fuel pressure, roll bar

[toplesshorse]

Can someone tell me the proper fuel pressure range for a 74 midget.

I am also looking for a scca roll bar that can be used with the top.

 

[Bugeye58]

The book says 2.8-3.8 psi. I run mine around 2.5, but anything between 2 and 4 should be OK.
As far as an SCCA rollbar, anything that is OK to use in the SCCA, and I'm assuming you are talking autocross, is going to be too tall for the top. There is a minimum height rule that precludes the use of the top.
If you just want to install a rollbar, VB is selling what look to be AutoPower bars.
Jeff

 

[Tullamore]

Wow, that really sucks, there goes a bunch of my plans. I've been to a lot of SCCA events, do they even check such thing? I have never had the roll bar on the Tiger measured.

 

[Bugeye58]

Tullamore, just what kind of SCCA stuff are you planning? I'll get my hands on a SOLO rule book and double-check the roll bar standards.
Jeff

 

[Tullamore]

I guess SOLO II autocrosses is what I have alway done in the past. The past years I have been doing SAAC and MCCI road track events.

 

[Bugeye58]

Okay, here is the response I got my from my Solo II buddy.
Both he and his wife are multiple Solo National Champions in their Corvettes.

"Since he has a question regarding the top and street use, I'll guess
that he
is not running a Prepared or Modified class.
That being so, the rule reads:"
For open cars in Stock, Street Prepared, Street Touring and Street
Modified
categories, the roll bar height may be reduced from Appendix C
(requires bar
at least 3" above and not more than 6" behind) to the highest possible
height which fits within an installed factory specified hardtop or
convertible top.
Also note Driver Restraints:
...non factory upper body restraints may only be used in open
cars..........when two conditions are met:
a. roll structure must meet requirements of Appendix C or Section 18 of
the
GCR.
b. The top of the roll structure may not be below the top of the
driver's
helmet when the driver is in the normal driving position.

So, it looks as if a bar that fits under the top is legal after all.
The SCCA is putting the rule books on-line, but I don't think the Solo rules are up yet.
I'll try to find it when it comes on and post the link here for all to look at.
Sorry for the confusion.
Jeff

 

[toplesshorse]

Thanks for the research. I know most rules only require that the bar be above the drivers helmet. I plan on running Corbau seats so I will place them lower than the stock mounts any way. Good thing I'm short. I may have to fab a bar to get it right.

 

[JohnnyB1275]

Does the SCCA check the type of welds on the rollbar? I believe that TiG welded rollbars are ideal, mig is ok, but there needs to be a lot of voltage used to get good penetration, stick isn't recommended because it can make the metal weak. 2"OD, 1/8-1/4 wall thickness should be ok i believe.

 

[aeronca65t]

Tube size for roll bars depends on car weight and tube material. Assuming that you are using normal "mild steel" and not chrome-moly, 1-1/2" is OK for a Spridget (nominal OD). 2" is used on heavier cars (my car has a 2" bar because it was free, but it's really overkill). Wall thickness should be 0.120" or greater (it can be thinner if bar is chrome-moly). You need to provide a drilled inspection hole to verify thickness (in a non-critical area). Full cages (as opposed to bars) may be made of smaller and thinner tubes (check the SCCA GCR for better details).
Note that some suppliers may spec tube sizes in nominal ID, so you have to be careful when ordering this stuff.
Mild steel tube should be "seamless", "DOM" (drawn over mandrel) or "ERW". The ERW tube is least desirable (and I'm not sure it's SCCA approved anymore).
Normal stick-type arc welding is fine for mild steel, assuming good quality welds and penetration. Mild steel pipe (also called "carbon steel" or "low carbon steel") does not heat treat and will not become brittle or weak due to welding. MIG and TIG are excellent methods (again, assuming good quality welds). TIG can be somewhat clumsy for welding around complex tube joints.

 

[Bugeye58]

Nial, here is the link to the on-line version of the 2005 GCR.

https://www.scca.org/Club/Index.asp?IdS=003739-4015BD0&x=030|070

Section 18 covers roll cages, and ERW tubing is no longer legal.
Jeff

 

[aeronca65t]

Thanks Jeff....that's a great resource.

 

[toplesshorse]

Yea they finally got the rules on line. An issue with my Kart racing. Appendix K says erw or dom. And provides the sae spec. I am a fabrication Materials Manager and am over procurement. I deal with the major service centers in the southeast and these materials are readily avalible. They also outline wall thickness by weight. Please note. Tube material is called out by od. and nominal wall thickness. ASTM specifies tol. on wall thickness.

I can provide any material specs. or avaliability needed. I just needed to know what was required. /ubbthreads/images/graemlins/cool.gif

 

[Bugeye58]

John, yes, the SCCA does check the welds on a roll bar/cage. They must meet American Welding Society standards. (D1.1:2002, Structural Welding Code, Steel, Chapter 10, Tubular Structures.)
Mig, Tig, gas, silicon/bronze are all legal if they meet the requirements of the above reference.
Jeff

 

[RobSelina]

[ QUOTE ]
Does the SCCA check the type of welds on the rollbar? I believe that TiG welded rollbars are ideal, mig is ok, but there needs to be a lot of voltage used to get good penetration, stick isn't recommended because it can make the metal weak. 2"OD, 1/8-1/4 wall thickness should be ok i believe.

[/ QUOTE ]

That's way overkill. 1.5" DOM with a 0.120" wall thickness for anything that would take a direct impact and 0.095" wall for bracing should be sufficient if it meets the SCCA guidelines.

Just to put 2" tubing into perspective, I run 2" 0.120" wall HREW on this thing:

/ubbthreads/images/graemlins/devilgrin.gif

 

[Bugeye58]

Rob, our tubing specs are based on the vehicle weight without driver. For anything under 1500 lbs, which covers all the Spridgets, it calls for 1.375" x .095" DOM, mild steel as a minimum size. .080" wall for alloy tubing.
Jeff

 

[RobSelina]

Thanks Jeff, that seems pretty reasonable. I'm going to have to read through that spec you posted out of general interest....