Another one brakes a crank, with 10.1 compression

[Gach]

Guys please don't try this, I know you've read articles about certain people running 10.1 compression, but there is allot involved in doing this, so please don't believe every thing you read.

[Gach]

Guys please don't try this, I know you've read articles about certain people running 10.1 compression, but there is allot involved in doing this, so please don't believe every thing you read.

[Brian Baker]

So, who broke this time? Was iiiiiiiiit, you? 'fess up.

[Gach]

Brian, I run 12.5 in the race car, and 9.5 in the street car, I would never tell anyone to run 10.1 compression in a 455 street car, with iron heads, but you sure can with aluminum heads, with no problem,or build anyone a motor with 10.1 comp with iron heads, not with todays gas.



[This message has been edited by Gach (edited 03-23-2000).]

[PONTIAC DUDE]

Gach, run the 58-62 Pontiac steel/rubber rods in your customers 10-1 engine, make a 1/4 mile pass, your compression will be lowered to 8.5-9 to 1 and he will be none the wiser & you won't have to worry about breaking a crank as it will probibly run on 87 octane when they get done flexing all over the freakin place. Later, dude

[Triggerman]

Gach, I must have missed some of these articles. I really don't recall any person or article suggesting that someone put 10:1 compression in a motor on pump gas and just go driving. I do recall some assertions that 10:1 can be accomplished on pump gas, but only with the most careful tuning and monitoring. Compressions ratios at this level have been accomplished on street driven cars, but it's certainly not for everyone. Each person needs to assess their particular experience level along with their desire to continually tune and monitor engine conditions. Keep in mind also that gas and weather types vary all over the country...what may be possible in sunny FL may not be feasible in other locales. T (gotta look at plugs and rocker arms every now and then)M

[Bob Dillon]

Huh? What crank? what article? whuuhh?

------------------
I want to die peacefully
in my sleep like my grandpa,
not screaming like the passengers
in his car.

[Triggerman]

Gach, now look what you did...you woke Bob up. TM

[Gach]

LOL..... Well some times he's a little slow, it wouldn't be because I didn't take the time to give a better explanation of the broken crank...LOL.. I don't think there was any specific articles on how to run 10.1 compression, but there are some who are doing it, that are knowledgeable, an others who try with out a full under standing of what's involved. I should clear this up a little as to why I posted this topic. I received an e-mail, which said, Gach you were right,
my motor was detonating, the guy at the machine shop said, it was what course my crank to brake. I think you can see why I didn't go into detail, I didn't want to have to give a name, but only to remind anyone attemping to try this. This guy never heard any pinging, but the bearings were
hammered, the minute he told me what the bearings looked like, that was my first response, and after having it check out, he found out I was right. Todays gas is like piss, my guess is that's more then likely some thing he over looked. Hope this answers my reason for posting this topic. Just
because you read some were that it's possible, does mean just anyone can do it. Hey Pontiac Dude I really like the reality picture....LOL

[Tom McQueen]

Well, Im about to go there. The 470 pistons came Friday and everything else is sitting in boxes waiting for assembly. The final CR should be 10.3:1, with 84cc E-heads and I intend to run pump premium. Have 6.8" eagles and steel main caps with studs (4-bolt). Will fill the block to the bottom of the freeze plugs. All sharp edges in the combustion chamber have been knocked down and polished and I am about to go over the valve pockets in the flat top J&E's. Using a strong street solid roller, .620" net, 264 @ .050 on 110 centers.

[PONTIAC DUDE]

Well, Hang on, here it goes!!!!! Misconception #1,just cause you can't hear it (detonation), doesn't mean it isn't happening. You can't imagine how many engines I've torn down with 10.25/10.75 with discintigrated piston tops. Misconception #2 You can run aluminum heads with 11.1-1. yes and no. Aluminum disappates heat, thus allowing you to run more compression (1 point higher is the norm in thinking), however if your cam doesn't blead off some static compression at lower rpms, detonation will occur. Then how do the newer cars do it? Computors that control spark advance ever step of the way, fuel injection, and knock sensors that retard timing at the hint of knock. Hard to do with a distributor that slings it's weights controled by a non variable small spring, & carb. I've developed more USABLE horsepower at 9.5-1 compression on pump gas. IT'S in the right CAM selection. If your on Kill mode for the street & want to run 10-11.1 with aluminum heads go for it, but be careful. #3 run an MSD or similiar control box with retard capability, & knock detection, This is how the Buick GN scene works on radical boost modes, so if your on pump gas you can retard if you experience problems, then recurve your distributor to this setting & start again. You can't get enough voltage. You will always hear the story of "I ran 11-1 on the street with no problems", however if you check the deck height, gasket they used & real cc's of the head, I BET it would work out to be a lot lower. How many early engines (400) had piston failure, then replaced them and no more problems thinking the compression is the same. Aftermarket piston manufacturer's come with bigger reliefs, Thicker head gaskets(.039) then they come from the factory(.018-.028), valve job that sunk the valves, raising cc's. creating a 9.8-1 engine from a 10.50 factory unit. So remember it can be done but there are RULES that need to be followed & still your taking chances for the average person without the resources to chase it. Boy, Am I tired....Getting to old for this SH*******T as Scott would say, Gach has more stamina then me for this stuff, Hahahaha. Later,dudes

