[. One experiement I tried with the old Malibu 305 was to modify a stock HEI distributor cap to allow for more advance on one bank by taking a little away from the other bank. This little trickery was easily accomplished with some deft Dremmel work on the contacts leading to the cylinders where slightly less timing was desired...I just removed some of the contact on the side that the rotor got to first, effectively 'retarding' spark timing to those cylinders by a little bit in relation to the cylinders with the stock contacts. Never got the car to the strip with that 'sneaky' cap on it, but it ran really well on the street like that. It was just another idea Chuck and I came up with and I felt compelled to try![/quote] What you're talking about here was tried by our old friend Smokey way back in the 60's. Some of his ideas SORTA paralleled yours. Only problem, to achieve what you were proposing can only be accomplished by modifying the phasing of the triggering mechanism (on his points ignition it meant grinding a new profile on the points cam altering the lobe centers in relation one to another. In the case of the HEI it would mean at least altering the spiked trigger wheel (with the spikes moved in relation to one another) and what ever else it would take to effect the change. What you did, did nothing as far as retarding the timing on the modified contacts. The cylinders were fired in exactly the same manner and moving the target for the spark will not change the timeing in that cylinder. It just means the spark will have to travel in a slightly different direction to "ground" itself on the contact. Frank
Could be, Frank...the car ran great with the modified cap, but it ran great with a stock cap, too. I never got it to the track to see if one cap offered an advantge over the other, but it was an interesting idea I just decided to try. Still, with the spark traveling through the contact on the rotor to the contact on the cylinder towers, it seemed logical to us that by, in effect, "moving" four of the towers a little further ahead of the others in relation to their original positioning, that spark timing as delivered to the cylinders would be delayed to a slight degree in relation to the four unmodified towers. I have several stock HEI caps on hand to try it out again sometime.
That's really impressive! Just goes to prove that spending time on the details is better than just spending money on the trick of the month. 420 hp from a smogger economy engine...damn! I wouldn't be able to drag out even close to that number, but just the thought that it can be done makes the 305 look a whole lot better...
Hey, wait a second...what you're talking about is altering the DWELL period on individual cylinders...modifying the cam that triggers the points, or the trigger wheel that trips the reluctor will alter the coil saturation time, and yes...it will also affect timing. (The old rule being "Dwell affects timing, but timing does not affect dwell".) So...if you effectively move the towers on the distributor cap around a little in relation to each other, you are in fact altering cylinder timing on the cylinders whose towers you've modified, in relation to the others. Looking at the contacts on an HEI cap, they're fairly wide. My concern when I removed a little maeterial from the leading edge of four contacts was that it would cut the contact time that the rotor had with the tower, possibly reducing spark duration as well as retarding the SPARK timing (not dwell rate) to that cylinder. Chuck theorized that the reduced contact area wouldn't be a hinderance to performance, so I went ahead and did the cap surgery. Think of it this way...if you could somehow reach down and move ONE tower on your distributor cap back and forth while the others stayed in the same location, you would be altering the amount of spark advance delivered to the cylinder that tower was connected to, no?
Cool idea! Specially if you would take it all the way... Exhaust split up into two 4 cyls, ( with different diameter and length tubing ) Quad webers with different venturi's and jetting, different port sizes and valves sizes, a dual ground Cam, and two 4cyl distributors with different curves for each of the "fours"...
That's the spirit, Metalshapes...but that also goes a little beyond my means and budget as well!! Gotta stick to backyard engineering to put my musings into action!!
No, frank is right. you are talking location, he is talking time.Without altering theTiming cam on points, or the pickup wheel on electronic ignition, the timing event happens the same time it did before you modified the cap contact. The spark just moves in another direction. Look at GM V6 distributor caps, the towers are ***ymetrical, with very long contacts. the same cap will work with even fire, 9 degree split, or 15 degree split timing. The trick is the distributor pickup wheel. The spacing of the spikes is adjusted to fire at the correct time, so they can still use the same cap.
Hack, By using your reasoning you could argue that putting on longer plug wires would retard the timing. Frank
One part of your equation you havent shed light on Greg ...is the vehicle a small light one ? ALso on a nother note -a buddy once built a 283 which would have had 9:1 compression [or near that] He installed a set of 350 heads with 74 CC combustion chambers... It smoked black smoke and ran real anemic PLUS used a ton of fuel per mile.....Hope this is useful...
