[LT4 650]

So I am talking to a performance shop that has a very good reputation in my area about doing some bolt on mods to my ZLE and they are saying unless I am planning to go big power (900 and above) that I should start with 1 7/8 headers, Roto (which I already have) and an upper pulley (2.30??). So a couple of questions about their approach because most people seem to go with 2" headers and lower pulley first.

1) Headers - they say that below 800 hp that the 1 7/8 headers do a better job of building torque and HP where you need it on the street. they say 2" headers without a bunch of other mods will only give you more HP than the 1 7/8 way up in the RPM range...is this TRUE?

2) Upper Pulley - They said the reason they go with an upper pulley along with these headers is because as great as headers are for letting the engine breath they can cause the blower to not push as much boost as stock...so they do the upper pulley just to offset the header affect and get the blower back to consistent boost (around stock)...is this TRUE?

Thanks for any info I can gain. PFA

[DemonZL1]

On my 2022 ZLE, I did a 9.17" lower and 2" headers with a huge gain in torque. 750, to be exact. The tune was done at Premier Performance in UTAH, so we also have elevation working against us.

That being said, everyones numbers will be different but I do not believe there is any loss with a quality 2" header.

i just ordered 2" for my 2020 ZLE and going with the exact same setup as before.

[CW3SF]

Hopefully they recommended cooling mods with the pulley. If you spin the blower faster it’ll make more heat. You don’t have to pulley to make power.

[AZIROC]

I just did kooks 1 7/8s, 2.3 upper and a tune and love the results. *already had a roto and ported t.b.



I went back and forth of the 2 different size headers and went with the 1 7/8s just for the hair better clearance since I road race the car. That and I don't plan on doing any other mods except possibly e40/e50.

[Z OH 6]

I've seen several dyno pulls with 1 7/8" vs 2" headers and there is no point in the power curve where 1 7/8" makes more HP or torque compared to 2". Granted the differences are small at lower rpms but the 2" pull away at the top end and even more as the mods increase.

[JSH]

Phase I for my car in 2020 incl. a 9.17" (10% lower pulley), stock upper, stock TB and SC, and headers [and a bunch of mods that aren't relevant to your question] and it saw MATs of 150-180F, but it nevertheless always ran well. So, I would do a lower and headers, both of which will work well with most future mods such as running Eth.

Originally Posted by LT4 650

So I am talking to a performance shop that has a very good reputation in my area about doing some bolt on mods to my ZLE and they are saying unless I am planning to go big power (900 and above) that I should start with 1 7/8 headers, Roto (which I already have) and an upper pulley (2.30??). So a couple of questions about their approach because most people seem to go with 2" headers and lower pulley first.

1) Headers - they say that below 800 hp that the 1 7/8 headers do a better job of building torque and HP where you need it on the street. they say 2" headers without a bunch of other mods will only give you more HP than the 1 7/8 way up in the RPM range...is this TRUE?

2) Upper Pulley - They said the reason they go with an upper pulley along with these headers is because as great as headers are for letting the engine breath they can cause the blower to not push as much boost as stock...so they do the upper pulley just to offset the header affect and get the blower back to consistent boost (around stock)...is this TRUE?

Thanks for any info I can gain. PFA

Attachment 1115676

[ChadSZL1]

Look at Ted Jennatty 125 RWHP package I have it and it’s amazing