old motorhead

Replace your 3.25" pulleys on the rear with a 3.5 (on the jackshaft) and 3.0 on back of the blower. You can use the same rear belt. With your o/d crank pulley, I think a 3.6" top pulley should spin the blower fast enough for well over 700rwhp.

Those blower speeds I mentioned earlier in the thread are wrong. That was me thinking I could do that calculation in my head. Apparently not I have a really nice desk top calculator right next to my mouse pad.....shoot.

So, with an 8" crank pulley and 2.8" blower pulley, your blower rpm at 6500 engine rpm is 18,570 blower rpm. That's pretty damn fast to be spinning a TVS. To contrast that, the Heartbeat TVS on my LS3 is spinning at about 15,300 rpm. It makes 660+ at the wheels. The pulley setup I mentioned in the first paragraph would be spinning the blower at 16,850. Sure, you can spin it faster, but at that speed, you're reaching the point of diminishing returns. Much past that and you get back into belt slip and IAT's that are hard to deal with.

How big of a motor are we dealing with here? If it's a stock cube LS2 or 3, you should be seeing WAY over 12psi with the pulley combo you're running.

Streetk14

First, I'll just mention that oldmotorhead probably has more experience with these blowers than anyone else on this forum. I'd listen to his theories.

My guess is also belt slip. I never logged the horrible slip I had on my old 122 blower setup, but it would do exactly what you're saying. Always looked pretty steady on my boost gauge, but it would fall off like that at higher revs.

Besides overdriving the rear pulleys as was recommended, I'd look into an upgraded tensioner from ECS. They used to make a very nice one, and I think they still do.

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Old motorhead: thank you, I'll ask my tuner for that pulley setup. We are actually pulling the blower off in the next week or so to fix the oil leak issues. Can change pulleys at that time. I assume Magnuson sells said pulleys?
As for engine, this is an LS7, sleeved 427ci. Stock heads but ported/polished. It's got plenty of air flow.

As for the tensioner, I actually have the ecs tensioner. The car has a **** load of extras that I am slowly finding out.

old motorhead

I'd check with Brian at superchargersonline dot com for the rear pulleys. They rarely come up for sale in the used parts section. Being that you're 8 rib on the front, you probably won't find that used either. If Brian doesn't have what you need, he can tell you where to find it.

A 427 with a Maggie TVS on top is just NASTY. You don't need a huge amount of boost when you're working with that many cubes. The pulley combo I mentioned should be good for 11 or 12psi. 700+rwhp.

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Sounds good! Thank you Sir!
Aj

01midmetws6

I am the one working with the tune on this one.
The current pulleys are as follows:
Crank pulley - 8.0
Front Jackshaft pulley - 2.8
Both rear pulleys - 3.25"
Effective drive ratio of 2.86:1
Max blower speed of 20,000 rpm @ 7000rpm

Boost fall off is very linear and starts to happen immediately but never jumps and is very consistent. For that reason I did not feel it was belt slip but I have been wrong before and am open to suggestion.

The idea of moving the bypass source from the inlet to the manifold base was to verify the vacuum present at the inlet was not enough to start opening the bypass. I did not measure vacuum but would bet it is no less than 1.5-2" under full load. The intake is not ideal and with a stock throttle body feeding a blower that is spun up that hard it could be enough to start allowing the bypass to reopen at higher airflow amounts.

My suggestion was to increase pulley size to a 3.0 or 3.2 to see if we can maintain consistent boost. A 3.0 pulley would end up at a drive ratio of 2.66 (3.2 would be 2.5:1) which is very close to the recommendation of a 3.6" with a 3.0/3.5 rear setup (2.59:1). i understand you are going to get much better belt wrap with the 3.6" but the cost vs a new rear setup makes it more palatable. This car should make 700whp with no more than 8-9 psi, carry power better and end up with a safer setup as well.

old motorhead

What you're saying makes total sense and I can't mount a real good argument other than to say that sometimes, these damn things don't react like we think they should.

Case in point...I had a really restrictive CAI on one of my trucks. You would think, or at least I would think, that boost would be normal down low and boost would go down as rpm goes up. Nope. Boost was flat before and after putting a better CAI on. It just made another pound and a half of boost everywhere. Go figure.

I'm betting you do have at least a couple inches of vacuum between the throttle body and the blower. I have that much on my rig running a 3.2" pulley on an LS3. With the amount of air y'all are moving with that tiny pulley, it can't help but be more.

