440 detonation issue

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340 8BBL

340 8BBL

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well im now the new owner of a 72 d100 se .it original 400 has been swapped to a 440 which wears hi-po ex manifolds,and judging by the balancer has a forged crank.other than this the engine is an unknown ,the builder is 6 feet under.the problem im having is it pings under full throttle no matter what i do unless i limit total timing to about 22*.this puts initial at 2*atdc.i randomly pulled 2 plugs at it cranks at 170+ psi.i think the problem may be a high compression ratio and a short duration cam.i tried fattening the mixture to no avail,checked plugs for the correct range,ran with the vac advance disconnected,etc.im out of ideas........
 
I forgot to ask with all the pm's we exchanged....are you runnin premium? ..........and if you are, you might try gettin some 114 Cam2 and seein what that does. If you can get 36 degrees timing outta it then, you pretty much know what the deal is. lol
 
You could try limiting the mech. advance by welding up the slots inside the dizzy. When does the dizzy reach full mech. advance? If its fairly early, you could also try one heavier spring inside.

...or it may be all carboned up. I'd try the "drip water down the carb while revving the snot out of it" method.

..or the plugs are too hot.
 
im running 91 premium pump swill lol.high octane race gas is the only thing i have not tried.i considered swapping cams to the 440/383 hp cam.
 
65Val said:
You could try limiting the mech. advance by welding up the slots inside the dizzy. When does the dizzy reach full mech. advance? If its fairly early, you could also try one heavier spring inside.

...or it may be all carboned up. I'd try the "drip water down the carb while revving the snot out of it" method.

..or the plugs are too hot.
Click to expand...
the plugs are autolite 85 which is the correct plug for an hp 440/383.the advance is all in by 2600.i thought about welding the slots in the dizzy,but still,having to limit total to 22* ?ill check for carbon build up.
 
Try some high octane swill first to verify that it will run without spark knock.....will be cheaper than a cam change.
 
If it is a compression problem, the only way to truely fix it is to increase the size of the compression volume (volume above the piston at TDC).

I had a 318 with a compression problem way back in the day. I had 10.5:1 TRW forged pistons and stock 318 heads. The engine would overheat after 20 minutes when the temperature was above 78° F. My Internal Combustion Engine class teacher told me that it was due to my compression being too high. I swapped the heads with 360 heads that had 6 cc more volume and never had a problem again - and was even able to run cheap pump gas!

If it is truely a compression issue. It is easier to swap heads to ones with larger combustion chambers, than to change the pistons. You can also consider using a thicker head gasket, but that may not solve the problem alone as well as a set of heads with larger combustion chambers.
 
im a little stumped on this one.my 340 dart has the same cranking psi,and it runs on 91 with 20* initial timing and 34 total.and is all in by 2200-2400.however the cam is pretty long in duration (284).
 
krazykuda said:
If it is a compression problem, the only way to truely fix it is to increase the size of the compression volume (volume above the piston at TDC).

I had a 318 with a compression problem way back in the day. I had 10.5:1 TRW forged pistons and stock 318 heads. The engine would overheat after 20 minutes when the temperature was above 78° F. My Internal Combustion Engine class teacher told me that it was due to my compression being too high. I swapped the heads with 360 heads that had 6 cc more volume and never had a problem again - and was even able to run cheap pump gas!

If it is truely a compression issue. It is easier to swap heads to ones with larger combustion chambers, than to change the pistons. You can also consider using a thicker head gasket, but that may not solve the problem alone as well as a set of heads with larger combustion chambers.
Click to expand...
interesting.....it has no problem like you are describing with overheating,or general driveablity.it runs and idles very well,and has no detonation under part throttle conditions.pulling the heads had crossed my mind,but only as a last resort.
 
