The run down.
I put on a set of the old 291 casting heads, with Comp Cam 286H. I developed a tick/ rattle shortly after only after it was warmed up.
​​​​​​When I use "we" I'm talking about machinist that put in the guide plates and hardened seats.

we seemed to believe that it was probably an exhaust leak (summit named brand gaskets).
I ordered a set of Mr. Gasket copper ones. Checked and rechecked valve lash, hot and cold.
The tick/rattle still there.
Then 8 months to get ready to deploy and then a 10 month deployment. (No time for car)
We changed the lifters.
The tick/rattle still there.
checked valve lash again.
I changed the header gasket to remflex
​​The tick/rattle still there.

​​​​I branched out. I talked to the wisest machinist I could find out the area. A rather older gentleman who was brash and blunt. Based on the sound in the video is the machinist did something wrong with putting in the new seats and probably a cracked valve guide, he also mentioned the machinist probably knew he messed up and sent me in circles and to get the head off because he knows me and knows how I'm very meticulous with engine work and based on the work done it has to be the head. I'll have the head off by Monday I'm hoping. I'll have the head to a a guy in the next city over for him to scour it for problems.
http://s864.photobucket.com/user/mlowe6417/media/VIDEO0193_01_zpsdaxc5q1i.mp4.html

 

In 1966 I had a tick that came up one day. Thought iy was a over rev thing an that the ball would seat. (hydraulic lifters). I did all the tricks with my hand over the rockers and adjusted the valves but still had the tick.
Finally changed the lifters and inspected for a broken valve spring, NADA, all springs were good and new lifters adjusted well.
I was stumped, then remembered that there is one more lobe on the cam that drives the fuel pump. I pulled the fuel pump and found a broken spring on the arm that was causing the tic. Took a spring off another pump and tic was gone.
Shot in the dark but worth looking into.

Dom

 

I've posted this before but my go to for pinpointing the source of noise is a 4 ft. section of 5/8 in. garden hose.
Cup your fist around the listening end, ear plug in the other ear...probe around to find the source. I've used a small elbow on the probing end to check vertical hard to reach places. This is obviously no good for deep internal noise but works surprisingly well to either pinpoint or put you in the area of the noise.

 

I found the noise, one valve guide was definitely either missed or not even looked at it is as loose as it can be. Can't even get a suction pop by the old valve pull and finger over hole. All the others are like new as I would expect with 1000 miles. It was a hard noise to pin point I have used a stethoscope, hose, screwdriver, piece of wood but nothing was definitely narrowed down.

 

It's been awhile since I've posted on here, since my last update to this thread, many things have been going on. The cylinder head problem was so bad that metal from valve banging around in the guide had entered into the cylinder and scratched the wall significantly.

I moved on quickly and started building an engine I have always wanted. A aluminum headed,roller cam, 406 sbc. I sourced some parts from this forum, some from machine shops and of course jegs and summit.

I found a good 400 (511) casting 4 bolt main block already .030 over. I'm using speed pro forged flat top pistons, 5.7 rods, and a stock 400 crank. ARP main studs and rod bolts. Lunati roller cam and lifers (conversion style) AFR eliminator 195 heads, ARP head bolts, lunati sportsman pushrods, comp cams 1.6 roller rockers.

I'm not planning on abusing it but some spirited driving of course is in the plans. I'm just about done, installed the shortblock this weekend and got the heads torqued down, I'm re using my weiand stealth intake manifold and Holley 750DP, and the MSD Pro billet distributor.

Should be a lot of fun, I'll update a video once complete, of course I have a ton of pictures I'll sort through and get posted as well.

 

For street use I highly recommend using a 600 cfm vacuum secondary Holley to limit the amount of throttle opening at low rpm. A 406" can only swallow 591 cfm at 6000 rpm with an 85% volumetric efficiency so a 600 cfm Holley would be ideal and it would provide the best throttle response at all engine speeds. The biggest mistakes people make are selecting camshafts that are way too hot and carburetors that are way too big for their tall rear end ratios.

For street engines the carburetor manufacturers have always recommended 1-1/2 cfm per cubic inch of displacement so going by their recommendations a 406" would require 609 cfm for wide open throttle/high rpm usage. Not big enough you think? How often does ANYONE run their engine at 6000 rpm and for how long? One second every week? As street engines spend about 99.99% of their time running at 1500 to 2500 rpm extra large carburetors just aren't needed.

To further illustrate my point here's the actual cfm consumption of a 406" engine at various engine speeds at an 85% efficiency (the ability to fill its cylinders):

1. 3000 rpm would only consume 304 cfm

2. 4000 rpm would only consume 394 cfm

3. 5000 rpm would only consume 492 cfm

4. 6000 rpm would only consume 591 cfm

As the C3 TH350 and TH400 automatic transmissions will force an upshift at 4500 to 5000 rpm your engine would never even reach 6000 rpm unless you manually held it in gear to delay the upshift. And mechanical secondary carburetors should never be used with automatic transmissions in street use unless the engine's displacement is very large and the carburetor's cfm is very small. If I recall correctly the 410" Mercury in the mid 60's used a mechanical secondary 600 cfm Holley for a couple of years but that was an exception.

 

You will love the 406.......

