400 sbc detonation issue

[72supermike]

I just built a small block 400. It's pinging at about 2k-2500 rpm. I've backed the timing off but it doesn't cure it enough. The engine is running premium fuel right now as well. The block is decked (not all the way to 0), .030 over, and the heads are camel humps 64cc. They have been trued up before so a little taken off of them at some point. I don't know the gasket thickness but probably normal, whatever that is. Talking with the machine shop when they have the block, they thought I should be at about 10:1 cr. I don't think it turned out that way.

Cam - ES 1013R Stage 2 High Performance Hydraulic Flat Tappet
.050 Duration 214/224
Camshaft Lift .295/.310
Valve Lift .443/.465 Lobe Center 107/117
Overlap 61


My question, what is the best way to fix this? preferably without spending loads of money on new heads.

Thanks!

[Chevydude56]

What pistons did you use ? Dished or flat top ?

[72supermike]

pistons are flat top. rods are 5.7's

[Captainfab]

That's your problem. Flat tops in a 400 with 64cc combustion chambers gives you way too much compression for pump gas. Especially with that small cam. You're probably between 11 and 11.5-1

Edit: I just did a quick online calculation of your compression, taking a guess at a couple specs, and came up with 11.2-1

[72supermike]

captain, what is the best cost effective cure for my issue? Can i go with a thick head gasket?

[Captainfab]

At this point the easiest fix will be to change the heads to a set with about 76cc chambers. Something like the original SB400 heads. I believe I have a set that will need rebuilt.

You're not going to be able to make enough of a change with a thicker head gasket.

I don't think a cam with a later intake valve closing will make enough of a difference either.

The other option would be to change the pistons to dished pistons.

Originally Posted by 72supermike

captain, what is the best cost effective cure for my issue? Can i go with a thick head gasket?

[72supermike]

I have some 400 heads that need rebuilt. I'd rather not pull the engine and replace pistons if possible. I can do heads in the truck. So heads would be the route I'll probably end up going. Bummer. Its a great learning experience!

Thanks

[b454rat]

Octane boost?

[jjzepplin]

Had my 400 heads redone with 2.02 valves bowls blended and screw in studs for $300. Runs like a scalded dog! 400-.30 over-flat tops

[burnin oil]

Figure out your cam specs and put them into the KBsilvolite compression calc. It will give you the true compression ratio (DCR), not the static. You could run 15:1 compression with the right cam on pump gas, theoretically. Dont forget to add 15* to you valve timing if they were taken at .050 lift. You may be able to retard the cam a few degrees and get what you need to stop the pinging. Other than aggrevasion you may get away for free if the timing chain has multiple key ways or a few bucks if you need to buy an offset crank key. A few degrees of intake valve timing can make a huge difference in DCR!
My current setup is a flat top 350 with 58cc heads and a small Lunati torque cam around 207/214 degree (numbers off my head). With the cam retarded 2* I have been running detonation free on 87 octane.

[72supermike]

Thanks guys for all the input so far. I called the machine shop and looked at my box that had the pistons in them and they are dished. So that makes me really start to wonder what is going on. I shouldn't be more than 10.5:1 cr.

Sealed Power Hypereutectic Pistons ZH615CP
Piston Head Volume (cc):+12.50cc

[burnin oil]

You really need the DCR. Like I said static means nothing. Depending how much DCR you have will determine what you can do. Sometimes richening the fuel mixture, changing mechanical advance springs (to limit timing/slow the rate), or even a colder spark plug can help to get rid of the detonation. Unfortunatley you need to figure out how close the DCR is.
http://kb-silvolite.com/calc.php?action=comp

[Captainfab]

I agree that the dynamic is the ultimate determing figure. I again plugged in the info given, plus guessed on a couple unknown specs, and he has 9.09-1 dynamic. That is still too high for iron heads on pump fuel. Especially those old school 461 castings.

Considering this engine is in a K20, it is my opinion that the best way to get the compression down to a managable ratio, will be to change the heads to larger chamber heads.

Originally Posted by burnin oil

You really need the DCR. Like I said static means nothing. Depending how much DCR you have will determine what you can do. Sometimes richening the fuel mixture, changing mechanical advance springs (to limit timing/slow the rate), or even a colder spark plug can help to get rid of the detonation. Unfortunatley you need to figure out how close the DCR is.
http://kb-silvolite.com/calc.php?action=comp

[72supermike]

Ok, so if this was your engine, what would you do? What heads would you put on it? I don't seem to read good things about 76cc stock heads. Is aftermarket just about the only way to go? Would vortec heads cure the issue? Thanks

[Captainfab]

I don't know if the more efficient combustion chamber of the Vortec heads will solve the detonation issue or not. A set of aftermarket heads with larger chambers will certainly be the better way to go. I suggested the stock heads since it sounded like your budget was pretty tight. Granted the stock heads don't flow all that good, but you may not notice a big difference compared to the 461 castings. I certainly wouldn't drive it with it detonating like it is......that's a good way to break a piston.

