Blower guys What camshaft? Will this combo work

Will this drive combo work.
I have aquired these parts cheap, probably not ideal but I need to get my car finished and can always upgrade the drivetrain later.

350 crate engine 8:1 comp( would like to swap the heads out for aluminum)
6-71 small bore blower (plan to run 4-5 lbs boost until I can replace pistons and crank)

2- holley 600 dp
3:90 rear gear with 29 inch tire
700 r4 automatic
What camshaft would you reccommend? Stall convertor? also What ignition are you guys running?
Going in a 30 model A sedan. for street use.

 

1. With the basically stock long block setup you describe, two carbs would be for looks only. One would be enough and much easier to set up and get right. You can always go for two if you build serious later.

2. Roots blowers don't need loose converters. That's the whole idea - they build torque from the get-go. Also, the 700R4 has such a low first gear, with the 3.90 rear, it will pull on it's own.

3. With only 8:1, too much cam will cost MPG and the cast pistons won't let you make it up with revs at the top end.

4. Even low boost puts a lot of pressure on valve springs. Even if you don't go with a high intensity cam, you'll need some more valve spring pressure.

jack vines

 

Call your favorite cam company (I like crane or lunatti for a modern build myself) and tell them you need a blower grind. Also tell them what you will be using the car for (stop and go takes a different grind that balls to the walls and shut down in 8 seconds).

A little advice on your heads, blowers like broad flat faces on the valves. sp keep that in b mind when you grind the valves.

4-5 psi is a good idea for a daily driver by the way, some of the fellas keep 'em down around 3 psi and are very happy with it.

 

This is what Blower Drive Service lists as their stage one small chevy blower cam - pretty mild, but I think the LSA is the key with a roots blower, also, more exhaust duration and lift.

<TABLE border=0 cellSpacing=1 cellPadding=5 width="100%" bgColor=white align=center><TBODY><TR><TD align=center>465/.490 lift</TD><TD align=center>270/274 adv. dur.</TD><TD align=center>221/226 @ .050</TD><TD align=center>110° LSA</TD></TR></TBODY></TABLE>

 

Thats a pretty good spec for stockish mill and a blower.

Problem is once you get decent heads on it, you could really benefit from a different grind on there. Or leave it as is . . . or the cheap way out instead of the cam might be higher lift rocker arms.

The idea behind a forced induction cam is you don't need a narrow lobe separation (more overlap) because the air is being forced in. More air/fuel coming in for the same duration means more exhaust duration to compensate and get all that extra air out.

Typically a forced induction cam will have a 112* or 114* LSA and about 8+ degrees more exhaust duration

Lift is usually dictated by the heads.

 

Thanks for the quick replys, at least knobody has said it won't work
Any ignition reccomendations? I've only ran hei's with msd boxes and external coils. Don't really like the look of an hei for this though plus it won't fit

 

Check out Matsuda racing on YouTube. It may not help you choose a cam but the guy has gone pretty darn fast with almost stock parts. You'll have to looks through several videos, he's run several different combos in his cars. Anyways...interesting videos.

 

If it were me, the LAST thing I would want to do is restrict the inlet side of a blown motor...

 

Each build is each builder's choice. For an essentially stock 350" long block turning no more than 5,500-6,000, how much CFM will it actually be able to use? A stock 350" will only suck 516 CFM max. A supercharged 350" can use more, but doesn't require it.

FWIW, a blower creates a depression below the carb and increases the flow rate beyond the 1.5" at which 4bbls are flow rated.

Here's what my go-to guy says about carbs for blowers:

<TABLE cellSpacing=0 cellPadding=0 width="98%" border=0><TBODY><TR vAlign=top><TD>A small carburetor will experience continuous vacuum at all throttle openings when positioned above the supercharger, and its vacuum-operated power system will never function. The power valve will remain closed, causing a dangerous lean condition which must be cured. This, and not the carburetor size, is what causes the lean condition. Attempting to cure this by increasing the jet sizes causes the engine to run full rich at all times. The cure suggested (large carburetors) reduces vacuum to the point where the power valve, metering rod, &c. is always open. This does cure the lean condition, but no longer provides accurate mixture for purposes other than full throttle.
With considerable testing, a power valve vacuum choice could be arrived at that will permit the valve to remain closed under the highest cruising speed and part-throttle acceleration the engine will see, but still open immediately upon throttle opening. This is an acceptable method, but there is no reliable way to tell in advance whether it will work or not. If the engine is too small (vs. carburetor size), vacuum will drop immediately upon throttle opening, and the range covered by a power valve may be too narrow to be acceptable for normal driving.

