Low boost due to smaller alternator pulley?

[Ass Eyes]

The seller of an advertised 600+ (@ 19 lbs boost) Kenne Bell'd Cobra is now telling me the 435 whp (@ 12 lbs max) I'm seeing may be due to a change he made to the alternator (smaller pulley) after the 6xx pull he gave me papers for.

This makes sense to me only if there's belt slip - there are no signs of that. Am I missing something?

 

[Ass Eyes]

The seller of an advertised 600+ (@ 19 lbs boost) Kenne Bell'd Cobra is now telling me the 435 whp (@ 12 lbs max) I'm seeing may be due to a change he made to the alternator (smaller pulley) after the 6xx pull he gave me papers for.

This makes sense to me only if there's belt slip - there are no signs of that. Am I missing something?

Is it that nobody knows the answer (unlikely) or that the question was as dumb as I think (highly likely)?

 

[01yellercobra]

It's not a stupid question. The smaller alternator pulley would only affect things if a shorter belt was needed, but wasn't used. Are you positive the dyno graph for 600hp is for the car you bought?

 

[IUP99snake]

A smaller alternator pulley isn't going to affect the amount of boost, even if a shorter belt is used. The proportion between the crank pulley and the blower pulley is still the same. You can change the size of all the other pulleys if you want, as long as the crank pulley and the blower pulley are still the same, you'll have the same amount of boost. (Assuming there's no belt slip)

 

[01yellercobra]

A smaller alternator pulley isn't going to affect the amount of boost, even if a shorter belt is used. The proportion between the crank pulley and the blower pulley is still the same. You can change the size of all the other pulleys if you want, as long as the crank pulley and the blower pulley are still the same, you'll have the same amount of boost. (Assuming there's no belt slip)

I mentioned the shorter belt because if one is needed and not used then he'd have belt slip.

 

[Ass Eyes]

It's not a stupid question. The smaller alternator pulley would only affect things if a shorter belt was needed, but wasn't used. Are you positive the dyno graph for 600hp is for the car you bought?

No, I'm not certain. I bought the car from a guy on this site and trusted what he said. He seemed stand-up but it turns out not so much.

At this point I'm thinking it's an airflow issue or the MAF is sending erroneous data causing the BOV to open early. Who knows?

 

[svtshadow]

Since when did the alternator become a boost regulator. OP, you are being played!

 

[IUP99snake]

For those centri people with a blow through MAF setup using a LMAF, there's a huge weak area. Since they have a flange on one end that would normally bolt to the airbox, there is an adapter used that bolts to that one side of the MAF so it can connect to the other side of the boost tube.

The problem is that the MAF doesn't have a perfect mating surface to the tubing adapter flange. It's really really easy to blow out that gasket in blow thru applications. This causes a loss of boost, poor drive ability, etc...

I spent what seemed like forever trying to figure out why my car only made 6 lbs of boost after I had my aviator motor installed and it started to run like crap.

I took some JB weld and made sure that there would never be another leak between the LMAF and the adapter flange ever again.

Instantly, the codes went away, it drove like a dream, and I got my 4 lbs of boost back, not to mention an extra 44 HP.

If you or anyone else has a LMAF in a blow thru configuration most commonly found on procharger kits, it's in your best interest to check the gasket for leaks and ensure it isn't a weak spot.

As for your KB setup, the MAF doesn't have any way to control the bypass valve. That's vacuum actuated.

Do you notice a lot of black dust in the engine compartment, especially near the blower pulley, that's a big sign of belt slip. Call KB tech support and see what they say... they're very very helpful. Ask the seller who installed the blower and tuned the car. Contact those people.

 

[Ass Eyes]

For those centri people with a blow through MAF setup using a LMAF, there's a huge weak area. Since they have a flange on one end that would normally bolt to the airbox, there is an adapter used that bolts to that one side of the MAF so it can connect to the other side of the boost tube.

The problem is that the MAF doesn't have a perfect mating surface to the tubing adapter flange. It's really really easy to blow out that gasket in blow thru applications. This causes a loss of boost, poor drive ability, etc...

I spent what seemed like forever trying to figure out why my car only made 6 lbs of boost after I had my aviator motor installed and it started to run like crap.

I took some JB weld and made sure that there would never be another leak between the LMAF and the adapter flange ever again.

Instantly, the codes went away, it drove like a dream, and I got my 4 lbs of boost back, not to mention an extra 44 HP.

If you or anyone else has a LMAF in a blow thru configuration most commonly found on procharger kits, it's in your best interest to check the gasket for leaks and ensure it isn't a weak spot.

As for your KB setup, the MAF doesn't have any way to control the bypass valve. That's vacuum actuated.

Do you notice a lot of black dust in the engine compartment, especially near the blower pulley, that's a big sign of belt slip. Call KB tech support and see what they say... they're very very helpful. Ask the seller who installed the blower and tuned the car. Contact those people.

The car has always run very well - no stumbles anywhere. It's just that it maxes out at 12 lbs. Based on the pulleys, it should do 19.

No black dust anywhere. I'm assuming you asked thinking there is belt slip. No signs of that.

KB hasn't been helpful. They neither return emails or calls.

 

[Ass Eyes]

Since when did the alternator become a boost regulator. OP, you are being played!

Had you read the original post you'd have noticed I didn't buy his explanation. I asked to be certain.

Thanks for your input. :nonono:

 

[IUP99snake]

How did you calculate that you should be making 19 LBS of boost? Remember, boost is only a measure of restriction, not power. The pulley calculation doesn't factor in other mods to the car. There are a number of factors that can affect boost such as the type of exhaust, whether there are cats, inlet restrictions, heads, cams, etc etc.

When I put an off road X pipe on my car, I lost 2 lbs of boost. That didn't mean it lost power.. it just means that theres more flow. I ditched the plastic procharger inlet pipe and got a power pipe and I gained those 2 lbs of boost back. You get the idea...