Jebby

 

its going to be an animal at any rpm
normal driving he can get by witha 600 but iwth modern heads he will choke if hes on it. Id get a 750hp todays carbs are very nice can fine tune them even wlth a lumpy cam
Sprung for an AED done just for this particular car with 82 deg of overlap its every bit as responsive as you couldhope for. Who says an 850 is too big for the street.


op your issue is common, to take an old setof heads and do them up right takes well over 1k not many guys willing to do it nor machinists willing to put the time in. Too many guys hope "a cheap valve job" maybe some seals will get them by its rarely the case those heads are just too old. If the guides are worn kiss that valve job goodbye nothing good comes of it.

 

I agree with the O.P. and cusinart about the bigger CFM. Not sure who came up with that volumetric efficiency formula and I know its used on Holleys web site, but it always seemed a little conservative to me. A modified 350 received a 500 something cfm. Yea right. Maybe the formula is too old for modern day heads & cams? For one thing a company does not want customers returning carbs because their mpg went from 18 to 12. So, someone might estimate CFM a little on the small side. A 650-750DP will rock with your setup, lowes-yellow.

 

Agreed on carb size - Don't choke yourself with anything less than 750cfm on the 406. Remember that most of our cars started with (or are still) being supplied air and fuel with a 700+ cfm Quadrajet with only 350-355 cubes. You will love the off-idle torque of that 406!! Good Luck with completion of your project!

 

Do you have an online calculator somewhere or can you "show your work" on how you obtain these CFM #'s given engine size, RPM, & VE?


Adam

 

He's not making it up, the link below is a typical calculator where at 85% VE you get those numbers. I'm not saying they are correct in the real world.

http://www.gtsparkplugs.com/CarbCFMCalc.html

 

I didn't think he was making it up; I totally believed him. I just wanted such a calculator/ calculation to play with myself.

Although not applicable, to carb-based engine builds, long-runner intake builds (TPI, Cross Ram, etc..) can achieve well over 100% VE at their peak torque RPM (EA Pro estimates my engine's peak VE to be 110.5% @ 4,500 RPM) -I'm guessing that the max airflow will still be at my HP peak of 5,800, though, but I'm interested to play with a calculator to see. -Helps with throttle body selection, anyway.


Adam

 

Modeled a 383 with a FIRST intake and cam with a torque peak of 4,500 rpm and a VE of 110.5% and ended up with 675 CFM. (617 CFM on a 350)

I have no idea what the engine VE is at 6,000 RPM; but if I go with 85% and the 383 combo it's 693 CFM so the HP peak still flows a little bit more air than the torque peak, even with a 110.5% VE @ the peak torque RPM, so using the HP peak seems like it DOES work even in the most extreme attempted counter-example. It is pretty cool to see these long runner intake's pushing ALMOST as much air at their torque peak as at their HP peak, though; intake wave tuning is so awesome! Like a "free" 3 PSI supercharger that only works in a 500 rpm range.

I likey!


Adam

 

Remember...4 BBl carbs are rated at 1.5" vacuum for standardization purposes. If you want to run your engine at the edge of strangling....and especially with a vacuum carb that may not open all the way....have fun.

Just don't be surprised when your buddy walks right on by you because he didn't go super conservative on everything. Can't tell you how many times I've made tremendous changes in performance by selecting the RIGHT carb vs the calculated carb.

Mechanical secondary carbs only get worse mileage because people enjoy playing with the extra power. Driven normally they will do fine. Vacuum carbs allow you to push harder on pedal "thinking" you're doing something but the carb holds you back.

Now ay I'd have less than a 750 on a 406....even a mild one.

You're putting together a nice combo that will be fun as heck!

JIM

 

The calculation seems to possibly be overly simple, no?

I just realized it doesn't look at piston demand for air at all; wouldn't a bigger stroke to bore ratio motor have significantly faster piston speed and therefore air demands at lower RPM than a shorter stroke to bore motor of the same cubic inches?

The calculation bases CFM #'s on RPM rather than piston speed (which drives the actual CFM demand).

I've heard it stated that F1 engines spin up to 20,000 RPM, while Nascar engines spin at roughly 9,000 RPM max, but both have roughly the same piston speed at their peak RPMs. You could build 3 different engines with the same displacement, but hugely different requirements for air at 6,000 RPM. The calculation might be "good enough" for typical engines and speeds, but I feel like using a tool like PipeMax that is going to generate the actual piston demand seems much more accurate / "safer".

Any thoughts from anyone with far more experience than me? (Because I have pretty much zero actual experience here.)



Adam

 

You're reading way too much into this. Let the O.P. pick a carb and slap it on. Either its a dog or a screamer.

 

Thank you to All, I ran the 750DP on the 360 SBC with the old worked over 291 heads, it did "okay". I had a 750 vacuum secondary originally but when I did the 4 speed swap I had nothing but stumble issues, I pulled it apart and changed throttle steps and vacuum secondary springs more than I ever want to again. I swapped it out for the DP set it to specs as per Holley except for a orange accel pump cam and it pulled hard no matter where I put it. I have learned a lot over the years from this forum, and enjoy spreading any all information I know as well. I did look at the carb size for engine size and my conclusion was even if they are talking about a worked over vortec head that flowed 180CC on the intake side the AFR 195 heads would be more than willing to take the added CFM. My compression is not ideal 12.7.1 as per piston,head gasket and cylinder head CC but for the summer car a nice sunny winter days ill get the higher octane as required.

I think its gonna break some hearts.

 

He's back, Toobroketoretire !

 

And his credibility is still uncredited.