Technical Breaking in an engine with a blower.............

I'm gradually accumulating the parts to build an engine and would like to use a blower on it. I have a used 6-71 that needs to be converted. Seems to be in pretty decent shape and spins freely. There is also a new Weiand 6-71 available that a guy bought and didn't use. If I go either route, I will have to do some fabrication to get one to fit the engine. Its a 500 Cad.

Parts for the Cad are "somewhat more" to "a lot more" expensive than a smallblock and harder to get some of them. So, if I continue along the path to installing a blower, I don't want to mess the engine up with overtaxing it right off the bat.

I'm thinking that I'd be better off doing the initial break in naturally aspirated (on an engine stand) initially. Maybe a few hours of assorted rpms and cooling periods. Then if everything seems fine, install the blower and take it to a dyno for final test and tune.

What do yall think?

Any reccomendations on the used GMC vs the new Weiand ? Appx cost to have an experienced someone rebuild the GMC ?

 

I like the GMC over the Weiand unit because of the three lobe rotor design...I didn't do any special breakin but I did keep the static compression at 7 to 1.... This was on a early 392 hemi...

 

Never run a blower, agree that breaking in NA would be safest plan.

Reduce the variables to get clean fast start up and break in.

Go drive it around NA, work out the bugs, then swap blower on.

 

On my sbc, with 7.5 boost, I did not do anything different than when breaking in a carb
motor. Never developed an issue. Blowers and all the accessories always seem a
bit mysterious, but they are pretty simple in the end. I did overfill my front bearings some,
and had some oil spray on the front of the motor, but an easy fix.

 

It only makes boost when you open the throttle enough. 99.98% of the time you're driving a Roots blown car, there is vacuum in the intake manifold. Which means that breakin is no different than any other engine.

and yes, I pulled the number out of my ass, but it should give you an idea of how it works.

 

But it's a nice number lol. Using a Jimmy blower on a gas engine is far removed from it's original application on a Detroit Diesel, which has no intake valves and is totally dependent on the supercharger to breath in 2-stroke fashion thru the ports in the cylinder

 

I spent some time on Drag Week explaining the 71 series diesel to some younger folks....and mentioned that it's production run was from 1938 to 1995. Rather mind blowing.

 

The inline 6-71 in particular was all over the place- trucks, marine, gensets- lots of fishing boats. I used to have a '51 GMC truck tractor with a 4-71 and 5x3 with a little peanut muffler on it- HOLY SCHIDT WAS IT LOUD. Pretty simple design, decent economy and performance- just NEVER run one out of fuel

 

Have all your ducks in a row. Set up for quick start, and break it in . You are not going to make boost on a engine run stand. I broke mine in installed in the coupe. Normal break in procedure. And no problems did I experience.

 

That is one of the great parts of the FE adapter plate that lets you run a 351C intake on an FE- you can put on a simple 1x4 with a proven carb and light it off, then easily swap on your 2x4 tunnel with no intrusion into water or oil, no re-adjustment of valves etc

 

Pun intended?

Lynn

 

I thought a roots blower made pressure from the second it starts turning and creates more as it increases in rpm. A turbo has to be spooled up to create pressure.

 

I have no experience with supercharged gasoline engines, but have overhauled over 100 turbocharged engines. Breaking in a boosted engine, gas or diesel, is no different than a naturally aspirated engine. Granted, the turbocharged engines I work on are designed for boost, but like Squirrel said, you won’t make boost unless you open the throttle far enough.

 

Well, yeah, it does create "boost"....but it is still a vacuum relative to atmospheric pressure. For example, you might see 10 in vacuum in the intake manifold below the blower, and 20 in vacuum at the carb adapter above the blower, at idle. You have to open the throttle to let in more air, and put a load on the engine, to get positive pressure to build in the intake manifold.

 

Just put a big pulley on top and break it in like normal, hit a few heat cycles for the rings and don't worry about putting it on a dyno.
Here's a video of one of the heat cycles on mine getting broke in

 

here's a video of one of mine getting broken in

 

A friend of mine ran a blown 500 ci caddy in his Austin drag car, it broke a lot, so much so that he abandoned the caddy and went to the cheaper more reliable big block chev.
That's why I said don't dyno it, no need to test the bottom end with the stress of a dyno.