You've never mentioned what heads you have.....unless I missed it. So...if you have open chamber heads already, changing heads will do you absolutely no good. The thing to do is what I have been trying like almighty hell to explain to you. Diagnose the thing and go from there. There are so many variables here, it is impossible to tell without having the engine torn apart to look at what all is there. Also...here is another scenario no one else has thought of. Carbon buildup is a major player in older engines that can cause an increase in compression and also cause just the symptoms you describe. Have you dribbled about a 12 ounce glass of water through the carburetor while running the engine at about 2K? Doing this will burn off any large carbon deposits in the combustion chambers that may be hanging out and raising compression and blow it right out the tailpipe. If that fails to make a difference, try the high octane swill and see of the detonation goes away. Also think of this. What would a simple, all out basic rering cost you? I am sure with all the knowledge you've displayed asking questions and whatnot, you can rebuild it....if you haven't built some engines already. Hell, I bet you could get buy with everything for under 300 bucks less cam and lifters doin a basic rering yourself. Why? So you can SEE the inside of that beeyotch and know what's there. You can blueprint the compression ratio and see what you really have. a TRUE honest to goodness flat out 9.0:1 engine WILL have problems running on today's premium with a short stock duration camshaft. I had a friend who had a numbers matching unrestored 1971 330 HP 350 LT1 Camaro when we were in school. That car had a sticker on the sun visor that said "USE PREMIUM FUEL ONLY" and that car was built was in 1971. It had MAJOR PROBLEMS runnin on anything other than pump premium in the early 80s. It absolutely LOVED 114 Cam2. Those cars "only" had 9.2:1 compression from the factory. A lot of people don't realize it, but an honest anything over 9:1 is pretty damned high.
 
Try the race gas, you should be able to get 38* total, if you can it's high compression and won't run on anything but high octane. That is without going to a long duration cam, and that may not even work. There is one more solution convert it to run on E 85.
 
thanks for the replies,ill try the water first to eliminate carbon,if that dont work its time for some high octane fuel.be back later with the results and some head casting numbers. to be continued.........
 
tried the water trick for carbon...no change.ill back with head casting numbers.......
 
Doesn't matter if there open or closed chamber, you can still have high enough compression with either. But it will tell you if a head change will lower your comp, provided you have closed chamber heads. So put some high octane in it and you'll know the story.
 
Purple Haze said:
Doesn't matter if there open or closed chamber, you can still have high enough compression with either. But it will tell you if a head change will lower your comp, provided you have closed chamber heads. So put some high octane in it and you'll know the story.
Click to expand...
agreed,and i just pulled a valve cover.i looked up the p/n and the has an 88 cc chamber.p/n is 3769902 which is a 74 440 head.the block says 4T 440 T, and is dated 74 on the side.
 
Danged if I wouldn't investigate the hell out of that distributor. I mean.....170 PSI should run on pump gas. Even with a stock camshaft. You gotta distributor you can swap it out with?
 
not at the moment,its got a stock electronic .thats the first thing i looked at was the advance curve.its all in by 2600.and its got 24*of mech advance.the 170 psi is if i remove 1 plug randomly.it would have more i think if i removed them all.
 
first, try pouring Coca cola in it( I know, but the sugar seems to knock out the carbon better than water; Ever taste carbon? kinda sweet; don't ask).
You have vacuum advance? Plug it and test. My first bet in the dist, next one, after getting carbon out would be: then mix race gas in. My experience- ex wife started putting reg gas in my 10.5 340; broke a piston.
Or put more duration cam in it, to bleed off compression. I needed to get a truck out of my way; I put a low comp 340 in it, with a middle purple shaft cam. It jumped all over the place at idle, but started moving at 3000 rpm. Killed every 5.0 mustang it saw. It would finally catch up at top of 1st gear, then jump 3 car lengths.
Check for total in the dist, with vacuum, then decide.
 
That's awfully low RPM to have all that timing in by with a stock cam. It almost has to have either weak springs in the distributor or someone has put some recurve springs in it. The wrong ones.
 
green1 said:
first, try pouring Coca cola in it( I know, but the sugar seems to knock out the carbon better than water; Ever taste carbon? kinda sweet; don't ask).
You have vacuum advance? Plug it and test. My first bet in the dist, next one, after getting carbon out would be: then mix race gas in. My experience- ex wife started putting reg gas in my 10.5 340; broke a piston.
Or put more duration cam in it, to bleed off compression. I needed to get a truck out of my way; I put a low comp 340 in it, with a middle purple shaft cam. It jumped all over the place at idle, but started moving at 3000 rpm. Killed every 5.0 mustang it saw. It would finally catch up at top of 1st gear, then jump 3 car lengths.
Check for total in the dist, with vacuum, then decide.
Click to expand...
i already ran it with the vac advance disconnected,it made no difference as well as tried water down the carb to de-carbonize...also no change.
 
StrokerScamp said:
That's awfully low RPM to have all that timing in by with a stock cam. It almost has to have either weak springs in the distributor or someone has put some recurve springs in it. The wrong ones.
Click to expand...
so what would be the correct rpm for full advance with a stock dizzy?
 
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