Need some engine advice....

[hunt2elk]

Since I am not very well versed in how everything works in conjunction to get a good running engine, I am hoping some of you more knowledgeable in that department can help me out.
So I had a 400 based stroker built, dyno'd, and tuned by a very respected builder. He put together a motor previously for me and it is great. This one, however I can not get to quit detonating. It happens all the time when the secondaries open, no matter if you gently roll into them, or hit it hard.
He sent it back timed at 36 all in at 3400 per his sheet. MSD ready to run with 2 medium blue springs. One odd thing about this is that when I checked the timing it came all in at 2500.
He had me back the timing down to 33 and then to 30. I put in the 2 heavy silver springs to slow the timing curve to be all in at 3950. Also had me replace the NGK6 plugs with NGK7's. The plug change didn't do anything, but the lower timing and spring change did help.
He thought my Carter 6903 mechanical pump was running out of flow when the secondaries open and causing it to go lean. Hooked up my A/F meter and saw that was not the case. Yesterday I installed a fuel gauge just to verify that. Found out that my pump was putting out 10.5 psi. Replaced that pump with another used one I had here and raised the float levels back up. Did a compression test, 3 pumps on each cylinder, warm with the carb wired open.
Last evening I went and bought 5 gallons of 110 octane race gas and dumped it in with the 11 gallons on 91 currently in the tank.
Now the thing runs great. No pinging/detonation and all dielsing/run on is also gone.
So my question is, with the info I have, do you think the compression ratio is too high to run 91 octane? Or have I been getting bad gas? I have bought it from 2 different branded stations over the course of 1.5 months, and put about 400 miles on the car.

 

[Darter6]

We all know that gas ain't what it used to be.I can't really see what the CR is from your paperwork.
Anyway, it is not uncommon to have to run race fuel mixed with pump gas.I do it and my car is 9.6 CR.
Just a added insurance for your engine.It may not take much,you can experiment to get to the happy point as how much race fuel to pump gas is needed.

 

[hunt2elk]

We all know that gas ain't what it used to be.I can't really see what the CR is from your paperwork.
Anyway, it is not uncommon to have to run race fuel mixed with pump gas.I do it and my car is 9.6 CR.
Just a added insurance for your engine.It may not take much,you can experiment to get to the happy point as how much race fuel to pump gas is needed.

He wrote down 9.9:1 compression ratio on his sheet. Can we tell if that is about right by the numbers I got from my test? Really hoping I don't have to mix race gas because it is not readely available around hear, not to mention $8.70/gallon. He knew that it had to run on 91.

 

[Ski 61701]

Have you checked your static compression vs dynamic compression? There are formulas on the web that you can use to give you a really good idea as to what the engine actually sees. I think Keith Blacks website might have a chart. Dont quote me on this but you use piston info, thickness of head gasket, information from cam card, of course bore and stroke. Combining the info will give you a really good idea about the motor and potentially what octane you might need.
I have a feeling if you continue to adjust distributor springs etc it might be more fun to drive.
I would seriously figure the static n dynamic compression and let us know what you find. We might be able to come up with a solution, and you save your sanity.

 

[451Mopar]

Curious that cylinder #4 is 15-20 psi higher than the rest of the cylinders?
What cylinder heads are on the engine?

 

[hunt2elk]

Curious that cylinder #4 is 15-20 psi higher than the rest of the cylinders?
What cylinder heads are on the engine?

I thought that was odd also. Trick Flow 240's.

 

[hunt2elk]

I have a feeling if you continue to adjust distributor springs etc it might be more fun to drive.

I'll have to check out that website to see if I can learn anything. Was hoping someone on here had a magic wand to tell me if what he wrote down was close.
No doubt if I continued running a mix of 110 I could get this thing really screaming. Advance the timing to 35, put in some lighter springs, play with the accelerator cams and squirters.
The power feels awesome now just not having the detonation and not losing power because of that.

