The Mad Parrot (Building/racing the 318 Poly)

I made a cardboard deal to show the relationship of duration to reduced compression. It is on my website under projects i think.
Many years ago I read an interview with Isky hisself. He said Intake valve closing was the most important event. I put that in my head but to be honest I never understood it till the snowmoible craze came along. I would buy granny machines and turn them into killers Maybe not for the race track but when daily riding I was not often smoked. (in fact I dont think ever that I can remember) I used a book Tuning for Speed by Irving and its companion book Two Stroke Power Units. I learned everything I could about two stroke engines which was pretty well overlooked in my training as an auto mechanic. I learned between his book and my own crazy way of thinking to lay out the port timing with a degree wheel which I already had for my car motors. Typically we would go in lay out a port and grind. The exhaust port would often be raised an 1/8 inch or so and it was obvious even to me we were giving up compression to gain RPM. Then the light came on. I understood what Ed had said even though it was probably 5 or 6 years later. No compression takes pace till the intake valve closes. There is a tiny bit from inertia of a/f but in PSI it is pretty minor especially during the main RPM range where the engine spends unfortunatley most of its time. .It was like someone turned the light on. I remember I said right out loud "Ah ha, So that is what we are trying to do. " I took that junk snowmobile and got a head from a smaller version of the same engine. I cut the same amount off the head that I had raised the exhaust port by and tried it. I thought if I understand this like I think i do this should work. Work?!!!!! After a few runs the head studs pulled out of the base and I had to heli coil them for 1/2 inch studs and make new ones from Drill rod. That thing must have almost doubled in power and I knew I had finally understood. In fact my neighbour still insists I was running them on Fuel or nitro. When spring came I applied this thinking to car engines and have never looked back from that moment. It changed my career and how I did things.
We were taught sort of that raising compression increases HP. And to some extent that is true if the compression ratio is artifially low to begin with. But if it is sufficient then I would say we are wasting HP making squeeze we dont need or cant use to impress people we dont like, maybe. I dont think that way anymore. I think we increase compression to RECOVER the compression we lose by holding the intake valve open late into the compression stroke. That effectively shortens the stroke. I call the compression or sealed portion of the stroke when it is actually making pressure in a sealed cylinder the effective compression stroke. You could caculate it by putting a degree wheel on your motor and turning it to intake valve closes. See where the piston is. How far up from the bottom of the cyl or BDC is it? Suppose you are a chevy guy and it is a bbchev with a 4 inch stroke. Lets us suppose you are up .125 " at intake closing. That means you have only 3 7/8" (3.875")effective stroke. "What will you DO"? As Cark Malden used to say. That means you will have less compression when you reach TDC because you had less distance of actual compression making stroke. Now at very high rpm the cylinder filling can so of cover some of that which is how a big cam works but below that you are giving up all the way. So if we put a corrsponding bump on the piston to raise the compression ratio to the point we will have at least design compression at the end at TDDC (Design compression means what the engine would have had cranking compression before we installed the big cam) or in other words recovered what we gave up by holding the valve open longer. Now at high RPM , way up at the end we are going to be a bit high because of cylinder filling but we can increase fuel octane and deal with it so it is no problem. The engine will now make a whole lot more average power and often a bit more peak power too, provided it is not detonating. As you suggested the key is to have everything working in concert. I spend a lot of time working at that. And it is because of that that we make excellant power with what are called by some "no nothing builds" or old tech. I have been at this long enuf to know what I want now without spending a week measuring . It has become after 35 years since I figured it out almost second nature. I now understand what works and maybe better why it works. It take discipline however to build this way. !00 guys who have never even built a fire will tell you are nuts. Even people who come to you for their race engines for 15 or 20 years KNOW better (but keep coming back) They read something in HRM or Rpm or whatever and all of the sudden they know. In the engine business we call them "the trick of the month club." I am sure you have heard or even said it. Because of the flack I have learned to insulate myself from comments like that. I generally keep such info to myself. I had to or I would go nuts (ok nuttier) You can tell a lot by a simple cmpression test.
A good reliable long living bracket engine has 175 to 185 cranking compresssion. (A serious street engine would be similar on the low side) As they get more serious they sneek up towards 200 + but if you have a mild cam say 268 @ 050 for instance and 225 psi you either have too much compression or not enuf cam. I hope that sheds some light on how i think about it anyway. After that it is a matter of insuring head flow can feed that many cubes to that RPM and the intake sytem is not restricting and the engine can suvive up there.
Don
just for example I tried this in the early 70s with a friend. A stock 327 , granny version has 135 psi on my gauge. When a 350 hp grind is installed it has only just over 90 PSI on the same gauge in the same shop in the same week. it was all there just no one explained it.

