skinny z

Personaly, I think with the higher SCR, that it NEEDS a bigger cam. That'll move me up the performnance ladder some which was intention with the original build in the first place but a cam will move me up further.
Having said that, I can understand the aluminum head angle. I could keep on track with my first intentions and that's to be build some modest performance and great driveability.
Yeah, they sound cooler too.
Lots to think about.

Orr89RocZ

iTrader: (20)

Lt1 guys push the upper boundaries of compression with aluminum heads and reverse cooling, and they run tighter quench heights than .040. I have seen .028-.031 used but thats tight and everything needs to be spot on.

You could try alittle tighter in the future. But i dont think that alone will change your current situation.
On cooling you could try running a line to the rear coolant ports. That will help keep everything atleast more uniform in temps

raynehr

On premium pump gas, I have gotten 11:1 out of an iron headed motor. You HAVE to have an MSD with adjustable timing curves however. Takes some tuning but can be done. Had an 11:1 Nova with an MSD 6AL setup, and a .573 lift cam. Street ran that car for a couple years.

** And was running cast iron Vortec's also...

1gary

The real question here is that SCR worth it??. What mean is the amount you left on the table because of the adjustments in timing equal to what you gained with that higher SCR.I think not.So it like building something and then in hind sight trying to get rid of it.Humnmnm.

If you follow these guide lines this thread wouldn't even got written.And I promise a matched parts build will beat anything else today and every day.

A SCR with iron heads of no more than 9.5 with a DCR of 8.5 and a quench of from .035 to .045 or with aluminum heads a SCR of 10.5.

I am here to bear witness to the fact you can hear a engine knock a ton better from 3500 rpm and below that you can hear it from 3500 rpm and above.It's that 3500 and above that will rear it's ugly head and cause damages forcing a replacement engine to be built.Yep=$$$$$$!!!!.

My point is what's the point of building a SCR when your playing with cam timing to blow it back out the exhaust and polluting the intake charge besides.Then play with ignition timing and end up with the same result.Or drowning the engine in fuel curves and yepper same end result.So if you get real lucky with fuel curves and you don't hear the low end knock,but rest assured it is still knocking at the high end where you can't hear it.Well that isn't untiringly true.You will hear once it is knocking so hard,you now know you have to take it apart to fix it or it knocks for alittle and then locks up.

It's no joke,this is serious engine life issues that have to be addressed A.S.A.P.It parallels the same as a engine with no oil pressure and I am fairly sure you wouldn't run a engine with no oil pressure.If you have a engine that is playing a tune to you pinging,it's time to get off it,turn off the key and park it until you fix it properly.And not those band-aid fixes that are a yin-yang results.Add SCR and then find a way to get rid of it.I mean really??. How logical is that??.

That is my bottom line.

Orr89RocZ

iTrader: (20)

Well this part is just where do you want the power band. If you are trying to do a max effort build and need to turn serious rpm, you need larger cams. Ofcourse you will have alot more overlap at low engine speeds and suffer reversion but you arent suppose to operate there. So you can build more static comp into the build to get dcr back on track with that larger stick. But you lose the streetability. Efi helps here tho.

I will say this tho, after being in some lower comp cars that have bigger cams making lower than ideal dcr's, they still run pretty damn good. So its better to be tad low in comp than to be pushing limits of pump gas.

FRMULA88

Gary is spot on!

But in retrospect, you did NOT build a "pump gas engine" so just throw better fuel in it.

They make high octane race gas for a purpose and the problem solved.

You may not like the notion.. but this is a realistic solution especially for a max effort build that spends more time at the track than on the street.

If you intended this build to be a "street car" the pump gas in your area in simply not adequate... so Alum Heads or drop the compression a bit.

A bigger cam would also solve the problem but create others, No power brakes without a vacuum can or electric vacuum pump will be the most obvious.

If you don't want to go into the engine at this time then just use better fuel.

You will burn an awful lot of race gas / blended gas before you come close to spending what you would need to switch the heads to alum.

