Tuning For Detonation

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RustyRatRod

RustyRatRod

I was born on a Monday. Not last Monday.
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If yall have paid attention to my new slant build, you know it has some pretty good compession. I'm encountering some light detonation. I knew going in it was a possibility, but, I forged ahead out of necessity.

As those of you who've followed the build know, the head ended up being damaged at the first machine shop,when it slipped off the broach on one end and Richard didn't catch it until some damage was done. No big deal. Mistakes happen. Richard was up front with everything and refused to charge me for it and even knocked a chunk off what I owed him for other work AND recommended someone who I've known a very long time, but I did not know he had the equipment that could fix the head.

Fast forward to Big Richie Griffin, in Gordon, Georgia. He runs a small, but very high end machine shop catering to really, really high end dirt tack boys. The the team he works for has two probably half million dollar a piece dirt track cars. Yup. Serious bidness. Anyway, Richie took the head on this and fixed it. That's how it got a total of .155" off.
ROTTLER.jpg


So, since I had already done the valve job that head, it had to be utilized. Static compression on the engine ended up dead on top of 10:1 with the piston in the hole .175" at TDC. A perfect habitat for detonation. So, I had to choose a camshaft with a late intake valve closing (IVC) to help combat excessive cylinder pressure.

After talking with Ken Heard at Oregon Cam Grinders, we decided on one with .465 lift, 250@.050" duration ground on a 108LSA. It has a 70 degree IVC. With the camshaft,that brought dynamic compression to 7.9. Hot dog, I got it licked, right? Naw. As luck would have it, that wasn't enough. The engine is experiencing a light detonation issue when crowded in 2nd or high gear. Follow along as I work to tune this out hopefully to run a high compression slant six on pump 87 swill. I've already made some progress which I will outline here as I continue to tune.

I have give all the credit to my beautiful wife, Kitty, because it was her who first heard it and continues to be my "tuning ear" since the spark knock is out of the range of my terrible hearing. According to her, we are about 2/3 the way there already.

Stay tuned. Pun intended.
 
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Keep in mind, although this is in the slant six section and is a slant six, these tuning tips will work for any engine that has detonation issues.

yellow rose has been really cool about advice and what not. Some things I was going to try already, others I hadn't thought of.

So we began off the bat with initial "about" 20. I hadn't yet measued total, as this was a new engine and I wanted to make sure eveything was all broken in good and "settled down" and everything else with the car was good.

Once all that was done, we started driving it around, first trip was to my friend Freddie's house, as yall saw in the video. On the way back from Freddie's Kitty says "what's that noise?" after I kinda crowded into it some. After a few more times, between me making it do it and her great description, we determined it was prorbably spark knock. Got back and dropped initial back to 15 and Kitty said although it was still there, it was not as loud. So, now we had confirmation.

So far, I've gone from RN14YC to RN9YC and blocked off the exhaust heat entierly. Doing both those has us where we are now. It only rattles now if I crowd hell out of it in 2nd and high gears at lower RPM than I really "should" and it does not rattle "AT ALL" until the temp gauge comes up some, so we're really close already.

One more footnote.....last tank of gas I got, I put in 90 non ethanol. If I can get it not to rattle on that, I am petty certain it also won't rattle on 87. Really have not noticed ONE BIT DIFFERENCE between 87 and 90. ZERO

My last step I did was put the FBO limiter plate in the distributor last night. It's back running again, but I've not yet set the timing back right, as I was tired last night. I put the plate on the 14 degree slots, as I want to run 20 initial, because the engine really liked that. This will limit the total to 34, 20 initial, plus the 14 mechanical. It was at 40 total all in at 3000 RPM without the limiter plate and on 15 initial, so the 40 was too much and likely why it was encountering spark knock. We should have it very close now.
 
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New update. We still have 40 total WITH the limiter plate. So, that can only mean the 14* slots are the SAME SIZE as the slots in the distributor governor and the plate is not acting as a limiter. LOL Story of my life. I will pull the distributor YET AGAIN and reposition the plate, but not today, as I'm not feeling well. I've also got to track down a fuel leak from "somewhere" around the fuel pump. Oh well. LOL
 
Slants don't really need more then 30* total advance. Back it down to that and the knock may go away. Also blocking the choke flapper is a waste of time. All you have managed to do is make the choke not work properly.
 
rustycowll69 said:
would it help if you lowered (raised numerically) the rear gear ratio?
Click to expand...