Ha Ha...I see what you're saying now... and that's a funny way to put it, too!!! No wonder the car didn't really feel any different with the modifed cap! (But doing the Dremmel work kept me off the streets for half an hour or so, so I suppose the cap experiment had SOME socially redeeming value, eh??)
Another thing. I never mentioned altering the dwell period in my post only the cam peak in relation to the others on the cam. The dwell would remain the same only the "degreeing" of the lobes in relation to each other would change. I see from the posts that have been made that Enjenjo understands. Frank
It's going into your basic little hot rod...essentially a t-bucket. Backed by a Powerglide with a loose converter and rear gearing in the 4.10/4.11 realm. Light car, tall gear, TCI street-fighter converter. A snarffin' 350 or 400 would blow the tires away...too much torque too early to my thinking...twist things all up...not pretty!! I wanted to go with a motor that came on strong about 2500-3000 rpm and had a flat torque curve to accelerate the car quickly once it was off the line. Many super short stroke "rpm engines" are peaky and tempermental, the 3.25 stroke represented a reasonable middle ground to me...halfway between 3.00 and 3.48. (True, a 307 engine is the same thing I'm doing with the benefit of a bigger bore...but I couldn't find a decent 307 builder when I was looking for one a while ago...whereas 305s are everywhere! To boot, the local crank grinder I deal with has 307 cranks ready to go, .010"/.010" under with bearings for under a hundred bucks! Slipped into my 305...it makes for an easy low dollar motor that fits my desire to pattern a small block Chevy after the 290 AMCs I dig so much...in a cheap package with lotsa performance parts available!!) I just got to dwelling on how Chuck and often discussed making my old 305 run like two four bangers, and this project seemed like a viable candidate to revive that old line of thought on! It gives me a focal point...a plan of attack, a Challenge if you will! (Like building a late forties car with early 80s econo-car technology to see if I could do it! ) Putting a garden variety 350 in the car would bore me before I got halfway to doing it...there needs to be a creative angle to things for me!
I get it now, Frank...and like I said, it explains why the car really didn't feel any different after I modified the cap. Getting by ME was one thing, but I'm surprised old Chuck didn't catch that! (Unless he was just sleepy that day...or letting me try things on my own...he always said "That's how you learn stuff that sticks!". He was probably waiting for me to get the car back to the track and go "What the ****?"!!!)
Wouldn't that tend to create a balance issue?? (Maybe not...being four and four equally??) I'm not looking for two completely different four bangers, just two pretty similar ones with overlapping torque curves to help reduce the "peakyness" normally ***ociated with higher rpm shorter stroke small displacement engines.
well, i think i'd have it balanced anyway.... #1 i don't thinkthere'd be THAT much difference in the torque curves that they wouldn't overlap. #2one of the reasons i mentioned stroking/destroking is so you could keep the CID at 285. wonder about "longroding" it? but that wouldn't use OEM parts...
That is something that I have thought about before. At NASCAR/Indy car levels (8-9K RPM or more) it would seem that the lenth of spark plug wire would make a difference in the timing, depending on If it is timed using the longest or shortest wire.
Not at the speed electricity travels...wire length would not come into play. I was thinking that when you adjusted your timing, you were moving the cap in relation to the rotor, and you are...but, as Frank and Enjenjo pointed out, you are ALSO moving the rubbing block on the points or the reluctor for electronic ignition in relation to either the cam or the trigger wheel as the housing is turned but the shaft (with the rotor and the cam or trigger wheel attatched to it) stays in it's original relation to the camshaft. I hadn't thought of that back then, and it must've escaped my buddy, too. All I really did back then was practice some precision grinding...but it sounded like a good notion at the time. Glad to be corrected before I did it again, though!!
