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Discussion Starter · #1 ·
So I bought a modded 2011 heads/stage 3 cam/injectors CTS V that has too small of a pulley for my tastes. Crank pulley is 9.45 and the upper is 2.38. I'd like to go to a larger 2.50 just to lower the ratio and protect the blower. I've been emailing back and forth with Pat G about a mail in tune after a recommendation here and he said the car may not need one but if drivability is an issue, he can hook me up. So my question is- has anyone done this before? Beyond a larger pulley, what all do I need? Can I reuse the same belt? Both the current pulley and the replacement pulley will be from Mont. I want to make it clear that I am more than willing to spend the money to get the car retuned but the entire point of the change out is to protect the blower bearings after a user here mentioned that at my ratio of 3.97, they become a wear item. If I can save the money because a tune is less likely to be needed when I'm going more conservative, I'm all for it.

I'm also unclear on if I will have an easy go of it like the guy in this video (ignore the terrible music at the 1 minute mark)-


Or if it will be more involved like in this thread-
 

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If you're swapping Griptec pulley's, it's as simple as the video shows.

I don't think you'll need a tune adjustment.
 

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Discussion Starter · #3 ·
If you're swapping Griptec pulley's, it's as simple as the video shows.

I don't think you'll need a tune adjustment.
I guess I should have mentioned I was only going more conservative when you recommended Pat G :D
 

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This change should only affect WOT if the tune is right. For wot, It all depends on how it's tuned. My guess is it will loose 1-1.5psi of boost or ~7-10 kpa. Depending of the resolution of your timing table, it will probably shift up one line. If the previous tuner was able to make a good call on that line and the one above it, it should still be fine. You'll be in part of the maf table that the car is already tuned for becuase it will be moving less air than before. Do you have a wideband?

I've made the change from 2.45 to 2.55 and back a couple times and never really had to make changes to the fuel or timing, but my car is pretty dialed in.
 

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Discussion Starter · #5 ·
This change should only affect WOT if the tune is right. For wot, It all depends on how it's tuned. My guess is it will loose 1-1.5psi of boost or ~7-10 kpa. Depending of the resolution of your timing table, it will probably shift up one line. If the previous tuner was able to make a good call on that line and the one above it, it should still be fine. You'll be in part of the maf table that the car is already tuned for becuase it will be moving less air than before. Do you have a wideband?

I've made the change from 2.45 to 2.55 and back a couple times and never really had to make changes to the fuel or timing, but my car is pretty dialed in.
I dont have a wideband but is drivability any indication of how dialed in the car is because it is very good in that department considering the cam.

Also, if I'm going from Griptech to Griptech, is it as simple as removing those torx bolts and sliding a larger pulley onto the shaft?
 

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What Mike said. I would suggest buy HPtuners , Put a wideband in and log it. If the previous tune was proper you'll be fine. the only way to know if the fueling is dialed is with a wideband and the only way to know if your pulling timing or could use more is with the scanner .....
 

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If you're lowering the blower's speed, I would not expect the car to need to be retuned. In its current higher-boost configuration, it has to go through the lower boost range to reach the peak. So by definition, it's already tuned for the lower boost levels. Now, if the tuning made compromises lower down to keep the motor from blowing up at peak, it may be that retuning for lower max boost could yield some power improvements. But as far as engine safety is concerned, it cannot be a problem to run a slower blower on a motor tuned for a faster one...
 

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You’re going to need a wideband for remote tuning. You should get one and at least see what it does cruising and WOT.

Drivability isn’t much of an indication of WOT tuning. Most likely your tune uses the maf only at full throttle, whereas it hopefully uses a blend of maf and speed density cruising.
 
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If you're lowering the blower's speed, I would not expect the car to need to be retuned. In its current higher-boost configuration, it has to go through the lower boost range to reach the peak. So by definition, it's already tuned for the lower boost levels. Now, if the tuning made compromises lower down to keep the motor from blowing up at peak, it may be that retuning for lower max boost could yield some power improvements. But as far as engine safety is concerned, it cannot be a problem to run a slower blower on a motor tuned for a faster one...
That makes alot of assumptions about the current tune. Id never trust that its ok without verifying it... Lots of IFs
 

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You’re going to need a wideband for remote tuning. You should get one and at least see what it does cruising and WOT.

Drivability isn’t much of an indication of WOT tuning. Most likely your tune uses the maf only at full throttle, whereas it hopefully uses a blend of maf and speed density cruising.


Well Put Mike. .(y)(y)
 

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At first I thought it was crazy to change pulley and not retune or at least have someone look at the log, but it would make sense that lowering boost should not change much

probably why pat said unless you feel driveability issues, but I see it as a retune or at least a log is cheaper than an engine.

ive Also bought a car that had all the right people touching it and I felt it drove terrible and it would lunge forward. I don’t see it lunging forward as a matter of opinion over how it drives
 

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im thinking if the air model is spot on all injector data and offsets then it should be close, but if those are not right then no ecu calculations will be right, im sure there is some maths for it like is the airflow the same for say 200kpa map reading if the throttle is 100% or with more pulley throttle 70% to keep same 200kpa map reading ?
 

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You're worried about the higher pulley ratio that was put together by someone who is supposed to know what they're doing, yet you're going to make the assumption that the tune is okay as-is? I don't quite follow that logic. Note those in this thread saying that it should be okay likely have knowledge about their current tune or are experienced in tweaking the tune themselves, neither of which applies to your situation. If I had bought my car modded, I would 100% check / retune the car even sans changes just to know about the tune.

As mentioned, if you pick up HPT and a wideband and post the logs here some of the more experienced guys can chime in as to where you currently stand and what the reduction in boost may do.

Welcome to the V, may your wallet never be full again.
 

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Discussion Starter · #16 ·
I wouldn’t worry about the blower. Unless you’re constantly hitting 6500rpm+ the blower will be fine.
Well this brings up another question that I haven't been able to get a clear answer on. At what boost levels do the pistons become a concern?
 

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Discussion Starter · #18 ·
Pistons don't care about boost, power is what matters. Keep it under 800rwhp and feed it good fuel and it'll live a long life.
The previous owner sent me a dyno sheet of 761 rwhp on 93 but also claimed the owner before him said it was at 816rwhp on E85- but doesn't have a sheet for that run. I am highly skeptical of that power level because I've seen a few cars with more work done including stroked motors barely making more than that. And even if the car is capable of that it just gives me more incentive to get the car retuned to make damn sure it's dialed in. I'm after longevity, not max effort.
 

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In that case it might be a good idea to swap pulleys and retune for piece of mind. That is a pretty aggressive ratio for 93.


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