Any Benefits To Aftermarket Distributor
- Thread starter Makdaddymac
- Start date
As I understand it, high power ignition systems are really only needed for blower/turbo/nitrous applications, where the conditions exist that you spoke of. Other than the tuning options a ignition system gives you (ignition timing, rev limiter, etc) I don't think the hotter spark does much for a NA street engine with a mild compression ratio.
You'd probably gain 20 hp by taking advantage of the ability to individually tune the cylinders by switching to an aftermarket dizzy in a 1000 hp car with a Stand-alone, cam synch, and crank trigger that needs the aftermarket dizzy or at least a modified stocker for the cam synch. Just switching to an aftermarket dizzy is not going to gain you anything in normal 5.0s if yours isn't malfunctioning.
Chris
Chris
My motor is a N/A and 10.75:1 compression(i'd consider that on the mild side) and it felt like a different car after i put a Digital 6 box in it... It revved much harder and i was shocked at the difference it made.
The stock distributors are fine as long as there is no play in the shaft, my timing was jumping all over the place with my old dizzy but other than that it did what it was supposed to. I swapped an MSD pro billet in and the car didnt make any more power with that over the stocker.
But the ignition box is definitly where its at
LiquidGT
Member
I swapped the pick up coil (pip) in the dist. for a new one, then I cleaned and lubed the dizzy shaft, checked for play and it was as good as new. Replacing the PIP is not something I recommend doing, you'll need a little 'practice'. 
My motor is a N/A and 10.75:1 compression(i'd consider that on the mild side) and it felt like a different car after i put a Digital 6 box in it... It revved much harder and i was shocked at the difference it made.
The stock distributors are fine as long as there is no play in the shaft, my timing was jumping all over the place with my old dizzy but other than that it did what it was supposed to. I swapped an MSD pro billet in and the car didnt make any more power with that over the stocker.
But the ignition box is definitly where its at
Can you run the engine on 87 octane? If the answer is "no", then I'd say you are no longer on the "mild" side, haha. Of course, there are a lot of other variables that determine combustion chamber pressure before ignition, but we won't get into that.
But seriously, I can see where your car would benefit from a good ignition system. For the rest of us 9:1 CR guys, I think its mostly unnecessary.
I wouldnt know about 87 octane, because in the 5 years that ive owned the car i only run 93. I'd say mild compression is 11:1 and under. Mild compression to me is whatever you can squeeze out of pump gas. Only a MOPAR guy would say"this is my dodge with a 10.5:1 high compression motor"If i had no choice and had to use 87 octane, my car would run fine and have no detonation issues. But for 20 cents a gallon i really dont mind. If i was running 13:1 CR then id sing a different tune
Well, I'm not going to get into a pissing match about what our personal definitions of "mild" are, but the fact remains that your 10.75:1 CR, 387 HP stroker (I've followed your other thread-seriously I love your motor) will benefit from a high dollar ignition system more than a mildly modded, 250ish RWHP, 9:1 CR 302 would in any regard.
While I'm at it, I'd love to see you stand by your statement about the 87 octane in your car. I'm skeptical.
Well, I'm not going to get into a pissing match about what our personal definitions of "mild" are, but the fact remains that your 10.75:1 CR, 387 HP stroker (I've followed your other thread-seriously I love your motor) will benefit from a high dollar ignition system more than a mildly modded, 250ish RWHP, 9:1 CR 302 would in any regard.
While I'm at it, I'd love to see you stand by your statement about the 87 octane in your car. I'm skeptical.
haha im not trying to argue about what mild is either... and im a little biased i guess cause my "street" car has no a/c, power steering, or heat, and i wouldnt have it any other way. Hell i think every street car should have at least a F-1 procharger or a 200 shot on it.
and dont hold your breath on the 87 octane experiment, like i said the cars never had anything but 93 octane and its staying that way. (with the "quality" of pump gas these days i really wouldnt be all that shocked if a gas station or two were sneaking in 87 octane where 93 was supposed to be)
10.75 can run 87 octane, but what would be the point? He'll have to pull timing which will lose both efficiency and power. He might be able to get away without pulling timing, but would not be able to put the car under load. I'd be willing to bet that his cam has plenty of overlap, and that would definitely help with his SCR, which is more important than the DCR. BTW, the pressure before ignition doesn't matter. We're not worried about preignition, what we're concerned with is detonation.
Oh and 90LX, to me that's a mild engine combination so long as you're not running a radical cam. Running 12 or 13 to 1 would qualify you as not being mild to me and to most others. There are production cars running around 11:1 on pump gas, and I would certainly call them mild. Manufacturer's recommendation on my Corvette is at least 91 octane and it's running 10.1:1, does that mean it's not mild? Of course not.
