[RHD ZL1]

Thought id ask if anyone has changed from a 9.17 to a 9.45 lower with stock upper on a stock un-ported blower and if there was any gain? Went to the track (drag racing) over the weekend and planning on going out again in a few weeks. Currenlty have a 9.17 lower on the engine and have a 9.45 that I'm thinking about fitting but unsure if there really would be much of a differnce? Seems like a 3% increase in blower rpm so unsure if it would even gain anything.

Thanks.

[2023_ZL1-AUTO]

Guys on here like ZLRob, ZLElvir, SOCAL.M6.ZLE, and many others have worked hard on LT4 stock blowers and also a maxed out Lt4 blower as well. They have done extensively tested on all of this. Such as different pulley sizes, different levels of porting, different intercooler bricks, etc. I'm sure they will chime in. But, the first thing everyone will ask you is: What other mods do you have, and that really matters!

My build, because I didn't know what I was doing at the time. Was a snowball at one point. I'm only full bolt on mods. I got to the point of running Flex Fuel @ E60 with just a FuelMax Voltage Booster and a great tune from Ted Jannetty. Then, I decided, hey why not a Kong X-port, that sounds great, and so does a Griptech 2.3" upper. When I got that done, my car couldn't run any E mix at all. The tune couldn't get dialed in and it was all because my car was starving for fuel and car was running like crap. I then had to go with more I wasn't planning on. I took my car to Katech and they added a new fuel system, new fuel lines, THPSI Port Injection, an interchiller, a 9.45 (+18%) lower and an ATI Super Damper and a few other things. Now my car runs awesome, 20psi+ boost and it whines like a newborn baby! Good luck on your venture!

[WhiteMale]

I think word around here was pully changes aren't worth it to spin the blower a little faster just makes more heat. Assuming you have no supporting mods.

[Megahurtz]

If you're on pump gas, pulleys are just going to make the car hit hard when you punch it and then the power will quickly fall off up top. Once you're heat soaked you will be slower than stock.

If you're running flex fuel, you can get solid and consistent performance out of 6-9% over drive but I wouldn't go more than that on the stock blower. You're just making crazy amounts of heat.

The easiest thing to do without porting the blower is to do a 2.3 upper (press fit or shrink fit hub), a flex fuel sensor, ported stock TB, drop in green filter, tune the ECU & TCM and run E50.

This a SOLID gain in performance without too much cost. This will easily shave 1.5 seconds off your 60-130 vs stock. IIRC I dropped 2 seconds off my stock 60-130 when I did this as the first round of mods while I waited on the rest of my parts.

[Patriot Motorsports USA]

My first mod was the 9.17" pulley kit from Lingenfelter with the ATI balancer and the green belt and I did it using the excuse that I wanted to be sure if I was road racing this car, the crank was not having belt harmonics solidly transmitted to the crank as well as the cast-iron pulley weight & mass absorbing all the heat from the three heat exchangers in front of it... sending that to my oil pump!

Still today, I am running the 9.17" which is a 12% overdrive and my car is making insane power for Road Course events as the tires have to be fully heated up to have any straight-line grip... but I want MORE!! The problem with MORE is that with the SC, there is no controlling the HIT in lower gears as my setup is currently making 830lb/ft of torque at 2350rpm.

I think the trick for me will be to use a "SmoothBoost Controller" coupled to a stand-alone MoTec or even a Holley to monitor engine rpm, load, wheel speed and then have it bleeding boost at lower speeds or set it up for Boost-By-Gear like I could program with turbos. This is another reason why my journey has been to find the best cooling systems, as I know what my future with this car has coming... something utterly ridiculous but very precise.

So to answer your question... go for it, but short-shift to keep the RPMs lower as the blower is going to heat soak instantly if you are using the stock SCHX. My setup will definitely reduce the MATs for a full pull and I just shipped another SCHX to Dubai, and taking one to Thailand this week on my trip... so AUS is not out of reach. The cheap and easy fix is also to install my Expansion Tank setup with a reverse flow of the coolant to gain fully saturated bricks and reduce the timing being pulled by higher MATs. Both products can be installed with zero tuning as the goal is to keep the ECU from pulling the timing & adding fueling you do not want to get to kill the power. Its kinda like #FreeHP!

[ZLRob]

Originally Posted by 2023_ZL1-AUTO

Guys on here like ZLRob, ZLElvir, SOCAL.M6.ZLE, and many others have worked hard on LT4 stock blowers and also a maxed out Lt4 blower as well. They have done extensively tested on all of this. Such as different pulley sizes, different levels of porting, different intercooler bricks, etc. I'm sure they will chime in. But, the first thing everyone will ask you is: What other mods do you have, and that really matters!

