all the way up to 1.64" diameter torsion bar with a 1,455 lb/in rate!

 

[racerjoe]

What’s the benefit of using the 6.1 heads versus eagle 5.7 heads?

Since I have an early 5.7, it has the heads the internet says are junk. In reality, they aren't bad, there are just better options from other engines. The 6.1 has bigger valves and ports. And more importantly, they have a smaller combustion chamber, so my compression will increase from 9.5:1 to around 11:1. Many people use the Eagle 5.7 heads on the early 5.7 because they are a cheap and plentiful and flow nearly the same as the 6.1. The problem is those have a very small combustion chamber and compression goes up to around 13:1. Thick head gaskets are available to remedy this and I was considering using the eagles. However, the eagles require eagle rockers and valve covers, and custom pushrods. Since the 6.1 was released while the pre-eagle was still in production, I can use my existing rockers, valve covers, and even valve springs. I may be able to get away with using my current pushrods too. They are Manley pushrods, so I'll be happy if I don't have to buy another set. I will have to get another intake. I was originally thinking of using the 6.4 intake so I could take advantage of the SRV, but they are stupid expensive and I'm not even 100% sure it would fit without hitting the firewall. So my options are either the 6.1 aluminum intake, or an eagle intake with spacers. (The intake runners are raised on the eagle heads so it clears the front of the block). Right now my preference would be the aluminum 6.1. I just need to find one at a reasonable price. In the end, I think the should be worth about 30-40HP more. The cam I have should like the increased compression too.

 

[mopowers]

There are a few, there’s a list for factory bars with their associated wheel rates and I know Firm Feel lists the wheel rates for all of theirs on their website. There’s a slight difference in the calculations based on the LCA measurement, I know there was a table in one of the magazines back in the day that was a little different because they used a slightly different LCA measurement.

It’s a pretty straightforward equation that’s based on the diameter of the torsion bar, the length of the torsion bar, length of the LCA and the spring constant for the material used. The same kind of steel is typically used so the spring constant is basically all the same (unless you actually measure the specific steel used).

View attachment 1716464697

This one covers most of the factory bars, there’s a table in the kitchen car/circuit car manual that has additional torsion bar offerings that went all the way up to 1.64" diameter torsion bar with a 1,455 lb/in rate!

Thanks. I hadn't seen that. I'm going for something on the softer side for my strip-oriented combo. Right now, I've got 450 lb/in coilovers - which based on that table - look to be equivalent to a 1.14" bar w/ the 0.77 ratio. That explains why it's so stiff.

If I'm going for something closer to a .870" bar, I'd need a 150-175 lb/in coilover. Am I doing the math right?? Seems super soft.

 

[75slant6]

Since I have an early 5.7, it has the heads the internet says are junk. In reality, they aren't bad, there are just better options from other engines. The 6.1 has bigger valves and ports. And more importantly, they have a smaller combustion chamber, so my compression will increase from 9.5:1 to around 11:1. Many people use the Eagle 5.7 heads on the early 5.7 because they are a cheap and plentiful and flow nearly the same as the 6.1. The problem is those have a very small combustion chamber and compression goes up to around 13:1. Thick head gaskets are available to remedy this and I was considering using the eagles. However, the eagles require eagle rockers and valve covers, and custom pushrods. Since the 6.1 was released while the pre-eagle was still in production, I can use my existing rockers, valve covers, and even valve springs. I may be able to get away with using my current pushrods too. They are Manley pushrods, so I'll be happy if I don't have to buy another set. I will have to get another intake. I was originally thinking of using the 6.4 intake so I could take advantage of the SRV, but they are stupid expensive and I'm not even 100% sure it would fit without hitting the firewall. So my options are either the 6.1 aluminum intake, or an eagle intake with spacers. (The intake runners are raised on the eagle heads so it clears the front of the block). Right now my preference would be the aluminum 6.1. I just need to find one at a reasonable price. In the end, I think the should be worth about 30-40HP more. The cam I have should like the increased compression too.

