Last Sunday I changed my D-1SC pulley from a 3.90" to a 3.40". The car ran well and the change in throttle response was noticable.

Then we got a cold front and things changed. When starting the car in the cold the blower would seem to be emitting a popping sound and would torque at the same time. My first impression was that the colder air resulted in the belt contracting and this was a bearing issue. But even after loosening the belt this still continued. The problem would go away once the engine warmed up.

I was informed that perhaps the added air from the smaller pulley was causing a rough idle during a cold startup.

The blower was torqing so badly this morning that the belt twisted and got frayed on one edge. As it was damaged, I cut it off. $40 gone.

Anyway, I have been using the 3.90" pulley for the last year with no problem. I plan on switching back to it just to make sure this issue is strictly related to the smaller pulley (and increased air).

I have found very little information on the web about blower tuning and related problems.

I would appreciate any insight into this issue.

Thanks!

 

Did it only do this on cold startup and a few minutes after? If so your belt didn't shrink when it was cold it expanded. You will have to tighten the belt if this is the case. Rubber belts shrink as they get warmer. Next time check the belt before cold startup to see if it loosened due to expanding with temp drop.

 

Yes it did this on cold start up. Once the engine was warm it stopped.

But is this related to a belt issue or something else?

Maybe it is an air intake issue during open loop?

 

Mine did this at first. I just had to tighten the belt to get the slack out of it when it was cold. Durring the summer months I never had the problem. Just remember belts loosen as they get cold and tighten as they warm.

 

So let me just clarify with you. You were experiencing the blower popping and moving during a cold startup and you fixed it by tightening the belt?

What pulley and belt size were you using?

Thanks.

 

https://www.thirdgen.org/techbb2/sho...highlight=chug

 

Thanks B4CTom1,

I just decided to go back to the 10# pulley and enjoy the system that I have had for the last year.

Guess the added air from the smaller pulley just aggrivated an idle issue?

Oh well, guess we will have to let Willie have all of the high boost fun!

 

Yep I fixed it by tightening the belt. BTW what kind of mods did you do to your motor? I am getting 10psi with a 4.25 pulley and a completely stock 305tpi.

 

That "chug" usually sounds like a metallic clanking…

From the description sounds like you're lean and getting a lean backfire/misfire. The cold makes it worse because the air is more dense requiring more fuel for the same volume. A quick way to check this is to crank up the fuel pressure a few lbs and see if it gets better.

 

I experienced the same thing with my p1sc. It was about 50 one morning and I was in CT at a friends. I left the car outside overnight, went out in the morning to start it up and clank......clank......While idling and the car warming up I experience the same phenom that you guys did. I actually saw the mounting bracket for my blower flex! It only happended say half a dozen times while the car warmed up. SO, while still under warranty I sent the headunit back to ATI asking them to re-certify it per say. They didn't come up and say anything was wrong but did take it apart and replace a bearing..not sure which one. My blower only had 3400 miles on it. I will have to see if it still does it when I put my car back on the road in April.

 

Yep I fixed it by tightening the belt. BTW what kind of mods did you do to your motor? I am getting 10psi with a 4.25 pulley and a completely stock 305tpi.

I have a blower specific cam, SLP headers and 3" exhaust. Otherwise the engine is stock. Guess my free flowing exhaust requires me to use the 3.90" pulley to get 10 psi.

Looking at the other posts on this issue, I am tending to believe that I am having a misfire problem. Did you have the clanking or chung noise too? I am suspecting that you were just getting some movement from slop in the belt.

That "chug" usually sounds like a metallic clanking…

Yes, that sound like what is happening. I am figuring that the smaller pulley results in more air at idle which is causing the misfire.

I do not have an adjustable fuel pressure regulator so I cannot adjust idle fuel pressure. However, I have an air/fuel ratio gauge and it appears that I am on the rich side (about 13:1) as expected during cold start up?

I reinstalled the 3.90" pulley yesterday. This morning it was cold with frost. Started the car and ran like it used to with no misfire and blower chung.

Since the car is better tuned for the 10# pulley I have decided to keep this pulley on the blower. Perhaps it is better this way as the 15# pulley would have brought the HP to the maximum the stock components can handle. I decided that I am not ready to rebuild the engine.

AC, you had the exact same experience as I did. Please update again once you get your car on the road.

Thanks for the input.

 

A misfire could cause a chug…

If you just have an occasional rattle/chug and no other symptoms, I wouldn't worry about it.

13:1… If that's on a standard O2 sensor then that is nowhere near accurate and you should be showing full rich till the engine warms up (once the sensor gets warm enough to work). If it's a WBO2, then you should still be richer then that with the engine cold, I would expect something in the 10-12:1 range. When engines are cold they need to be pretty rich to run anything resembling correctly.

 

correct me if im worng, but isn't 13:1 a little lean, not rich? 11:1 would be a little rich right? also i would expect that a cold start would be a little lean due to the denser air

 

14.7:1 is stoich… above that is lean.

When cold you need it to run pretty rich to work, but its unlikely you'll be able to accurately measure the ratio anyway when cold, which is the reason I originally suggested just trying it…

 

Just checked the A/F ratio at initial start up. It bounces around in the low 12s. However, this is with the larger pulley.