</TD></TR><TR vAlign=top><TD colSpan=3> A power valve carburetor can be modified to a boost-referenced power system. This references (controls) the power valve (or metering rod in Carter, Edelbrock, Rochester) to the engine rather than the supercharger. The concept is simple:
1. Find the small port in the carburetor base plate (facing the engine) that conducts vacuum internally
to the power valve or metering rod. It&#8217;s probably between the two primary throttle plates.
2. Plug the hole with a piece of lead shot or a set-screw at the gasket surface in the carburetor
baseplate, so that vacuum cannot enter this passage from the manifold.
3. Drill a hole horizontally in the side of the throttle body into the port above the plug.
4. Insert a tube or hose into this hole.
5. Connect the tube to a fitting in the intake manifold. This will provide vacuum to the power valve
normally, but permit the valve to open and enrich mixture when vacuum drops at open throttle

</TD></TR></TBODY></TABLE>

 

Sorry, I disagree. Nothing like heating the incoming charge to help induce WOT detonation. How you figure a blown motor is going to only use 516 cfm is beyond me. Yes, I am familiar with "the formula". 1.5 HG (which is what "the formula" actually calculates) constitutes an inlet restriction, and a blown motor, even at 5 psi will exceed 100% volumetric efficiency by a wide margin, so even if you DO accept "the formula" as valid or meaningful (I do not) your 516 cfm number is incorrect, and the WOT throttle vacuum number will be considerably higher than 1.5 HG. But like you said, its each builders choice.

 

x-2

 

I went with the 600 Because I will probably build a 383 next. I doubt 1 stock 350 will last this car a lifetime I plan to boost reference the carbs. Not sure what jets or power valve to start with I will probably ask holley after I get the cam and heads.

 

What the OP said:

How many of what CFM would you recommend and by what calculation?

 

I am running a +.030 350 with 18cc dished forged pistons, on top of a forged DSS Racing rotating assembly, 180cc runner Dart heads with 76cc chambers, Comp Cams NX262 series cam (COMP Cams K12-556-4), 142 CID Weiand supercharger and a 700 cfm Holley Blower carb. I have a air/fuel ratio gauge on the truck and have found that it is running very rich out of the box.

Our static compression is approximately 8.2/1 and the truck runs very good to about 6K. I used the smaller blower because I wanted to make torque in the streetable range (2-5K) for pulling a trailer. This is in a '58 Apache with a T-5 and 3.73 gears in the rear end. I set up a conference call with DSS Racing, Comp Cams and Holley/Weiand to get everyone together hoping that it would iron out some of our configuration questions. This is my first blower motor and I went in with lots of questions.

Now that it is running and has about 500 miles on it I am planning on starting the tuning process. I got the jet kit from Holley this past week and have the weekend wet aside to work with it. One thing I've found so far is that you get lots of advice from people (even the tech folks from vendors) that doesn&#8217;t necessarily fit your application. The Holley tech said to run a hose from the PCV valve up to the bottom of the breather for crankcase ventilation. I have already noticed that I was getting a lot of oil mist around the filler on the valve cover. I called Holley back and the new tech guy said the first guy's advice was all wrong.

The only complaint I have so far is how rich the carb runs out of the box but I kind of expected it. According to the Air/Fuel ratio gauge we are running around 10.5 and the ideal (textbook) recommendation is 14.7, but we will be happy to hit near 14. I averaged 12 MPG going to Dewey in May which is way below the 20 MPG we used to get with the 283 that we pulled out of the truck. I will be happy with anything close to 17.

Consider all advice (including mine) then see if it makes sense on your application. The people who ended up being the most free with advice while I was building up the engine had never even touched a supercharger before seeing mine. I'm not implying anything about other posters here, so please don't think that is the case. I did get some good information from several HAMBERS.

Two things I really recommend is a boost gauge and the air fuel ratio gauge. It is nice to be able to monitor from the driver&#8217;s seat.

Sorry, I missed a couple of your questions; I am running a MSD mechanical advance distributor, a MSD 6BTM ignition box and the boost gauge reads about 4 psi under load.

 

Ok, lets start from the faulty premise that this formula is based on, namely that 1.5" hg is the manifold vacuum # that you want to target at WOT for optimum performance (its not, but we will deal with that later).
Atmospheric pressure at sea level is approx. 14.7" for the purposes of this demonstration, lets call it 15". The OP is talking about making 4-5 lbs of boost, for the sake of keeping the math simple, lets settle on 5 lbs. So we are looking at an additional 1/3 atmospheric pressure, or 1.33 times atmospheric pressure.
Ok, at this point, lets do the math based on the original false premise that the users of this formula operate from (If anyone who cares and is following this doesn't understand where the 1.5" hg number comes from, say so, and I will do a quick run-down of how a flow bench works, it will go a long ways to explaining just why it is that this hackneyed old formula really is a complete crock of shit, and why the numbers it generates seem to bear so little relationship to what carbs actually work in the real world, and why even most OEM's "overcarburate" according to the formula).