I knew the 6.1 and Eagle heads flow about the same and the 6.1 had bigger combustion chambers but wasn’t aware of what all would or wouldn’t work with the two different heads.

 

[DionR]

Since I have an early 5.7, it has the heads the internet says are junk. In reality, they aren't bad, there are just better options from other engines. The 6.1 has bigger valves and ports. And more importantly, they have a smaller combustion chamber, so my compression will increase from 9.5:1 to around 11:1. Many people use the Eagle 5.7 heads on the early 5.7 because they are a cheap and plentiful and flow nearly the same as the 6.1. The problem is those have a very small combustion chamber and compression goes up to around 13:1. Thick head gaskets are available to remedy this and I was considering using the eagles. However, the eagles require eagle rockers and valve covers, and custom pushrods. Since the 6.1 was released while the pre-eagle was still in production, I can use my existing rockers, valve covers, and even valve springs. I may be able to get away with using my current pushrods too. They are Manley pushrods, so I'll be happy if I don't have to buy another set. I will have to get another intake. I was originally thinking of using the 6.4 intake so I could take advantage of the SRV, but they are stupid expensive and I'm not even 100% sure it would fit without hitting the firewall. So my options are either the 6.1 aluminum intake, or an eagle intake with spacers. (The intake runners are raised on the eagle heads so it clears the front of the block). Right now my preference would be the aluminum 6.1. I just need to find one at a reasonable price. In the end, I think the should be worth about 30-40HP more. The cam I have should like the increased compression too.

The Eagle 5.7 intake ports should match the 6.1 heads. Might be another lower cost option.

Any issues with the bigger 6.1 valves and the smaller 5.7 bore?

 

[racerjoe]

The Eagle 5.7 intake ports should match the 6.1 heads. Might be another lower cost option.

Any issues with the bigger 6.1 valves and the smaller 5.7 bore?

Yep, I mentioned the eagle intake in my post. My understanding is the intake contacts the triangle part of the block in the front. I also understand it can be modified to make fit by heating it with a heat gun and making a dimple, along with some clearancing on the block. Or just use the spacers...

According to the internet, the smaller bore shouldn't be a problem. Apparently many people have done the swap.

 

[DionR]

Yep, I mentioned the eagle intake in my post.

You're right, sorry. I missed it.

My understanding is the intake contacts the triangle part of the block in the front. I also understand it can be modified to make fit by heating it with a heat gun and making a dimple, along with some clearancing on the block. Or just use the spacers...

I remember people having to heat and form the 6.4 intake to fit the early blocks, but don't remember issues on the Eagle 5.7 intake. Not saying it doesn't need the same work, I just don't remember it.

I am sure your info is much more recent and accurate than my recollections.

 

[72bluNblu]

Thanks. I hadn't seen that. I'm going for something on the softer side for my strip-oriented combo. Right now, I've got 450 lb/in coilovers - which based on that table - look to be equivalent to a 1.14" bar w/ the 0.77 ratio. That explains why it's so stiff.

If I'm going for something closer to a .870" bar, I'd need a 150-175 lb/in coilover. Am I doing the math right?? Seems super soft.

So

Wheel Rate = Spring Rate * (Motion Ratio^2)

The HDK has a motion rate of .807, so yeah a 450 lb/in spring yields a 293 lb/in wheel rate.

If you wanted a wheel rate more like 120 lb/in and you had the same ratio you’d need a 184 lb/in spring.

If your motion rate is .77 then your 120 lb wheel rate would mean a 203 lb/in spring.

As far as seeming soft, a 300 lb/in torsion bar is 2.5x stiffer than a factory .87 bar (120 lb/in), so it’s a pretty similar change.

 

[mopowers]

So

Wheel Rate = Spring Rate * (Motion Ratio^2)

The HDK has a motion rate of .807, so yeah a 450 lb/in spring yields a 293 lb/in wheel rate.

If you wanted a wheel rate more like 120 lb/in and you had the same ratio you’d need a 184 lb/in spring.

