Smaller SC pulley?

Subject: Re: Smaller SC pulley? Wed Nov 04, 2009 6:28 am

I recommend buying an MPS, Multiple Pulley System, if you are going to start playing with pulley sizes. If you get one of the more popular sets with a 3.6, you can easily find used 3.4s and such out there for future easy bolt-on changes.

But you need to open up the exhaust manifolds a bit and watch out for KR before you start dropping pulley sizes. I couldn't run a 3.4 with no KR until I had 1.9 rockers installed.

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'98 Buick Riviera; Gen V 3.25 pulley, N*, VS Cam, 180 stat, Custom PCM (Powrtuner), headers & HF cat , 42.5 lb inj.

Grant-built/PRJ/Thrasher trans 3.29 gears, 7/8 chain, zzp hardened IS

Subject: Re: Smaller SC pulley? Wed Nov 04, 2009 7:27 am

I couldn't even run a 3.6 w/o getting several degrees of KR, and that was with typical supporting mods already in place. If you can't scan for KR, DO NOT drop pulley sizes!

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Dave G
98 Riviera
Gutted, 3.8, 180, 104'S, front PEM, 3" DP & Cat, Caddy STB, GR2's. DHP 1.5

Subject: Re: Smaller SC pulley? Wed Nov 04, 2009 10:11 am

Quote:

Dont drop pulley sizes until you open up the exhaust a bit and have some way of scanning for knock. You could probably get away with a 3.6" pulley but it's still a risk.

You can run a slightly smaller SC pulley without opening the exhaust, although a downpipe can help you make more power. Read page 1 of this thread for more info we've collected on this.

A few degrees of knock is not the end of the world. Even stock engines knock from time to time. The engine will hold up. This is why you can run a 3.6" pulley safely. Most can run a 3.5" safely as well, but here is where you need to start scanning for KR.

I agree with Deek, an MPS is the way to go. I also agree with Dave that you never can be 100% with dropping SC pulley sizes. There are always things to watch and maintain. Scanning is very good insurance to have.

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Subject: Re: Smaller SC pulley? Wed Nov 04, 2009 11:41 am

AA wrote:

Quote:

Dont drop pulley sizes until you open up the exhaust a bit and have some way of scanning for knock. You could probably get away with a 3.6" pulley but it's still a risk.

You can run a slightly smaller SC pulley without opening the exhaust, although a downpipe can help you make more power. Read page 1 of this thread for more info we've collected on this.

A few degrees of knock is not the end of the world. Even stock engines knock from time to time. The engine will hold up. This is why you can run a 3.6" pulley safely. Most can run a 3.5" safely as well, but here is where you need to start scanning for KR.

I agree with Deek, an MPS is the way to go. I also agree with Dave that you never can be 100% with dropping SC pulley sizes. There are always things to watch and maintain. Scanning is very good insurance to have.

Well if his stock motor is knocking 3* with the 3.8", and he adds another 3* with a 3.6", then he's up to 6* KR which is pretty high IMO. Especially when you figure he's running about 10* of timing at that point and is probably slower than with the 3.8". Although each engine is different so a scanner is essential.

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1996 Riviera, 1.9s, 3" DP, FWI, 180, AL104s, 3.6", DHP PowrTuning...
Soon: SSACs, Stage 1 TB, and a 3.4

Subject: Re: Smaller SC pulley? Wed Nov 04, 2009 12:15 pm

Yes, it's possible for that to happen, but it probably won't. KR depends on a lot of factors other than your SC pulley and level of modification. Fuel, air temperature, terrain, vehicle weight, condition, and maintenance history all come into play. This is why some cars have more KR than others.

If I put a 3.6" pulley on my car with no other mods, and saw 6º KR, I would suspect a serious problem. I had about that much KR running a 3.4" pulley for several thousand miles on a basically stock engine (only mods were t-stat, plugs, and gutted box). I don't suggest anyone do this, but my engine did okay.

I agree scanning is a great idea for 3.5" and smaller, but the 3.6" is supposed to be a safe upgrade. A 3.5" pulley is considered a safe mod for a totally stock GTP or GS, but they are slightly lighter cars.

I've routinely seen 10-12º timing advance at WOT without much, if any KR. I don't detect any loss in performance. I also don't notice much of a performance decrease from moderate amounts of KR - see link:

http://rivperformance.editboard.com/series-ii-scans-tuning-pcm-f5/the-consequence-of-kr-t1548.htm

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Subject: Re: Smaller SC pulley? Wed Nov 04, 2009 12:50 pm

AA wrote:

Yes, it's possible for that to happen, but it probably won't. KR depends on a lot of factors other than your SC pulley and level of modification. Fuel, air temperature, terrain, vehicle weight, condition, and maintenance history all come into play. This is why some cars have more KR than others.

If I put a 3.6" pulley on my car with no other mods, and saw 6º KR, I would suspect a serious problem. I had about that much KR running a 3.4" pulley for several thousand miles on a basically stock engine (only mods were t-stat, plugs, and gutted box). I don't suggest anyone do this, but my engine did okay.

I agree scanning is a great idea for 3.5" and smaller, but the 3.6" is supposed to be a safe upgrade. A 3.5" pulley is considered a safe mod for a totally stock GTP or GS, but they are slightly lighter cars.

I've routinely seen 10-12º timing advance at WOT without much, if any KR. I don't detect any loss in performance. I also don't notice much of a performance decrease from moderate amounts of KR - see link:

http://rivperformance.editboard.com/series-ii-scans-tuning-pcm-f5/the-consequence-of-kr-t1548.htm

Right, but if you are upping boost and losing timing just to break about even with performance, then it seems kind of pointless to drop the pulley size anyway. Especially when you consider the unnecessary danger added with the moderate knock. The money would be better spent on the mods needed to support the pulley before dropping sizes.

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1996 Riviera, 1.9s, 3" DP, FWI, 180, AL104s, 3.6", DHP PowrTuning...
Soon: SSACs, Stage 1 TB, and a 3.4

Subject: Re: Smaller SC pulley? Wed Nov 04, 2009 1:19 pm

I have seen STOCK GTPs with 4-5 degrees of KR at WOT, so just because it's stock doesn't mean everything is okey dokey already. That's why a lot of people say 'oh it's probably okay' when for some it may not be. Before and after scanning is important. You need to know what's going on before you start modding.

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'98 Buick Riviera; Gen V 3.25 pulley, N*, VS Cam, 180 stat, Custom PCM (Powrtuner), headers & HF cat , 42.5 lb inj.

Grant-built/PRJ/Thrasher trans 3.29 gears, 7/8 chain, zzp hardened IS

Subject: Re: Smaller SC pulley? Wed Nov 04, 2009 1:29 pm

Some '04-05 GTPs had 4-5º KR, due in part to their hotter timing tables. Series II engines should not be seeing much above 1-2º at most. This is why ZZP only recommends using 3.5" pulleys on stock Series II cars. Also remember these stock cars had the u-bend, whereas we do not.

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