Hi,

I'm in the middle of tuning my new SC'ed S2k (Paxton 1220, 3.4" pulley) on Hondata KPro. However, there is an odd behavior once the MAP exceeds 12 psi during a full power full.

At 6400 rpm I'm at 10 psi.
At 6900 rpm I'm at 11 psi.
At 7400 rpm I'm at 12 psi.
And then it gives up... at 7500 rpm I'm back to 9 psi, then at 7700 I'm at around 8 psi... and that's where it stays flat all the way until redline.

I heard someone else had a similar problem caused by a "mushroom" type intake filter. With the filter removed, boost built throughout the ramp for them. Now I don't have that filter, but I might try a full pull without the filter connected, even though I don't love the idea of running without a filter connected.

Any other ideas for why this could be? Has anyone seen anything similar?

Thanks!

 

Your belt is slipping or you have a boost leak somewhere

 

Ok. Ordered a boost leak tester and a compressor off of Amazon. Let's see what I can find.

 

Might as well grab a Gates belt tension tester too! Better than the arbitrary twist test. I think the 91107 is what you want

 

aye aye, captn

 

Belt slip is my guess as well.

 

Ok. Waiting for a (delayed) belt tensions tester to arrive from Amazon.

if it is in fact the belt slipping, what would be the recommended/likely solutions? New belt? Just retensioning it? More parts to add? I think I saw something about an idler pulley for more contact surface somewhere. I also think I read something about spraying hairspray on the belt

 

Get a GripTec pulley. An additional idler may help, but isn't the absolute cure. Larger crank pulley for more belt wrap. The easiest and quickest solution is a Griptec though. They're a 2 piece pulley, so if you ever want to run a different size you'll only need to order just the ring portion of it. DM Chase Holyoak on FB, he's the connect for those.

 

Before trying any new setup I highly recommend stopping... taking a step back... and reassessing. It is not normal for the 3.4" to slip like that.

You are on a 3.4" pulley so it should experience little to no slip. It's not until you start messing with 3.2" and 3.0" where slip is a bigger/big issue. People then crank that tension up which is BAD for your SC bearings and for your expensive S2K crankshaft/engine.

1. Tension of the belt should be realistic. Use your hands to apply good amount of tensions as someone else tightens the bolt. Twist the belt, it shouldn't go past 45 degrees, but Gates tensioner will correct me if needed..
- Do NOT use a crowbar that folks place under the tensioner pulley for leverage as someone else tightens the bolt. Dyno shops will do that. I've been there, guilty of it. DO NOT do that.
2. New belt plays the biggest role and not the he-man like tension. New belt grooves are nice, tight and supple and as RPM increases it'll "sink" into the pulley groves and hold onto the pulley more and more.
- Old belt due to slippage has wider groves, rubber is less grippy and possibly glazed from slippage as your SC pulley was "polishing" it.
- Belt contamination plays a role, from age or from you constantly touching it with dirty paws as you tighten. Clean the pulley prior to installing a new belt.
3. A shorter longer* belt helps too as it wraps around the SC pulley more. Say 1/4 shorter longer where it's just enough to not bottom out the tensioner.

I did all three things on my 3" pulley setup and I now have no/minimal slip. New belt, made a big difference.

EDIT:
Here is my run from a few days ago. Blue line shows kPa (boost). This displays no slip on a Novi1000 3" pulley pull with a new, shorter longer, belt that was hand tightened:

 

^^ I think you meant to say a longer belt - to get more belt wrap for better traction, not a shorter belt.