FRMULA88

This should be a "sticky" on this forum.. excellent source or information regarding detonation & pre-ignition.

FIW, the author, Allen Kline, is the GM Engineer who designed the
North star engine.

I really like this article because it is well written and without any 'engineer's jargon'

http://www.contactmagazine.com/Issue...ineBasics.html

FRMULA88

"Production engines are optimized for the type or grade of fuel that the marketplace desires or offers. Engine designers use the term called MBT ( Minimum spark for Best Torque) for efficiency and maximum power; it is desirable to operate at MBT at all times. For example, let's pick a specific engine operating point, 4000 RPM, WOT, 98 kPa MAP. At that operating point with the engine on the dynamometer and using non-knocking fuel, we adjust the spark advance. There is going to be a point where the power is the greatest. Less spark than that, the power falls off, more spark advance than that, you don't get any additional power.

Now our engine was initially designed for premium fuel and was calibrated for 20 degrees of spark advance. Suppose we put regular fuel in the engine and it spark knocks at 20 degrees? We back off the timing down to 10 degrees to get the detonation to stop. It doesn't detonate any more, but with 10 degrees of spark retard, the engine is not optimized anymore. The engine now suffers about a 5-6 percent loss in torque output. That's an unacceptable situation. To optimize for regular fuel engine designers will lower the compression ratio to allow an increase in the spark advance to MBT. The result, typically, is only a 1-2 percent torque loss by lowering the compression. This is a better trade-off. Engine test data determines how much compression an engine can have and run at the optimum spark advance.

For emphasis, the design compression ratio is adjusted to maximize efficiency/power on the available fuel. Many times in the aftermarket the opposite occurs. A compression ratio is "picked" and the end user tries to find good enough fuel and/or retards the spark to live with the situation...or suffers engine damage due to detonation."

FRMULA88

technology is great but don't put all your faith in your AFR gauges,

Learn how to read your spark plugs, to look for signs of detonation.

http://en.wikibooks.org/wiki/Automob...ir/Spark_plugs

skinny z

11:1 is fine to say but without camshaft duration specs it's doesn't tell the whole story.

skinny z

Please don't take this the wrong way because I really do appreciate your input but it's these kind of comments that get under my skin.
Have you forgotten how I got here? I thought you understood but I guess not.
This didn't happen as a plan. It was intended to be a 10:1 engine with a smallish cam (274/282) and run easily on pump gas premium. Hell, I'd already built one and I know it works. With the oiginal shortblock scrapped after having been run and tested with the new heads and cam, (and YES, detonation-wise it was a non-issue) it wasn't until the new short was literally slipped uner the new heads that these problems began.
Please. Give me a break here.
I understand the consequences too.

It's these comments that tell me you clearly haven't grasped what's going on here.
I'll say it again, I appreciate your insight and suggestions but please, understand what's happened and why I started the thread.
It's not a question of logic. It's a question of a build going one way when it was intended to go another.

skinny z

Gary misses the point.
The end result was an accident.
Now all I'm trying to do is find out the limits other people have experienced and go from there.
After all of this, I've learned what the limits are first hand.
Now I have to decide what I'm going to do about.

skinny z

That little read says a lot.
In fact, it enforces how I've been thinking as I fiddle and fart around with the timing. Even if I can overcome the knock issue with less timing, the engine will be so lame that it seems to me that it would defeat the whole point of building a performance engine.
It makes considerably more sense to back off the compression whether by increasing the camshaft duration or lowering the actual SCR rather than neutering it with no timing.
Thanks for the write up.

skinny z

Been doing that since the beginning and haven't seen any obvious signs of detonation. Short of a microscope I can't see anything that indicates any trouble at all.
Evidently, there hasn't been enough to leave any kind of impression on the plugs.
Having said that, I HAVE been taking care not to beat it up too much. I can here the knock plainly and only induce to check on timing or fuel trim progress.

skinny z

And for what it's worth, I re-did the timing curve again today, with a fresh cap and rotor (the old cap shows no signs of distress). 8 initial, advance doesn't start until nearly 2000 rpm and the 20 degrees is all in by 4000.
Still knocks heavily . Reduced, but still knocks.
That's all the timing I care to experiment with.
Next up is some 110 octane.

