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Old 08-18-2010, 08:26 PM
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Blown 1971 Corvette - Help new young hotrodder with questions

Hello all! First post from me here. I have lurked for awhile drueling over all your beautiful rides. But now I joined the club so time to chirp up. I have descriptions of issues first and pictures of it all are at the end of this post and replies I made directly after this. ANY and ALL help, replies, and comments appreciated. You guys are my only hope. Let me know what you see in these pictures.

I just bought my first car without a computer this weekend. A blown 1971 corvette with NOS, 4:11's, 4 speed, PS,PB, and more. Since this is the engine forum I will not get into all that and post all the pictures so here is a link if interested in the car
http://picasaweb.google.com/randmansmith/Jul202010#


I am hoping that some of you can help me out with some questions. And now that I am a member perhaps I can help someone else. It is clear this car spent some time at the drag races. With me, it will not be a drag racer. I want to make it more street friendly but still a fun little dependable hot rod with plenty of power.

This car was sold at an estate sale and the original owner of the car cannot be located so history unknown.
I am 30 yrs old and know snowmobiles and motorcycles mostly, I have rebuilt a few so my feet are mechanically wet. I design engine timing components currently for a living and understand how an engine works, however this engine has some things that I am not familiar with.

Right now it has a few issues I need to address. I will only address engine issues in this thread since this is the forum for it.

I cannot find model numbers on the carbs. They have been painted to match the car.

The choke plates have been removed for some reason. Wondering if I should order some up. The dual carbs appear to be Holly 4160's and 390 CFM each? The previous owner had it flood often and the car wouldn't run. He messed with the float heights. Sure enough, my first ride it crapped out and flooded and I was stranded . I heard there are clear bolts with a window or something to make them easier to set? Hopefully I can find a how-to on setting them. I need to take them all apart and clean them up.

Second immediate issue is there is a trace of compressor oil leaking from the bottom at the rear of the blower. I think the base gasket for it is leaking. When I hammer on the throttle, the exhaust is blue. I am pretty sure that must be from the compressor since if that gasket is leaking in the rear, compressor oil must be getting sucked in and burnt up especially on hard acceleration. Once again, I can't find a part number on the blower. Appears to be a B&M 144? Someone engraved flowers all over the thing (and the steering wheel) . I am thinking of sanding them off and polishing the unit. I have never had a supercharger. I see BM turned into Weind and Weind became Holley. Is a BM144 what I have and is it the same as a Weind 144? I want to order a base gasket for it and maybe a seal rebuild kit. Is that what I should do while I have it off the car?

A belt squeels when I hit the gas and when I downshift. Video here - http://www.youtube.com/watch?v=tRHUU...eature=channel
I am thinking it has to be a blower belt. I want to replace all the belts on this thing with what is supposed to be on it. The previous owner told me he guessed when he just replaced a few belts. How do I know what the correct blower belt is? Someone told me they need to be cogged? Any help or links MUCH appreciated.

Motor also has hooker headers on it, 350 block (I don't know the HP of the block, how do I look that up?), BM intake (how do I tell what one?), Date code on block is " A 73 1 ", heads are 71-72 LT1 75cc chamber heads with casting number 3973487 and have full roller rockers.

Tach - Auto-Meter Sport Comp "monster". http://www.jegs.com/i/Auto%20Meter/1...0002/-1?CT=999
It is OK at idle but when I am acelerating it jumps all over the place. I believe it is an electric tach. It looks stupid in the car and I wish I could get the stocker work but i think the stocker is mechanical. Either way, if I could get this one to work and not jump all over the place that would be nice. Suggestions appreciated.

Boost Gage - While going down the road it says -15 or so. If I hammer down on it it goes to +4. Why doesn't it say 0 when I am going down the road at 55mph?

Fuel pressure regulator - Is it in the right spot? It is at 6 psi at start up and 5 psi while going down the road.



