Hot Rod Forum : Hotrodders Bulletin Board

Hot Rod Forum : Hotrodders Bulletin Board (
-   Engine (
-   -   400 sbc (

hotboy454 07-21-2012 09:39 PM

400 sbc
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. Looked over my build sheet from the engine shop i was given the wrong piston for one. I thought i had the flat tops for 10.1 compression instead i was given dished piston for 8.75:1 factory compression im running an elgin 1015p cam thats asking for 10.3:1 or less compression. could it be the problem causing ideling issues. It run like a champ driving it in traffic seem to want to die out with out keeping my foot on the gas. I'm looking in cranes 274 h06 cam how is it. I'll give you my parts list could you tell me what need to be fixed.

400 sbc
600 summitt carb
performer intake
stock factory heads for a 400 from a 1975 caprice
Elgin 1015p cam 224/234dur. @50 468/488 on 110 adv dur 290/300 10.3:1 compression 2,000-5500 rpm stock stall ok. Remember Im running 8.75:1 compression Flowtech headders 1 3/4 2 1/2 exhaust into flow 40 dumped. gear drive. forgot to mention 2500 stall conveter.

help me please solve my idling issue and sputtering while driving. Already purchased the crane cam and will replace all wires cap rotor and spark plugs any advice will help. thank much fellow hotrodders.

vinniekq2 07-21-2012 09:48 PM

more info please? how long did the truck sit? did you check the carb,pull a valve cover,check for vacuum leaks,old fuel?what kind of ignition? hei/points?

hotboy454 07-21-2012 10:24 PM

400 sbc
@vinniekq2 the motor sat in my in another project for about 1 1/2 years. I started it up twice a week maybe drive it around the block just to move the fluids around. I did check the carb it leak up under the 1inch spacer replaced the gasket no leak problem solved on that one. but it still run rich. I check the spark plugs for gap it was alright just black from it running rich and those plugs are new. I'am running and hei unit. The cap and rotor appears to be in good shape. I tried installing a new fuel filter changed to 91 octane with a little additives still nothing. The motor sat in my truck for 4 months. before i actually started to drive it. all was well to well i thought. every time i would go around a corner i couldnt keep the rear tires from spinning even on lite throttle. this is even with a heavy 20 inch wheel. even nailing this @2000 rpm even worse i would lay rubber with no problem. All fun ended with the backfire through the carburetor. If it was my guess i would probably say it was a power valve along with jetting for carb issue. Now ideling in stop and go traffic the just going from park to drive without the car dying or the hard bump from park to drive i just dont know. everything from the motor to the transmission is fully rebuild. I would love to drive it, its just i spend more time tooling than enjoy this truck. I ready to replace the cam, to carb. and hopefully that will fix it right up. But if you have any suggestions on what to do then i will jump to it readilly. Thanks once again for the rapid reply and sorry for writing a book.

vinniekq2 07-21-2012 10:32 PM

first thing I suspected was the power valve too.I dont know anything about the summit carb and was trying to get more info posted for obvious reasons.did you pull the valve covers,did the distributor move,( is it loose)

hotboy454 07-21-2012 10:48 PM

@vinniekq2, we did check valves everything is inline there. I checked timing everything is still spot on from rebuild to break in. We even moved timing around to see what we get for vacum less than 5hg. Something is really wrong there. Was at 15 inch of vacum before the carb. Backfired. I was told that I didn't have enough compression to support the cam also. It would idel comfortable at 1000 rpm brought it down to 9. Put it in gear it would barely stay on. Moved to 1100 then in gear it would idel at 900. In traffic a complete nightmare I would have tree the stop.light to keep it from dying off and the only way to solve would be to have the idel set way above normal I consume more gas than alittle bit.

F-BIRD'88 07-21-2012 11:19 PM

this 224-234 deg cam does not like a stock timing curve.

You need to modify the distributor curve as follows.

20- to 24deg base initial timing at idle.

34 to 36deg max mechanical maxing at 2800-3200rpm.

You must shoren limit the mechanical advance curve travel stop
to around a 10-12deg mechanical advance curve to allow this.
then use 2 medium tension advance springs or 1 light 1 medium
to get the curve rate just right.

Vac advance use ported vacuum
not full manifold vacuum. Limit the vac advance to around 12deg max
Limit the vac advance travel stop. then adjsut the rate by drive testing.
8 to 12deg at hiway steady cruise.

right now the spark advance is falling off when every you put it in gear
cause the distributor is set up wrong for the cam.
replace the carb power valve 4.5" so it stays closed at idle in gear
when manifold vacuum is lowest.