1gary

You put a knock sensor on it the timing would drop like a brick in water.................

Someone just kill me for saying that!!.

FRMULA88

This is the point I have been trying to make.

To properly read the plugs you in fact need a "scope" also called a spark plug flashlight...

under 10X magnification you WILL SEE the signs of detonation on the spark plugs and more importantly which cylinders it is occurring at. This would provide very used information. especially if it is isolated to the back half of the engine versus all eight cylinders, versus one or 2 holes.

You could also have cooling issue that is exaggerating the problem.

I mentioned this all in a previous post.

skinny z

Without a doubt.
I know one thing and that's I'm not going to drive without a reasonable timing curve.
In the meantime, I take it easy.

skinny z

I recall you saying that.
I haven't had a fresh set of plugs in it until recently and these don't have any run time to speak of.
I'll have a look at the old set(s) and see if anything is visible. I have several options regarding any magnification.
Speaking of magnification (and yes I know how to read a spark plug, I've been around a while) the article reiterates what I've always understood and that evidence of detonation can be plainly seen.
To quote,"You will see small ***** of fuel and metal deposits on the porcelain tip and smaller ***** of debris on the electrode tip. The metal case will look as if it were sandblasted (inside the engine the piston will also look sand blasted)."
This is what I've been looking for and have seen quite clearly in the past (I'm not referring to this engine). This isn't to say that a magnifier won't aid in detection and I will take it to the plugs I've removed for a really thorough examination..
On a similar note, and this is something that I've never come across before and haven't found in any tech papers, what is the condition that causes a yellowish-green plug tip. Rather than the tan that's indicative of a proper mixture, at one point last season I had plugs that were tinted that colour. At the time the engine had been pulling a lot of oil past the guides but there was no evidence of oil fouling. Very strange colour.

FRMULA88

Tan or any other color on the porcelain is irrelevant, those are the additives in the fuel, to read A/F on a plug you want to look for the soot ring at the base of the porcelain.

I can tell you from experience you will "see" a lot more under 10X mag than the naked eye... what looks like clean plug to the naked eye is not the same under the scope.

it's a cheap investment.

obvious massive detonation damage will be visible without a scope but the damage indeed starts at the microscopic level.

skinny z

http://www.contactmagazine.com/Issue...ineBasics.html

That's an excellent article. Besides a very precise explanation of what's going on during abnormal combustion, it offers some comfort in that it says detonation can be tolerated for considerable periods of time (relative to the power output of the engine) before damage is done. I haven't really leaned on this engine during testing other than to bring it to point where I hear the knocking. Nothing sustained and that's a good thing.
I experimented a little this evening to verify when and under what conditions the detonation could be induced. Based on that, I'll be running some tests tomorrow with a 50/50 mix of 110 unleaded racing fuel and 91 unleaded ethanol free pump premium and trying to repeat the testing results. It should be interesting.

FRMULA88

keep us posted.. the problem should go away with higher grade fuel.


FWIW I found a local source (1 hr away) for 110 & 116 unleaded.

so after I burn thru this C12 I have I am going to switch mainly because I don't want myself or more importantly our kids exposed to lead tainted exhaust fumes.

NASCAR switched to unleaded fuel this season, screening of drivers & pit crew showed elevated lead levels in their blood. Imagine if they tested the fans in the stands, especially the hard core ones that follow the circuit.

Now granted my exposure will be limited and far less than a NASCAR pit crew but still why bother if a lead free fuel with same octane does in fact exist and it actually cost the same.

I think that eventually what happened in Canada will happen here, my guess is California will be the first State to ban leaded fuel for off-road use and when that happens IL, etc. will follow.