 

Never thought about that one before, makes a hell of a lot of sense. This is why I read your posts, makes me think out of the box.

Len

 

Don, your logic is so simple that all of the high tech guys can't see how it could possibly work. Hard to explain to people that just because something is new or complicated doesn't necessarily mean it's better.

Old age and treachery will beat youth and enthusiasm any day!

 

I agree with about 98% of what you are saying here. I picked out some of the points i wanted to elaborate or comment on. Honestly Don, if it wasnt for your and your posts, i wouldn't even be talking about this stuff on here, its usually not worth the grief on a open forum.

1) Damn straight, Ed got that right. But you are leaving out one piece of the holy trinity, and thats lobe separation angle, or lobe displacement angle. To illustrate, I will use a sym of the 327 I am building for my current project. I am not going to enter into a big discussion about the compression ratio, as it will sidetrack the discussion away from Dons points about intake closing point. Yes, its high.
So with a 240@.050 intake lobe, and a 114LDA and the cam in straight up, the intake closing point is 54 deg abc, and the cranking compression is 197 psi. Idle vacuum is 14.9

If I change the LDA to 108, and leave everything else exactly the same, the intake closing point is 48 deg abc, and the cranking compression is 216 psi. Idle vacuum is 12.5. Keep in mind, these numbers are off a computer sym.
I am also not going to digress into the other various OTHER effects cause by manipulating the LDA, as I have discussed it elsewhere, on several threads on here, and again, it will sidetrack us from the point Don is making.

2) A Truly GREAT book, I read it for the first time when I was 12, have referred back to it 100's of times since, and sat down and read it cover to cover a couple more times for good measure.

3) If I had a $100 for every time I have read some mindless jack-ass in some magazine article talk about needing "more overlap" to bleed off compression, I could stop working for a living. How in the HELL they think that something that occurs almost ONE FULL CRANKSHAFT ROTATION away from the compression stroke (Overlap occurs at the end of the exhaust stroke) can have any direct effect on cylinder pressure is beyond me. And, in fact, it leads people in the OPPOSITE DIRECTION! Tightening the LDA (which is what increases overlap for a given amount of duration) Closes the intake EARLIER and INCREASES cylinder pressure, just as my earlier computer sym illustrates.
The simple fact of the matter is, most of the guys writing for the magazines do not even have a grasp of how a 4-stroke engine functions. If they did, they wouldn't come out with idiotic statements like this.

4) I look at it a little differently, but its the same fundamental principles at work. I balance off LDA and duration against the mechanical compression ratio to arrive at the cranking compression I am targeting. How I decide whether I should go with a tighter LDA and a lower compression ratio, or a wider LDA and a higher compression ratio, depends on what characteristics I want to emphasize in the finished engine, and the R/S ratio of the engine in question, as well as its propensity for reversion. How I arrive at the cranking compression number is a whole nother matter, and about 3 more paragraphs, so I wont get into that.

5) Its so simple when you understand the fundamentals, isnt it Don?

6) And BOY did you say a mouthful there!

I'll say one thing for you Don, you really get me talking about things I might otherwise not say anything about. I really enjoy your posts. Maybe I will save #7 for another post on another day. I figure I can go on for another 6 paragraphs on that one just by itself!

 

#5
Yes,and that is the problem. People think it is black magic or something . It is cold hard fact easy to understand and not changable. Tis simply how it works.period. And it always worked this way and it will a hundred years from now. There is no Hi tech. There are just new and shiny parts perhaps a little better cam profile , a bit better intake maybe but how it works and why you do it has never changed. Suck squeeze bang and blow.

Don

 

Don: What are your thoughts on quench/swirl relative to making power ?
A lot of study and thinking has gone into this in recent combustion chamber/engine design

 

EXACTLY! But so few guys want to learn this stuff, its not "glamorous". If you sit down in the local bar, and start talking about this stuff to your car buddies, their eyes glaze over, and they quickly try to steer the conversation back to the usual BS that they just read in Car Craft. This may sound mean and nasty, but if you dont have a CLEAR understanding of valve motion relative to piston motion, you have no business making cam recommendations.

 

I just had an A-HA moment. Thanks for posting that.

