My engine is back out of my car, and disassembled. On the tops of the rod bearings I found the metal worn away in the obvious pattern that shows I have some detonation, in every cylinder. Im new to engine building, so after I put this all back together with new rod bearings, I want to make sure its not going to happen again.

Im running stock heads (yeah, I know...they're being ported before they go back in), CC306 cam, -16CC inverted dome pistons, and FelPro head gaskets. I just installed the timing chain how it is supposed to be, dead on and no degreeing of the cam. MadZ28 mail order tune. The exhaust smells like im running rich.

What should I do? Any suggestions?

 

Not enough info to be specific. In general, detonation/pre-ignition may be de to too much ignition advance, plugs that are too hot, hot spots in the combustion chamber, fuel without enough octane, CR too high, engine temps excessive, high intake air temps, or mixture too lean. Obviously, one influences the other.

Driving habits can also produce detonation. Large throttle openings at low engine speed would be the main culprit here.

Rich

 

Yeah, I really dont know what to check for at this point, seeing that everything should have been hooked up right, so I'll just reassemble it with new rod bearings and run some tests while driving the car. Any more suggestions would be great though, thanks for the help!

 

Ya need to get some brgs that will take the action and not peal like the cheap ones.
Figure your DCR and see if it is below 9.0. If it is check A/F ratio and timing. Also check your quench distance and try for a .035-.040,this will help the detonation cause. With those dished pistons if they aren't a reverse dome that could be part of the problem with no quench area on the piston(D dish has quench)

 

Get it dyno-tuned. No offense to madz28, but it is very hard to get a correct mail-order tune without at least verifing the tune on the dyno, then sending in the a/f and datalog info for fine adjustments. Differences in injector build tolerances are just one variable that can make a good tune on one car, unsafe on another even if all build specs are the same.

Check for knock counts in the computer and get the thing tuned, that problem will show it'self and hopefully you can fix it. With a 16cc dish piston you are looking at a max of 11.5 compression with decked heads and zero deck block, that will allow you to run pump gas and not ping with a decent tune.

You getting any oil smoke out the exhaust? That would indicate bad ring seal and can cause detonation...

 

I was running the Clevite 77H bearings, should I go with better ones? Also, Im new to engine building, so how to figure the dynamic compression ration, and the quench is something i hae no idea how to do, lol.

The engine builder missed some stainless steel beadblasting shot when he cleaned my engine, this got into the top end and put nice lines down the length of the cylinder walls, so I was definately burning some oil as well.

I plan on getting it dyo tuned, I just dont want to have to pay that epense twice, so I was getting all my mods done first.

Also, I was running stock heat range plugs, thats definatley gonna cause a problem as well, seeing that Im going to be looking at 400+ rwhp, what plugs should I run and where do I buy them?

I do have -16cc inverted dome pistons as well, but while the engine is out and dissassembled, should I have it 0 decked? Is that a good idea?

Thanks ahead of time for your pateince in answering my questions, Im new to all of this being only 18 and building my own engines.

 

The engine builder missed some stainless steel beadblasting shot when he cleaned my engine, this got into the top end and put nice lines down the length of the cylinder walls, so I was definately burning some oil as well. WHAT?!?!?!?!?!?!??

before you rebuild get some cross buffs and carbide burrs used for head porting, and polish your combustion chambers, little imperfections can cause small detonations. and make sure that your mechanical advance in your distributor isnt loose and advances and springs back smoothly no play without tension

get an air fuel ratio meter or have the dyno guy do it make sure you get that rich condition figured out, and then replace your plugs, you need a dyno tune because in all likelihood the detonatin is caused by a lean condition somewhere, so you'll need the jets set up and carb tuned right, timing light, make sure your damper mark is at zero and initial is around 10* to start, make sure you dont overadvance up top, generally 36*-40* is where you want to stop advancing, make sure you run 93 octane, make sure you dont overheat, and run electric fans,

that's what i've learned for detonation, usually lean, overadvanced or overheating. next quench, piston geometry and combustion chamber geometry can make hotspots in he combustion area, that's why i told you to polish it out, that casting flash can really screw the flux over your combustion surface up and in a hot engine ignite that fuel....

and lastly yell at the engine builder, that's completely unacceptable to leave beads inside the engine

 

i think o decked will make your problem worse my idea is that you have too high of compression and the cc306 does not have enough overlap to bleed off the cyl pressure thats what happned to me so i sent my heads to lloyd elliot and bret bauer is making me a new cam a solid roller this time plus alot of other things so i'd say get a cam made for your motor that cc306 cost me alot of money in the long run

 

ok most of that doesnt make any sense seeing that I have a fuel injected opti spark distributor car, but the cc polishing is gong to be done by the machinist already

yeah, I know. I planned on having this engine in my car for years, not hours. Hes doing a good job fixing it so far, we'll see though what he tries to charge me for as far as new gaskets and rings goes though. An attorney may have to get involved.

 

thats some interesting info....the CC306 causing the problems...hmm. Can anyone else back that up? I dont want to have to drop another 500 if I dont have to. I thought the -16cc pistons would help me with that.

 

If ya had 77's and see detonation spots on them,ya could have heard the detonation a block away. Are ya sure ya know what detonation looks like on a brg?
The 306 could cause it due to early intake closing for the compression resulting in to much DCR.
Are the pistons a "D" dish or round dish? What is your quench? What is your DCR? If ya don't know these things ya can't just through parts at it to make it stop what is believed to be detonation.
The brgs may have digested some of that NO CLEAN UP from the blasting (WTF are ya blasting a block for) that wasn't cleaned out.
I wouldn't let that shop do any of my work and an LT1 is no different than a SBC,ya still have to check things on both.

 

I have been reading in various publications (mags, books) that a polished combustion chamber is not necessarily a good thing. The thinking is that leaving a pattern on the wall around the intake valve will aid in keeping the fuel properly mixed resulting in better and more homogenous combustion, which should result in lower chance of detonation. I have been running my CNC'd LT4 heads unplolished for 4 yrs with no detonation. I just dynoed at 417 rwhp at 6600 and 38 deg of advance. Also of interest here is my a/f was like 15:1 when these runs were made. I know, my tune was off, but it illustrates the point. I am now seeing 13:1 a/f, but didn't pick up much hp from this change. I was thinking of polishing my chambers as well, but now I don't know.

 

alright that didnt help at all, lol. now I have no idea what Im going to do. anyone have any more info to add?

 

It’s not as easy as one works and the other doesn’t. a smooth, polished chamber prevents hot spots and reflects more heat back into the chamber rather then absorbing it. Something with a pattern to it causes turbulence and keeps atomized fuel in suspension resulting in a better, faster, more complete burn. The problem is figuring out what you actually need.

Probably the best way to do it is to polish everything up, run it for a while, disassemble it and then check the burn pattern and see if there are any spots that are getting fuel washed and dimple/rough up those spots till you get a nice, even burn.