hi guys I am new here just wanted to say hi and I hope someone can help. I have a 91 silverado that had a 305 I have put a 400 in it with the heads and intake from the 305. Now when the engine gets warmed up and I put a load on it I get a noise that sounds like a deisel enging. I have messed with the timing but think it still may be wrong. I have told to set it anywhere from 10 to 14 if anyone can help I would really appreciate it
help with 400
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well, first off..I assume you drilled steam holes in the 305 heads.
Secondly, the 305 heads on a 400 would bump your compression up considerably... to the point that you will have to run premiun fuel...if that will even be enough. & even than I dont think your knock sensor will be able to accomidate that kind of compression. the computer will likely not adjust for it.
Secondly, the 305 heads on a 400 would bump your compression up considerably... to the point that you will have to run premiun fuel...if that will even be enough. & even than I dont think your knock sensor will be able to accomidate that kind of compression. the computer will likely not adjust for it.
I bought the engine from an uncle and he put the heads on for me and he did drill the steam holes in it now if I did need to run premium gas in it and some octane boost do you think that would help.
Now if that were the problem wouldn't the engine sound like a diesel all the time. One other thing when I shut the engine off I have to wait a while before I start it up or it wont start. It sounds like the battery is going dead.
What should I set the timing at?
Now if that were the problem wouldn't the engine sound like a diesel all the time. One other thing when I shut the engine off I have to wait a while before I start it up or it wont start. It sounds like the battery is going dead.
What should I set the timing at?
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The 400 originally came with 76cc heads. I don't know off hand what the 305 came with, but I know it was a lot less. You may had too high of compression. There are a few things you can do to reduce or eliminate the detonation.
*Run a 160o thermostat
*Find out what your ignition timing is set at. Get an advance analyzing timing light.
*Run a higher duration cam
Since your engine is kicking back at start up I bet your ignition has too much initial advance. This combined with high compression will make it hard on the starter.
Octane booster will not help. When the label says it will raise your octane a few points, they really mean thenths of points. 91 octane gas may only go up to 91.3 octane with the additives.
Check your timing first and then get back to us here on this board. The worse thing you may have to do is buy a set of heads for $500 or so. You can get some aftermarket heads for that much on Ebay. But again, get your timing squared away first.
*Run a 160o thermostat
*Find out what your ignition timing is set at. Get an advance analyzing timing light.
*Run a higher duration cam
Since your engine is kicking back at start up I bet your ignition has too much initial advance. This combined with high compression will make it hard on the starter.
Octane booster will not help. When the label says it will raise your octane a few points, they really mean thenths of points. 91 octane gas may only go up to 91.3 octane with the additives.
Check your timing first and then get back to us here on this board. The worse thing you may have to do is buy a set of heads for $500 or so. You can get some aftermarket heads for that much on Ebay. But again, get your timing squared away first.
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Is the computer still in use on this vehicle? if so what knock sensor are you using? if your using the one on the 305 this won`t cut it, knock sensors work off frequenceys, and different bore sizes create different frequencey`s and the 400`s bore is a he** of a lot bigger than a 305`s, 4.125 compared to 3.736. The knock sensors job is to pick up detonation and control the timing down to keep detonation away, but it can`t cure a problem when the grade of fuel isn`t enough for the compression ratio given, it`ll just keep retarding the spark timing until the engine won`t run. second, if your using TBI it will need bigger injectors, but on both counts here, neither a knock sensor or injectors were ever made for a 400 small block.
If the computer is still in use a custom chip will also have to be made, were talking 95 more cubic inches.
Lastly, 305 heads on a 400 was not a good idea, this put the compression ratio in the high 10:1 range, the noise you hear is detonation, which will quickly destroy any engine. the compression ratio is too high for pump gas, and the tbi can`t provide it with enough fuel being it was intended for use on a engine with 95 less cubic inches. you`ve mentioned you`ve reset the timing, with the computer in use are you disconnecting the plug at the distributor while your doing so then disconnecting the battery afterwards so the computer will dump the previous setting and take set of the new one? the engine will want less timing due to the higher compression ratio. The engine is likely running so lean it will likely burn a hole through the piston or cook some valves.
If the computer is still in use a custom chip will also have to be made, were talking 95 more cubic inches.
Lastly, 305 heads on a 400 was not a good idea, this put the compression ratio in the high 10:1 range, the noise you hear is detonation, which will quickly destroy any engine. the compression ratio is too high for pump gas, and the tbi can`t provide it with enough fuel being it was intended for use on a engine with 95 less cubic inches. you`ve mentioned you`ve reset the timing, with the computer in use are you disconnecting the plug at the distributor while your doing so then disconnecting the battery afterwards so the computer will dump the previous setting and take set of the new one? the engine will want less timing due to the higher compression ratio. The engine is likely running so lean it will likely burn a hole through the piston or cook some valves.