OK, here's the thing with the theory of building 4 cylinders that tune at one RPM, and 4 at another. At any given point, you're wasting the power of the set of cylinders working closest to peak effeciency because you're generating parasitic losses with the other four. if it was a viable thing, racers would be doing it. And I don't know any that are. The rest of the post, however, I'm all into. Short stroke, big bore, low dollar motors are cool as far as I'm concerned. I spent part of today taking apart my $25 283, only to find that I have less than .001 wear in all 8 bores, so a cleanup hone and rings save the cost of pistons! One thing I don't get though is this idea about getting the intake valve and exhaust valve close to the same size....that doesn't seem like a good idea to me, given that your intake charge is "larger" before combustion. The only advantage you'd be getting with a small intake valve is that it's pretty much unshrouded by design, but shrouding is easy enough to fix with proper work in the chambers....am I missing something here? If anybody needs, em, I've got a set of small chamber, small valve "520" heads off said 283. I'll stick with my 462s
Hillbillyhell, the reasoning behind going with an oversized exhaust valve is the same reasoning behind running a dual pattern camshaft, it allows the cylinder to expell the exhaust more completely, leaving more room in the cylinder for the incoming intake charge. The larger exhaust valve worked really well on my buddy's old 350, and good 1.60 exhaust valves for Chevy heads are cheap enough to make running them worth the additional expense. On the theory behind "overlapping" torque curves, I'm not looking to create radically different torque curves for each of the selected four cylinders, I'm just aiming to broaden the engine's overall torque curve by giving half the cylinders a wee headstart towards their torque peak, so that as they start back down, the other four will have arrived at THEIR torque peak and will stay there a bit, broadening the overall torque band...in theory. (It's like the concept behind a dual plane intake manifold...you have longer, curved runners overlapping and one plane invariably produces a SLIGHTLY different torque band in the four cylinders it feeds thatn the other plane does in it's four cylinders. Thus, they 'overlap' a little bit...making for a smoother torque curve.) If you could measure the efficiency and power output of each individual cylinder, you'd find that they are ALL going to be slightly different anyway...100% efficiency isn't really possible! So, I think it's a good idea to tailor things like header design, manifold selection, and valve timing to specific cylinders in an effort to help them all work better towards the goal of producing a flat, useable torque curve. In engines with a centrally located carburetor, it's tough to get all eight cylinders fed the exact same mixture at the exact same velocity, etc. Therefore, doing a few changes to your header and valve timing stratagies, along with other subtle tuning tricks will help equalize the cylinders. In a system with a centrally located carb in the middle of eight intake ports, it's easier to match two sets of four cylinders, or to tune two sets of four cylinders than it is to expect optimum efficiency while making everything the same on all eight cylinders. Now, in a dual quad tunnel ram with zoomie style headers...you got the makings of a very well balanced eight cylinder engine...and it's probably why recent studies have dispelled the old myths about tunnel rams being bad for street machines...it's been found that they actually increase midrange power...something I always thought they would do, just looking at the way they feed all eight cylinders pretty equally. With good carbs and carefull adjustment, a dual quad tunnel ram is a killer street combo...but not exactly what I want to run on this car/engine. So, some compromises are in order! Like I say, it's something that I believe in, and the results I got out of my old Malibu with the unequal headers and dual plane intake made me think that there just might be something to that angle, and it's something I'm looking to explore. It may turn out that I'll end up with a really oddball noisemaker running wierd looking headers that doesn't perform worth a darn...but I have to find out for myself...I'm stubborn that way! (More often than not, my crackpot theories prove valid, so I'm at least reasonably confident!)
well, yeah, I get that I think what I was more curious about is why run the tiny intake valve? SBCs, even the small displacement ones, are pretty horribly under valved. Is it just one of those deals where you're looking at these heads with the itty bitty chambers, and are sticking with the 1.7 as a cost savings deal, or is there more to it than that?
When a sustained high RPM single 4 barrel V8 engine (NASCAR) is designed today, the camshaft duration/overlap is altered on the 4 cylinders closest to the carb verses the others in an atempt to acheive the highest volumetric flow possible. Even the rocker arm ratios are different, for example the Dodge NASCAR engines will run 1.72 and 1.78 on the same engine. Todays NHRA ProStock engine does acheive 100% volumetric flow. One other item to keep in mind in the fine tuning art is the amount that the tip of the spark plug extends into the combustion chamber. Going from a .030 tip to a .045 protrusion changes the total timing by 1 degree. IN our Champion race plugs, we have several designs made for these engines, and from Team to Team, and track to track, they all have a different design. Plug gap also plays into the equasion, which is based on numerous issues in the engine design. Regarding spark plug wires, our latest design we crated for NASCAR does not have a measurable power gain on the Dyno, but the higger effiectancy in voltage allows one of these cars to complete 2 additional laps on a 1 mile+ track on the same amount of fuel. Interesting isn't it .