 

[65Fury440]

So it looks like you are monitoring the AFR, that's good.
Have you pulled the plugs to see if one cylinder shows more sign of detonation than the others? Maybe see if you have one cylinder lean and verify with an infrared thermometer?
What temp does your engine run at?
Here is my experience- my 4.35 x 4.375 (520) RB with TF 240 heads, 10:1 CR 260/266 108 lsa cam.
Installed cam @104, it ran dirty down low, 165-175 psi compression. Never any detonation,I always use 90 octane non ethanol fuel because it's all I can get here besides race gas.
At the suggestion of someone, installed the cam @ 102, bumped the psi readings up about 5 psi.
Cleaned up quite a bit down low, but would get slight detonation if it was hot, like coming away from a long stop light and really loading the engine up.
If nothing else works, maybe you could do opposite and retard the cam a couple few degrees. Your static CR is under mine, with aluminum heads you should be able to run on the street, and maybe add some timing back in.
One other thing that comes to mind,retarding the timing might be diminishing returns.

AndyF said this about a 512 build-
"With the TF heads and that cam I'd start with 20 degrees initial and 34 total. For street driving you'll need some vacuum advance. The Trick Flow heads will get super hot at part throttle unless you give them some advance. If I was programming a curve I'd put 40 degrees at cruise and light throttle."

 

[451Mopar]

First, I would check the #4 cylinder valve lift to make sure the cam is not going flat.
Next try reducing your Intake Air Temperature, and maybe run a 160-degree thermostat, and/or a fuel cooling system, A bypass style regulator helps keep fuel cool too. This will reduce the initial air/fuel temperature before compression and may help.

 

[bigbluedodge]

Any idea how much dish the pistons have? I'm surprised the compression is that low (9.9) with 76cc heads and .010 deck height.

Bryand

 

[66Satellite47]

I was also wondering how the static CR was calculated, don't know the dome/dish of pistons, or head gasket bore & thickness. With a .010 deck & 76cc heads, not sure how he got to 9.9 CR.

 

[33 IMP]

Sounds like the second coming of @Kern Dog s engine. He tried most of the tuning tricks too, finally put thicker head gaskets in. Problem solved.
And, like 451 says, look closely at #4, at least rerun the compression check.

 

[Curiousyellow71]

I 2 agree w 451mopar....need to look at the cylinder w higher pressure for a problem and examine the intake lobe. Possibly readjust the valves on that cylinder it may be a little loose.

What thermostat are you running?

After that...I would keep taking more timing out and see where it quits or if it quits. Find the place where the detonation is gone. Then start tweaking figuring out how to put more back in. Its doesn't make sense to me to try a hotter plug if you have detonation.. When you are dealing with detonation your best results will be running the coldest plug you can get run. Putting a hotter plug may have made the issue worse if you did it at the same time as your dist recurve, they may have canceled each other out.

 

[hunt2elk]

Just checked #4 again. Yesterday I had all the plugs out and did 3 compression strokes. This time I just pulled #4. After 3 pumps it was at 165. Did it again and on the forth it went to 180 and didn't go any higher with more cranking. Then tried #7 for the heck of it. 3 pumps was 170 just like yesterday, on the fourth revolution it also went to 180. I bet they will all be around 180 psi.
The motor runs very consistantly at 190 degrees.
I have no idea what pistons are in it and he just listed them as CP Custom.
I believe a buddy who knows a whole bunch more about this stuff than me is coming over later. He wants to put a camera in to see what kind of piston is inside.
All I know is that I am getting very frustrated with the amount of money I paid for this engine and it not running thr way I specified.....

 

[451Mopar]

That looks like really nice parts in the engine. I'm sure it was not cheap.
Is the air filter under the hood, or do you have fresh air or hood scoop?
If the air filter is under the hood, and the thermostat is 190-degrees, the under hood temps from the air being heated by the radiator, exhaust system, and base engine temps can be 200+ degrees going into the carb. When you compress a gas the tempature increases even more and can get so hot the fuel ignites like in a diesel engine. If you can lower the initial air/fuel temp entering the chamber before compression, the total cylinder temperatue after compression will be lower reducing the chance of pre-ignition and detonation.

