Chassis Rigidity - Replicas v. Origianls

[Randy V]

The ERA chassis doesn't have the stiffening ribs nor do CAV and RCR.

(The pictures below are taken from the CAV and RCR websites. The first two pics are CAV's chassis, the third RCR's.)

I believe that the current RCR-40 does have the stiffening rib that runs directly across the front of the seats now.. I'm not 100% certain why it was added.. probably to meet some SVA requirement or some such.

Stiff? My chassis is stiffer than anything I've ever seen before - While I can't give you specifics, all I can tell you is that when you jack it up and put it on Jack stands, you always have to shim the jack stands to keep the chassis from rocking.. Not a millimeter of sag or flex in this thing...

 

[Bob Putnam]

The ERA chassis has had ribs ever since we went to stainless steel about 12 years ago.
(This is a chassis in progress before the top of the rear structure was installed.)

 

[Ron Earp]

The ERA chassis doesn't have the stiffening ribs nor do CAV and RCR.

My RCR Lola chassis has the ribs inside the sills. Looked at them with a mirror while mounting a tank sender. I don't know about the CAV.

 

[John]

How is it that "modern" GT40s carry only 20 gallons of fuel while the originals held 31 (I believe)? There's only so much room under the sills.

 

[Jim Craik]

John,

I do not know for sure but I bet the new Ford GT does not have fuel in the sills. It has to meet modern car design rules and I'm pritty sure that the tank needs to be surrounded by more "car" than that.

 

[JimmyMac]

John,
The originals use flexible bag tanks that fill most of the volume of the sponsons and have recesses in them to fit around the ribs.

 

[Fran Hall RCR]

Dont forget that some of the originals also had huge ..and I do mean huge..crossover tubes running across the center of the car and through the chassis/dash structure...the original chassis in a Mk2 was crammed full of as much fuel as they could possibly get in...

 

[JimmyMac]

Dont forget that some of the originals also had huge ..and I do mean huge..crossover tubes running across the center of the car and through the chassis/dash structure...the original chassis in a Mk2 was crammed full of as much fuel as they could possibly get in...

Like this :

 

[Bob Putnam]

Our rocker sills were made a bit narrower than the original's because we made the seats wider.
To fit our fat


wallets. ;>D

 

[John]

Chuckle, chuckle, Bob. And Jimmy Mac, no WONDER the tanks in my SPF take so long to fill up. Look at the size of those drums under the filler caps on the original!

 

[Jac Mac]

Our rocker sills were made a bit narrower than the original's because we made the seats wider.
To fit our fat


wallets. ;>D

Your Lucky...after paying for the car, I did not think the wallet problem would exist...

 

[F1Ash]

Thanks for the link, Brian. It was an interesting discussion.

What brought my question to mind was the claim by SPF that so many of the parts on their cars are interchangeable with the originals. I understand their chassis aren't as complex as originals and it got me to wondering about rigidity.

In the discussion at that link, someone said the Mk IV GT40 had a torsional rigidity of just a bit over 10,000 ft-lb/degree of twist. I wonder if MK1s and MK11s were ever tested. I wonder if an SPF was ever tested.

I didn't read through your entire thread, so if someone already posted this, I apologize for the redundancy.

In reference to the Superformance GT40, I pulled this from there website:

"...The chassis, at over 12,000 pounds per degree is stiffer than any other chassis on the market, and is made up of over 244 laser cut and bent or pressed parts...."

GT40 Specifications

 

[Rick Muck- Mark IV]

In reference to the Superformance GT40, I pulled this from there website:

"...The chassis, at over 12,000 pounds per degree is stiffer than any other chassis on the market, and is made up of over 244 laser cut and bent or pressed parts...."

GT40 Specifications

That is a slight bit of puffery that is several years old (I must remind Lance to update that site) Now what is posted is true, a lot of parts and the 12,000 pounds part. What may or may not be correct is the competitive comparison as most others have not been tested nor results posted. So it is possible that another "GT40" has a stiffer chassis/tub. But there is a point of diminishing returns. And if you are not going into a "vintage" series where original design is required as part of the entry requirements then such a car may be right for you. Again, you will not be racing a "GT40" but a "GT40 replica". A GT40 body installed on a Ferrari Italia will be very fast but it will not be "GT40"........