My build, because I didn't know what I was doing at the time. Was a snowball at one point. I'm only full bolt on mods. I got to the point of running Flex Fuel @ E60 with just a FuelMax Voltage Booster and a great tune from Ted Jannetty. Then, I decided, hey why not a Kong X-port, that sounds great, and so does a Griptech 2.3" upper. When I got that done, my car couldn't run any E mix at all. The tune couldn't get dialed in and it was all because my car was starving for fuel and car was running like crap. I then had to go with more I wasn't planning on. I took my car to Katech and they added a new fuel system, new fuel lines, THPSI Port Injection, an interchiller, a 9.45 (+18%) lower and an ATI Super Damper and a few other things. Now my car runs awesome, 20psi+ boost and it whines like a newborn baby! Good luck on your venture!

Originally Posted by WhiteMale

I think word around here was pully changes aren't worth it to spin the blower a little faster just makes more heat. Assuming you have no supporting mods.

Originally Posted by Megahurtz

If you're on pump gas, pulleys are just going to make the car hit hard when you punch it and then the power will quickly fall off up top. Once you're heat soaked you will be slower than stock.

If you're running flex fuel, you can get solid and consistent performance out of 6-9% over drive but I wouldn't go more than that on the stock blower. You're just making crazy amounts of heat.

The easiest thing to do without porting the blower is to do a 2.3 upper (press fit or shrink fit hub), a flex fuel sensor, ported stock TB, drop in green filter, tune the ECU & TCM and run E50.

This a SOLID gain in performance without too much cost. This will easily shave 1.5 seconds off your 60-130 vs stock. IIRC I dropped 2 seconds off my stock 60-130 when I did this as the first round of mods while I waited on the rest of my parts.

These guys are all spot on the money here. The law of diminishing gains is SUPER applicable when you are talking about pulley changes and ramping heat production. On these cars, without proper supporting mods, overdrive lowers and/ or running smaller uppers is not advisable when running standard octane pump fuel, as you will introduce more and more heat soak and with that higher degrees of knock into the system. The factory tune maximizes the hardware already on the car by running a very aggressive calibration. To allow any appreciable gains to be had from pulleys you are talking about running ethanol. The higher the better until you can run full (many say full benefits are obtained at around E50 if I remember right, but my time in testing has shown different results).

Depending on your goals, the easiest thing to do, just to echo what Megahurtz said, is to run a ported stock TB, flex fuel sensor to allow for the most ethanol fuel allowable within your setup, green high flow filter (NOT A K&N or similar), and a pulley no larger than 5-9% over OEM size. I would also consider and recommend some sort of external LTR reservoir so you can minimize the chances of having air in the supercharger coolant loop setup.

I used to run a 5% 8.45" ATI lower pulley when I was more limited in my high side fueling, it still allowed a pretty decent amount of ethanol content with a more OE setup without heatsoak.

Food for thought: if you are chasing boost numbers, you are pursuing the wrong methodology, as boost is just a measure of engine restriction.

There are so many people off of this board who run much larger pulleys than OEM without any understanding of the actual harm that they do without proper supporting mods. Once you start going larger pulley sizes it turns into a modification cascading domino effect if you understand what each mod requires from your fueling system. These are not your old school supercharged vehicles that have room for expansion. They are close to maxed out from the box and without the supporting mods you can cause some serious harm to the engine REAL quick. Don't be like those people. Run the right combination of parts that works within your budgetary constraints, but keep the setup efficient and optimized for its combination. An efficient supercharger is a happy LT4!

[2023_ZL1-AUTO]

Originally Posted by ZLRob

These guys are all spot on the money here. ... Don't be like those people. Run the right combination of parts that works within your budgetary constraints, but keep the setup efficient and optimized for its combination. An efficient supercharger is a happy LT4!

I will edit ZLRob post for him: "DON'T BE LIKE 2023_ZL1-AUTO"... hehehe (just kidding)!

But, what everyone above said is truly spot on. I went too far with my mods not knowing all these mods needed to work together. I made a few popular mods to my car, not realizing by doing so it required other mods to be made. I went from loving it every time I drove my car, to almost dreading it every time I drove my car!

I introduced so much heat soak in my system, I was worried it was too high and didn't drive the car much. I'm talking IAT.2 186°+. I then reached out to Katech, they told what they recommended and BINGO! I have a fast ass and powerful ride that is consistent and keeps IAT.2 below 130° ALL THE TIME !

Now I do the 1/4 mile @ 10.673 @135.12 (and that was my first run down the drag strip in my ZL1) and ZERO knock !!! These guys on this forum that know their STUFF, know their STUFF! Everyone ZLRob mentioned and everyone I mentioned (plus a few more!). They have done the work, so we can benefit !

[RHD ZL1]

Thank you to everyone for their reply’s. TBH I didn’t even expect a reply hence why my initial post was short and without too much details. To answer some questions and add some clarity to what I’m trying to achieve, I have a 2019 ZL1 A10. Mods are, 9.17 as mentioned, RotoFab regular, full Exh system 1 7/8” into twin 3”, BAP, Flex that I normally try to keep between E50-55 however was E56 the day I raced and a AEM WI kit running boost juice. Other than that everything else is stock, stock cam, stock upper pulley, stock un-ported blower etc.

