Valve spring shims

[citiracer]

Our rules don't have anything against it so I was considering trying it on a 602.
1) Is it even worth messing with?
2) If yes to 1, how much can you shim before getting in trouble with the springs binding?
3) How much of a performance gain can be expected from this?

Thanks!

[BPRacing29]

It doesnt have to be in the rules , you can shim it and it helps , but it increases spring pressure!! So, i dont know what the pressure can be because I run a 604. But if its over 105 on a 604 your illegal!! Any spring pressure increase helps these motors a ton!!


BPRacing29

[Egoracing]

It doesnt have to be in the rules , you can shim it and it helps , but it increases spring pressure!! So, i dont know what the pressure can be because I run a 604. But if its over 105 on a 604 your illegal!! Any spring pressure increase helps these motors a ton!!


BPRacing29

It does have to be in the rules. Fastrack allow it, if you go into the tech shed at a Nesmith race with shims under the valve springs and only 40 lbs of seat pressure you will be illegal and thrown out for them.

[rubbinsracin]

our rules specifically state you cant run any shims. i guess thats why you see guys buying 4 or 5 boxes of springs and finding the best set.

[Racer63]

No expert here but I do know too much spring pressure and you will pull the studs out of the head.

[BPRacing29]

It does have to be in the rules. Fastrack allow it, if you go into the tech shed at a Nesmith race with shims under the valve springs and only 40 lbs of seat pressure you will be illegal and thrown out for them.

That was my point Ego, they were allowed for some of the older heads b/c of bad machining or whatever it was - but you still have to know what you have and if you shim it that increases spring pressure right? I hear people all the time say I'll just get more spring pressure with the shims and they have no idea what they have!! So that was what I was saying about the guy saying theres nothing in the rules about it -so it doesnt have to be in the rules, you should KNOW what its supposed to be!!

[Egoracing]

It doesnt have to be in the rules , you can shim it and it helps , but it increases spring pressure!! So, i dont know what the pressure can be because I run a 604. But if its over 105 on a 604 your illegal!! Any spring pressure increase helps these motors a ton!!


BPRacing29

You said "It doesn't have to be in the rules, you can shim it and it helps."
That is NOT correct, there are ONLY limited places you are allowed and in most you CAN NOT shim them and be legal. Sorry if I miss under stood what your intent was but that is what you said.

[JTSjet]

you can shim the spring all you want as long as you're:

- at or above the specified minimum installed height for the spring

AND...

- at or under the specified spring seat pressure.

The GM manual refers to this also.

i'm not very familiar with ne smith but it's in their rules. ndra refers the the GM manual. it is legal to shim the valve springs.

[Egoracing]

you can shim the spring all you want as long as you're:

- at or above the specified minimum installed height for the spring

AND...

- at or under the specified spring seat pressure.

The GM manual refers to this also.

i'm not very familiar with ne smith but it's in their rules. ndra refers the the GM manual. it is legal to shim the valve springs.

Short answer is NO.
From Nesmith :Beginning in January 2010 Competitors may run a maximum of a .020” shim under valve springs on repaired or rebuilt engines, or on new engines.

From Fastrak:GM 602 Car and Driver: 2250 lbs (Touring events allow 1 lb per lap „burn off‟ in feature only)
GM 604 Car and Driver: 2400 lbs (Touring events allow 1 lb per lap „burn off‟ in feature only)
All Engines and parts must be as from factory and all components thereof. THIS MEANS ALL!
The ONLY time a change can be made is with a letter of approval from FASTRAK Corporate Office.
Any “unauthorized” changes will result in disqualification, no points, fines and other possible penalties including but not limited to being barred. This includes, but is not limited to, harmonic balancers, valve springs, push rods, rocker arms, and after market valve covers etc.

Nothing about shims being allowed anymore in Fastrak rules. In Nesmith you are only allowed .020 even if it is NOT at height rules you can not put any more shim or you are illegal.

[JTSjet]

soooo....i'm confused, ego. first you say, per ne smith rules, you will be dq'd in tech for valve spring shims. Now you're saying a .020 is legal. Which is it??

[Egoracing]

When it was brought up I looked at the set of rules I had printed and it said nothing about it being legal and they had said at their races when other places/series allowed it that they did not. I checked on line to see if it had changed and it did, January last year, after the race at Eastbay in December, to allow .020 shim.
Also it is not listed in Fastrak anymore that it is legal?? It was in the rules but is no longer.
So no you can not shim them all you want as you posted, at the most you can only shim .020.

[brad hibbard]

FASTRAK goes by the GM tech manual part #88958668 and in that manual on page 21

it states that a .020" shim is acceptable to correct valve spring installed height.

This is how we interprut that statement (FASTRAK only)

You may use (1) shim in addition to the factory locating shim
it will be a maximum of .020"

The installed height can NEVER be less than 1.780"

FASTRAK competitors please call me if you have any questions

Brad Hibbard
330-540-7223

[Egoracing]

FASTRAK goes by the GM tech manual part #88958668 and in that manual on page 21

it states that a .020" shim is acceptable to correct valve spring installed height.

This is how we interprut that statement (FASTRAK only)

You may use (1) shim in addition to the factory locating shim
it will be a maximum of .020"

The installed height can NEVER be less than 1.780"

FASTRAK competitors please call me if you have any questions

Brad Hibbard
330-540-7223

Thanks for the info, I thought they still did it just could not find it in the rules.

[brad hibbard]

just wanted to put the thread back up top had several calls today