This was part of the reason I tried to use E85, but just not enough octane (98 R+M/2) for my application.
bummer because I have as station 4 blocks from my house that sells it.

skinny z

After my trip to the local circle track yesterday I learned from the track manager that the leaded fuel ban was never implemented here (Ontario, Canada) although the threat existed at the beginning of the season a few years back. The argument was that a lot of the events had a strong American contingent and with no leaded fuel available, these events would essentially fold.
As such, there's no ban on leaded fuel for racing. That said, the platform for unleaded fuel was prepared and it's availability is plentiful.
At $3.60/litre or roughly $15 U.S. a gallon, it's not cheap. Then again, the rep from Pro Racing Fuels suggested the 50/50 mix I described earlier. That takes some of the edge of anyway.
Weather looks good. Going to check the plugs, take a few pictures and do a little testing.

FRMULA88

LOL you mean the 50/50 mix I suggested 2 weeks ago,, LOL...

LOL,, ugly Americans with their leaded race gas.

The truth is no modern race engine actually needs lead (TEL) for valve seat lubrication, but TEL is still a cheap way for the refinery to raise octane level.

If you built a race engine that needed 110 + octane, leaded fuels were the only choice for decades.

I am glad there are other options, even VP has a 105 unleaded product but I want to make sure my setup is OK and get some run time in (tired of engine getting rebuilt)

Now that NASCAR switched to unleaded, I think it will only be a matter of time.

Why use a known neuro-toxin if you don't need to. ?! Not too mention parts like the spark plugs last longer

skinny z

OK. Credit were credit is due!
There's been so much information thrown out here (and at SpeedTalk) that I find I have to go back and re-read the posts. A perfect example is the link you posted to the detonation/pre-ignition paper. I didn't check it out when first posted but after going back, I had a 2nd look. Great read. Something I'll file away in my library.

FRMULA88

Since I could not "hear" mine detonating I am going to invest in one of these..

simple and effective and for less than 300 $ more economical than a rebuild !

FRMULA88

here's the info

skinny z

That is awesome. I have plans to build one but as the advertising blurb says, they're difficult if not impossible to compensate and/or calibrate for engine noise.
When do you think you might have one installed? I'll be Stateside the middle of next month and have an enormous shopping list. This might be on it.

FRMULA88

The install is very straight forward but I need my engine back from my builder.

I reached out to the vendor to see if I can use their light with a stock GM knock sensor.

I can mount this on my cowl or I am thinking about putting it next to my shift light... which glows amber.. so while I am at WOT and shifting thru the gears if the red knock light comes on I can lift on the pass. I can see the amber shift light in my peripheral vision so I can keep both eyes on the track and or scan the other gages crankcase vacuum, engine temp, and fuel pressure.


This is when I miss the data logging feature I had with my projection system

Orr89RocZ

iTrader: (20)

Never to late to go back to efi

FRMULA88

true, but I can buy alot of carburetors for the price of a new efi system.

The problem with aftermarket EFI systems is they keep evolving so you spend good money only to have an obsolete system in 2-3 years.

The next model ALWAYS has the features you wish your current model did.

So after playing with a used 4Di system for 10+ years on my 383 (no knock sensor on my model) I made the choice not to play the " I gotta have the newest efi system game " and went back to good old reliable carb for my latest engine build.

Orr89RocZ

iTrader: (20)

While that is true, you dont need alot of fancy features. A stock tpi ecm and harness adapted to a single plane efi intake will do everything you would need. Its basically an electronic carb, because a carb doesnt have fancy features so why would you need it for efi? Lol. Give me spark and fuel, pumpshot and decel enleanment. Thats all you need.

FRMULA88

actually the projection 4DI had all I wanted / needed, the issue was I had the TBI system (only good to 650 HP LOL) and would have to start over with a MFPI system to support 780 + HP which meant starting over.

So at that point I decided to go carb. cheap, simple, stupid, yet effective.