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Last edited by arcticcatmatt; 08-18-2010 at 08:37 PM.
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Old 08-18-2010, 08:28 PM
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Old 08-18-2010, 08:29 PM
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HERE IS WHERE I SEE THE COMPRESSOR OIL LEAK BELOW


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Old 08-18-2010, 10:34 PM
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you should have boost when going down the road and only 4 psi at wot sounds like you got super charger problems get that boost fixed you might fix that flooding problems
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Old 08-19-2010, 05:16 AM
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^ The boost gage looks far from new. Perhaps the gage is just screwed up. I think its pushing 4 lbs because that is what it is set up via its pulley size
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Old 08-19-2010, 10:42 AM
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whats your vac at at idle is it higher then 15 psi on the other hand it may just be the carbs if its only set up for 4psi that just seems a bit low to me

Last edited by rtyauch301; 08-19-2010 at 10:48 AM.
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Old 08-19-2010, 10:58 AM
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^ I have not checked. I talked to Holley customer service today and they sent me an old PDF for the BM supercharger 144. I have to measure some bolts tonight. For reference for others- I was told SBCs can have a 144 charger or 162?. The way to tell is measure the blower to manifold bolts. If they are 9.75 apart it is a 144. If they are 10.5 apart it is a 162?

They sell belts and base gaskets for it. He told me to send it out to get rebuilt at PSE superchargers for 5-600 bucks. I am not about to do that. I am going to change the base gasket before I do that.

They could not tell me what my carbs were without a special number that is inside under the air filters next to the choke tubes so I have to get that tonight.

He told me my boost gage is fine at -15 running down the road and +4 when hammering on it. That was normal.

Any replies and comments are appreciated and welcomed!
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Old 08-19-2010, 01:54 PM
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I'm not familiar with BM superchargers at all but I do have a Kenne Bell SC on my truck. The 500-600 to have it rebuilt might be worth considering. It will be completely torn down all seals replaced clearances assured and any parts in question will be addressed as well. The boost bypass actuator is a common problem with SC's especially if an aftermarket camshaft is being utilized. Aftermarket camshafts often offer much less vacuum especially when cruising the highway. If your bypass actuator isn't functioning properly that causes all kinds of problems and eventual damage to the supercharger. These sort of problems occur over long periods of time so they'll often go easily unnoticed since the problems tend to creep in vs a sudden onset of problems. These Superchargers are complicated systems and a clean bill of health for one goes a long way when trying to nail down issues that a motor is having. Good luck.

Roach
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Old 08-19-2010, 08:02 PM
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Quote:
Originally Posted by arcticcatmatt
^ I have not checked. I talked to Holley customer service today and they sent me an old PDF for the BM supercharger 144. I have to measure some bolts tonight. For reference for others- I was told SBCs can have a 144 charger or 162?. The way to tell is measure the blower to manifold bolts. If they are 9.75 apart it is a 144. If they are 10.5 apart it is a 162?

They sell belts and base gaskets for it. He told me to send it out to get rebuilt at PSE superchargers for 5-600 bucks. I am not about to do that. I am going to change the base gasket before I do that.

They could not tell me what my carbs were without a special number that is inside under the air filters next to the choke tubes so I have to get that tonight.

He told me my boost gage is fine at -15 running down the road and +4 when hammering on it. That was normal.

Any replies and comments are appreciated and welcomed!
Expect to see manifold vacuum at idle and while cruising.Boost will occur when you crack the throttle open under load only.
Stick with the serp belt,they are designed to slip if you backfire.Going to a cogged belt will require a pop off valve under the blower.
Looks like dual 390 vac secs.Should be enough potential cfm at wot to feed that baby blower.Someone installed an adapter plate,seeing how these street blowers typically are single carb units.At least, run a vac line between the secondary dash pots so they roll open evenly.
Forget the plastic see thru sight glass for float bowl level adjustment.They fail and leak and can be a fire hazard.
With side saddle carbs..drop the fuel bowl level a tad under the threads and set the idle mixture screws at 3/4 turns out vs 1 1/2 turns out with a single carb as a baseline for rich idle issues.
I would replace the blower to manifold gasket.Good chance the previous owner ran it pig rich and compromized the gasket to the rear.With a fuel soaked gskt like this,an external sweat will look like a fluid leak and a prime source for a vacuum leak.
If it is a purpose built blown unit with a low compression and a somewhat healthy performance camshaft..set your initial timing high but limit your total.
A safe starting point would be 20* initial and another 12-14* mechanical for a total of 32-34* all in @ 2800 rpm.
If you spray it..you may need some form of spark retard,be it a throttle switch or a 2 bar map sensor thru a cd box.
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Old 08-20-2010, 11:15 AM
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Thanks for the feedback! I took what you all said into account and called holley with the pictures in this thread.