 

[Jim Rosenthal]

The flexible bag tanks add some capacity versus the metal tanks that have to be slid into place. Actually I think the bag tanks add quite a bit. In my car, with metal tanks, all that volume for carrying fuel is lost- there is an air space around the tanks. But for most of us, who aren't concerned with driving at top speed for 24 hours, the lost tank volume isn't a problem.

We have a date, my car and I, to bring it (when completed) to the Marriotts museum and compare the two vehicles (although theirs was actually elsewhere getting some maintenance done) The curators were interested to see it and look over the two cars side by side. Until that time, I won't have a chance to directly compare my chassis to an original car. But all the photos of mine under construction that I have been able to compare with original photos and diagrams illustrate that the sponson stiffening ribs are exactly as original cars had them- not notched out, but complete rings. How much this affects torsional rigidity I don't know. The figure of 12,000NM/degree of twist was mentioned back in the day of the first GT40s. I don't think the sponson ribs contribute that much to it, though; I think more comes from the three-dimensional structure of the tub and the multiple bracing effects of all the chassis weldments triangulating each other. Mind you, this is the kind of opinion you'd have from a doctor, not an engineer, so it probably isn't worth much

 

[Ian K]

I didn't read through your entire thread, so if someone already posted this, I apologize for the redundancy.

In reference to the Superformance GT40, I pulled this from there website:

"...The chassis, at over 12,000 pounds per degree is stiffer than any other chassis on the market, and is made up of over 244 laser cut and bent or pressed parts...."

GT40 Specifications

Hmmm, CAV published their numbers sometime ago:

"This translates to 32 154 Nm/deg of twist or 23 715 ft-lbs /deg of twist"

http://www.cav.co.za/pdf/Torsional_Stiffness_Test_Results.pdf

RF once posted that their measurements were outside the tabulated results which stopped at 12,000 Nm/deg, and extrapolated results to over 20,000 Nm/deg (14,751 ft-lbs/degree), but for ADR compliance, they only needed to exceed 6,000 Nm/deg and therefore only claim in excess of 12,000 Nm/deg.

Ian

 

[Alex]

While we're talking about gt40 fuel tanks, I've always wondered how (in replicas) they're held in? Are they bolted down, or welded in, or what?

 

[Seymour Snerd]

While we're talking about gt40 fuel tanks, I've always wondered how (in replicas) they're held in? Are they bolted down, or welded in, or what?

Bolted to an SPF. Below see pictures of the rear end of an SPF tank. Other three mounts are similar.

 

[Alex]

Bolted to an SPF. Below see pictures of the rear end of an SPF tank. Other three mounts are similar.


View attachment 50772

Thanks for the pics.

Btw, don't know if that's your car or not, but if it is I'd be careful about hose clamping braided stainless line - tried it twice, failed twice.

 

[Seymour Snerd]

Thanks for the pics.

Btw, don't know if that's your car or not, but if it is I'd be careful about hose clamping braided stainless line - tried it twice, failed twice.

Tell me about it. SPF did that. AFAIK all 200+ of them are the same way.

I'm not happy about it either but right now I don't feel like pulling the tanks and welding on a proper fitting. I wish there were some kind of "clamp-on" 8AN male flare I could put on. Hmmm.... maybe I could flare the end of the hose barb.....


Any ideas?

 

[Dimi Terleckyj]

With regard to the clamping of stainless fuel hose.

If the hose is rubber with just a stainless braid covering then it is alright to use hose clamps.

If it is the Teflon inner hose then as you tighten up the clamp it causes the Teflon to extrude out from under the clamp.

If the fitting on the tank has a ridge to grip the hose, when you tighten the hose clamp the ridge will cut through the Teflon due to the amount of pressure the clamp exerts and the minute surface area of the ridge.

Even though it feels secure because of the stainless braid the Teflon hose will leak where it has been damaged by the clamp allowing either fumes or fuel to escape.

Dimi.