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Part throttle KR... How bad is it... really??

97AutoXVette

97AutoXVette

New member
I believe these GTPs have part throttle KR from the factory (often seen on 4th gear in the highway, during part throttle cruise, when the engine is loaded and right around the vacuum/boost crossover point). I remember when I was logging with HPT one day on a pump gas build I did, I would see while driving in 4th gear 10* of KR at times when the engine was under load. This KR would be non-existent though when doing WOT pulls and heavy acceleration, etc.

I have since tuned out the part throttle KR via transmission table setting changes (modifying the TCC tables, adjusting the downshift tables, etc.)

My question is, how bad is that part throttle KR for these motors?? If they are so prone to it from the factory, and MANY people who go throw on a downpipe and a smaller pulley likely have a TON of it, does it really damage the motor in ways that other KR does? (Like WOT KR under much higher boost pressure and cylinder pressures??

The responses to this may get interesting haha... But if folks have experience and think it is fine to have some part throttle KR in 4th, I may not modify my transmission tables any further and just allow a few degrees of KR from time to time. Having very little amounts of TCC (allowing a lot of slip) and downshifting from 4-3 all the time is not ideal in my opinion
 


take the sc belt off see if its still there. kr is kr. i suppose it could still chip a piston.

have you touched your cruise timing? like raise it because of the corn? if so lower it closer to stock, or stock will also work.
 
i dont see injectors in your sig's mod list. upgrade them yet? you need like 60's 42's wont cut it. stock wont make the show either.
 
It's not as bad as wot kr. Most likely it'll never hurt anything with no boost, or just a couple of psi. 10* is kind of excessive, but 1-2 will most likely never hurt anything. But I am also very surprised you get any kr on e85 at part throttle.
 
I remember taking a scan when I was doing a fair amount of highway driving. the scan would show blips of kr at 70 mph just crusing down the highway at maybe 15% throttle. the blips were never higher than 2*. I asked about them and the response was not to worry about it.

In your case, 10* does seem excessive, so maybe there is something vibrating that the knock sensors are picking up.
 


from his sig

2002 GTP sedan: 3" downpipe|PLOG|poly mts|160 T*|ZZP Intake|1.8 YT RRs|Ported Gen3|Ported ZZP S2 TB|E85|Caspers FP rewire|WP UD Pulley|3.1 MPS|HP-Tuners
 
Ok. At 15% throttlemail when you see the blips of kr, what does your vac/boost gauge read? Or map sensor?
 
Updated my sig to show that I do in fact have 60# injectors installed (still plenty of head room/duty cycle left on E85 with my current build). 2002 GTP sedan. mods in sig are updated now.

The KR usually occurs right around when the engine crosses over into boost in 4th gear on the highway (anywhere from -1psi, up to 1.5psi or so) before it downshifts from 4th to 3th gear, based on how I have the transmission shift tables setup. I usually only see 1-2* of KR at the condition described above, but it still seems weird. I could always make the 4-3 downshift happen at a bit lower throttle position to downshift before the engine crosses over from vacuum to boost, or I could modify my PE table to come on sooner so it starts adding additional fuel right at that crossover point. Just pondering options at this point, and if that couple degrees of KR is really worth worrying about since I am only at like 20-25% throttle position at those conditions.
 
If it was my car, I wouldn't even care one bit.

Own a few GEN 4 LS trucks and you'll see them knock even more under minor load in high gear sometimes, yes they don't have a blower but the knock does no harm.
 


Fivefingerdeathpunch said:
If it was my car, I wouldn't even care one bit.

Own a few GEN 4 LS trucks and you'll see them knock even more under minor load in high gear sometimes, yes they don't have a blower but the knock does no harm.
Click to expand...

Thats what I was thinking.. two of my previous GTPs had that knock in 4th much worse than this one (because I was newer to building/tuning on this platform and didn't even realize it for a long time). Neither of those motors ever had issues as long as I owned them :)
 
Not sure why it baffles anyone.

This doesn't have to be spark knock. Vibrations or struggling against the torque converter can easily create false knock and have that show up in a log. E85 isn't the god of fuel to rule over all knock retard events.
 


Fivefingerdeathpunch said:
Not sure why it baffles anyone.

This doesn't have to be spark knock. Vibrations or struggling against the torque converter can easily create false knock and have that show up in a log. E85 isn't the god of fuel to rule over all knock retard events.
Click to expand...

First you claim it's false knock. Then you claim it's detonation/preignition.
 
I didn't "claim" anything. I simply said it can easily be false then later said included that wonderful word "ALL", meaning ANY knock related event.

That means real knock, false knock, spark knock, burst knock.

Stop nit picking everything and get real here.
 
My car knocks as well in 4th locked up. Here in SD the speed limit is 80 and I too will see a degree or two of knock right as it crosses over into boost. Climbing hills I may see as high as 10*
 
When I was working in SD, I pulled timing back quite a bit while driving through the hills. But that was on 87 octane. With e85, I could run as much timing as I wanted to.
 
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