Merc63

I went to the track last night for the first time in a couple seasons. I've lost 4-5mph and 0.30-0.50 seconds on my 1/4 mile.

The car has about 40,000km with the stage 3. Just wondering if there is anything I should be looking at refreshing? When I rev the car quick I hear a bit of a squeal sound, also at idle in the back driver corner I can hear a bit of a puffing noise. I've felt around and don't feel any boost coming out, hoses all seem tight on the back.

Any else have their belt to start to slip? I'm just trying to think of what would cause this power loss.

O2 sensors and spark plugs have probably 10,000km on them. I'm wondering also, can the tune degrade over time or need a re flash?

BadCompany

Tunes don't "degrade" over time. However, if something changes with the car, the tune will be "off." Have you thoroughly checked for any vacuum/boost leaks? I mean doing a real leak test - not just feeling around. At idle, you aren't going to "feel any boost coming out." You'll be pulling vacuum. Are you seeing/feeling anything that would indicate belt slip? I'm assuming you aren't running a good boost/vacuum gauge...

BLKROKT

I'd start off by doing compression and leak down tests. That should tell you if it's something outside or inside the engine and give you a better idea of where to start looking. Hope it's minor dude.

JimGnitecki

The squeal you hear when you rev it could be belt slippage.

I remember that when my buddies and I put blowers on the Chevys and the Fords, a stronger tensioner was always part of the kit because otherwise the tensioner would eventually cause the belt to slip.

Jim G

BadCompany

I doubt that squeal is from belt slip. Belts don't typically slip from quick revs. They slip while flogging the car higher in the rpm band. And yes, I've got first hand experience with owning high boost supercharged vehicles. The reason I asked about the boost gauge was that if he had one and the belt slipped, he see his boost drop. The other way to tell if your slipping is that you'll be eating the belt up. There is usually black powder (the belt) in the engine bay around brackets, etc. If his tensioner went, he'd likely be having other issues. Doesn't hurt to press on your belt and see how it feels though.

Mazspeed

Wrong. They can and do.

BadCompany

A properly spec'd belt with the right tension won't. I'm assuming you have experience with the Weistec kits and know something I don't. I didn't say it can't happen. I'm saying it is unlikely. Especially if he isn't seeing dust.

Mazspeed

I can't tell you what his issue might be, but belts on super chargers can slip. It happens. It happened to me. You can have proper tension and still slip. Lots of factors can happen under the hood. Little bit of oil or foreign liquid getting on the belt, not enough belt width and or not enough going around the pulley, too much heat. Crazy stuff happens under the hood to say it won't happen from quick revs, or from slow pick up. I just don't want him discounting that based on a forum post.

BadCompany

I understand what you are trying to say. Yes, weird things can happen. I think that an undersized belt is unlikely. It is a Weistec kit and I don't think there are many reports of the belt being too narrow, If his belt is slipping so bad that it slips near idle or from quick stabs of the throttle, he'd be falling on his face under WOT. A belt won't slip under low load/low rpm and grip under high load and higher heat. The OP doesn't say that his car was falling on its face. And, again, if he is slipping and went to the drag strip for multiple passes, he's going to have dust all over the pulleys. Based on the foregoing, I think I'm making a reasonable call in saying it is unlikely.

OP - is there belt dust around your pulleys? How does your belt look? Glazed? Hardened? What about your pulleys?

zcct04

Just curious - The car has a stage 3 and a total of 40,000km, or you actually have 40,000km with the stage 3 on the car? If the latter, that's pretty impressive.

bhamg

You may well be on to something here that warrants further diagnostic effort.

Merc63

Well I took it to the dyno today for the first time ever. Only making 5-6 psi when it should be 10-11psi, there's my power loss.

Belt doesn't appear to be slipping, no dust, etc. The boost slowly climbed and wouldn't climb anymore. It didn't climb and fall or jump which leads me to believe the belt is not sleeping.

I had my laptop hooked up and watched/log'd some engine parameters. The throttles are opening at 87%.

I'm thinking either the blower bypass set screw or something is not working correctly and air is being bypassed around the blower. I'm going to change the stock OEM air filters out, they didn't look very dirty and don't have many km on them. Might throw a new belt on it just to make sure.

Might do some pulls with no air filters in and see what happens too. will report back to update in case anyone else runs into these issues.

Merc63

35-40,000km on the stock engine with stage 3 power.

604 C63

35-40,000 of the funnest km of your life, amirite?

What a great motor.

mr747

check for belt slip if not check for boost leak? also check little valve behind supercharger is not releasing boost

Also check icetank hoses are not blocked

What were you IATS? did you check timing while it was on dyno?

Merc63

I just pulled the air filters, cleaned the boxes and ran it, still 6psi.

I'm going to get that gates green belt that I had on it before, will install a new one tomorrow and see what happens.

That valve is of concern, it controls the blower by pass valve, so under vacuum of idle it's open and letting air straight into the intake, when boost happens, it closed and lets air into the blower. It has a set screw that stops it when closed, the screw looks fairly seated.

I do hear a noise, where it's the belt or boost leak I can't tell. I don't know where would be leaking boost... my fuel trims are pretty damn good around 5% so if there was a leak I'd assume they would be out of whack.

I emailed the data log to weistec for their input... will see what happens tomorrow with the new belt on.

Merc63

Even at 5-6psi it still puts a grin ear to ear. When it's actually making full psi, it's a scud missle that can make you smile or scare the crap out of you.

mr747

Start with the belt are you sure all vac lines are connected?
if it is leaking i recon its arounf the back of the blower where the valve is

Merc63

Anthony at Weistec has been helping me trouble shoot, he's a smart guys and follows the logs for clues. The mass air flow values are down from a normal running stage 3 which he said is a sign of not losing compression or boost. The air flow coming into th blower is down. Leads me to believe it's the belt losing tension or slipping, or possibly that by pass valve not functioning properly. Changing belt today and will report back.

Merc63

Mr747, did you run the smaller stage 3 pulley with the stock engine? What was the result?

hachiroku

FYI...belts slip on superchargers all the time...there is a reason why upper tier superchargers as well as upper tier dry sump oiling systems use cog drive

hopefully a new belt fixes your issue!

Merc63

It was belt slip fellas! The old belt was 2" longer than the new green gates belt. No signs of slipping or dust. Hitting 9-10psi now.

BLKROKT

Bet it feels great now. Glad it was minor dude.

JimGnitecki

A 2 inch stretch on a serpentine belt is a LOT. You are fortunate the belt did not snap, or at least come off the pulleys. Given the miles you apparently put on the blower kit, if this was the original belt supplied with the blower kit, you got really excellent life out of it.

Jim G

Merc63

The two belts I'm comparing are different. They should be around the same size I assume. The new belt is way tighter and working great.

This is my third belt now. It's the gates green belt, seems to work good. I park the car for winter, 6 months. I'm going to take the belt off the blower to reduce the stretch in the future.