Pulled the proverbial trigger!

[hutchenc]

So after talking with Chevynut a few times and visiting his place in Ft. Collins, I've pulled the trigger on the front C4 conversion. I found a local buyer for my entire front end, steering, and brakes as well as a few other parts I had laying around so that eases the blow to the pocket book quite a bit!

Looking at an April timeframe for attaching the front stub.

I should be able to get it on the road by summer I think. :)

[chevynut]

I look forward to working with you on the project Chad.....and you have to give me a ride when we're finished. ;)

[hutchenc]

It's gonna be fun Lazlo. You should take some shots of the car in the jig (when we get it to that point). Local buyer is picking up the other stuff in two weeks...gotta start tearing her down this weekend!

This will give me the opportunity to clean up my firewall like I have wanted to do for, oh, about 10 years now ;)

[JT56]

Look forward to this! Shouldn't there be a weight savings too?

[chevynut]

JT, yes there is a weight savings. For a full C4 conversion it's around 150-200 pounds. Don't remember what the front is.

This is the first time I've attempted to attach a clip with the body on the frame, but it shouldn't be too hard. Famous last words. :)

[hutchenc]

JT, yes there is a weight savings. For a full C4 conversion it's around 150-200 pounds. Don't remember what the front is.

This is the first time I've attempted to attach a clip with the body on the frame, but it shouldn't be too hard. Famous last words. :)

You shouldn't admit that in a public forum Laz!

I think we'll be fine! Gotta put those 2" lowering blocks in the rear though so you can get the front ride height correct.

BTW...I spoke to Viking today and I cannot re-use those coil-overs that I have unfortunately. I gave them the ride height of 12" so they can come up with a shock, but they had some questions about the springs that I couldn't answer. Motion ratio, total and side/side front end weight, shock angle, etc...looking to find a spring rate if I want to go with coil-overs for a late model front end. I'm looking for a firm but not beat you up ride. I like the way my 2005 GTO rides...true touring car that can handle it's own in the curves if needed, but it won't handle like a 'vette. Viking has variable coil-over spring rates btw. Not sure if that's a good idea or not.

You know my front engine setup...Dart SHP with aluminum heads. I think the SHP is about 25 heavier than a standard GM SBC. I'm sure my SBC is lighter than your 502...don't know by how much though. 150 pounds maybe?

P.S. Laz...my girlfriend has been giving me s**t for not taking her to the drive-in in Ft. Collins in my '56. That may very well be the time it gets to Ft. Collins. That Muncie and 3.73 rear doesn't help though...287 isn't too bad though, I could putt along at 55 MPH and give people the bird!

[chevynut]

Chad, I've thought through the whole clip attachment process and don't really see any big issues. I think there's at least one of my customers who may have attached a clip with the car intact, but I'm not sure about that. I think he's one from NJ and he finished his 57 pretty quick so that's what makes me say that. You will have to address the brake and fuel lines, which I hadn't really thought of til now. What are you using for a steering column now?

I'd be interested to see what Viking comes up with on spring rate. I have a spreadsheet that calculates the rate so I pretty much know what you need, but how about giving it a try with them?

Shock angle at ride height 22 degrees
Motion ratio 15/12 (balljoint/shock)
Length at ride height 12"
Front corner sprung weight ~865 (with driver)

I believe in using the softest spring you can use that will hold the car at the correct height You can use a stiffer spring to accomplish the same thing, but the ride quality will suffer. I think that's why coilovers sometimes get a bad rap....guys over-spring them. I've never really looked at progressive springs but the wheel rate at ride height would have to be the same. The wheel rate is what determines ride quality.

Let's see what Viking comes up with for your car.....but don't order them until we review. ;)

In '73 I drove my '55 from Loveland to Kansas City with a 427, Muncie, and 4.11 gears. Should have left it in Loveland. :cry:

[hutchenc]

Laz,

I have an Ididit tilt column. Not sure on the length.

Not too worried about brake and fuel lines. I have a junction in the brake line behind the firewall for the rears so I'll re-do it if need be. I want to re-do the fronts anyhow. No biggie.

Fuel supply line changes from hard line to soft at the firewall, return is soft all the way. Not worried.