Chris
Oh and 90LX, to me that's a mild engine combination so long as you're not running a radical cam. Running 12 or 13 to 1 would qualify you as not being mild to me and to most others. There are production cars running around 11:1 on pump gas, and I would certainly call them mild. Manufacturer's recommendation on my Corvette is at least 91 octane and it's running 10.1:1, does that mean it's not mild? Of course not.
Chris
i agree 100% with the way you think. and as far as timing, i wouldnt need to pull any cause my tune is safe enough and there really isnt much timing in it anyways, 10 degrees BTDC and i think 26 total
The difference in the new production cars that run "high" compression ratios is that they are fitted with knock sensors that ultimately control ignition advance, and variable valve timing that can also influence combustion characteristics. A traditional pushrod motor like 90lxcoupe's simply does not have the kind of technology to compensate for using low octane fuels. Like you said, he would probably have to de-tune the motor to run 87, and even then it might not work depending on his cam specs, operating temperature, combustion chamber geometry, etc.
And it IS the pressure (and temperature) in the combustion chamber before ignition we are concerned with, as that influences how the combustion process is going to occur with various levels of octane (or other compression-ignition resistant additives) present. I'm sure you understand this, but maybe you misunderstood my statement earlier.
I'm sorry that this thread is going waaaay off topic, haha. As much as I hate to admit it though, I love a good debate.
And what does the engine do when it senses knock? It pulls timing and adds fuel, which ends up exactly the same as what 90lx would likely have to do. There's nothing unsafe or less drivable, and it isn't as if tuning with an MSD Digital 6 or better box takes any time at all. Furthermore, knock sensors are not a prerequisite... they just make the tune idiot-proof.
No offense, but it seems like you're trying to cloud the issue with technological mysticism. Variable timing doesn't change the need for octane in a high compression engine. Now you have 2 cam profiles that your engine will have to be able to run on without detonation, and interestingly the more aggressive profile is typically the least likely one to detonate on a given tune. It isn't as if the engine senses knock and then switches to a different cam profile to eliminate it.
But those other cars don't have the technology available to 90lx in his ability to manually control the tune. He can simply have seperate tunes for different types of fuel. In fact, he could simply switch to a new tune and run E85 if his fuel system were up to the task. Let's say he's going on a long trip, he could set up one tune to run 87 and another that ran premium. He might find that its cheaper to run 87, but when he wants to go back to 93 he just waits until the tank is low, refuels, and switches back to the more aggressive tune.
I respectfully disagree. The probability that he'd have any issue running 10.75:1 on 87 is nonexistant with enough timing pulled (and it wouldn't be as bad as you think). Plus, detuning the motor isn't some involved process. They actually make selectors he could mount in the cabin that allow you to switch from one tune to the next.
You said that you'd like to see him stand by his statement that he can run 87 octane in his engine because you were skeptical. Now you're striking me as the know-it-all type with no hands on experience tuning cars. If that's the case, then you're probably not interested in learning anything from guys like us, but I'll give it one more shot, and then you can choose either to learn graciously or to twist words and save face. I'm cool with either.
I don't know why you're sticking to your guns about the pressure/ temperature before ignition, but I'll say it again with more detail and clarification. It follows from the fact that we are trying to avoid detontation, as opposed to preignition per my last post, that our concern is the pressures and temperatures after ignition. The pressure and temperature prior to ignition has no direct impact on the likelihood of detonation or even on the pressure and temperature after ignition. What we are actually concerned with, if we are trying to avoid detonation as I believe is the point of this discussion, is the pressure and temperature of the end gases after ignition. This is where detonation occurs. By retarding the spark timing, we directly reduce the peak pressure/temperature of the end gases because the point at which the flame front approaches those end gases will happen later into the combustion stroke. By making this happen later, there is more volume in the cylinder as the flame front approaches the end-gases. That means that they will be lower pressure/temp. Hence if the timing is retarded enough, the end gases will not reach the detonation threshold and will burn uniformally until the flame front reaches the cylinder wall instead of the end gases all combusting at once at the detonation threshold.Though these really aren't necessary for the topic of our conversation, here are some tuning and building factors that help to reduce detonation on high compression engines:
- tight quench, increases squish or swirl (or whatever vocabulary term you prefer to use) and reduces the likelihood of detonation.
- non projected tip plugs are cooler and so they resist det on race motors.