The formula basically calculates the engines swept volume, multiplies it by RPM, adds a variable for volumetric efficiency, compares it to (theoretically at least, for the most part, even this isn't true, a lot of "cfm" ratings are based more on marketing decisions, rather than any actual flow bench data, but I digress) a cfm number generated on a flow bench by drawing air through the carburator an arbitrary pressure drop(in the case of most domestic 4bbls, 1.5" hg) and this is supposedly the "informed" way to make a carb selection.

So the formula goes engine CI X rpm/3456 X volumetric efficiency, lets run the numbers.

355 x 5500 rpm=1952500/3456=564.95blablabla to the tenth decimal, lets call it 564. Now, times 1.3 for the fact that you are shoving an extra 1/3 of atmospheric pressure in, and we get 734 CFM (for our purposes we can safely dispense with the decimals, as carbs are generally in 50 cfm increments anyway.

So at this point, assuming that we even accept the original premise that swept volume times rpm is a valid method of carb seletion, we have 734 cfm, and 1.5" hg manifold vacuum at WOT, wich constitutes a serious inlet restriction.

Now lets convert this number for a lower, more realistic WOT pressure drop. Even the least sensitive of the the half dozen or so booster designs (Holley nozzle bar, in case you are wondering) we would be looking at in thisq application will accurately meter fuel down to around .7 hg", so lets be really conservative, and target .8 hg" as a realistic intake pressure drop. Now the math is gonna get a little more complicated here, but its a formula that ANYONE with ANY flow bench experience will instantly recognize (Of course, anyone with any flow bench experience, that thinks beyond the most superficial level will KNOW the formula is a crock and understand why).

So you take the original pressure drop, divide by the the new pressure drop, take the square root of that number, and you get your correction factor. So lets apply that to our example. 1.5/.8 = 1.875 x sq. rt = 1.369306393.... = 1005 cfm, or just about what you would normally see in a typical mild blow street application. Wow! Hey, about about that!

Ok, just for the sake of demonstration, lets go back, and apply the formula to a stock 350 chevy, apply a correction factor of .8 hg, and compare that to the 750 cfm of a stock Q-jet. Any guesses that maybe JUST MAYBE the GM engineers had it right, and a bunch of hambers mis-applying a bogus bunch of math might just have it wrong? Any takers?? Lets see what happens.

So we do the basic formula for 350 ci @ 5000rpm we get 506 cfm, times the correction factor to increase wot intake flow to a reasonable level, and Whoh! How about that??? 693 cfm, or right close to what the small q-jet flows. For the sake of consistancy with our earlier example, I used .8" hg, if I used .7, it would probably come out right at 750 cfm. Whoda guessed that a bunch of silly old GM engineers had it right, and a bunch of guys spouting off on the internet had it wrong???!! Will wonders never cease??

For the most part, I completely ignore "carb" threads on the HAMB, they always involve this formula, and the formula is such a complete crock, and anyone that would use it really has so little understanding of what CFM actually means, and how a flow bench works, that its honestly just not even worth arguing about.

How you get the "cfm" has a huge influence as well, and "the formula" doesnt even address that. If you can increase cfm by removing a flow restriction above or below the booster venturi, without increasing venturi size, the signal to the booster venturi with actually INCREASE, not decrease.

Different designs of booster venturis will meter fuel accurately at lower pressure drops than other designs, and by the same token, different booster venturi designs will also present more or less of a restriction to incoming airflow, and cause two carbs that are otherwise the same "size" to flow a different amout of cfm at the same pressure drop. None of this is addressed by "the formula" either.

The "optimum" carb for a given engine will also vary greatly based on intake manifold design, with a split plenum dual plane requiring a larger carb than a dual plane with the divider milled out, or a single plane. Again, "the formula" doesnt give a shit.

Some of you may think I am "grandstanding" or "showing off" here. Nothing could be further from the truth. I sit here day after day, and open threads like this, and see that stupid formula being trotted out again and again, by guys who really couldn't even accurately explain just what they are even talking about when they say that "you need a 650 cfm carb", and I just sit back and laugh, and move on.

Its honestly not worth the grief to attempt to straighten them out, because they really have no idea what that 650 cfm number means, how it was arrived at, whether its wet or dry, what pressure drop it was taken at, how much it would change if that pressure drop was changed by a couple points, how much effect a few degrees in temperature would have on that number, or if its just an advertising number. I responded to THIS thread because if the OP actually uses a 600 and DOES NOT boost reference the power valve, he will actually make enough manifold vacuum @ WOT to pull the power valve closed, and lean it out severely enough to shatter a cast piston and put a rod through the block.
TO BE CLEAR, boost referencing the power valve will NOT change the amount of manifold vacuum he sees @ WOT, it will only prevent the power valve from being pulled close by it.