Will see what Viking comes up with when I call them. Based on the info in their catalog (here: http://magazinevolume.com/12765BF/#/22/) which assumes a motion ratio of .70 and a correction factor of .88, they're saying around 500lb/in using the C205 shock and a 9" spring. Does that seem high? I used a total overall front weight of (865x2)-200 (so as not to count a driver twice) which is 1530. What ballpark rate are you thinking I'll need?

Going off a correction factor of cos (22 degrees), which is .927, and a motion ratio of .8 using 865 pounds, I'm getting 518 lb/in.

[chevynut]

Chad, you got the C4 motion ratio and shock angle correction right. You want to run the shock about halfway compressed, and with the adjuster nut off the bottom of the shock a ways so you have both up and down adjustment. I plan about 1.5" off the bottom. That preloads the spring so it's already holding some weight (1.5 times the spring rate) as soon as the shock moves off of fully extended position. Then you have 1/2 of the stoke before you're at ride height. So assume the shock is straight up with no motion ratio and calculate the spring rate required at ride height. Then correct for the angle and the motion ratio.

You might be a mechanical engineer. ;)

[hutchenc]

Laz...so that number at 518 lb/in for a 9" spring seems correct to you? I used the spring pre-load number Viking supplies which is 2.25" (I think). It looks like they offer springs in a 50 lb/in increment. Do I go with a 500 or a 550 lb/in rate?

You must be running something close to 550 lb/in with a BBC if my math is correct right? Maybe I'm off.

FWIW...I really enjoy this aspect of planning a build! Can't argue with basic math!

[chevynut]

Chad, my spreadsheet says around 450 lb/in is the right spring rate for the numbers I used above. However, I'm not seeing how you get to 518 lb/in using your numbers. I think you did this, which is incorrect:

865/2.25/.8/.927 = 518

The 2.25 is the preload but you haven't accounted for the compression at ride height which is half the stroke. Also you need to square both the motion ratio factor and the spring angle correction factor.

It seems to me that 2.25" preload on the spring is really high for a 9" spring. With the ride height compression you would have around 4.26" of spring compression at ride height and 6.25" at full compression. Seems like you might get coil bind there, but I'm not sure. If you really can use that much preload the spring rate should be lower, which is a good thing.

I typically recommend 10" springs on a QA1 coilover. Why are you leaning to Viking instead of some other brand? I'm sure they will work fine, just curious.

Here is the calculation I use....again you need to square both the motion ratio and the shock angle correction in the calculations. The 3.5 is the total compression of the spring at ride height, 1.5" for the nut preload and 2" for half the stroke.

865/3.5/.8^2/.927^2 = 449

Of course you could use a lower spring rate and run the nut up further, or a higher spring rate and run it down. If you go to 2.25" preload you get 370 lb/in spring rate.

On my Nomad I'm using a 600 lb/in spring which I think is going to be just about right. I won't know until I get the car assembled and adjust the shocks, but that's what my spreadsheet gives me. The front end weight is higher than your car and I was generous with the weight of the added sheetmetal, engine, radiator, A/C, accessories, and other stuff. Anything added forward of the rear axle increases front end weight and my Cadillac power seats are pretty heavy and I added a console. The engine is around 700 pounds. As a cross-check to my numbers the front of Wade's Nomad weighed 1870 pounds on an actual scale. Mine is almost 300 pounds heavier by my calculations and most of that is engine since he has an LS-1. Remember that you need to remove the unsprung weight for the calculations.

[chevynut]

By the way, I used 500 pounds for your SBC engine, 100 for your 4-speed, 200 for engine accessories and 150 for other added equipment over a stock car. Not sure how accurate some of those are. I assumed 170 pounds for a driver but no passenger. You have quite a bit of adjustment on the shock if these numbers are off some. Ideally, you should weigh the front of the car, but I think Wade's numbers give a pretty good idea and sanity check.

[hutchenc]

Laz...I see what I did wrong there. Thanks.

I don't have A/C but do have power steering and a big cross-flow radiator (it's aluminum, but higher capacity than a stock radiator). I'm also running a scattershield so I think that is a good deal heavier than an aluminum bell...not sure by how much. I'll likely be running caddy seats too since I have your brackets :)

As far as the Viking deal...they're about the same price as QA-1's and they're double-adjustable. I think they have a part conversion chart. What's the QA-1 you recommend (part # I mean)?

[chevynut]

I doubt your scattershield is much heavier than an iron bellhousing, though. The weights are all estimates but I think they're close.

The QA-1 is the 401/402 depending on whether you want bearing or poly ends.