You might be able to make a 3.0" work if everything else is optimized. That's damn sure cheaper than buying the o/d pulleys. I know the front 6 ribs are a hundred bucks a copy. The rears are 10 or 12 rib. Hate to think what they might cost. Sounds like you have an upgraded tensioner which will sure help. I wouldn't try to run that small a pulley on an LS2 or 3, but boost/load on an LS7 should be lower allowing it to work. We've had good luck running Gatorback belts. They seem to grip a little better and stretch less than standard belts.

That should be an insanely fun ride when you're done. I want a ride

LedfootLarry

Agree with most said here.
But you should test with a vacuum gauge at TB to see how much vacuum,
as that is a lot of boost drop. A 102 TB is probably a good idea for 700+,
but I tried 3 TPIS TB's , and none worked! The Nick Williams tends to slam shut.
So I went with an old NW 102 mm with the LS6 motor on it , my boost is 13lbs from 2500-7000 rpm.
These blowers like no restriction in front!
If you want the most out of it, overdrive cogs in the rear are the way to go.
I would not even spin it that fast, as in hot weather , your IAT's will be
very high, and then you will be down on power .

old motorhead

I'm still waiting on a "slam dunk" throttle body upgrade for my Heartbeat. Best I can tell is that you can spend a bunch of bucks and it "might" work. I'm still lovin' it at my meager power levels. A few more would be nice, but I'll wait and let someone else spend the money and do the r&d.

The cogged rears IS a slam dunk fix if you think the rears are slipping. Plus, I think the cogs are a little more overdriven vs the standard ribbed pulleys. You have to count the cogs vs measuring the diameters. Some folks like the increased whine and some don't.

01midmetws6

What was the issue you were having with the TPIS throttle bodies? I have never had an issue with c5's but have had a few problems on large positive displacement blowers. The NW102's have over rotate and then push closed at high airflow amounts which cannot be remedied.

I would have a tough time with cog noise personally but agree there are no more issues with slip I have successfully tuned a bunch of TPIS throttle bodies and they seem to work well on Gen4 ECU's.

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So we worked on the car a little bit more with the belt slip issues. I was under the understanding that the previous owner put a new belt on the car. Well it was new but the length was incorrect. My current is a 2.8 pulley so we're going to put a 3.0 pulley and hopefully no belt slip then. Stay tuned, I'll know more tomorrow.
Aj

whatcop?

I'm too lazy to read it all but the oil you are seeing is due to blow by which leads to oil being burped through the pcv system. The oil coming out is very evident of a leak and if it can leak a liquid it can leak air. Tighten her down and if she still won't hold then it needs to be cleaned and a new gasket put in. Also level boost and then starting to creep down is evident of a boost leak on a PD blower setup.

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^^^ Yes, the PCV system was routed horribly. That is all fixed now.

Its pretty much belt slip that is causing the issues. We changed to a 3.0 pulley and its still loosing boost. I think the next step is to change the rear belts to a cog setup. Anyone know where I can buy those from?

old motorhead

Your belt slip is all on the front end. You don't necessarily need cogs on the rear unless you're trying to spin the blower faster than a 3.0 front with 1:1 rears. If you do get the cogs, I think you'll also need to clearance the fuel rail next to the rear jackshaft pulley. If you just go with the ribbed O/D pulley set, you don't need to do that and you can also use your existing rear belt. Much less $'s.

Superchargersonline dot com is where I would go for the pulleys.

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^^^ Thank you

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As a quick update:
We changed the rear pulleys to the 30mm cog over drive kit from LPE. Did not need to mess with the fuel rails. It all fit fine.
Front pulley is 3.2" with a new belt.

No boost drop off anymore. Pulls strong 12# all the up into the 6k rpms. No Dyno numbers yet, still working on some oil leaks off the blower. The rear unit was overfilled and pushing out oil but now, proper level and still pushing out oil. So we may need to send into Magnuson for a rebuild.

Just an update for you all in case you're ever seeing the same problem.

old motorhead

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Thank you especially old motorhead!

Woodstoc

Rodney to the rescue!

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Updated vid

The car now makes a full 12# of boost, but still 650/650 @ wheels. Blower was completely refreshed and now, zero oil leaks or wear and tear. Any ideas why it's not making power?

I am being told the throttle body is just too small. It's not able to suck in enough air on the top end. Last fall when I was on the track, I could feel the top end just die off.

Who makes an upgraded TB for this tvs2300 system?

Any other thoughts? Thanks guys.
Aj