Ok so i built my 383 fully forged close tolerance but within spec from piston manufacturer. I break in the cam ok all is good. After its broken in i let the car cool and 4 hours later i start to tune the carb. Car ran great while tuning but the next day it sputters and backfires/pops through the exhaust. Im running 93 octance both days. I adjust the timing from 16* to around 6* the car doesnt hesitate as badly and limits the backfire/popping through the exhaust. Now it just sounds like a weedeater kinda. the exhaust sounds nice and throaty but the engine sounds like utter crap no choppy idle or anything. I also cant get it to idle under 1300 RPM's. Im not sure what pinging sounds like but i know my compression ratio is around 10.9:1. not to mention i took it on a short ride (.5 miles round trip) and the car shook EXTREMELY bad when cruising (5 speed) and accelerating from a stop. Oil seems to be leaking a little but cant pin point the leak (thinking its the valve cover) but i am checking it everytime i start it up to make sure its not low. Why does it sound like that and shake so bad?

Now for the specs of the motor:
Comp cams XE284H-10
.060" over forged pistons
700 double pumper
Points ignition with accel blaster coil
3" exhaust with gutted cat
Hedmann shorty headers
.040" head gasket (installed thickness)
62cc combustion chamber iron heads


Thanks for the help, Chas

 

11:1 comp on iron heads is a ton. What's your spark curve look like?

 

whats spark curve? Is that like vacuum advance? i have that unplugged b/c it starts to run like crap at idle with it plugged in. Could my distributor be advanced one tooth and still read 6* or 8*? Im at a total loss. When i re-built the motor i made sure that the timing mark lined up with 0* mark on the timing tab. i also made sure the distributor pointed to the number 1 plug on the cap when I installed it. I have no idea what could be wrong, i might try retarding below TDC mark and see what happens.
On a side note i have no idea what the WOT timing degree is.

Thanks again, Chas

 

This kind of thing right here is exactly why I changed my mind to run a stock bore 350 with nitrous instead of a stroker. I can assure you the Iron heads are not the problem though.

 

alright so its prolly timing issue?

 

That's what I'd say, and that oil leak, It's most likely the valve cover seals, they tend to go bad quicker on engines with Iron heads, they retain more heat.

 

Is that a typo or did you seriously convert an HEI system to points?

 

He might of not even done it, original owners of 1986 Irocs frequently swapped out the 305 TPI's for carbureted 350's with points ignitions. Same story with my 86 Iroc, and a friend'ss 86 Iroc.

 

ya the guy i bought the car from had a 350 in it but I wanted a 383 and the dizzy that came with it has a canister like external coil with the points rotor and cap. Its def a weird set-up but im in the process of ordering a HEI dizzy. Im going o try and retard the timing back before TDC and see what i get. If anyone has any other ideas im willing to try them seeing how i cant seem to figure this out.

 

Start with the basics, get a new air filter, run it with some STP carburetor or injector cleaner whicher you have. Possibly take it to a dyno, best places around for air/fuel and timing.

 

I would take it to a dyno but im afraid to run the car and screw something up (cant trailer it b/c i dont have a truck/dolly). Anyone have a good link to what spark knock sounds like? Im thinking i might run some octane booster to raise the octane to see if its spark knock/pinging.

 

That could be it too, run some octane booster, you might have youself a case of pre-ignition.

 

I was just watching some videos and it def sounds like spark knock. I must have higher compression ratio than what the calculators figured. That just seems wierd but o well. Ill try the octane boost and see what happens any good brands? Im just guessing but my piston to deck clearance must be less than .025"

 

STP usually gets the job done.

 

when you unplugged your vac. advance did you plug the line?
also could be time for points and a condenser

 

yup i plugged it. Is the timing supposed to advance when the rpm's increase with the vac unplugged and plugged? Mine does but im thinking its supposed to do that.

 

yea thats the mechanical advance
also your valves could be too tight how did you adjust them ?

 

go to your local race track and buy some real high octane gas, octane boosters like STP etc. only boost octane a percentage of 1 point, meaning they are pretty much worthless as far as actually boosting the octane level any appreciable level.

 

I adjusted the lash by feel b/c its hydro lifters. I have 1.5 roller rockers and i adjusted till i felt resistance then 1/2 turn and tighten the lock screw.