For what I paid for the projection system on ebay and the time I had it, over 10 years it was money well spent on the 383 build.

FRMULA88

I could always machine my Brodix intake and weld in the injector bungs rails, go back to efi in a flash.

just have other priorities right now (children) so a carb is just fine and has been doing the job on race cars for over half a century !

LOL

1gary

I question how fast it is??. Is it a matter so much after the fact??.

If it works like I would hope,I might consider one for my BBC 13.1 race car.

skinny z

While I haven't gotten around to testing the fuel I have spent a little time working through a few engine simulations and looking at running compression and reduced static compression ratios.
The results are interesting I think. I've attached dyno sheets and DCR values for various options I have regarding this short and these heads (yes, iron).
1) The current cam combination is installed straight up with a SCR of 10.39:1 and 8.4 DCR.
2) A XR288HR at 10.39:1.
3) Current cam at a reduced 10.03:1.
4) Current cam installed 4 degrees retarded at 10.39:1.
Looking at the DCR values and dyno tables, I like what I see with the current cam and reduced compression and the current cam laid back 4 degrees.
With the first choice, dropping my compression ratio increases the quench by .016". I'm not sure how much of an impact that'll have on detonation resistance. It just may be a step sideways. Having said that, I ran a 10:1 Vortec that had almost .060" squish and it was relatively knock free.
With the 2nd choice, (-4 degrees), I keep the 10.39:1 and the .040" quench. The DCR drops to around 8.1.

I know the current cam as it's installed isn't going to be streetable. At least not my definition of streetable anyway.

skinny z

Here are the other 3 options I'm considering:

skinny z

Interesting, the option I prefer (as this point) is the one that involves the least amount of work, is the lowest cost and also keeps some the design I've built into this engine from the start.
Retarding the cam by 4 degrees lets me use the cam I spec'd and keep my tight quench (which is known to aid in knock resistance).
I also have the infrastructure in place to make the cam timing very change very easily.
The points of peak torque and peak horsepower are moved about 500 rpm up the rev range. One advantage of this new shortblock is that it's built for more rpm than my old one. Steel crank, Elgin rods. Plus it's fresh. more or less.

1gary

Skinny.By now with two pretty much active threads on two different forums and multi posts on both,you would have it fixed.Abit of advise.You can test until the cows come home and then it gets down to taking it apart to actual inspect it to see what the problem is.Also the higher percentage issues are the most likely going to be the problem.

For me,it isn't common to pull over and park on a thread vs just surf over a thread.I don't operate on internet time so I know repairs don't happen in those kind of time intervals.But I got to tell you a thread that drags on I do loose interest in as I think most guys have the same effect on them.

Do I think you have a transitional from primary to secondary fuel problem??. I do.A more serious effort above just jet changes are required to fix that.Power valves,cam changes,and on vacuum secondaries spring changes are key.BTW if you nick a jet changing it with a common screwdriver,it doesn't flow as it should.

So here is the bottom line.Although you can hear the mid range knock,given the SCR,I would be tons more worried about what in the higher ranges I know for a fact I can't hear.Remember I spoke about the higher percentages.Your case for that is over the top.So for me to continue to advise on this thread,I need to see you make progress in Getting-It-Done.

skinny z

I hear you loud and clear Gary.
As for the testing, timing is everything and despite my posts here and over there, there just hasn't been suitable space for me to get into it. I've had a few other projects on the go, most noteably my daily driver/service truck and that requires my immediate attention.
What I have found is that posting and surfing can offer a wealth of information in a few minutes that might othewise take me hours of experimentation. All you have to be able to do is "seperate the ***** from the Shinola" and learn from other people's efforts. That's the reason I started the thread in the first place, which is something I keep coming back to.
As for the actual repairs, which I'm reasonably sure will involve dialng back the cam timing by 4 degrees, that will wait until the early spring. You see, for me, this is strictly a hobby. I can put it down when I need to and pick it up later. The forum stuff is just another part of that.
Thanks for the input. I hope you don't lose interest.