[This message has been edited by PONTIAC DUDE (edited 03-26-2000).]

[Gach]

Pontiac Dude, what a great response. I really like reading your post, it's always informative. I feel I learn some thing every time you post, one thing I like is you don't get supper technical. Also great to get unbiased facts with out feeling like some one is trying to discredit you, I'm sure that comes with having experience, in knowing what the hell your doing, love your sense of humor.

I have to agree with you, there is more useable hp to be gain at 9.5.1 compression then trying to go for the limit, and just like you said, when you really come down to it, you find the claim of 10.1 to 11.1 really isn't there, because if it was" they'd be braking cranks or pistons. If you were running a total of 34 degrees, and you've retard the timing 2-4 degrees, an pick up ET by doing that, it's because you had detonation, an not because the motor likes less timing.

One question for you Pontiac Dude, I like the idea of knock sensors that retard timing at the hint of knock, are those adaptable for running on our old Pontiac's, sounds like another tool that can be use, for that detonation you can't hear, and if your going out on a limb an trying this a retard set up is another good idea.

Tom, with your aluminum heads that compression sounds real good, and Like Dude said be careful of what static compression your cam will produce. That's another good topic I'd like to get into, maybe some one can give some idea's on how much static compression you can run, with your
compression ratio, and how to figure out' how you compute what you'll have for static compression with any cam, I just don't feel comfortable I could do a good job in explaining it.

It's reality time Gach

[Ccass]

Good topic! Too much technical info to leave in the Lobby.

[GP-K]

Great Thread Gach,

You are right, too many guys want to run way too much compression with unleaded premium pump gas, and don't understand the consequences.

You hit the nail on the head when you said that you don't have to hear spark knock to have a detonation problem in your engine.

The common mis-conception of detonation is that many guys confuse detonation with pre-ignition. While the two are somewhat related, detonation will destroy an engine, as Gach has confirmed, and pre-ignition is a low rpm symptom of some detonation related problems.

There are several aftermarket ignition systems, including MSD, Electromotive, and Halmeter which do have knock sensors which can be used in a Pontiac V8 (or nearly any other engine) to adjust ignition advance to optimum, depending on fuel quality, air temp, engine temp, etc. I have heard good things about the Halmeter and Electromotive systems, but both are very expensive, crank trigger, distributor-less systems. I plan to use the Electromotive system on my autocross car when I change from Webers to fuel injection. $$$

Later,

K.

[Triggerman]

Gach, the familiar formula which involves the volume of the cylinder and chamber being compressed into the chamber volume only gives the motors mechanical compression ratio. However, as you are aware...as the piston is rising to compress the intake charge...nothing gets compressed until the valves are closed. If you pull the intake closing figure off your cam card (or take actual measurements with a dial indicator) this will give you the rotation degrees that the crank will turn from BDC until the cylinder is sealed. Either measure the actual piston rise to that point or calculate with a Fourier crank slide formula. Now complete your compression calculation with this "shorter" cylinder. A second method that is much easier. Most inexpensive engine analyzers do this calculation for you. I have ran different durations to see what effect it has on the dynamic compression ratio of some known running combinations. I have also found that just advancing or retarding the cam has some appreciable impact. If there is an interest I could post some examples of these effects. TM

[Jim Hand]