They told me the carb setup I have is wrong. These are the WRONG carbs for a supercharged motor. They are not blow thru. Someone must have plugged the power valves and jetted it rich. There is no boost master reference and no secondary balance kit. They said that is way to much carb for this setup and its something people did many years ago for "looks". There was a company making these adapters to run 2 carbs instead of one and thats where the adapter probably came from.

They HIGHLY suggested I remove them, the spacer blocks with the NOS, and the dual carb adapter... and order up this http://www.holley.com/0-80572S.asp and use a single carb setup. It will be ready right out of the box to work with my setup. I am seriously considering it. I looked at the edlebrocks and called them and they really don't have a carb thats great for this setup, they have no boost master lines and I would have to change the needle/seats and jet it rich.. no thanks. Holley has the better setup for this but at more money.

If I buy the new holley carb and ditch the NOS setup I am wondering if there are any other changes I have to make. My hood is made for this setup but oh well, I will have to get another hood and cut it for this new setup.

The blower rebuild is $600 from PSE superchargers + I pay shipping both ways. I don't even know if it needs rebuilt. I think I will just remove it and sand the flowers off and get a new base gasket and put it back on the intake with the new holly carb.
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Old 08-23-2010, 07:25 PM
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I know that this will just add to the confusion but here goes.


Your boost gauge is correct and yes +15 and -4 are good numbers. Since you have 15" of vacuum you should be able to safely get away with a regular Holley carb, not boost reference.

Here is why...... When you choose a powervalve in a carb you take you engines vauum reading.... In this case 15 divide it in half which would be 7.5.

A power valve opens up when you hammer on your engine and provides the car with extra gas, hence the name POWERvalve.

When you install a blower and run boost you have to take this into consideration. The boost will try to suck the powervalve shut at wide open throttle and if that happens it will lean out your engine and you can say GOODBYE to it. But you only have 4lbs of boost and should be running close to a 7.5 powervalve. There is no way it will get sucked shut. Holley will not tell you that. They want to make $$$$ and blower carbs are expensive.

oops noticed this post is a few weeks old... haha well its already written so i will post what I have.
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Old 10-13-2010, 04:12 PM
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Holley is F O S. Keep the dual carbs and the rare B&M dual carb blower adapter.

The carbs can be easily modified for boost referenced power valves and joined vac sec diaphram lids.

The power valve boost reference mod is a 1/2 hour job you can do at home.
tear down both carbs.
Drill the new external passage in the side of the carb body, press in a steel tube and block the stock passage with epoxy or seal all. Its that easy.
reassemble with new gaskets.

The center bodys can be swapped for a Proform HP replacement allowing air bleeds tuning as well as down leg boosters and more flow. Get a wide band AFR meter to help dial in the carbs. jetting etc.
even a cheap narrow band type is great.
its not that hard. You don;t need to ditch the carbs or the dual carb adapter or the nos.

If you want to sell that dual carb adapter, let me know.
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Old 10-14-2010, 02:07 PM
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You mentioned the carbs were 390 cfm but you kind of 'sounded' uncertain- is that what they are?

You can get the carb number from the choke tower, looking at the "front" of both carbs- actually you'll be standing on the passenger side looking at the carbs to see the number, since the carbs sit side-saddle.
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