Technical BBC BLOWER , SUPERCHARGER SPARK PLUGS, AND HOLLEYS

Trying to figure what is a good plug to start with for a base setting ? And also my holleys I bought used and were setup for a blown jet boat. Trying to figure out a good base to start with for the carbs( jet sizes, power valve sizes, squirters size) The plugs are black, and the motor takes all the gas I give it no hesitation , just loads up at idle. Motor specs;
BBC 427
671 WEIAND
aries blower pistons 8.5 to 1
6lbs. of boost
merlin rectangular Grumpy Jenkins heads hogged out
Big hyd. comp cam for supercharger
2 750 holley double pumpers, no power valves and billet metering plates
Vertex magneto plug gapped at .018
Here is me driving the car in the garage.
http://api.viglink.com/api/click?fo...www.facebook.com/video.php?v...20232877061644

 

Run a power valve on the primary side of carbs. And hotter plugs, two steps hotter maybe. And some fine tuning . My plugs get a little dark when idle around to much, but clean right up when driven a little. Has never fouled a plug. Just some suggestions only.

 

I'd start with stock jetting, etc on the carbs. I don't know about mags...does it need that small of a gap to idle?

Which plugs probably depends a little bit on the heads, I would not run hotter plugs though. It sounds like it idles ok, you can play with the idle mixture...if it's surging/rolling at idle, then it's rich enough. If you lean it out and it stops surging/rolling then go back a little richer so it just starts again, it is probably where it should be.

 

The plugs I was thinking about trying out ( a suggestion I found on another forum) were NGK BPR7ES ?
On a mag I have been told to run around .018, same gap I'm running in my boat to with a mag. Sounds weird compared to if you had an electronic ignition

 

Vertex Mag says .018 to .036 on plugs, I would open them up some. Colder on plugs, like squirrel says, is better than hot till you get it sorted out. I have dual Holley 750 on a Willys in the shop, set up by BDS. You could call them and ask what they set their carb jetting at.

 

I would restrict the idle passage in the metering block to lean it out, it sounds like (no hesitation) that your accelerator nozzles and pump size are about right. Jetting will not change your idle too much, only driving.

 

Will try gapping plugs at .028 and see how that works, and put my power valves , and also need to drill my Cragar intake for a vacuum port

 

How do you restrict idle passages? different size plugs, if any?

 

Can you kill it with the idle air screws? If you can't then I would restrict the idle passages with some wire, I don't have a pic.

 

If I remember correctly, it will die out when I close the screws, but will check, thanks

 

Are you running a fuel pressure regulator with return line on tank? The needle and seats can only take so much fuel pressure ..................................................................

 

Running just a Holley blue and regulator, set a 6lbs, no return line.

 

Magnetos unless they are pretty extreme (think top fuel here) normally run a tighter plug gap than a hot distributer. I am not familiar with the mag in question but I would think it would run a wider plug gap that that. I used to run 18-22 on my bike but I was kick starting it.

Also any engine that is built to rev will soot the pugs at idle, or lower RPMs, with the exception of an EFI motor which can make adjustments on the fly. if they will rev that will have a tendency to run fat @ lower RPMs and if they run clean @ lower RPMs that have a tendency to lean out @ full song.

That said listen to @squirrel with carb suggestions and the other fellas that are running blower motors every day they pretty much have a good handle on it.

 

I'm assuming the OP is running a Vertex OAC (internal coil) mag. I've always been told the reason for the tighter (point / plug) gap is to eliminate spark arcing inside the unit and plug wire cross firing. Gives it a more "direct path", so to speak.

 

Well that could very well be but the reason most of us keep them tight is the weak spark at cranking. A magneto makes more spark as revs build and at low RPMs ( like when being cranked) they won't jump a big plug gap.

 

I'm assuming that you already know, but with the power valves installed in your Holley carbs you will have to do the carb mods to boost reference the power valves.

 

Supposedly they were blower carbs(used) I did not have the vacuum lines run to boost reference the carb(I didn't want to pull it apart to drill a vacuum point in the intake) Will be doing that now Also a buddy told me to pull the power valves out and go up a couple of sizes, that didn't work, So I really did not know what has been done to the carbs, just trying to get a good base to work from again. What size power valve do I need to start with yawl ? Any plug recommendations

 

6 psi boost, you really don't need to do the boost reference thing, you can get away with stock jetting and power valves. I only say that because I did it for 100,000 miles + with a street driven 6-71 blown 454 running holley 650 double pumpers.