Possibly, and I plan on that in the future as I have a Ford 9"narrowed to A body width that's getting 4.10s and aDetroit Locker.
 
kesteb said:
Slants don't really need more then 30* total advance. Back it down to that and the knock may go away. Also blocking the choke flapper is a waste of time. All you have managed to do is make the choke not work properly.
Click to expand...

That'll be your little secret. The choke will work fine since it's electric.
 
kesteb said:
Cool, still need the flapper to heat the bottom on the manifold.
Click to expand...


That is the very LAST thing you want with relatively higher compression ratios and pump gas. That’s a waste of energy and it kills the cooling effect of the fuel, raises the in;ET air temp and causes detonation.

Bad. Very bad.
 
My slanty is only 9.5 and I went down the same road, with a smaller cam, much smaller. Sorry, that engine was assembled in 1994 and the only parts I remember are 9.5Scr, short Power-Timing, Late stall-timing and 87E10.
A SuperSix 2bbl intake, but not set up for power, rather, set up for fuel-economy. I ran her at a minimum coolant temp of 195.

I hope you can achieve your goal

_________________________
BTW; I still have that 1980 Volare,(going on 27 years now) and this spring it fired right up with just a lil fresh gas dribbled into the intake. Probably the best starting carbyd engine I've ever had, and the only reason I haven't yet hauled away that rusty hunk of junk . Oh and the trans has been thoroughly de-bugged as well.
 
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kesteb said:
Cool, still need the flapper to heat the bottom on the manifold.
Click to expand...

Again, a complete myth for a performance engine. Manifold heat needs to be blocked off on peformance engines. That's why there are gasket sets with block offs included in some sets.
kesteb said:
Cool, still need the flapper to heat the bottom on the manifold.
Click to expand...

This is both correct and incorrect. Lemmie splain, Lucy.

As we all know, combustion causes heat. In a high compression, high performance engine, heat is the enemy. The more heat the incoming air/fuel charge has, for example makes it more difficult to combat detonation in a pump gas situation. So, for this build.....and lots of similar ones, blocking manifold heat is not only correct, but very beneficial to the engine.

Now, were we talking about a stock or mild build I would tend to agree with you. Also, there's the argument for people using headers or Dutra Duals. No manifold heat there.....unless they go to the trouble to make a coolant box under the intake and most don't and they see zero side effects, except maybe a longer warm up period. But they do see increased performance due to keeping heat off the intake charge. All of the "fuel atomization" crap you read and hear about putting heat in the manifold is really only beneficial before an engine reaches it's intended operating temperature. Once there, there's no need for it and it actually costs power and mileage, too.
 
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AJ/FormS said:
My slanty is only 9.5 and I went down the same road, with a smaller cam, much smaller. Sorry, that engine was assembled in 1994 and the only parts I remember are 9.5Scr, short Power-Timing, Late stall-timing and 87E10.
A SuperSix 2bbl intake, but not set up for power, rather, set up for fuel-economy. I ran her at a minimum coolant temp of 195.

I hope you can achieve your goal

_________________________
BTW; I still have that 1980 Volare,(going on 27 years now) and this spring it fired right up with just a lil fresh gas dribbled into the intake. Probably the best starting carbyd engine I've ever had, and the only reason I haven't yet hauled away that rusty hunk of junk . Oh and the trans has been thoroughly de-bugged as well.
Click to expand...

Thanks! I think we'll get there. We're right on top of it now.
 
RustyRatRod said:
If yall have paid attention to my new slant build, you know it has some pretty good compession. I'm encountering some light detonation. I knew going in it was a possibility, but, I forged ahead out of necessity.

As those of you who've followed the build know, the head ended up being damaged at the first machine shop,when it slipped off the broach on one end and Richard didn't catch it until some damage was done. No big deal. Mistakes happen. Richard was up front with everything and refused to charge me for it and even knocked a chunk off what I owed him for other work AND recommended someone who I've known a very long time, but I did not know he had the equipment that could fix the head.