Bought some STP and no difference, I was thinking that seeing how im running 93 pre-ignition shouldnt be a problem with my cam.

This is really pissing me off. I might be taking it to the shop for someone to have a look. My so called friends dont want to come over for 10 mins to take a look.

I noticed one thing though, when i floor it it bogs and revs slow to about 3000 then wants to take off. this is all in neutral not driving it.

this cam is supposed to be a choppy idle but it sounds like a damn weedeater here is a crappy clip

http://www.youtube.com/watch?v=jLsfAmoamK0

and another:

http://www.youtube.com/watch?v=2ZdPrnctCRw

 

It's not the cam. It's the compression ratio. 11:1 is a lot. 10:1 with iron is pushing it on 93. That cam isn't that big.

 

ya i know im thinking its pre-ignition... is that the consensus?

 

looks like i might be buying new heads...i have a .040 head gasket already and i have no idea how to do a "o-ring motor"? for coppers.

 

It's my opinion. Might not be all the problem, but it's the biggest.

As 89Rs suggested, take it to a track, fill it up with race gas, then see how it runs.

 

can it ruin the engine driving it while it pings?

 

Detonation is bad. I've seen it blow holes in pistons. Yes, it can kill engines.

 

I've never heard of anyone ruining an engine just because of pre-ignition due to lower octane gas, but I sure as hell wouldn't run it hard like that.

 

ok i found a set of copper gaskets but i have no idea if they need O-rings...what are these o-rings they mention...here is the set...

http://store.summitracing.com/partde...8&autoview=sku

i need head gaskets that are at least .062 compressed thickness but the bigger the better...

 

Just because you've never heard of it doesn't mean it doesn't happen. Preignition or whatever name you want to call it can do a ton of damage if left unchecked.

 

By o-ring they mean the part of the seal around each cylinder, it's part of the gasket.

 

I have a question reguarding vacuum advance. It advances the timing at a lack of vacuum i.e. open throttle right? So if you have it disconnected, wouldn't you be running at full advance? I don't know about carbs and stuff I just mess with fi.

 

no it advances the timing by the amount of vacuum being pulled. So the higher vacuum the higher the advance. When you WOT a motor the vacuum will drop to zero then back up to some amount. The amount depends on the cam and the advance depends on the distributor springs and weights.

 

The springs and weights are the centrifugal advance - completely independant of the vacuum advance.

Running with the vaccy advance disconnected is called base timing. The vacuum advance is more or less a "dynamic" load compensator. Under limited or no load conditions, it advances the ignition further to help improve running conditions.

 

Did I ever say it's never happened just because I've never heard of anyone doing it? No.

 

Wait wait, I have to quote this. Did I ever say it's never happened just because I've never heard of anyone doing it? No.

 

i was thinking about this one, did the timing chain get installed stock or was it advanced a little there. If i had a big cam, id get Rhoads Tappets. as i would rev the engine, fluid would fill and make them bigger hence getting more lift, but the slower the rev, then they shrink and get a smoother idle. I think its an ignition problem, (hence the weedeater motor sound. Ive worked with points b4 and they suck. Id check the basics, wires order, plugs, maybe even gap the plugs bigger. test the old coil, and adjust the points. In my experience if the engine sounds like a motorcycle, its a miss(vacuum related, or unplugged injector) and since you dont have injectors then thats eliminated.. do you have a vacuum rez? pcv? i recommend FEELPRO's reusable Permadry gaskets for the valve cover. and points always give me headaches with popping exhaust. id, feeler gauge it and maybe go wider. check grounds and maybe look into a jetting for the carb and new centrifugal weight kit for the dizzy? OH and check the endplay on the dizzy shaft, sometimes they need to be shimmd to 0.010"-0.008. i had spark scatter of 16* deference jumping back and forth at idle. but shimming fixed it. if its a coil in cap, then check the ground from coil, and the spring. Try tdc your crankshaft and see if your rotor is pointing to terminal #1 in the dizzy cap. peace.

 

the timing is dead nuts on but i had a buddy of mine take a look at it and its definitely spark knock...im going to get a set of coppers to get the compression down a bit but i just have to save a lil money (250 a set.) the timing doesnt jump more than 2* if that when its idling. Im buying a HEI dizzy when i buy the gaskets so i wont have to worry about the points.