If you want to know what's really happening, put a wideband O2 sensor on the car.

 

My combo is a bit different but I'll put it up for you for reference. I'm running a stroker big block Ford with a 6-71 @ 7psi. Relatively small .600 lift flat tappet and SCJ heads. NGK 8's. Twin 950cfm holley HP 4150 blower carbs. 80 jets all around (I am a mile high FWIW). No power valves anywhere. I'm not using the boost referencing built in. I'll explain why it didn't work for me. Its a larger ci motor with an efficient aluminum radiator that needed to fit within the confines of the '32 grill shell. Even with a 55 gpm electric water pump she'd climb in temperature in summer NM traffic badly. Simply not enough surface area in that radiator to pull enough heat from a blown stroker motor. Tried different thermostats, shrouds... no real help. With power valves, my primary jetting was smaller. Removing the pv's meant upping the primary jet size by roughly 8, fattening up the lower end of the fuel curve considerably. Down went the temps. The creeping temps in summertime traffic immediately got under control. You just don't want to let it idle forever without whacking it to clean off those plugs. My experience anyhow. The car also hits much harder and more consistent setup how it is. My combo likes the fuel curve fat on the bottom no doubt.

 

OP, If you want a starting point on the Holleys I have a book with what they started life as. I would need the list #ber to look up. Just beause they were already on a blown motor really means nothing at this point. You need to take it for a 10 mile run and check plug color.........................................................

 

Thanks for the pointers

 

Thanks will get it

 

Min runs warm to, not sure if it is the cheap eBay radiator or the setup, Just got to unearth the coin for a custom radiator

 

When running the Vertex mag, set your point gap at .020 to .022 - is how we run all of them. How much advance do you have in the mag . . . or is it locked down? You'll need to be careful with your total advance - I'd probably start with about 32 total degrees.

On the plugs, I'd go with about an 8 or 9 heat range (NGK - the higher the number, the colder the plug). The power valves won't be open at idle anyway, so that isn't your issue related to loading up. As noted by others, you probably need to have the carbs setup for your application - will make a world of difference in how it runs. You should try to get a 'return bypass' style fuel pressure regulator - don't run the 'dead head' style . . . you want a return line back to the tank to get accurate and consistent fuel pressure. Also, the fuel pressure regulator needs to be boost referenced as well - same issue as the power valves. Take a look at an Aeromotive A2000 or a Weldon A2040-281-A-15.

 

With all do respect B&S the power valves can come into play IF they are blown or IF manifold vacuum is lower than rated power valve. Yes I understand OP has no PV's installed just stating for other readers!

 

I can think of a few good reasons to run a return style system, but it's not necessary. I don't have one, and the only issues I've had that the return system might help would be the heat soak thing that my 55 did with the blower on it. But it's even worse without the blower now, so I don't see how having a blower makes much difference there.

With a blow through system, where the air going into the carb is pressurize, you would need that. This is nothing like that...it's a draw through system, the carbs only see atmospheric pressure, so you don't need or want to regulate fuel pressure with boost reference.

 

Thanks everybody, I like pointers, I do it all myself so everybody's opinion helps out, again thanks with response

 

The wide band 02 sensor takes all the guess work out of it.
It so much more accurate that it's almost not any fun anymore.
It tells you where you're at, all you need to do is figure out what to change. Who cares where it came from the factory.

 

Actually, with carbs, the O2 sensor just makes my head hurt

It's amazing what the numbers are on a carburated engine, that runs just fine.

 

I'm a big believer in referenced power valves. Let's you go lean and happy at idle and cruise with full enrichment at pretty much any measured boost. With air/fuel dialed in there should be no surging or loading up at a stop. A good place to start for jetting, PVs, squirters would be a factory Holley blower spec (0-80573 ?) with maybe a couple size bigger jets to be safe, #31 squirters front and rear and a lower power valve to match the choppy cam. Could also call someone who deals with blower builds regularly, never dealt with them but a place called Big Al's Toybox advertises all kinds of blown crate engines regularly. Probably a ton of blown 427 dyno info on the net too.