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The compressioin isn't too high at 10:1. Especially if we are talking about a fuel injected engine. Most new cars come from the factory with 10:1 and higher.
The problem is that the engine isn't tuned for higher compression. If computer controlled, it will need to be recalibrated to be able to run with the engine beign used.
The problem is that the engine isn't tuned for higher compression. If computer controlled, it will need to be recalibrated to be able to run with the engine beign used.
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If this is a stock 400 with fully dished pistons there is no Quench to help combat the problem, also with 400`s using the shorter 5.565 rod the engine is asking for detonation to set in, yes there are ways to beat detonation and run high compression on pump gas just as you`ve posted about a 100 times, but it`s not going to be done by just calibrating what he has, 400`s are known to be quickly self distructive on high compression with pump gas due to detonation.
ok guys bear with me I have never heard of a knock sensor. Yes the computer is still being used. It is tbi and I am going to get a kit to open the fuel through it. How do you recalibrate the computer? Yes I have unpluged the advance but I haven't disconnected the battery.
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If you drove my Camaro just once Double, you would see why I am such a fan of higher compression. It idles and drives like stock, but is as fast as any of those lumpy cammed cars that suck to drive.DoubleVision said:
Why not try and combat the detonation through tuning before tearing it down. If you'll read also, I suggested getting a set of heads on Ebay. There are plenty of the "SR" stock replacement heads for the same price as the real stock heads.
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Ask your uncle what pistons, rods, crank, etc. it has. Then you can calculate and find out exactly where your compression is.stropes said:
Do a compression check. What is the pressure reading at the gauge?
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Are you getting ping at idle and just reving up? If you are and your timing is correct which is 0 deg. for your comp controlled 305 or 5.7 in a 91 gm truck. you better pull those heads off and check combustion chamber size and piston type. If its pinging going up hills and the timing is correct,make shure your EGR system is working,that too works to cool combustion.
Are you getting ping at idle and just reving up? If you are and your timing is correct which is 0 deg. for your comp controlled 305 or 5.7 in a 91 gm truck. you better pull those heads off and check combustion chamber size and piston type. If its pinging going up hills and the timing is correct,make shure your EGR system is working,that too works to cool combustion. Also a colder plug can help with detonation.
Are you getting ping at idle and just reving up? If you are and your timing is correct which is 0 deg. for your comp controlled 305 or 5.7 in a 91 gm truck. you better pull those heads off and check combustion chamber size and piston type. If its pinging going up hills and the timing is correct,make shure your EGR system is working,that too works to cool combustion. Also a colder plug can help with detonation.
my timing is set at 0 and I don't get any ping unless I am going up a hill or putting some kind of a load on it. What do you mean by a colder plug? I did put a new egr valve on it when I changed the engine67 Deuce 4 Me said:
I asked my cousin about the pistons rods and crank and he said the pistons are single brow flattops and the rods he said were 400 rods and so is the crank
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If that is the case you are at, at least 10:1. This means you need get your distributor curve correct.
You can add a bigger cam with more duration and your problem may go away. It will most likely not sacrifice any bottom end doing this.
Or, you can change your heads. Either way, if the engine is running well aside from the pinging, you have a good bottom end to work with. That is a big plus.
You can add a bigger cam with more duration and your problem may go away. It will most likely not sacrifice any bottom end doing this.
Or, you can change your heads. Either way, if the engine is running well aside from the pinging, you have a good bottom end to work with. That is a big plus.
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Colder range plugs .for instance if your using a r45ts a/c plug you may want to go down a # to r43 ts. the plug electrode doesnt go into the cylender as far and is quicker to cool down.Make shure the egr valve is working, just putting a new valve on doesnt mean the valve is working. Put a vacuum pump or a vacuum source directly on the valve, with the engine at idle, if its working it should kill or neary stall the engine.the egr solinoid is controlled by the ecm. comes on under loads and crusing speeds. Make certain you have good vacuum at the solinoid. 2 eyebrow flat tops and you probably have 58 cc heads is quite a squeeze, too much for pump gas. try to confirm cumbustion chamber size of the heads, if there 58cc, you might as well plan on getting another set of heads. no less than 70 cc.Good luck
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Id put 76cc heads back on rather than the 305s 58cc heads, get the compression back where the computer wants it...althou, Im not sure the computer will like the 400 CID with out being recalibrated.
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Racing fuel.......Problem solved! 
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I don't know where you guys get 10:1 compression. A 400 with 305 heads is every bit of 12:1 compression unless the piston is sitting way down in the hole. If you are running pump gas you are detonating, and tuning isn't going to help. A set of 76cc heads will get you about 10:1-10.5:1 and you will need a large camshaft to make this set up work with iron heads and pump gas. You can make it live easilly with a set of 76 cc aluminmum heads and a camshaft with at least 220-230 duration at .05 lift.
Good luck
Good luck
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