- debured and polished combustion chambers
- Aluminum heads conduct heat away from the cylinder much more quickly, which suppresses detonation
- long cam duration and overlap kills cylinder pressure, especially at low rpm
- a small cfm carb or intake reduces volumetric efficiency thus limiting peak cylinder presssure at higher rpm. ( high compression helps make up the diffference)
- richer mixtures cool the burn and help suppress detonation though at the cost of a little power. At high temps in the cylinder the rich mixture still has fuel trying to vaporize, which absorbes thermal energy that would otherwise increase the mixture temp
- Grooves cut on the head quench decks causes high swirl @TDC and increased mixture quality which allows a little more cr without knock
- At high RPM, detonation is less likely for several reasons: high piston velocity causes a better mixture, the flame front speed is the same, but the piston speed is much higher so the flame front reaches end gases further into the combustion stroke, at high RPM volumetric efficiency typically decreases, which results in lower cylinder pressures.
If you take advantage of all of these factors, you can run engines over 12:1 on 87 octane. The thing you'd have to ask yourself is why? Just about everyone willing to go this far, is trying to make power. You'll always be able to make more power with higher octane fuel and a good build. Why would you limit yourself to 87?
Chris
Is it too late for me to save face now?
I'm worried that you've already passed judgment on me, and anything I say from here out will make me sound like an *******. Maybe, but bear with me here.
Is it true that I'm young and young to the game, especially compared to some of you StangNet veterans, but then again I'm not just some kid sitting here with a Hot Rod magazine. I do not question your automotive knowledge. Notice in my above posts I was not directly disagreeing with what you said, but instead offering conversation-stimulating responses.
This statement is misleading. Saying that the fuel/air mixture pressure and temperature before ignition has no direct effect on the pressure and temperature on the gasses after ignition would infer that adding a supercharger or turbocharger to an engine has no direct affect on power output, and ignores the thermodynamic fundamentals of the Otto Cycle altogether. I accept and agree with most of the information in your post, but I feel like you're fighting my P&T statement just so you have something to combat me with.
I am a bit of a know-it-all, but I'm dealing with it, and hopefully getting better. My girlfriend reminds me about it every day, believe me.
My efforts at "technological mysticism" were to avoid the work involved with posting a 500 word essay to get my point across. You did just that. Good info, by the way. I will read that article.
P.S. PM sent.
i didnt mean to start a war about pump gas here... but i stand by the fact that my motor would run fine on 87 octane, with NO timing change and no change in the tune.
if anyone has experience with trick flow heads, they know that they make power with very conservative timing. When my car was on the dyno we made pulls with 30 degrees total and it made no more power than when it was at 26 degrees.
if anyone has experience with trick flow heads, they know that they make power with very conservative timing. When my car was on the dyno we made pulls with 30 degrees total and it made no more power than when it was at 26 degrees.
No, this response was a pretty good one.
I'm not trying to combat you. Though I recognize that I was being a hardass in my last response.
First, take my statements in the context of this thread please, we're not talking blown or turbod engines, just 90lx's.
Second, I didn't say that there was no relation, just that it is not a direct relation. The pressure/temp of the mixture before ignition will directly impact the tune, and if you're starting from scratch and building an engine that you expect to have higher pressures/temps then it will affect how you build the motor, too. At that point you can do specific things to mitigate the chances of detonation listed earlier. I've got a turbo 331, and because I'd like to run higher boost I dropped my SCR to help compensate. If you want to take it to an extreme, one could demonstrate how retarding the timing too much could result in a lower peak cylinder pressure/temp on a boosted motor than an n/a motor with advanced timing, assuming that they both ran. It is a confusing bit, but there really isn't a direct relationship between temp/pres before ignition and peak cylinder pressure unless you hold the other variables constant. When you assume the other variables constant, particularly the tune, then your point of view is absolutely correct. Then, there will be a direct correlation between the temp/pres before ignition and the one after. Because we would constantly adjust the tune depending on all of the other factors, the tune is what directly impacts peak temps/pressure.
Oh and I want to correct something I said earlier.... Switch DCR with SCR in this statement. I'm blond so I put them backwards DCR is definitely the more important of the two:
BTW, that's a damn strong trap speed for an n/a 345... You're making north of 400 rwhp? What are you revving to? Solid or hydro roller?
Your shortblock is built like a brick ****-house - very similar to mine. Would love to know your cam specs.
Chris
I ALMOST called you out on this, but seeing that you knew what you were talking about with everything else, I figured you had swapped them by accident. I knew what you were getting at.
And you're right, my argument was based on a standpoint of, what do they call it, "ceteris paribus". All else equal. Variables like timing can and will most certainly affect combustion pressures.
90lxcoupe, no worries man. Its like I said before, I enjoy a good debate. And I still think your motor as badass. You don't see a lot of R blocks around.
Now about that distributor...
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