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Hey guys.
Just had the car retuned today and I am a lil disappointed in the numbers. A lil perplexed to the issue too so here's the background.

Setup: built/forged motor. Cam, heads and full exhaust. Tvs2300 blower with 12psi.

On the dyno, after a good clean up on the tune, it made 650whp and 675rwtq. The boost comes on strong at 11.5psi but as the rpm climbs, the boost creeps down to 8.5psi.

There is oil leaking from the base of the blower. I don't know if that's related but I assume it is.

Anyone have any clue as to what's going on here or any opinions. My tuner didn't have time to get back in touch with me today but we're gunna follow up tomorrow. I can post back what he thinks. Wanted to start this thread to get your guys' input.

Thanks!
Aj

Ls2gtoowner

My first thoughts is as the rpms going up and boost dropping is belt slip. What kind of belt are you running and is it properly adjusted?

Doubt the blower leaking oil is the issues but I wouldn't let it get work. Leaking isn't a good thing.

old motorhead

Yeah, you have belt slip happnin'. Boost should stay pretty much level throughout the run. What pulley combo are you running front and rear? Find the source of your oil leakage. The Maggie doesn't hold much oil, therefore it can't afford to lose much. If it's leaking anywhere near the serp belt or rear belt, you have no chance of getting rid of the slip before fixing the leak.

thegreenman

If you have the stock six rib belt system it is only good for about 650HP.

I agree with the others, probably belt slippage. You need a belt system upgrade to 8-rib or as I did 10-rib pulley system (planning for the future).

When mine was being tuned with the six rib belt my tuner said it was smoking and he could not get a good run due to the belt slippage.

lt1z

What impeller?

Check belts, bypass valve

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Once I talk with my tuner this afternoon, I will report back with more details.

The belt setup is an 8-rib currently. very good belt wrap on the front side of the engine. The rear of the blower is where the oil is leaking and I think that's a good suspicion that the oil is getting into the belts there and making it slip. Totally makes sense to me!

The front pulley is a 12psi pulley, the rear is a 1:1. Bypass valve is fully operational and no leaks there.

Will report back in a few hours. Thank you guys for the comments, def helps me make sense of the situation.
Aj

old motorhead

8 rib is all good. But, you have to be running a really small front pulley to see 12psi with upgraded cam and heads along with 1:1 rear pulleys. I'm guessing less than 3". A front pulley that small is really inviting belt slip. You need to strongly consider a set of overdriven rear pulleys to replace your 1:1's. That and/or an overdriven crank pulley is absolutely necessary if you want to spin the blower that fast.

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Ok so I talked with my tuner. the front pulley is a 3" and the rears are 1:1. There is zero belt slip, this wasn't the issue for the boost creep. He called Magnuson and it is concluded that the big cube motor might be pulling too much vacuum that the bypass valve may be prematurely opening while under boost. It only takes 2-3" of vac to open up that valve. My tuner is going to re-route the bypass valve vac line to the blower base and see how she runs on a WOT pull. Also, as you guys implied (old motorhead), the smaller pulley is over spinning the blower. Something like 20k rpms where suggested max is 17K rpm. We will be going to a larger blower pulley to stop it from over spinning and hopefully it makes more useable/consistent hp/tq. My guy is doing a lot of research and working with Magnuson so hopefully it pans out.

As for the oil leaks. the base gasket of the blower unit has given out. Magnuson said this must be an older kit b/c they used an aerobic gasket. New version is anaerobic. Soo.. I need a new base gasket.

Arrghh... Just bought this car too. Was suppose to be turn key and im already 2k into repairs with another 1500 at least to go. Such is the game of highly modified cars...

Aj

old motorhead

Just to be clear, I wasn't saying you're spinning the blower too fast. My daily driver (front drive Maggie TVS2300) is using a 3.1" pulley. Nothing wrong with the speed you're spinning the blower. You're by no means overspinning it. Just that you can get the same blower speed using a bigger front pulley (less potential to slip). You can use a 3.5" front pulley to run the same blower speed you're running now if the rears are overdriven.