I log every pass at the track, the IAT’s were 12 Deg C (approx 22 Deg F) lower at the finish line at the top of 6th gear than what they were on the start line just prior to going WOT. No doubt I attribute this to the AEM kit as well as it allowing me to run E56 on the OEM fuel system with the 9.17 lower/headers/full exh system.

I was hoping to see if anyone had gone from a 9.17 to a 9.45 and had logged the boost change if any, id expect maybe a larger gain in boost at lower rpm (less than say 3500) and less of a boost gain above say 4500 rpm. I’m happy with the cars performance down the ¼ mile however any racer knows what its like, we are always just looking for that little bit extra hence my question about the pulleys.

Thanks.

[2023_ZL1-AUTO]

Originally Posted by RHD ZL1

Thank you to everyone for their reply’s. TBH I didn’t even expect a reply hence why my initial post was short and without too much details. To answer some questions and add some clarity to what I’m trying to achieve, I have a 2019 ZL1 A10. Mods are, 9.17 as mentioned, RotoFab regular, full Exh system 1 7/8” into twin 3”, BAP, Flex that I normally try to keep between E50-55 however was E56 the day I raced and a AEM WI kit running boost juice. Other than that everything else is stock, stock cam, stock upper pulley, stock un-ported blower etc.

I log every pass at the track, the IAT’s were 12 Deg C (approx 22 Deg F) lower at the finish line at the top of 6th gear than what they were on the start line just prior to going WOT. No doubt I attribute this to the AEM kit as well as it allowing me to run E56 on the OEM fuel system with the 9.17 lower/headers/full exh system.

I was hoping to see if anyone had gone from a 9.17 to a 9.45 and had logged the boost change if any, id expect maybe a larger gain in boost at lower rpm (less than say 3500) and less of a boost gain above say 4500 rpm. I’m happy with the cars performance down the ¼ mile however any racer knows what its like, we are always just looking for that little bit extra hence my question about the pulleys.

Thanks.

Sounds like you understand great how your car is working. I have data logs that go from stock lower to a 9.45" lower, I can look at the boost and try to see the differential between the two, it might give you some kind of usable data.

I'm sure it's the tune each of our cars have, but, when I hit the beam at the end of the quarter mile I'm only in 5th gear. My TCM is tuned, and it auto shifts aggressively for the drag strip. So, it might be that mine holds a few gears longer at higher RPM (It shifts in some gears at +7100rpm.

If I can ask, what is your 1/4 ET, MPH and 60ft time? I'd be curious to compare to mine as I too have all stock internals.

Take care!

[KingLT1]

I would get the blower ported or move to a 2650. I wouldn't run any more pulley with a stock blower.

[clg82]

Originally Posted by 2023_ZL1-AUTO

Sounds like you understand great how your car is working. I have data logs that go from stock lower to a 9.45" lower, I can look at the boost and try to see the differential between the two, it might give you some kind of usable data.

I'm sure it's the tune each of our cars have, but, when I hit the beam at the end of the quarter mile I'm only in 5th gear. My TCM is tuned, and it auto shifts aggressively for the drag strip. So, it might be that mine holds a few gears longer at higher RPM (It shifts in some gears at +7100rpm.

If I can ask, what is your 1/4 ET, MPH and 60ft time? I'd be curious to compare to mine as I too have all stock internals.

Take care!

My new tuner mentioned that the old tuner set my shift point to 7100rpm as well, he said the stock internals don't hold up well to shifting at that high of an RPM. I wonder if he was just trying to make the previous tuner look bad, or if he was on to something. Just something to think about and worth a conversation from the experts here on whether or not that RPM is an issue. Would hate for something to happen to the engine before you had the chance to pull the trigger on that 2650.

[radz28]

Oof. 7000? I missed that...

Would higher boost try to hold the valves open, too? I've tried to keep auto' shifts at about stock as boost started going up. I know we have Ti intake valves, which help a bit, and stock cams are no lift/duration so maybe that keeps us out of danger, too?

I'm looking to learn more about this, too.

[clg82]

Originally Posted by radz28

Oof. 7000? I missed that...

Would higher boost try to hold the valves open, too? I've tried to keep auto' shifts at about stock as boost started going up. I know we have Ti intake valves, which help a bit, and stock cams are no lift/duration so maybe that keeps us out of danger, too?

I'm looking to learn more about this, too.

I'm not revving out at WOT to 7k anymore, the new tuner said that could be bad on stock internals etc.

[RobZL1]

Originally Posted by clg82

I'm not revving out at WOT to 7k anymore, the new tuner said that could be bad on stock internals etc.

This for sure. I wouldn't trust AFM lifters or stock springs to 7000+ on a regular basis. Maybe a hero dyno run, but that's it. Aftermarket valvetrain is a different story.