[Eldi Z]

One of the issues with the LT4 Head Unit, when installing a "ZL1 setup" on the LT1 SBE (11.5 CR) is the high boost level of ~ 10.5-11.0 PSI.

I only have access to 93 octane pump gas, which has absolutely no "E" content (not even 10%).

In order to get the boost level down to a safer ~ 8 PSI of boost, without! touching the upper pulley on the HU's snout (and leave it stock..), which size (smaller) damper / lower pulley would be correct in order to reach this reduced boost level?
Which pulley/damper type / size should be sourced and where best found?

Can the stock OE LT4 belt length still be in a correct range, in case of such lower pulley size change?

[D3adch1ld]

http://www.atiracing.com/products/da...ts/damserp.htm

Take a look at the underdrive pulleys from ATI. Based on the ratio, it looks lime the 7.48" (P/N 917314) would get you where you want to be.

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[SSUNDVL]

I would just get the pulley changed on the upper, if you go zpe upper you can change the upper in 5 minutes and use griptec pulleys. Some run 2.75" and some at 3.0". That way if you want (likely will at some point) to change pulleys you can. It probably same cost as an ati lower.

If you add catless headers you will have less boost too.

Stock lt4 pulley belt will not be same due to spacers.

[Eldi Z]

Originally Posted by D3adch1ld

http://www.atiracing.com/products/da...ts/damserp.htm

Take a look at the underdrive pulleys from ATI. Based on the ratio, it looks lime the 7.48" (P/N 917314) would get you where you want to be.

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Thanks I shall have a look

[Eldi Z]

Originally Posted by Eldi Z

Thanks I shall have a look

I had a look and see that Part#P/N 917314 is for a 6-Rib belt... the OE is 8-Rib...

[Eldi Z]

Originally Posted by SSUNDVL

I would just get the pulley changed on the upper, if you go zpe upper you can change the upper in 5 minutes and use griptec pulleys. Some run 2.75" and some at 3.0". That way if you want (likely will at some point) to change pulleys you can. It probably same cost as an ati lower.

If you add catless headers you will have less boost too.

Stock lt4 pulley belt will not be same due to spacers.

I would do that, but have been warned that once the OE pulley is removed and replaced by an aftermarket one, the balance is not going to be perfect and eventually the stress is going to take its toll on the snout. There is also some glue work to do, right?
Not saying that it is not being done...it is, but if I can avoid tinkering with what has been prepared at the factory, then I will.
Question is, can I find a suitable lower unit which can fit.

Did I miss something in the ATI catalog? All of the pulleys there are 6-rib?
I must be missing something, because it reads that they fit LT4 engines

[Eldi Z]

Learned that the 6-rib is for all the Accessory items - my bad.

Bottom line: I would need a Supercharger lower crank pulley ring of ~ 6.5" to reach a lower boost level of ~ 7.8-8.0 PSI, when remaining with the upper Head Unit 2.5" stock pulley.
I just could not find such smaller pulley on the ATI pages...