37 replies to this topic

[NJ Racer]

Did anyone run an "Iso" based F1 or Can-Am/GT chassis in Columbus, or has anyone built and raced such a chassis elsewhere recently? Any thoughts on the "Iso" design?

[W. J. Dougherty]

Ray,

To my knowledge, all the Pirro-built chassis have been Iso style chassis; mine is. You have seen them race and should know that they work very well.

Are you coming to the Chesapeake Retro Rally in June??

[NJ Racer]

Thanks Bill and good to hear from you.

I agree Pirro's chassis works very well, and should do well on the Gerding King. I am looking forward to racing in June, it will be great racing and hopefully some party time also.

[JerseyJohn]

Don Raymundo,

Many from Jersey are saying 8t pinion for Chesapeake. What are your feelings on that.

Your belly himan,

JJ

[GTPJoe]

Hi Ray!

The Pirro chassis I've seen appear to be PLUMBER designs, not ISO. They have rails which hinge under the guide tongue out front and the pans are connected to these rails giving a up and down, front to back movement. Unlike the floppy pans up and down side to side movement.

And for more on the Iso you guys got the master, Tony P. He's the guy to talk about the Iso design.

See ya!

[tonyp]

All the Pirro's I have teched have been standard chassis with a plumber set-up and shaker pin tubes.

An Iso which is not IRRA legal is a chassis with the motor attached to the guide like most retro chassis, but the front wheel assembly is a separate component which is hinged right in front of the motor or behind the motor. This allows the front wheels to move up and down while the guide carries all the weight of the motor, pans, etc.

[Noose]

One problem that I've seen teching these the Pirro chassis is the front clearance area. IRRA rules require .015" clearance from under the front axle forward. These chassis tend to meet the clearance under the front axle but not at the front because the plumber tubes hang down. Guys using them have had to reset the clearance on them. Other than that, they work very well.

[MarcusPHagen]

Guys using them have had to reset the clearance on them.

How do they reset it? Do they bend the parts ahead of the axle upward, or do they resolder and just accept the fact that the clearance under the axle will be more than .015"?

I'm curious, since if I use pans ahead of the axle, I'd rather set them up at build time instead of modifying them at tech.

Just getting ready for the Sano.

[Noose]

Some grind down the tubes so they were flat and others just reset them by resoldering the front end simply by putting something .015 thick under the front portion while on a block with the tires.

[NJ Racer]

Noose/Tony,

I beleive some people may have plans to build an Iso frame based on the current IRRA chassis rules, specifically described under "Hinged Movements" as follows

c. Hinged Movements: Other than a drop arm, all hinged movements must be oriented in only one direction on any individual chassis. A chassis may have transverse hinges (examples: Iso-fulcrum hinges and plumber hinges) OR
it may have longitudinal hinges (example: side pan hinges) but the chassis may not have both types. The number of individual hinges is not restricted. Centerline hinges are NOT allowed

The rules do not state Iso-fulcrum chassis are not legal. What are these folks missing?

[tonyp]

My fault. I guess they are legal then. In East Coast they were only F1 legal. Sorry.

I did built an F1 Iso and it sucked. It was so bad I never showed it to anyone.

[Noose]

Yes, they are legal and I'm sure that a lot of guys out there would think that chassis sucked, Tony!

[tonyp]

Here is the teching issue with an Iso.

When you set the chassis on a test block with the guide in the recessed area and the front tires touching, the center section drops down and no longer clears the .015".

The only solution is to add a spring to keep the guide (center section) from dropping when you lift the front tires and this defeats the chassis design.

[Jairus]

... or stops. An Iso should always have up and down stops to limit movement in both directions.

[tonyp]

As long as it runs on a track with the braid below the track surface, the clearance will always be less, unless you space the guide down far enough so the front is correct on the track (.015" under the chassis and the front wheels touching). As long as it can drop down at some point it will be lower than legal regardless of stops.

It makes more work for the tech crew. The chassis will have to be teched on a block with a recess equal to that of the track so the guide is against the "braid" supporting the weight of the center section, clears .015" in the front and the front wheels are touching.

[tonyp]

Noose says he has it handled. He has blocks with different braid recesses to tech on...

[Lou Cicconi]

Man, Tony, what a piece that frame is. I can't belive you showed that to us... Isn't that the car you ran at my house the last race???

[Dominator]

Just want to make sure I understand the clearance correctly. The .015" is measured from the furthest forward point of the chassis to under the front axle?

[Noose]

Dom, that is correct.

[NJ Racer]

So, Tony, now that I clarified the "Iso" issue. LOL, LOL.

How about I give that Iso chassis a test drive at Dom's this Friday? I will be in Dunellen, NJ, tomorrow.

[tonyp]

It has long been taken apart and used to make something that works. LOL... I think the bracket and guide holder are on Rob's sports car.

[NJ Racer]

Tony,

Well, I am sure you are already thinking about a new design.

[MSwiss]

I'm not a chassis expert but I would think an Iso would only be good on an extremely bumpy track.

[Phil Smith]

I don't think I've ever seen an Iso chassis in person, so I obviously don't know anything about them either. But I was thinking the same thing.

Is there any reason for running an Iso on today's smooth tracks?

[NJ Racer]

Last one I tried was this, many, many moons ago.