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Topic Review (Newest First)
08-14-2012 07:27 AM
Cridder
poor man's racing heads

[QUOTE=hotboy454;1582207]@f-bird88 I know this topic is about 2-3wks old. You mentioned something about poor man's racing heads. I was breaking down a motor this week 400sbc in. The casting number was block 3956618 & heads are 3932441 what info could you give me on this. I know you said in a comment back that porting these heads on a 400 would scream. QUOTE]
at one time the 441s would have been a score, i built a 11 to 1 400 with heavyly ported 492s (simler to 441s) for my super street stock and it did scream. I ran around there at half trouttle till the idiots had crached themselfs out and then when there was just 6 of us left i could open her up, get the rears just smokin hot.
Rebuilding those old heads is hardly cost effective today, they dont have the hard seats in them ether the exasut seat is gona wear if it ant worn out already.
08-12-2012 09:30 PM
cdminter59
3956618 & 3932441

Check out nastyz28.com forum they have the block and head casting numbers. That block could be a 69 302 4 bolt main, 69 327 2/4 bolt main, 69 350 2/4 bolt main. Measure the mains if 2.3 it's a 327, 2.45 it's a 350. The heads could be 67-72 327 or 350. 1.94 intake valve, 1.50 exhaust valve. Then it also has them listed as 67-79 76cc chambers. I also saw another site if they have the steam holes and have 1.94I & 1.60E they could be a 400 head. Check out 3932 441.
08-12-2012 09:19 PM
cdminter59
400 sbc

I have been following this thread. I read that you said you has 15 inches of vacuum before it backfired. You also said you replaced the old power valve with a 4.5 power valve. To get the right size power valve you take a vacuum reading at idle and divide it by 2 and replace it with the closest number to your reading. EX: 15*2= 7.5. Summit racing list 6.5 for the 600 cfm. While you had the carburetor off you should have backed off the curb idle screw. About .020 of the two slots in front of the primaries should be showing. Next you would need to setup the distributor If setting the initial timing at 20* you will need to set the mechanical advance at 16* max. Do a search on here about setting the mechanical on a HEI. This is with the vacuum hose off and plugged from the distributor. So you have 20 initial + 16* mechanical = 36 total. Now you ready to fire it up and make adjustments to the carburetor. Hook up a vacuum gauge to a manifold vacuum source and adjust idle screws until you get the highest reading. To check the total timing set the dial at 34 and check timing. it should be reading close to 0 on the scale if you have everything set right. You asked about the springs on the dizzy, yes you can use 2 light springs so the timing is all in by 3000 rpms.
08-12-2012 01:18 PM
hotboy454
400sbc

@f-bird88 I know this topic is about 2-3wks old. You mentioned something about poor man's racing heads. I was breaking down a motor this week end that came out of this 73 c-10 short bed before I put the 400sbc in. The casting number was block 3956618 & heads are 3932441 what info could you give me on this. I know you said in a comment back that porting these heads on a 400 would scream. I was going to rebuild this motor as a street deal for my 73 vega any comment would help.
08-05-2012 06:01 PM
vinniekq2 the timing light only indicates the timing thats happening with or with out vacuum. 34 ish with out vacuum is where you want to be,or close to that.
08-05-2012 05:34 PM
hotboy454
400sbc

Ok but on the distributor it need the two med. Spring but which weights. On my timing light there is a 34 mark set it there and watch the pointer on the tab move to 0 degrees is what you saying and that will give me 34-36 timing and that's with the vacum advanced plugged
08-05-2012 05:26 PM
vinniekq2 you need to use a timing light that has a scale on the gun. set it to 34 then look when the light matches zero. or put a timing tape on your balancer. When I had no money I used to make a crayon mark on the balancer.
08-05-2012 05:14 PM
hotboy454
400 sbc

Ok I had a little time this week so I installed the power valve on the primary side 4.5. Then installed new spark plugs. Upon pulling the #3 plug it was arcking out on the hedders and I thought the sputtered was due to the backfire much smoother now. But I still need to recieve the distributor. And ill post up. How do you know when 34-36 degress of timing is met when the timing mark only goes to 18. And do I capp the vacum advance when doing so.
07-23-2012 11:44 AM
cobalt327
Quote:
Originally Posted by hotboy454 View Post
Yes both carbs were running.rich. it ran smooth.but not as.smooth as.it should.be. I change to carb to summit brand still the same thing. Exhaust black and gas through exhaust. My wife hates when I start that thing up it get all in the house and the smell on my clothes. We tried idel mixture screws.didn't change. Thing. I almost thought that it qW the carb spaced drawing to much fuel. Tried 3 sets of plugs all are dark within days. The motor was broke in many months ago. It just sat untill I took the motor out and put it in my truck. Now its being driven under a full load. Oh by the way that's Joe gibbs break-in oil not Hubbard. My phone tries to think ahead of me.
OK, I see. In any event, I usually try to sort the timing out first, THEN set about fine tuning the carb. But in this case it sounds like something is amiss, like the fuel pressure way too high, that sort of thing. I say that because you've had two different carbs perform basically the same way. Odds are against that happening, but just the same, unless they are known by you to be jetted stock or at least within reason, I would want to baseline them (or it) back to stock to eliminate that from being the problem.

Someone mentioned power valves earlier. If it's blown or the wrong number it could be adding fuel when it's not needed. If there's any doubt replace it w/a PV more to the middle ground like a 65.