If your motion rate is .77 then your 120 lb wheel rate would mean a 203 lb/in spring.

As far as seeming soft, a 300 lb/in torsion bar is 2.5x stiffer than a factory .87 bar (120 lb/in), so it’s a pretty similar change.

Thanks. My math was slightly off. I didn't realize the wheel rate was based on the square of the motion ratio. Great info.

 

[bjkadron]

Hit the autocross at Cruisin the Coast twice this week, driving back and forth both days. That equals about 350ish miles of interstate driving and I likely did about 30 autocross runs total. I only stopped because tires aren't cheap! As usual, Finch Performance was there with his "Share the Ride" program and his bad *** C10 trucks. If you don't know what those are, look them up. I was running within a second of these trucks and their hand picked seasoned drivers. Granted, they are bringing people for rides and likely not trying to put down fast times. However, whatever I was doing caught the eyes of many people. Several came over to look at the car and comment on how fast it looked out there. I even had a few random people ask for rides, which is always awesome. Oh, one of the share the ride drivers even gave me a thumbs up. I'll take that as a win! The car ran great with the AC on cruising at 75-80MPH. One more day of CtC but this one will be relaxed and just hanging out. Time to turn it back into a street car, i.e.; change wheels and driver seat. Have I ever said how awesome it is to have a car that can pretty much do whatever you want it to do and be comfortable doing it?
Oh, I also scored a set of 6.1 hemi heads. Time for more HP!

This is my eventual Goal. Cruiser and bruiser all in one! I have a lot of work to do.

 

[racerjoe]

This is my eventual Goal. Cruiser and bruiser all in one! I have a lot of work to do.

Finished off Cruising the Coast yesterday with another successful day. We finally had a small "cool" front come in which brought a beautiful sunrise on my drive to the coast. If you look close, a fried with a 67 Pro Touring Mustang is in front of me, and behind me is a friend with an original paint 57 Belaire with a 582ci big block and T56.

 

[DionR]

Are you still running 2 degrees of camber?

If so, do you run that all the time or do you dial it back some when set up to just cruise?

 

[racerjoe]

Are you still running 2 degrees of camber?

If so, do you run that all the time or do you dial it back some when set up to just cruise?

I run the same alignment for everything. It takes too much time to bother with changing it. The only thing I change for "streetcar" mode is the wheels and driver seat. One notable difference is how much quieter the street tires are compared to the RE72RS tires.

 

[DionR]

I run the same alignment for everything. It takes too much time to bother with changing it. The only thing I change for "streetcar" mode is the wheels and driver seat. One notable difference is how much quieter the street tires are compared to the RE72RS tires.

I understand not wanting to change stuff that doesn't need to be changed.

Thanks for the info. I am working on doing my alignment and have always used a 1/2 degree of negative camber, but see that there are some late model cars running 1 degree negative. I think I am going to bump it up.

 

[JBrian]

I understand not wanting to change stuff that doesn't need to be changed.

Thanks for the info. I am working on doing my alignment and have always used a 1/2 degree of negative camber, but see that there are some late model cars running 1 degree negative. I think I am going to bump it up.

I'm running -1.6 camber. There will be a big difference in steering response once you cross -1.3ish. I run my numbers as a compromise to street driving and autocross. If you want to have immediate steering response, dial it up.

 

[DionR]

I'm running -1.6 camber. There will be a big difference in steering response once you cross -1.3ish. I run my numbers as a compromise to street driving and autocross. If you want to have immediate steering response, dial it up.

What I want is for the dumb thing to drive down the road straight. Camber isn't going to make that happen, but if I have to mess with the alignment, might as well dial that up some.

Pretty sure my Borgeson box went bad and that is the issue I have been fighting all summer. The nervousness and twitchiness seem to be gone after swapping in an OEM PS box, but the alignment is junk so it still doesn't drive great. Just need time and at least one more nice day to test drive it and get it over to storage so I can get back on my G3 swap car.