I have a forged 383 stroker LT1 with every supporting mod you can beef these things up with to make the internals as bulletproof as an lt1 can be.

It has LE3 very ported heads, LT's, 58mm TB, GMMG Catback, lingenfelter ported intake man, flow match custom groud CAM (pretty heavy).

On this I am running a Vortech S-Trim Supercharger with a FMIC and the 14lb pulley (measurement for a stock application).

I was hoping to hit somewhere around 10-12lbs but am only seeing 6lbs max. Vortech said this is possible because of the volume of air my very good flowing motor requires. This just doesn't seem right. What boost should I be seeing?

I also am running the stock BOSCH Bypass Valve, I've seen it can hold up to 12lbs. Is this true? The reason I ask is i recently sprung a BAD leak out my back intake manifold valley seal and have an oilfall coming down my bellhousing. I have heard some worries that if my Bypass malfunctions I could blow the seals out on my intake. What worries (if any) should i be aware of or is the leak probably just a bad seal on my part from the initial build. Motor had 100 miles when leak started.

Thanks for the help,
Brandon

 

Sounds about right to me, especially if you have an aggressive supercharger cam with lots of overlap.
Find the compressor map and plot your rpm (if you know the pulley sizes).

 

I too have a 383ci FI Camaro (97ss w/ MM6). A good flowing intake/ heads/ exhaust is the best. I run a D1 with a small 3.4" driven pulley and can only make ~12psi. Flow is everything, and a low reading is actually good.

I also run (2) two bosch bypass valves. I have re-engineered the springs for 15.6 Lbf spring seat load. This allow me some bypass @ low speed with a max capacity of 18psi of boost pressure. When the throttle valve closes, the valve will open and allow bypass.

I have also had my share of leaks (manifold/ rear seal/ front pan).
I modified the rear manifold with a 1/32" groove to retain the RTV sealant. This worked for me.

Two + years ago I went to an external crank driven Vac pump after trying all the other crank vac management techniques. The external pump sealed the rings and less blow-by, and, allowed an increase in cylinder pressure. Also, this fixed all the rear-seal and front pan leaks. I only run 1/3 atm vac on the wet-sump.

LT1's leak alot when applied to FI.
Hope this helps.
B.

 

I don't think you have any problems. Back when my motor was still stock bore- I was only seeing 5.5 lbs of boost at 6k rpms when Procharger claimed 9lbs. That was just with a Comp 'blower' grind cam and cleaned up heads and intake.

A lot of people get hung up on how 'lbs of boost' they want and 'need' to attain a certain goal or status. If you have a air-hungry motor capable of breathing easy then you aren't going to see high 'boost' numbers- but you'll be able to brag about making high power on relatively low 'boost' numbers.

i.e.- my first dyno tune- stock bottom end cam/heads/intake and Procharger reading 5 lbs of boost at only 5500 rpms made 476hp at the rear wheels. I thought that wasn't too shabby...

 

This is a GREAT idea!!! I'm going to do it. Will it work on the front?

Not really sure what you mean about an external crank driven Vac Pump. Do you mean Oil pump or vacume. Is this part of your wet-sump or is this a different topic. Sorry for my lack of knowledge on the subject. Any pics, part numbers, or conceptual broken crayon drawings (I like these) would be very much appreciated. Anything to help the health of my motor i'm totally game for.

Thanks again everyone for the smart insite!

 

TTT... Please Help Me With This.

 

What exactly do you need help with...?

 

I just wanted some more information about this.

 

My experience is that the stock Bosch Bypass Valve is only good for around 9 psi, and typically fail open allowing boost to continue to bypass. I'm running 10 psi of boost and killed 2 stock Bosch bypass valves over time.

 

They're just crank driven vacuum pumps. Commonly used on racecars. Google it.

 

Boost is all relative to how much restriction there is. Larger more heavily ported heads will not yeild as much boost as a smaller set would. (One reason I am running AFR 180 heads).

One other thing to note, you stated you had a setup that was as bullet proof as it could be internal wise, but you then went on to list top end parts which have nearly nothing to do with the stress that FI takes its toll on. It is all within the bottom end of your engine in which the "bullet proof" parts will be needed. What pistons are you using? What CR? What rods? What crank? These are the items you need to worry about. Not your heads, cam, and intake.

 

Yeah, what he ^ said. You're looking at a stock sized pulley to make near the same boost on a heavily ported set of heads and 33 more c.i. with a larger cam. You need to maybe get the better bearings and spin the s-trim to its max to attain 10-12 psi on your setup. You honestly are going to need a D1SC or a YSI-trim to feed that beast.

 

Thank you for the responses and I appologize for not going into detail on my bottom end. I have a forged scat 383 crank, forged scat pistons, forged scat h-beam rods, hardend pushrods with guideplates, splade four bolt mains, melling high flow oil pump with canton deep pickup, hardend canton oil pump driveshaft, and canton 6 qt pan. I'm not sure there is much of anything else you can do to these besides sleeving them to make them stronger without going to crazy.

My wonder was why I have such bad oil leaks. Now after some research it seems quite common with boosted applications. I just want to know what the silver bullet is to fix the crank case vent problems. I've read everything from reworking the AIR pump to pull vacuum at WOT or under Hobbs boost to the crank driven pump stated earlier. This isnt a race car but it is fairly high output and I plan to take it to higher RPMs than stock on some ocasions. I just dont want to get a low oil light every time I do.

Thanks again and I look forward to any more inputs.
-Brandon

 

The more boost you run, the greater the crankcase pressure will be. The best way is to adapt a good catch can system to recirculate the oil and still vent the pressure.

Depending on how much you are creating, breathers may be enough. I am running about 15#'s of boost on a cold day in my setup. I have 4 breathers on my valve covers (2 large breathers and 2 small ones), and I notice that if I do a lot of WOT runs that it will vent a little oil where I will need to add a small amount again. Thats where a catch can system would benefit you. However, my breather system adequatly seems to vent the crankcase pressure, and works just fine as long as I moniter the oil levels from time to time. I have never had to add much oil though, even for a TON of WOT runs.

If you are to the point your low oil level light is coming on after some WOT from starting with the appropriate oil level, then you've got some serious problems that need to be adressed beyond crankcase pressure venting.

 

I'd forget about what anyone calls a 'pulley for this boost' or 'pulley for that' boost because it is misleading. You need to know the diameters of crank & blower pulley, max engine rpm & max blower rpm. Then you can see where you're at on the compressor map.

With an S-trim you will want to pulley the blower so that it maxed out at your max engine rpm. Vortech used to have an online calculator for this as well as maps.

If not, let me know what pulleys you have and where you shift and we can figure blower rpm. I bet you are well below max.

Scott