I'm not at all understanding the potential for the bypass valve to be giving you trouble. Once you're into boost (out of vacuum), it's shut....end of story. 1psi or 12psi, the bypass valve is out of the picture. If it's shut at 3000 rpm and 12 psi, I can't imagine a scenario where it's going to open as the rpm goes up as long as you're still in boost.

Slow down and try to understand what's going on before throwing more money at your Vette. I don't think you have anything wrong that a well chosen set of pulleys, a good tensioner, and the correct size/top shelf belt won't cure.

Streetk14

Maybe I'm thinking about this wrong, but I suppose what Magnuson is saying could be possible if you had a big enough restriction before the rotors. At least on my Heartbeat, the vacuum reference line connects right behind the throttle body. So it's in an area that shouldn't ever see boost. So MAYBE, just maybe.... if you had enough restriction from the air filter or throttle body, it could cause the bypass valve to open.

I know you've done some testing on various setups checking vacuum readings under load, so maybe you'd be the guy to say whether having 2-3 inches of vacuum in the intake system at high rpm is remotely possible. That seems like a lot to me, but then what do I know.

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Forgive me old Motörhead but I'm new to FI on the vettes. It's been about 15 yrs since I have had a s/c'd vehicle. Still learning all the ins and outs again.

I think what Streetk14 said is what's happening. That's how my tuner explained it. Sorry, I couldn't rephrase it that way. My restriction is the factory 90mm throttle body. I was told I should look into a 102mm TB.

Getting the car back today so we shall see the outcome.

old motorhead

Very plausible. Just because I haven't seen that scenario play out doesn't mean it can't. Plus Streetk14 is never wrong.....I've had several Magnuson rigs in the 12psi range and it's never happened to me. Lots of TVS2300's being spun in excess of 20,000rpm without this issue. At 6500 engine rpm, your blower would be spinning 19,500 rpm with the 3" blower pulley. It should be easy (and hopefully inexpensive) to check. Good luck and let us know how it works out

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Well rerouting the vac supply on the recirc valve did not help. The boost still creeps off.
My tuner is telling me I need a bigger throttlebody as the big Cube motor is not getting enough air.
For now I'm going to leave it. I have a few bigger issues I need to deal with. All the gaskets in the blower head unit seem to be leaking. I guess TVS made a new design on the gaskets so I need to get that in there.

Unfortunately that's my only update. She won't be making any more power this year. I am strongly contemplating selling the blower and going with a turbo route over the winter. So we'll see.

And yes old motorhead, The Bloor spinning at its current speed is A-OK. Belt slip is not an issue. My tuner was running the logs and you can see it's def not belt slip. All the joys of a modified car...

old motorhead

I'm going to play dumb here. It's an easy and natural act for me....How can you tell, by looking at the logs, that belt slip is not an issue?

BLWN1

What cam

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My tuner had his lap top hooked up and could read the pulls. He said if it were belt slip, the power loss and/or boost leakage amount would be far greater. He assures me it's not belt slip. Plus, the belt wrap system is pretty darn good. I don't know personally how the whole tuning stuff works so I'm just relaying what he said.

Cam: Lingenfelter 227/239 114
Blower pulley: 8" lower, 2.8" upper
2" American racing headers

schpenxel

Boost bouncing up and down, belt slip.

Boost building smoothly, no belt slip

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Boost isn't bouncing back up tho. It's a drop from 11psi @ 5k rpm down to 8psi at 6800rpm.

old motorhead

That's pretty much classic Maggie belt slip. I see you're running an o/d balancer with a 2.8" top pulley. That's an absolutely perfect way to get slip. Oversize lower with a tiny upper. If you and your tuner refuse to believe it, so be it..

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I'll relay the information to him. I'm not saying I don't believe it but I'm just saying what he's telling me.
What is your suggestion to eliminate belt slip?
Thanks for your input Old Motorhead, do appreciate it.