I discussed this issue with Willie last night. He noted that improving the bypass flow might help out this problem. Perhaps adding a second bypass and butterfly valve.

Any thoughts on this?

Would be an easy check. At idle slightly pull the inlet tube from the TB thereby relieving some air flow from the intake. If the chungging stops then you have confirmed it is an air issue.

 

I doubt that it's just airflow but you can try it I also doubt that you're getting accurate a/f ratio readings unless you're preheating a WBO2 before you start it up…

OTOH, I've never played for any period of time with a supercharged engine that didn't have a completely open bypass setup at idle.

 

...you're getting accurate a/f ratio readings unless you're preheating a WBO2 before you start it up…

The A/F gauge is from FJO. It does warm up before it begins to read. So there is some warming of the engine before I begin to see gauge readings. So you are likely correct that the richer reading are not seen while the WBO2 is prewarming.

OTOH, I've never played for any period of time with a supercharged engine that didn't have a completely open bypass setup at idle.

Actually, I have checked the bypass and it is completely open. It was just suggested that this bypass may not be enough to vent the air produced from the smaller pulley.

Note that the only difference between my privious set up and the new set up is a shorter belt and a pulley that produces more air flow.

All I know for sure is that the engine and blower now work perfect with the larger pulley and belt back in place??

 

I have done some further research through the old post and have found some additional information.

I have read of problems with the ATI surge valve at higher boost levels.

I see that some members have added either larger surge valves or a second valve to help with blowers producing high air flow.

This seems to be mainly used for compressor surge problems occuring after letting off of WOT, but it seems like this would also help relieve additional air flow during idle.

 

I am revisiting this issue and believe that the chugging problem can be relieved with the addition of an additional ATI surge valve to vent off the additional air pushed into the throttle body.

Willie has suggested this and I would think it to be a reasonable conclusion. Less air to the intake elimated the problem once I went back to a larger pulley.

Anyone encountering a chugging of the blower after going to a smaller blower pulley?

 

Re reading this thing I had a few reactions:

• yenko, I really doubt that belts shrink as they get warmer… from reading what you wrote it sounds like you’re describing belt slip, which is pretty common on blower cars at cold startup, and is usually more noticeable in colder weather. It is not because the belt is changing size but because on cold start up the belts see the most load as the alternator starts trying to recharge the discharge from starting, the PS starts trying to pump cold ps fluid… then in cold weather add stuff like a defroster running, more likely to have your lights on… and you’ve put a MUCH bigger load on the belts. You can usually spot which belt is loose on a blower car with more then one belt by paying attention to when you hear the noise and figuring out what conditions caused the noise.
• WRT to a surge/chug at idle, it can be pretty bad on some cars. On my brother’s car we ended up welding a butterfly (like another throttle body) to some of the ducting between blower and TB with a cable linkage to the TB as a bypass valve. Essentially, a positive linkage that only closes the bypass at WOT, the rest of the time it’s open. This ended up fixing a number of issues including some surging and constantly blowing hoses off.
• Have you checked to see if your ECM might not be thinking that you’re not actually idling when this is happening (funny tps, maf, map… readings)? Probably the easiest/most obvious sign would be if your ignition timing is all over the place, which would cause similar problems.

 

Yep check out the properties of rubber belts. They shrink when warm and grow when cold nothing new there. Happens to be the opposite of what one thinks, but true none the less.

 

No chugging problems here with the 3.4" pulley but I vent mine to atmosphere if that makes much of a difference. I do noticed she's venting a lot more air at idle and it's much louder, I'am thinking of putting the surge hose on because of it.

 

On my brother’s car we ended up welding a butterfly (like another throttle body) to some of the ducting between blower and TB with a cable linkage to the TB as a bypass valve.

Sound like a good idea. I was considering adding a second ATI surge valve and control it with a switched actuator as per Willie's recipie.

Did your brother's car have chugging all of the time, only during warm up, or during cold weather? Mine was only during cold weather with the 3.40" pulley. The car ran fine with the 3.90" pulley.

Have you checked to see if your ECM might not be thinking that you’re not actually idling when this is happening (funny tps, maf, map… readings)?

I had a custom chip made which required a lot of data to be collected over a period of time until everything was just right (speed density). I had no unusual readings. I am confident that the ECM is fine as the car now runs perfect with the 3.90" pulley. Willie felt that the increased air from the smaller pulley was forcing too much air into the TB. This makes sence as the only difference between the 3.40" and 3.90" pulley is the air flow, which as noted by Tony89GTA is seen even at idle.

 

I would love to see some documentation of this, where do you find properties for multi v belts?

Not that that really makes a difference, I gave a pretty accurate account of why belt issues tend to be worse at cold start up.



Well, it’s a home built eaton blower setup… you’re destined to have chugging of sorts with a roots type if you do not have a sufficient bypass, the lobes feeding the engine “lumps” of air just about guarantee it. Even under boost datalogs show stuff like one frame that will show full boost pressure, and the next will show no boost. It’s the nature of the beast.