I just asking because the engine combination looks fine if the compression ratio is really 9.9:1

 

[khryslerkid]

I used to do just three compression strokes when checking compression and noticed doing one or two more might show more. So now I'll just crank it three, four, five and when there's not anymore advancement in the reading I'll record that.

Is there any info on where the builder set the cam's degree?

I'm no expert but would having the cam set straight up have less compression than a 2* advancement? Might cure a detonation problem to not have the advancement verses straight up?

 

[Kern Dog]

Another note on compression tests:
Do it with the throttle wide open. That will give a higher number.
Back when I was dealing with my detonation, my engine showed the same symptoms as yours. Great until I hit the secondaries, then detonation. The only thing that helped was 110 leaded race gas. 100 didn't stop it, 104 didn't either. The 110 mixed with what was left of some 91 allowed it to really run strong. All other efforts made no difference.
I have a 440 based 493, 2" headers, aluminum heads and it knocked. The fuel jetting was changed, an air/fuel meter installed, tried 1.6 rockers, a different cam, slowed the distributor advance rate, the only time I could hammer it without knocking with 91 octane was when the engine wasn't up to temperature and I don't like to do that. My calculated compression ratio was 10.8 to 1. After rechecking things with a much closer look, I was actually at 11.02 to 1. My cranking compression was in the 185-190 range.
My final move was to have the heads ported and to slip in thicker head gaskets. Some suggested it, others thought it would make the problems worse.
It worked. Now I am at around 10.2 to 1 and it runs great on 91 octane.

 

[hunt2elk]

That looks like really nice parts in the engine. I'm sure it was not cheap.
Is the air filter under the hood, or do you have fresh air or hood scoop?
If the air filter is under the hood, and the thermostat is 190-degrees, the under hood temps from the air being heated by the radiator, exhaust system, and base engine temps can be 200+ degrees going into the carb. When you compress a gas the tempature increases even more and can get so hot the fuel ignites like in a diesel engine. If you can lower the initial air/fuel temp entering the chamber before compression, the total cylinder temperatue after compression will be lower reducing the chance of pre-ignition and detonation.

I just asking because the engine combination looks fine if the compression ratio is really 9.9:1

I am running a 180 Stant Super Stat. The air cleaner is the factory Ramcharger setup. K&N oval filter and I always leave the trap doors open for fresh air. Intake is a Weiand Action+ with a 3/16" base gasket.

 

[hunt2elk]

I used to do just three compression strokes when checking compression and noticed doing one or two more might show more. So now I'll just crank it three, four, five and when there's not anymore advancement in the reading I'll record that.

Is there any info on where the builder set the cam's degree?

I'm no expert but would having the cam set straight up have less compression than a 2* advancement? Might cure a detonation problem to not have the advancement verses straight up?

I read somewhere to just do 3 revolutions of the motor also, so that is what I did. Apparently this one maxes out at 4 like you found out too.
The lobe separation is 112. Not sure if this is what you ate asking about? This is all Greek to me as I am only a lowly HVAC guy.

 

[hunt2elk]

Another note on compression tests:
Do it with the throttle wide open. That will give a higher number.
Back when I was dealing with my detonation, my engine showed the same symptoms as yours. Great until I hit the secondaries, then detonation. The only thing that helped was 110 leaded race gas. 100 didn't stop it, 104 didn't either. The 110 mixed with what was left of some 91 allowed it to really run strong. All other efforts made no difference.
I have a 440 based 493, 2" headers, aluminum heads and it knocked. The fuel jetting was changed, an air/fuel meter installed, tried 1.6 rockers, a different cam, slowed the distributor advance rate, the only time I could hammer it without knocking with 91 octane was when the engine wasn't up to temperature and I don't like to do that. My calculated compression ratio was 10.8 to 1. After rechecking things with a much closer look, I was actually at 11.02 to 1. My cranking compression was in the 185-190 range.
My final move was to have the heads ported and to slip in thicker head gaskets. Some suggested it, others thought it would make the problems worse.
It worked. Now I am at around 10.2 to 1 and it runs great on 91 octane.

Yep, I wired the carb open when doing the test.
I remember reading your thread when you went through this. Hope this doesn't turn out to be the same thing....