 

HEY!! I "reached" somebody! Cool, glad I could help.

 

Don,

Just backing up a bit . . . what's with reversing the pistons? Never heard that one before.

Thanks

 

Reversing the pistons reduces drag inside the motor because in a stock piston, the pin is offset to load the skirts against the cylinder wall to make them run quietly in the bores. Reversing the pistons defeats this and frees up some horsepower that would have been used to overcome the extra drag on the the skirts. The motor is then a bit noisier, but who cares?

 

My thoughts on Quench and swirl. Are you sure you want to ask.?;.)Ok brace yourself.
I hear discussions all the time about quench . I know in most cases I am listening to a Parrot. Very few people who talk about it know what it is or how or who developed it. Usually they are parroting something they read in a certain magazine. (I didnt think he knew what he started talking about either when he said it BTW) Swirl is gift I think. I personally would prefer swirl to quench everytime.
JAg was one of the early companies to design a bit of swirl intotheir engines. Quench takes power to make & swirl is free.
That is all I will say. I don't want to get into a dicussion about it except I wil say this The quench discssion is one of the most overdone discussions on engines I have ever seen. I devote about 5 minutes per year thinking about it and suspect I overdo it.
Don

 

I got it, Thanks. Looking at the 440 piston sitting on my desk right now, yep its offset.

 

Actually as one who has reversed pistons for 40+ years when using stock istons I have never heard the noise everpne talks about. Forged racing piston have n offset unless youorder it. Smokey used to order his with it so he could still have a reverse or neg offset or so he said in one of his books. It is about 14 HP free. About the same gain as one gets from a windage tray and it doesnt wear out. So lets suppose we reverse hang the pistons and install a windage tray. We now have approx 28 HP that wont wear out or fail and cost us diddly squat just for the taking.
The above description is right so i need not add to it.
Don

 

Which brings us nicely to some more free HP. Plugging the heat crossover on an intake manifold will give a substantial boost too. Almost as much as the previous two combined. We are now up to approx 56 free non wearable never fail HPs and we havent even started. That is how you build killer stuff ofnwenig $$$$$$$$$. (little) Not popular, not fancy but man is it effective!!!!!
Don

 

Don

Been following this thread for a bit now. Thinking about running my 318 LA in my rail (if I ever get any other projects done) From most everything I've found, the heads were the main restriction on these. Are or were there any decent factory heads that flow?

 

Or am I looking at porting the stock heads? (Which is what budget dictates)

 

I use when doing a SB mopar the J heads from 360 or late 340. With a good port job I got 258 cfm intake which is enuf for over 500 hp if you needed to go that high. They are inexpensive and very good heads. Helped a friend with one last year, a 360 in his wifes street piece. Flat top pistons (9 to1) a good quality build , a extreme hydraulics cam from comp , an RPM plus intake from Vic and an old reworked 3310 holley from me. It idles in gear at 550 , runs on pump gas and when he went to Shannnville it turned , are you ready ? 12.96 on street tires (good ones mind you) and 3.91 gears. It is his wifes summer car.
We did everything right but spent so little it is embarrrasing. He told me he figured probably 14s but a 13 would be nice just once. He is still smiling. Now that is a 3400 lb car. Knock that back to 1700lbs for a rail, up the compression with a matching cam and i bet there will be low tens high nines on the ticket. I did these heads for him here. Just as I described to you. Js .
Don
In fact I have a pic of that run Just a minute

If you have zoom check the little circle at the top of the back window.

 

Cool, thanks Don! Just to forwarn you I may be picking your brain a bit. Not many die hard Mopar guys in my neck of the woods.

-Nope, tried zooming in, it just got fuzzy.

 

Don, just to be clear, are you talking about quench area, or squish clearance? The two terms are often incorrectly used interchangably, which leads to a lot of confusion.

 

Wow, pretty dang close to my 360 from my Duster. I used a stock bottom end and milled the heads to bring the compression up. Low 13's out of mine. No quench either LOL!

 

As I said i dont spend anytime anymore thinking about this . It is mostly nonsense and not much you can do to change it anyway short of spending $$$ on super duper trick heads . It is not part of my bag of tricks. I am not going there as I already said. It is a no win discussion and both designs make very very good power so it is pointless. Use what you have or what makes you happy.
Don

 

Don, do different engines use different amounts of wrist pin offset? I'm just asking to see if I'll run into any issues using SBC pistons in a MoPar block...and a friend of mine called me a traitor for using SBC pistons, but the pistons don't know what they're supposed to be used for ...put it this way, it's the difference of $700 custom made pistons or using other off the shelf parts for $400, shaving off half of the piston weight, gaining .135 squish, far less drag (shorter skirts and longer rods) and for almost half the price...damned right I'll be running "SBC" pistons...and it's all thanks to your posts that lead me towards thinking outside of the box...