 

Just broke in a BBC with an 871 on top. Not much different than any other break in I have done.

 

Pretty much has a lot to do with the type of cam . Just like any other initial start and run.

 

Just a technical question. Can you “break an engine in” not under a load?
I’ve ran a couple fresh builds on engine stands. Put several hours on em. But the exhaust temps were different from the stand and in the ride. Much lower on a run stand than after driving
Just curious

 

Not completely, because you can't load the rings effectively. But It's a start, and it will make leak checks, timing and speed changes easy.

 

Squirrel is right, a blower isn't some mystery piece, it just moves air. The type of running you do initially should produce no boost. If you haven't driven a roots blown car, you'd be amazed at how little time the needle crosses into the positive side. Of course as soon as it does, You get so busy steering the thing, you stop looking at gauges!

 

I was all set to build a Cad 500 for my Stude, but at the time (2005) intake manifolds were $1,800, so I went 454. I think a 6-71 is too small, but if you want about 6 lbs boost and a mild cam/head, it will be ok. The Cad is great on a budget at initial buy-in, and if you want to keep it stock, you're all set. However, putting a blower on it will cause it to gain RPM very quickly, and then all the shortcomings become expensive to fix. (valvetrain, oiling, piston/rod).

 

oh yeah.

Mostly the only time I see boost for any length of time in my Chevy II is when I'm running down the quarter mile, wide open. It gets up to 135 in ten seconds. That keeps me busy...sometimes I quickly glance at the oil pressure gauge, but my eyes rarely make it all the way over to the boost gauge.

 

Is this a flat tappet cam?

 

don't mean to hijack the thread but the Ybloke's 4-71 Y block blower intake has a dual pattern.

you can run the 4-71 or just bolt up the carb adapter plate from on top of the blower straight to the intake to break it in without the blower. based on what everybody is saying, break-in with a blower is no different than a normally aspirated motor.

now if i was just running a single four barrel atop the 4-71, i'd be tempted to break it in with the blower. but i have to be stupid and run four strombergs on it. i'm thinking break in the fresh build on a single four barrel, then switch over to the four 97's and once they are dialed in and sync'd, slide the 4-71 in and do the final tuning.

what are everyone's thoughts on my plan?

 

That sounds like a good idea. If you're just running an AFB or a pair of them, not much can go wrong...but four Strombergs...hmmm

 

i do have a pair of 400 cfm AFB's but am still looking for that elusive weiand 7161 carb adapter

 

What you are saying is pretty accurate. I had a 365 Cad with 2x4s in a 33 Ford when I was younger. Interesting story was that the motor was originally stolen. The bold thieves stole the car, removed the motor and then returned the car to its original location. They even had a picture of the owner in the newspaper........standing in the empty engine bay. I aquired the car/engine years later and wasn't involved in the theft. Just learned about it from the older guys who knew the real story. Anyway, always had a soft spot for Cads and want to build something a little different.
Yes, the buy in price for a 500 Cad is usually dirt cheap and they make great truck engines. First thing needed to upgrade them is some good rocker arms, and I bought some Harland Sharp roller rockers, and Johnson roller lifters....and have a Howards roller cam on order. Have professionally ported heads with larger valves to go on it. Forged pistons and H beam rods for the lower end. The cranks and blocks are pretty durable from the factory. A few small mods to aid water and oil flow in the block and probably a high volume oil pump. Ignition will be by a crank trigger set up. I'd like for it to make 500 hp but even ported heads don't flow like many of todays replacement heads. So, at the least I expect it to make over 450 hp.
If I add the blower, I'd like to make about 600 hp.........I figure thats about all thats actually usable on the street. I have the tools and experience to assemble the engine and get the tolerances where I want/need them, but using a blower is new for me. I have a Boogieman single plane intake that I will make an adapter to mount the blower on and there will be some custom machining (done by me) to get all these things to work together. Also, plan to adapt a Rattler Vibration Dampener (from a Chevy) to it along with the crank trigger.
It will be a time consuming build, so I don't want to overlook anything in the build and break in process.

Thanks for your input.......

 

Well if it's a roller cam, there's not much break-in to do.
Isn't a 460 Ford intake a easy fit to the Caddy engine?