Fast forward to Big Richie Griffin, in Gordon, Georgia. He runs a small, but very high end machine shop catering to really, really high end dirt tack boys. The the team he works for has two probably half million dollar a piece dirt tack cars. Yup. Serious bidness. Anyway, Richie took the head on this and fixed it. That's how it got a total of .155" off.
View attachment 1715730592

So, since I had aleady done the valve job that head, it had to be utilized. Static compression on the engine ended up dead on top of 10:1 with the piston in the hole .175" at TDC. A perfect habitat for detonation. So, I had to choose a camshaft with a late intake valve closing (IVC) to help combat excessive cylinder pressure.

After talking with Ken Heard at Oregon Cam Grinders, we decided on onewith .465 lift, 250@.050" duration ground on a 108LSA. It has a 70 degree IVC.With the camshaft,that brought dynamic compression to 7.9. Hot dog, I got it licked, right? Naw. As luck would have it, that wasn't enough. The engine is experiencing a light detonation issue when crowded in 2nd or high gear. Follow along as I work to tune this out hopefully to run a high compression slant six on pump 87 swill. I've aleady made some which I will outline here as I continue to tune.

I have give all the credit to my beautiful wife, Kitty, because it was her who fist heard it and continues to be my "tuning ear" since the spark knock is out of the range of my terrible hearing. Accroding to her, we are about 2/3 the way there already.

Stay tuned. Pun intended.
Click to expand...

why not move up to 89 or 91 , and fugetaboutit ?
 
RustyRatRod said:
New update. We still have 40 total WITH the limiter plate. So, that can only mean the 14* slots are the SAME SIZE as the slots in the distributor governor and the plate is not acting as a limiter. LOL Story of my life. I will pull the distributor YET AGAIN and reposition the plate, but not today, as I'm not feeling well. I've also got to track down a fuel leak from "somewhere" around the fuel pump. Oh well. LOL
Click to expand...
Rusty are you running a vacuum advance?
40* total at what rpm?
 
famous bob said:
why not move up to 89 or 91 , and fugetaboutit ?
Click to expand...
I know folks at .org that have ran double Fel Pro head gaskets to resolve similar over compression issues.
Another fix would have been to spring for a custom thickness copper head gasket. Then you get the compression you want and the engine also gets the timing it wants.
As you know, taking timing out of the engine to reduce knock is also taking performance out of the engine.
 
New update. I removed the distributor and moved the limiter plate to the 10 degree slots. Kinda wish it had 8 or even 6, but 10 is it and then zero. So, reinstalled and now at "about" 20 initial (I say about because the balancer mark is about 5 degrees off the scale), it has 35 total, so that's about all I can do with the limiter plate. I'll back off the extra 5 degrees back to 15 if I have to, but the engine really likes that extra 5 degrees. Haven't driven it yet, as I need to address the fuel leak. I'll do that tomorrow and then we'll test drive it.
 
512Stroker said:
Rusty are you running a vacuum advance?
40* total at what rpm?
Click to expand...

It was 40 at 3000 RPM with 15 initial. Now it's 35 at 3000 RPM with 20 initial. Yes, I am running a vacuum advance.
 
famous bob said:
why not move up to 89 or 91 , and fugetaboutit ?
Click to expand...

89 won't make a difference and super here is 3.25 plus a gallon.......but if I have to do that, I will. My question is, why not tune it correctly first so it can run on the lowest octane I can get it to run on?
 
RustyRatRod said:
89 won't make a difference and super here is 3.25 plus a gallon.......but if I have to do that, I will. My question is, why not tune it correctly first so it can run on the lowest octane I can get it to run on?
Click to expand...


Keep chipping away at it. You’re almost there. Prove the naysayers and nattering nabobs wrong.
 
yellow rose said:
Keep chipping away at it. You’re almost there. Prove the naysayers and nattering nabobs wrong.
Click to expand...

Ha! Well, I really cannot do anything else to limit total timing more. I have the plate installed in the 10 degree slots. If there were 8 and 6 degree slots, I'd experiment with those. I did email Don to see if he might make something custom. We'll see. I think though, the 5 degree drop in total might do it. It's gotta be really, really close now. I'll know tomorrow after I fix the fuel leak and drive it.

Nattering nabobs. LMAO
 
yellow rose said:
Keep chipping away at it. You’re almost there. Prove the naysayers and nattering nabobs wrong.
Click to expand...

Also, keep in mind, this is ALL without the high flow 160 thermostat. It'll be here Monday. I also still plan on scheming up some kinda cold air intake. I appreciate your help and guidance more than you know.
 
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