Gach,
I have a question for you. You referred to "another" broken crank as a result of running 10 CR - would you mind telling us about the FIRST crank and who it belonged to? I am sure you were not referring to the crank that failed from normal performance use in my car in 1995. As we have previously described many times, the crank that I broke had well over 2500 drag strip runs on it, and it had never been checked for cracks. Additionally, there was never any indication of any damage of any kind ever to the soft parts in the engine - things such as pistons, rings, ring lands, and bearings. Even after the crank breakage, all of these parts were still in perfect condition, except for the assorted bruises suffered during the actual breakage event. There simply is no way that anything as strong as a crank will fail before definite signs of abnormal wear on the softer parts mentioned above. Additionally, I sent part of the broken crank to a well known University for stress analysis and review of the break, and the results confirmed exactly what we have previously advised - it failed from continued power input over an extended time. Jim Butler has reported that he finds many used cranks that come in to his shop with cracks - for normal pure street use, they could run for a long time, BUT after making some 2500 drag strip runs in the 12’s dragging two tons along, they may eventually give up. So a suggestion for all, in addition to all other work prior to assembling an engine, have the crank carefully checked for any cracks. For additional information on running optimum CR, take a look at the article on Eric D’s great site at
http://www.wauknet.com/douthitt/compresi.htm

This article goes into great detail about many aspects of this subject, and has a lot of data on relationship of cam timing to actual compression. I also would like to ask all readers for feedback on that article - if it is incorrect or needs clarification, please advise so I can correct it. So Gach, please tell us more about the first crank you were referring to, and also please tell us more about the second crank - did the owner have any prior indication, such as bearing noise, or did it simply fail as he was driving down the street? What size was his engine, what heads was he running, and what cam did it have in it? All of these facts are pertinent when analyzing parts failures, and we are all interested in preventing similar problems. Jim Hand
http://www.wauknet.com/douthitt/compresi.htm



[This message has been edited by Jim Hand (edited 03-27-2000).]

[Gach]

Triggerman, Great post! Yes please do, I'd be very interested as I'm sure many others would to. You sure can do a better job then I could. I get this question all the time.

[Gach]

Jim, I think if you go back, and read my responses on this topic you'll find your answer. The Subject: line refers to another broken crank, as I'm sure there has been many from trying to run 10.1 Compression. So there is no first one, just like I'm not going to reveal, who's crank broke, that's not the purpose of this topic. I would never recommend anyone trying this unless he has a full under standing of what's involve, and that is the purpose of this topic. I think it has become very interesting, lets not get off what the real subject is about. Now weather or not your first crank broke from trying
to run 10.1 compression, I can't really say, remember denonation is silent, an there's not always signs, especially if a motor has been freshen up often. When you have occasional silent dentonation, it fatigue's the crank, and it's possible that's what cracked the crank, so at that particular moment the
crank broke, there may have not been any signs. every thing could look perfect. A simple thing like retarding the timing which could have pick up ET, because of weather or track conditions, tell's me that more then likely there was some occasional dentonation. There is just to many factors involve to try and list all the possibility's. I hope I've answer your question.

Now to answer the second part of your question I'll repost my third responses
**** LOL..... Well some times he's a little slow, it wouldn't be because I didn't take the time to give a better explanation of the broken crank...LOL.. I don't think there was any specific articles on how to run 10.1 compression, but there are some who are doing it, that are knowledgeable, an others who try
with out a full under standing of what's involved. I should clear this up a little
as to why I posted this topic. I received an e-mail, which said, Gach you were right,
my motor was detonating, the guy at the machine shop said, it was what course my crank to brake. I think you can see why I didn't go into detail, I didn't want to have to give a name, but only to remind anyone attemping to try this. This guy never heard any pinging, but the bearings were
hammered, the minute he told me what the bearings looked like, that was my first response, and after having it check out, he found out I was right. Todays gas is like piss, my guess is that's more then likely some thing he over looked. Hope this answers my reason for posting this topic. Just
because you read some were that it's possible, does mean just anyone can do it. Hey Pontiac Dude I really like the reality picture....LOL ***


Now, all I know is it's a 455, we never got into the details of his complete motor combination. I think it's more important, that we give some kind of an idea on how to pick the right cam, and being able to tell what your static compression is with any given cam, rather then get into who's crank
broke in 1995. Learning how to do that, is what's important, and I think would be very interesting, because I get ask this question all the time.