 

Ruiner, a friend of mine used to piss off all kinds of Ford/Chevy people. He built a race engine using all kinds of Chevy parts--in a Ford 302. The only things that were Ford was the castings and the external bolt-on stuff. Ran like the per-viable raped ape. If it fits-use it is what I go by most of the time.

For specifics, I am sure Don can tell you. I can just tell you things that I and my friends have done.

Len

 

The basic premise behind Hoover motors is tightening the squish clearance, or piston/head clearance. '72/'73 340 piston has a compression distance of 1.74, combine that with a 6.123 rod, the 360 crank and the factory nominal crank centerline/deck distance of 9.599, and you get a nominal positive deck hieght of .054 out. You usually have to take a light squaring cut off the decks to actually hit this number, as the production tolerances on the crank centerline/deck numbers are a little tall. Add a typical Fel-pro .039 compressed head gasket, and the top of the piston is still projecting .015 into the chamber. This is why you have to clean up the circumference of the chamber. I used to cut them more than that. I built a couple Hoover motors when I was young, they all came out in the 11.5/1 range. I also flat-milled the 906s on the 440 I ran in my duster .080 which effectively turned them into a closed chamber head. Of course you can also run the #915's which are pretty scarce (I have two sets), or port a set of the early sixties #516's. So there are LOTS of ways to get active squish in Mopar motors without aftermarket heads, you just have to look beyond the info in the magazines. As far as that goes, pre '72 340's have a nominal factory deck hieght of +.018. I have cut the decks and ran them a damn sight farther out of the holes than that. One of the first motors I built in my late teens was a early 340 with reversed L2316's & a Direct Connection .528 solid, it was at 11.5/1, and it flat out RAN. In fact, that was first experience with building pump gas street motors with higher mech. compression, tight squish and wider LDA's. Not saying your way is wrong Don, but there are other ways, without resorting to aftermarket heads.

Think I am gonna sign off on this one now, it was fun.

 

A dumb question probably...I assume turbo blow thru six Mikunis? If they are slide type carbs [I don't know if any have throttle plates] how does the boost affect the slides being forced open?

 

I wish you would get off this squish thing so let me help you .I asked we not get into that subject because it has no end or no solution. You take the 915 or the early 516 and do anything you want to them I willl take a set of 452s and you will eat my dust and it will not be even close. How do i know? Because I have tried them all. The Hoover engine works and was built not having anything to do with that. There were no hot pistons available back then for the new 360 so you could takea set of 340 late model (after 72) and punch the 360 040 over. You had to machine the pistons to fit as they were stll a bit high . I have tried them flat, tapers I5 degrees the long way and tapered only at the edge. No decernable difference that i could see in performance. I have built more hoovers around here (the general area I live in)than anyone else of that I am sure. I also developed the 380 from a 340 deal.
Now please can we get on with something else. I have been in too many dicussions in my life over this and I have already expressed my strong opinions, all of them. Maybe you need a quench /squish thread for those who want to discuss this. As you might have guessed I dont. It will just be a gunfight but no winners. I am too old and too tired to get into it.
Don

 

There are thottle plate carbs too. I used to know the number but it escapes me now. I thiink they were a 34MM carb though. but I have not used them I used Tilotsons.
Don

 

Well Don you and the guys have taken up a good portion of my evening with interesting reading. I like to think I understand cam timing and I agree with what I have read here (I get a funny look from people when I tell them I am retarding my cam), but I never heard the reverse piston trick. I have my FED engine on a stand right now, the 322 that is, and I think the pistons are gonna swap direction before it goes back in. It makes perfect sense. the "D" motor in my Uni will have to wait till tear down for this to happen, of course it doesn't matter in the "C" motor as the pins are centered.

Keep it coming, Tim

 

well, when you start exceeding that self-imposed limit of 180 psi cranking compression on pump gas, then you will start to get a handle on the reason for closing up the squish. Don, as it stands, why dont we agree to disagree? Had to happen at some point that we werent going to agree on EVERYTHING.