Love/hate my 406

[85montemj]

I have a 406, 10:1 compression, mild to aggressive cam, blue print and balanced, all aluminium 4 core rad with dual electric fans, weiand aluminum intake, accel distributor and a edelbrock 600. The motor was originally a short track motor my dad used to race on 113 octane. I've been having some serious problems with pinging. I run 93 octane and it doesnt help. I know the small carb isnt helping(it was on the 350 i had before) but i dont know whats causing it! It runs about 180-195 so its not too hot. The pinging tends to go away once its over 3500 rpms, but cruising or under mild loads its unbearable. It also wants to stall once hot at stop lights and when slowing down pretty fast. I'm thinking ignition? Alternator maybe? PLEASE give me any ideas. I'm tired of this thing.

 

[khan0165]

if you're dad was running 113 octane, I bet you he had it tuned to 38-39 degrees advance...
... dial the advance down to 34-35 degrees total @ around 3500rpm... or roughly 18deg advance at idle.

Run a 750-850cfm carb. In the mean time, re jet the carb to give it more fuel on the primarys, and retune your idle mixture.

... what do your plugs look like? Running cooler plugs will also help. Look up the OE plugs recommended for a sbc 400, and go 2 or 3 heat ranges cooler.

when the engine is up to operating temperature, use a squirt bottle to spray some water thru the carb. The steam will wash the carbon build up in the chambers. Spray about a half cup of water, slowly without letting the engine die.

And check your valve lash... is it a hydraulic or solid cam?

 

[crotchss]

What cylinder heads are on it and what pistons, flat top or dish? Also check the timing to make sure it's not locked.

 

[85montemj]

Its a hydraulic cam and flat tops. I havent adjusted the lifters since may when we dropped it in. All of those ideas sound really good!! i still have the original plugs that they had in it but i put new ones in(what we thought were the most similar) . But ill look up some cooler plugs. I am going to be buying a new carb in the next week. I've just been putting that off.

 

[UMI Sales]

Do you know the cylinder heads or combustion chamber size? With flat tops it could easily be higher than 10:1...

Sounds like a fun engine!

ramey

 

[85montemj]

I forget which number heads they are. They are decked though. I dont know the size of the chamber either. The motor was built in 91 (before I was born haha) and my grandpa and dad both forget all of the specs.

 

[crotchss]

Are they a oem cylinder head? If they are they could be a 64cc chamber and that will make around 11.2-11.5:1 compression, depending on how far down in the hole the pistons are. If they are a 76cc chamber you're looking more at 10:1 for compression. And don't forget to look into that distributor and make sure it's not locked in, check it with a timing light it should move up with rpm, if it's not locked.

 

[85montemj]

Like i said, its brand new, and yes its not locked in. It definitely advances as far as it should when the rpms go up. But good call, I never even considered it.

 

[khan0165]

you mentioned your dad used to run 113 octane, probably for racing... And the heads are decked.
... this is sounding more and more like a drag motor, with lots of timing advance and big fuel demands.

like crotchss mentioned, check to see the dizzy is not locked on full timing. This is a common practice in race motors, locked out timing, and lots of timing advance. It works with high octane, but not so good with pump gas.

I recommend a good dizzy, something like a Accel HEI if you're on a budget... or MSD system. Being a nice torqy motor, very light rotor springs will get you a quick timing curve.

on pump gas, and high compression 34-36 deg advance is a good base for most sbc motors... you may need up to 38.
... and you don't wanna bring that much advance right off idle... you can play with spring stiffness to bring it in quicker or later...

my 350 is at 34deg total, all in at 3700rpm with medium stiffness springs. That seems to keep my motor happy with 10.5:1 on 91 octane.

you'll need to play around to see what your motor likes. But keep in mind, if you want to run lots of timing advance, you need to consider colder plugs and higher octane fuel... Iron heads shed heat slowly, so keep that in mind.
Look at your spark plugs... if colouration is too far down the ground strap, it means too much advance... if colouration is too close to the tip, it means not enough advance. You want the colour right at the bend of the ground strap. That will tell you your plugs are getting perfect timing and they are shedding the heat quickly enough.

depending on the cam, your motor may not like anything under a 700cfm carb... and it'll ask for even more at high revs.

 

[85montemj]

Like i said, i have a brand new accel hei. But thanks for all of the advice!!! i'll give it a try once i'm able to.