Gach

[PONTIAC DUDE]

I'll have to agree with Gach on this one, only for the fact that most people when they build an engine they go to the book & pic a cam that there buddy in their Cheby uses. (in profile). Also If you look at the grinds out there, most,75%, are single pattern cams, Why, ease of production?,it works in other brands?, you tell me? The few people that have experience, thru knowledge, or experience can get away with it. 99% can't!!! Lingenfelter has run 12-1 on the street with pump gas (in a Cheby SB) by using the right cam timing. But It wasn't an OVER THE COUNTER cam. Why even take the chance of the 1/2 to 1 point of compression you gain (about 12-20 HP depending on the level of performance) when you can make it up in cam & flow work. I mean gas even changes from day to day. even sitting in the ground. Do you really think your getting EXACTLY 93 EVERY time. come on dudes, wake up and smell the coffee. I mean, I've seem octane booster that won't even help. Seen different brands of booster, ALL act differently. This compression thing is for National records & race cars, not DAILY drivers. If your an occassional Friday night racer and trailer Queen, MIX or use Race gas, but you didn't hear it for me, No, I DIDN"T say to use RACE GAS on the STREET. My hand did it without my permission. I deny any knowledge of the above thread and this tape will self destruct in 5 seconds. BTW, Haven't experienced broken cranks, but PLENTY of hammered bearings & wiped cranks from the compression deal as they don't HEAR knock & run the normal 34-36 Pontiac timing. Most people don't know, it's not their fault. They just go by what they hear & sometimes even if you tell them it isn't practical they do it anyway.

[This message has been edited by PONTIAC DUDE (edited 03-28-2000).]

[tempest455]

I receive literally hundreds of E mails per month about this topic and thought I would share a few facts.

Pontiac Dude made a good point which I will elaborate on. Each gas manufacturer has their own formulations and specifications. These blend variations will vary between manufacturing plants and terminals. Meaning, the end result is different than the lab specified octane. Example: One of the primary constituents in gas is Xylene. Depending on the manufacture, the octane of Xylene will vary considerably with its isomer ratio. This will significantly change the octane rating. Ethanol is now used as the oxygenate and also as octane booster in gas. Ethanol actually has a higher RON than Toluene which is the chief constituent in race gas. This means that current pump gas (premium grade) can have a higher actual AKI than pump gas 10 years ago! The main problem with Ethanol blended pump gas is, the leaning effect Ethanol has on the A/F ratio. If you are running 10% blended Ethanol, you must jet richer to compensate for the stochiometeric 9:1 ratio that Ethanol has. Additionally, I have read data that suggests you can run an octane test on the same fuel back to back and get different results. So much for octane numbers!


What does all this mean? Often, the octane number represented on the pump is meaningless and for many reasons. Therefore, don't get too hung up on octane ratings.

By the same token, I would not get too hung up on actual compression ratio numbers because they are somewhat meaningless as well. As Triggerman pointed out, the mechanical ratio is meaningless without consideration of the valve closing. Lobe separation, duration, deck height, chamber design and finish, engine temp, air temp, bore size, plug heat range, rod length .......... and a million other variables determine how much octane is needed for a given engine combination. Above and beyond the engine combination is the total combination. A 10:1 engine in a 3,200 car might run fine on pump gas with a 3,500 RPM converter and 4.10 gears. The same engine with a stock converter and 2.41 gears in a 4,000 lb. Grandville might have problems. Anyone ever drive a stock mid 70's TA with a 7.6:1, 400 and get detonation? I have and it's hard to believe. Lean Q-jet, EGR, hot thermostat and 2.41 gears make it possible.

For these reasons I think an absolute maximum compression number on pump gas is nonsense. People that arbitrarily set a number are misinformed. If an individual sets his motor up at 10:1 and uses a stock type cam, then he is being foolish. However, 10:1+ ratios are entirely possible providing some common sense is used. I agree, higher ratios are not for everyone and if in doubt a lower mechanical ratio will minimize potential problems for a beginner.

In closing, insufficient octane can be a culprit for broken parts. However, a Pontiac crank is a pretty stout piece. Did anyone ever consider the crank was machined improperly or had an inherent flaw?

Feel free to E mail about this topic as I don't visit this BB very often.

Sincerely,

Eric D.

[Triggerman]

Yow! I was thinking about trying to post some comparisons between mechanical and dynamic compression ratios given different cam duration and maybe some advance/retard scenarios. I pulled up Eric's site and found that anything I would ever want to say about the subject was already there for anyone to read. Good deal for me. I may still post a few bits about the effect of advance/retard. Eric nice job on that site. It is at http://www.wauknet.com/douthitt/compresi.htm
TM