Getting back to timing, you saying the idle screws do nothing tells me the throttle blades are probably open too far in order to get it to idle w/the initial timing set where it is. Having the primaries open too far is enough to cause it to run partially on the transition circuit. Fixing the timing by adding to the initial (which will increase the idle speed) while keeping the mechanical from adding TOO much will allow the throttle blades to be closed back down enough that it will be idling primarily on the idle circuit- and then the idle screws will become responsive again.

For testing purposes you can basically ignore the mechanical advance just for now. Add the initial timing, lower the curb idle screw setting, and see if that lets you get control w/the idle mixture screws and see if that improves the idle situation. You can even drive it that way as long as you are gentle on the throttle and don't romp on it. Keep the revs down and keep it from pinging by being gentle on it.

You can make a temporary timing tape if you don't already have a timing tape on the damper or a dial back timing light. That'll let you see the advance beyond what the timing tab can show you.
07-23-2012 11:16 AM
hotboy454
400 sbc

Yes both carbs were running.rich. it ran smooth.but not as.smooth as.it should.be. I change to carb to summit brand still the same thing. Exhaust black and gas through exhaust. My wife hates when I start that thing up it get all in the house and the smell on my clothes. We tried idel mixture screws.didn't change. Thing. I almost thought that it qW the carb spaced drawing to much fuel. Tried 3 sets of plugs all are dark within days. The motor was broke in many months ago. It just sat untill I took the motor out and put it in my truck. Now its being driven under a full load. Oh by the way that's Joe gibbs break-in oil not Hubbard. My phone tries to think ahead of me.
07-23-2012 11:04 AM
cobalt327
Quote:
Originally Posted by hotboy454 View Post
Break-in went smoothly. I used Joe Hubbard break-in oil no problem. The carb just ran a little rich even with the eldelbrock carb switched to a sumitt brand still the same. The carb was running rich after break-in. I just started to drive it under load since removing the motor del my project car to my truck. Three days under load is when the backfire through the carb happened. Started back up then the sputtering started. Looked at my plugs all of them are black and these are new plugs.
Could be nothing more than the engine needs some run time to finish breaking in and a new set of plugs will likely clear up the miss- although the root cause of the carb being too rich obviously still has to be dealt with. Did I understand correctly that both carbs ran rich, or was the engine running rough w/both but not necessarily too rich?

But, if you're getting an eye watering exhaust smell, that's unburned fuel from not enough initial timing, not a rich a/f mixture. So if that's the case, the odor will go away when the base timing is high enough. Now, that's not to say adding timing will suddenly make the carb spot-on. You still may need to fine tune it. And the idle mixture will need to be checked/reset after changing the timing, too. Set it to fastest clean idle or the most vacuum at idle if you have a gauge.
07-23-2012 10:50 AM
hotboy454
400 sbc

Break-in went smoothly. I used Joe Hubbard break-in oil no problem. The carb just ran a little rich even with the eldelbrock carb switched to a sumitt brand still the same. The carb was running rich after break-in. I just started to drive it under load since removing the motor del my project car to my truck. Three days under load is when the backfire through the carb happened. Started back up then the sputtering started. Looked at my plugs all of them are black and these are new plugs.
07-23-2012 08:02 AM
cobalt327
Quote:
Originally Posted by hotboy454 View Post
hello, I have a sbc 400 that i had rebuild 2 years ago it sat in a project now that I'm building a 468bbc for. I took the motor out and put it in my 73 c-10. This motor had 0 miles on it. far as i took it was around the block Since it been in my truck. I started to drive it to iron out all the bugs one day it backfired through the carb. then started sputtering upon acceleration idling it does fine but runs rich. I cant seem to get idel dialed in without it shutting off. 1100 rpm its where its comfortable at in gear 400rpm something weird there.
Hopefully it IS the timing.

The cam has to be broken in correctly or it can fail. If a lobe has worn off (along w/the bottom of the lifter in most cases), it can act how you are describing.

So, did you use cam break in lube on the lifters and lobes as well as break in oil or oil additive like ZDDPlus? At least 2000 rpm w/NO IDLING for the first 15-20 minutes? Details here.

If you suspect this may be the problem you can measure the lift at the retainer. Sometimes it can be seen by just removing the valve cover and checking for excessive looseness of the rockers. This is often (but not always) accompanied by a loud or ticking valve train, and it tends to not hold the lifter adjustment- it will keep loosening up on you.
07-23-2012 02:45 AM
Cridder
Power valves and back fires

Quote:
Originally Posted by hotboy454 View Post
How is the power valves causing it to run rich and making the spark plugs black? Also you can smell the gas coming through. Is the a indication of it running rich and needing to be netted to or just power valves and adjusting the idel mixture screws. Also the description for the cam said Cai idile with lope can't hardly tell. Elgin1015p cam. Or crane 274 h06.
When the the power valve is acted upon by manifold vacum it stays shut and no additional feul inrichment complemnts the jetted curcit.
A backfire if severe enough effectively blows the small diaphrame in the power valve, now fuel is drawen through the holed diaphram into the engine.
you can see the raw feul in the power valve cavety when you take the carb apart, this area is normally dry.
07-22-2012 12:14 PM
hotboy454
400sbc

Ok, I thought it was the jets. Because right after breakin that's when I noticedit running rich. Assuming that summit carb. Bought a edelbrock and it was doing the samething. I all by the recieve kit and in a few week look into the heads, vortex or something. But first I need to know what I have. I pretty sure raising the compression to a ponit or even a half a.point.with better flowing heads will wake it up. I'm almost considering having a dunk tune and let them calibrated everything.
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