Its Just Not Running Correctly.. Why?


The Grumpy Grease Monkey mechanical engineer.
Staff member
heres a quote that might get you thinking a bit
GUYS,I have a 84 monte that i put a 350 in recently.the engine was fine but the oil pressure dropped very low in the summer in park and i didnt want to put any boltons that i had on it for that reason(heads cam etc)locally a sbc 383 popped up and it was within my budget.he claimed brand new but has been sitting for years in a project that never took off and now he was going to put a diesel in looked brand new and as far as i could see it had only been run by blueprint(the mfgr)for the dyno #s which were over 420.he bought it wo intake and balancer.he put a victor jr and the correct balancer for it.the victor is a single plane.i do believe the engine is new but its older so it had a flat tappet cam and lifters.weput it in place of the 350 and got it idled poorly but i got it as stable as i could .the nxt day it ran terrible and the plugs all fouled out.i bought a new set of the same (ngk r5672a-9 ) and they too fouled quickly.the jegs site says to use these plugs.on the blueprint site it says to use ngk 7938 so i did and they havent fouled.the engine idles terrible with no consistancy at all and i cant get more thal 11 lbs at idle.even that is jumping from 9 to 11.5.the performance is crap.the 350 i took out had as much or more power from standstill to 65 mph.i have the timing set to 35 deg at 3500 in park with the vac disconnected.i had the vac advance on ported vac but it seems it will idle a little better if its on full vac which bumps the idle timing up a little.what do you think the big loss of power is from?
here are the stats.
blueprint 3833834ct1
edelbrock victor jr single plane intake
correct balancer
holley 670 street avenger about 1 yr old (ran nice and smooth on the 350)
200r trans.....just rebuilt with shiftkit and new converter (dont know the stall but probobly around 2000)
monte ss 10 bolt rear with non posi and 323 gears.

i dont mind spending money on this but i have to get to the root caiuse of why this feels like a 305


don,t guess start with the basics, step back, mentally,
take a few deep breaths and start verifying,
not guessing or assuming, deal in facts

you currently don,t know even if that engines a 383,or the compression or the cam specs/
that engine might be a 307 or 350 with a new external paint job,
and a few external add-ons like that intake manifold,
or a new cam improperly installed for all you know,
you need to start by verifying the bore/stroke and casting numbers on the block, heads and verify the engine came from the source you think, etc.
Id have pulled it down and checked the engine bearings and rings long before installing any unknown SBC engine in my car
ID ,stickers can be removed and re-attached to a different block,
and paperwork can be used from a different engine
I've run a performance engine building garage for decades,
not much still surprises me anymore
everything may well be exactly like the guy who sold it to you says it is,,, its up to you to verify
I learned decades ago that you can,t trust anyone on what you buy used,
so its your responsibility to visually inspect and verify the components in the engine you buy,
and its up to you to verify bearing clearances and valve train parts condition ETC.

a couple of hours of careful inspection, tearing it down, checking and careful reassembly, testing and verifying,
and some plasti-gauge and a dial caliper and a new set of gaskets,
could save you a great many potential issues best avoided.
keep in mind many intake manifolds are not interchangeable with all other SBC cylinder heads,
this is especially true if you use some standard and some vortec parts,
IE mixing intake and heads with standard SBC parts


felpro # 1204=Port Size: 1.23" x 1.99"=2.448 sq inches

felpro # 1205=Port Size: 1.28" x 2.09"=2.67 sq inches

felpro # 1206=Port Size: 1.34" x 2.21"=2.96 sq inches

felpro # 1207=Port Size: 1.38" x 2.28"=3.146 sq inches

felpro # 1209=Port Size: 1.38" x 2.38"=3.28 sq inches

felpro # 1255 VORTEC=Port Size: 1.08" x 2.16"-2.33 sq inches

felpro # 1263=Port Size: 1.31" x 2.02"=2.65 sq inches

felpro # 1266=Port Size: 1.34" x 2.21"=2.96 sq inches

felpro # 1284 LT1=Port Size: 1.25 x 2.04''=2.55 sq inches

felpro # 1289 FASTBURN=Port Size: 1.30" x 2.31" 3.00 sq inches

(1) do a compression and leak-down test

(2) verify the cams correctly dialed in(INDEXED) and verify the valve lift on each lobe, you may be dealing with a worn cam

(3) if the cam physically checks out PROPERLY ADJUST THE VALVES,


(4) verify the oil stays above about 15 -20 psi at idle and reaches at least 45 psi by 4000 rpm and fuel pressure is consistent at about 5 psi and/or under 6.5 psi for the carb inlet at all rpms

(5) verify the ignition firing order is correct, remember there ar 4/7 swap cams

(6) verify the piston to valve clearance

read these threads and sub links


degree wheel


Dial Bore Gauge

Pushrod Length Checker
Proform Pushrod Length Checkers 66789 SBC 3/8" rocker studs

Proform Pushrod Length Checkers 66790 SBC 7/16" rocker studs
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