 

Ya big showoff, George...lol. Seriously...that was awesome.

If I ever build a supercharged engine, you and I are gonna have a talk or three, pal.

 

Btw...while you're here, will you quickly address blower roll? I hate blower roll.

I read a good article years ago that talked about how to avoid it...but I can't remember.

 

This is the cam I went with on my 350, 7.8 comp, is basically a nitrous cam very cheap and effective, and I suggest a
msd 6al btm (boost timing master)and a msd coil and distrubitor . The carbs should work just keep the boost moderate like you plan you will have to rejet them tho. This is in my model A
Andy

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The whole post (with the exception of increasing volumetric efficiency to correspond with the amount of boost) is not blower specific, it applies to carb selection for naturally aspirated engines as well, and the pressure drop I would shoot for would vary based on booster venturi design, intake type, and the final use of the vehicle as well. The real point is, "the formula" is BUNK, and has no scientific basis. Its based on a false premise in the first place. I dont really expect to change any minds, and there are dozens of other guys on here that already know what I posted, chapter and verse, and just arent willing to waste thier time arguing with the guys who insist on trotting out this hoary old myth every time carb selection comes up. As bullshit old hot rodders tales go, I guess at least this one is traditional.
I've stirred enough shit for one day, I'll shut up and let them bandage up that old sacred cow, so some other guy can trot it out of the barn tomorrow. I promise I'll go back to just snickering to myself and moving on to the next thread.

 

Sorry, missed this the first go-around. Smaller IFR. You can go to a larger idle air bleed as well, but tuning the idle mixture through the air bleed also tweaks emulsion of the idle mixture. I prefer to tune right at the IFR. Depending on cam timing (BIG, SCARY LOBES!), you might not be able to eliminate it entirely. Carbs are probably better in this respect than mech. fuel injection. Personally, if the motor is raunchy enough, I kinda dig it. Nothing like a REALLY bad-ass blown injected old school, blackie carbon burner going uHHhuHHhuHHhu... Yea, I'm immature like that...

<iframe width="420" height="315" src="//www.youtube.com/embed/hjX3eXCpB_4" frameborder="0" allowfullscreen></iframe>Oh baby!

 

one sick ass motor in that boat!!!!!!!!!!!!!!



i'ld give anything to have an extra hemi that sounded like that for Lil Beast

 

One thing I did get wrong, I mis-read this post, in conjunction with Jacks suggestion that 516 cfm was sufficient for a blown 350, and thought the O/P was going with a SINGLE 600. I see he is using two, which is right in the ballpark for a virtually stock 350 with a 6:71 @ 5 psi.

 

George,

I would swear that you were on the conference call I had with the Holley / Weiand engineer! You and he were almost word for word in sync. I wish I had talked with him (or you) when I called the tech about the PCV connection.

The first thing the engineer brought up was almost as if he was reading the last paragraph you wrote about boost referencing, running lean and killing an engine. The Holley carb I bought was specifically designed to run on supercharger applications.

Guys like you make the HAMB what it is!

 

damn george that was some very good reading.
thanks for taking the time to wright that.
> saved as text <

 

For the start if you are going to build a different engine some time sooner or later I would leave the stock cam in it and change the valve springs and maybe put 1.6 rockers on it.
Save your money for the real blower engine.

You will be surprised how well a stock engine will run with some boost.

 

"Smaller IFR."

Oh shit. I had to look up IFR.

I see...you'd need a smaller

Instrument Flight Rules. Nah, that can't be it.

International Financing Review. Nope.

Institute of Food Research. Ummmm...probably not.

International Federation of Robotics. That must be it.

Cool. Thanks George!...........................................Crap!
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Wait...there's one more. Idle feed restrictor.

 

Thanks for all the replys. Thanks for the explanation George.
I wish I had the $ right now to build an engine like that boat! Wow!
Might have to overcam mine just to make it sound tuff.

 

Chief on you crank case ventilation I always suggest a vacumm pump. I know it sounds extreme but a street motor really sees more extreme than a 1320 bandit when you get right down to it. one can be done very cheaply with a junkyard smog pump off of a '70s Ford.

I know that this is off topic for this thread but the question has arisen. Sorry fellas.

For ignition I am pretty much a mallory guy, but I have set a couple up using a mallory and an MSD box ( I don't care for the mallory ignition boxes) even an old points distributer works well with the MSD box. You can get MSD boxes reasonable with stepped retard and use a boost referenced switch to step your retard. Works really well on the street.

 

Not off topic at all. I will take all the blower advise I can get. I don't know anyone local that has ever been around them.
How hard will it be to come up with a tv cable setup for the 700 r4, for the sideways dual 4 setup?
Does anybody run an od trans behind something like this or am I just a fool?

 

No, it really is #4, that International Federation of Robotics is WAAAY too big...