This cam does not really like a stock low stall torque converter
a 3000 stall is much better. This cam like gears too.

it will idle and drive just fine once the distributor advance curve is sorted out.

You cannot fix it by just swapping advance springs.
The idle timing must not drop when you put it in gear.
20-24deg at idle.
the crane cam will need the same distributor curve modification so just fix the distributor.

F-BIRD'88 07-21-2012 11:35 PM

How to correct the compression ratio.
You can mill the heads to 70cc (aprox a .040-.050" cut) and swap the head gasket for the GM 350 .026" head gasket. You must drill the 400 steam hole in the gasket yourself.

If you were to home port the heads while they are off the motor
it will change the whole nature of this motor by making all these corrections.
What is the 400 cylinder head casting number?
use champion RV8c or AC R42T spark plugs .035" gap.

hotboy454 07-21-2012 11:42 PM

400 sbc
@ fbird88 I have a stock hei distributor would a pro bullet or msd sreet fire hei work better. With the timing set up as you laid out. 2500 stall is that not enough for this cam. Now the elgin 1015p cam asked for 10.3:1 compression or less I'm at 8.5:1 will this be a issue. It ran really well. Just having trouble with the idel and running rich.

F-BIRD'88 07-21-2012 11:47 PM

If you were to upgrade this 400 with my Poor Mans Racing Head.
Fully ported 194x 1.60 valve 305HO cylinder head you;d see how a 400SBC really goes. The finished chamber size ends up going just right 62-64cc

They flow a whole lot more than stock smogger heads.
Just right for the dished pistons and that cam.
if your 400 heads are the right casting you can do a very similar thing.
By generously home porting them and shaving them.

You'd be leaving the Big block in the garage.
The only trouble you will ahve is wiping the grin off your face
first time you rug it.

the performer manifold needs the heat risers blocked or restricited
a wood, divided carb spacer is nice too. The summit carb may need some rejetting and the accelerator pump calibrated.
You probabily poped the power valve in it. plugs are probabily finished.
the summit carb should work well once dialed in.

hotboy454 07-21-2012 11:50 PM

400 sbc
These are factory 400 heads from a 1975 caprice classic. When I acquired this motor I had limited knowledge. I was given all the wrong info on how to build this motor. In building my 468bbc right now so tearing the heads off at this time is not a option, but a future upgrade that I will be sure to take using your format. So I have to use what I have since I'm knee deep in this big block using the info you gave. This is a set back. This truck is my toy and da.ily driver

F-BIRD'88 07-21-2012 11:55 PM


Originally Posted by hotboy454 (Post 1575845)
@ fbird88 I have a stock hei distributor would a pro bullet or msd sreet fire hei work better. With the timing set up as you laid out. 2500 stall is that not enough for this cam. Now the elgin 1015p cam asked for 10.3:1 compression or less I'm at 8.5:1 will this be a issue. It ran really well. Just having trouble with the idel and running rich.

the idle has nothing to do with the engine compression ratio.
Just fix the distributor you got.
its easy.
Any other distributor will need the exact same modification.
So just fix the HEI distribuor you got.

vinniekq2 07-21-2012 11:58 PM

still need to repair the car or carb back to when it ran well.Can you borrow a working carb for testing?I have a few but Im a little ways away I bet

F-BIRD'88 07-21-2012 11:59 PM

If the heads are crappy 882 or 624 castings start with better castings.

#441 487 920 etc or do the low buck ported 305 HO #416 head deal.

vortec heads would scream on this motor too..
Be sure the HEI distributor is seeing a full 12vDC power.
The ignition 12v + wire on that old truck is a resistor type for points.
Be sure the engine is grounded to the truck body with a ground wire to the firewall.

F-BIRD'88 07-22-2012 12:08 AM

Once you have corrected the distributor remove the carb and flip it over.
look at the throttle plates and idle fuel transfer slots. reset both the primary and sec throttle idle stops
so the transfer slot exposure at idle is correct .020" .030" ish and even.

If the throttles are too far open and or too uneven at idle it will idle like crap.
The extra idle base timing 20-24deg allows correct trahsfer slot exposure at idle
with that cam. The Performer RPM manifold is a much better intake for that motor and that cam.

vinniekq2 07-22-2012 12:15 AM

just looked up your cam.107 intake angle/117 exhaust, extra 10 degrees exhaust. That 400 can use all of that cam.If its not damaged and the carb is the problem I wouldnt rush out to buy a new one yet.dial in what you have before pulling the grille on your truck.You could advance it 2 degrees if bottom end is low out put.I cant see it though

All times are GMT -6. The time now is 12:08 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright 1999 - 2012. All Rights Reserved.