[72supermike]

Yeah, I'm not going to be running the engine at this point until after I get some different heads put on. In don't like spending money but sometimes it's better to do it right the first time. Do you have any heads you would recommend?

[burnin oil]

Where is the valve timing at? I couldn't find specs on that cam. He might be able to advance it to get what he needs. If he could get the valve around 50* he may be alright. With a 400SB I would try moving into a bigger cam before switching heads. With the added cubes and stroke a 400 has the OP does not need a torque cam. My old 400 had flat tops, 76cc heads, and 300hp 327 cam. Power was idle on up. A little wilder cam would have ran perfectly fine.

**EDIT**
Looks like he would need a cam with a ABDC of 68-70 degrees to get into a good DCR. Heads are pretty much needed to get the pump gas area. A set of heads with 76cc chambers and a cam with a ABDC of 50* would be a DCR of 8.2-8.3 range. If I were going to spend the money on new heads I would check out the JEGS heads. You can get some nice alum heads made by Pro-Filer for about $1000. Might need headers to mate to the d port exhaust. If he can use 72cc chamber heads those are even on sale right now for even less cash!

[storm9c1]

Now that we suspect it may not be your piston setup, has anybody asked what your distributor setup is yet? Are you running vacuum advance or not? What type of springs and weights are you using? What is your initial timing set to with vacuum advance unhooked?

[72supermike]

I don't have vacuum hooked up to the dist. I'm unsure of the weights and springs in the dist. I can't back the timing off enough to eliminate pinging without the rpm dropping off a lot. I've had it at 0 advance and it idles like crap and still pings at higher rpms. I haven't even driven it. I've only run it in the garage. So any load I put on the motor would probably make it worse.
Posted via Mobile Device

[storm9c1]

Originally Posted by 72supermike

I don't have vacuum hooked up to the dist. I'm unsure of the weights and springs in the dist. I can't back the timing off enough to eliminate pinging without the rpm dropping off a lot. I've had it at 0 advance and it idles like crap and still pings at higher rpms. I haven't even driven it. I've only run it in the garage. So any load I put on the motor would probably make it worse.
Posted via Mobile Device

The weights and springs can make all the difference in the world. I've chased these issues at length before, and it's all guesswork until you get a good digital timing light to see exactly what is happening with your distributor. If all of your advance is coming in way too early, you will ping like crazy. I'm not saying this is your issue for sure, but it would be the first place I would start at this point.

[72supermike]

I was going to set my total timing at about 32 degrees so I marked 32 on the dampener and I never even got it that advanced. I don't think it's coming in too early.
Posted via Mobile Device

[Captainfab]

I hope you ran the engine long enough to properly break in the cam, along with a breakin additive.

Originally Posted by 72supermike

I don't have vacuum hooked up to the dist. I'm unsure of the weights and springs in the dist. I can't back the timing off enough to eliminate pinging without the rpm dropping off a lot. I've had it at 0 advance and it idles like crap and still pings at higher rpms. I haven't even driven it. I've only run it in the garage. So any load I put on the motor would probably make it worse.
Posted via Mobile Device

[Captainfab]

In my opinion these heads are hard to beat for the money, and these should work with your engine combo. However we should double check that they will before you order them or something like them.

http://www.summitracing.com/parts/drt-127221/overview/

Originally Posted by 72supermike

Yeah, I'm not going to be running the engine at this point until after I get some different heads put on. In don't like spending money but sometimes it's better to do it right the first time. Do you have any heads you would recommend?

Edit: With those heads' 72cc chambers, and your current cam your DCR will be aprox 8.4-1. That is probably doable. However if you were to step up the cam, as has been mentioned, to say a Summit 1107 cam, your DCR would drop to 7.6. That cam might be a little much, depending on how you want to use your truck, but it does give you a trouble free compression ratio.

[72supermike]

I ran the engine for a good 15-20 min at 2k-2500 rpm while getting some adjustments done. I have a good zinc additive in it so it should be fine. I messed with the detonation issues after an initial break in run.

What information do you need to help me double check that those heads or ones similar will work? by the way, I don't live in harrison anymore. I moved to cda/post falls area. I'm now south of the river, so not too far from civilization.

Thanks.

[Captainfab]

Well I did guess on some of the info to get the results in my edit to the post above. To get more accurate numbers we need to decide on which head gaskets will be used upon reassembly, and what the compressed thickness is as well as the bore of the gasket. Also need to find out what the deck clearance is. Did you assemble the engine or did the machine shop? If they assembled it, they might know what the deck height is.

Originally Posted by 72supermike

I ran the engine for a good 15-20 min at 2k-2500 rpm while getting some adjustments done. I have a good zinc additive in it so it should be fine. I messed with the detonation issues after an initial break in run.

What information do you need to help me double check that those heads or ones similar will work? by the way, I don't live in harrison anymore. I moved to cda/post falls area. I'm now south of the river, so not too far from civilization.

Thanks.