(It's like the concept behind a dual plane intake manifold...you have longer, curved runners overlapping and one plane invariably produces a SLIGHTLY different torque band in the four cylinders it feeds thatn the other plane does in it's four cylinders. Thus, they 'overlap' a little bit...making for a smoother torque curve.) Quote, Hack I suggest you spend some time researching the theory/application of dual plane/180 degree manifolding. If you find any reference to the production of different torque bands being a desirable/sought after characteristic I would be really interested. Frank
Mr. Hack. Just a coupe of quick questions: How do you feel about the lack of quench in that comination? Which you said would move the piston down .125" in the hole. What do you think about the 4,7 swap camshafts? Might that make exhaust routing a little easier? And most of all Good luck! Cool idea if ya ask me.
wow. I have read thru it a couple of times, still not getting all of it... would really love to see the final numbers on squish and cam profiles...it looks to me on paper to be some what anemic and prone to detonation.... good luck...and have a barley pop for me Fred
I never read that anywhere, it's just something that occured to me looking at different intake designs. I said this whole idea might be way off base...but it makes sense to ME, and so, I've got to give it a whirl. When I was little, I came up with the bright idea that you could link two small hobby store electric motors end to end at the output shaft, hook their wires to each other, then give the shafts a good spin and one would act like a generator providing power to the other, making it turn like a motor, driving the 'generator'...and they'd run forever that way. My Dad said it wouldn't work, but that grown men he worked with were 100% convinced that it would as well as I was (at age 10). So...I got two identical motors, some wire, vacuum tube (to hook the shafts together easily) and mounted them on a board. Gave 'em a spin and...nothing! It doesn't work! But then, a couple years ago when building my motorbike, my Dad said the design was severely flawed and couldn't possibly work. Everyone else agreed with him, but I built it anyway...and it worked great. Ya win some, you lose some...but you gotta TRY.
Hi Fred! I'll be the first to admit I don't know a THING about this here "quench area" that a few people have asked about, so maybe I am walking into a pretty solid brick wall (much to Frank's delight! ) with this cornball idea. In my head, this would be a LOW compression motor, figuring about 7.5:1 or roughly thereabouts, buring LOW octane fuel to make it's best numbers in the 3,000-6,500 rpm range to my best guess. The low octane (cheap) gas ignites and burns quickly, and is the only fuel that will even WORK in a super low squeeze motor, as I learned with small engines. With low compression, and a little smoothing of sharp edges on top of the piston and in the combustion area...how would it be prone to detonation? Cam specifics are still up in the air, but I actually love Isky's line of Dump Truck Cams, and with the oversized exhaust vale trick, my run one of those!
7 1/2 to 1 compression! Why would you do that!?!? Naaaaa....make it sensible and give it some squeeze! The little engine already has an uphill battle going on already. Experiment on one aspect of the engine at a time...thats the only way to get comparable results. Just because you have 10 ideas doesn't mean they all will work together as you invision them. Maybe two or three will be successful but the others will bring it down a notch. You need to figure it out bit by bit! Do your thing with the double 4 setup but with as much compression as you can handle to gain some grunt and give the little thing a fighting chance! Once you get tired of that, it will be easy to find heads with bigger chambers so you can try a lower compression ratio. (But keep an extra set of gaskets handy so you can quickly replace the high comp heads cause your gonna like them way better! LoL)
Bill, you have a valid point of sorts there. I may run the engine as it is (in stock 305 form) with my intake carb, ignition and headers on it, and see what it does...to establish a baseline, and THEN pull it down and do the crank swap to see how the 285 cube motor does with the shorter stroke. Pulling a motor in or out of a typical little roadster isn't a big task at all, so that may be a viable approach. But, I would like to start off with the 285 configuration, since I already KNOW what a 305 can do! It will largely depend on the internal condition of the 305 I'm starting with as to what the 'baseline' engien will be I guess...305 or 285!
The Jalopy Journal
