After seeing the post B*** made last night regarding Tri-Y headers, I typed a response touching on some details pertaining to the new Chevy 305 I decided to build. I mentioned the header design, but it was 2am and probably not my clearest rambling ever, so I figured I'd let my guard down a bit and spill the beans here for ya. Backing the story up a little ways to 1988-89 when I was working with a guy named Chuck at an auto parts store, we had the good fortune to be able to spend hours on end comparing notes on small block Chevy modifications for the street and strip. Chuck is one of those guys who lives and breathes engines, and he's been into making horsepower since the late 70s when doing so was pretty cheap! He favors large displacement small blocks based on the 400 Chevy block with 6" rods, whereas I prefer small displacement small blocks based on the 305 block with the common 5.7" rod. Though we were a study in contrasts of sorts, we were always open minded to each other's thinking and bounced ideas back and forth daily. His jones was fire breathing, 10-second streetable Chevelles with 400 based engines, where my hook was daily driven 14 second Malibus with incredible throttle response and respactable mileage. We balanced each other pretty well. Chuck tried to talk me into running a 'stock' 400 in the old Malibu, and I knew his reasoning was sound. He started his Chevelle project out in teh early days with a stock 400 equipped with a fairly tame Crane cam, Z28 dual plane intake, Holley 750cfm carb, HEI distributor and headers. That motor, backed by a TH400 with a Corvette converter and 3.55 gears was good for mid 13's in his old "Lab Rat" 72 Chevelle. The same combo woulda worked fine in my Malibu, but I had a burning desire to see what the old 305 was capable of. Without re-hashing that whole experience again (you can read about it in my 305 post in the Tech Archive), I managed to get decent ETs and mileage figures outta the 305. But, one thing I didn't mention in that old tech post was the fact that the car 'accidentally' ended up with two different headers on it...one bank had longer tubes and a longer collector, while the other bank had shorter tubes and a shorter collector. I was a little concerned about it at first, but Chuck theorized that if I tuned each bank carefully, that I'd essentially have two four cylinder engines linked to a common crank that had slightly different torque curves, but that those torque curves would overlap some and help each other out...giving the motor a very broad, flat torque curve...in theory. Well, by hook or crook, it seemed to work. The engine was ULTRA responsive and very efficient. I met my goal of propelling a stock, all steel four door 77 Malibu Cl***ic with stock trans, stock torque converter and stock rearend gearing down the quarter mile in the 14 second range with nothing more than bolt-ons and tuning on the original 100,000+ mile 305. I didn't alter the car's ch***is any because I was using it mainly as a dyno mule to evalute mods to the 305 and see what could be done by working with the engine alone. I'm sure that with a set of steeper gears, a looser converter and a little weight loss program, that could have been an easy high 12 or low 13 second mild mannered four door sleeper running the much-hated 305! Anyway, (still with me here?) after all was said and done, Chuck and I both agreed that there was indeed some merit to treating the 305 as two four bangers and overlapping their corresponding torque curves to make for one gutsy midrange motor, but we both also agreed that it would be better to split the cylinders up more evenly, through the firing order, rather than bank to bank. I decided I'd give that a try...someday! Well, here it is Someday! I got an early 305 and decided it would be worthwhile to try out our old theory of treating the motor as two engines in one and making modifications that would take advantage of this thinking. To add another dimension to it, I thought I'd also have a go at another goal I'd been harboring for some time, and that was to package one of my favorite late 60s musclecar engines, the AMC 290, into a small block Chevy 'disguise'! The 290 AMC was a screamin' little motor in the hands of early Trans Am racers, and I always dug AMC anyway. Knowing that the 290 AMC featured a bore x stroke configuration of 3.75" x 3.28", and that my beloved 305 Chevys feature a stock 3.736" bore with a 3.48" stroke borrowed from the 350, it wasn't hard to see how a similar design to the AMC 290 could be acheived using common Chevy parts! As luck would have it, 307 Chevy engines conveniently feature a 3.25" stroke borrowed from the 327...so taking the two small blocks that everyone hates, the 305 and the 307, and doing a little switcheroo yields a 285 cubic inch mill with a standard 305 bore, or a 290 cube motor with a .030" overbore! Presto! By putting a 307 crank into a 305 block, you got yourself a small block Chevy with a 3.736" (standard) bore and a 3.25" stroke! Very close to the old AMC blueprint! Go here to have fun with bore and stroke numbers http://www.donsautopages.co.nz/enginespecs.htm So...with the logistics of how to build my 285 Chevy out of the way (many thanks to Glenn for help in nailing down the combo parts-wise), I got to thinking of things such as cylinder heads, cam profiles, intake combos and header design. Tearing a page out of my own history, with the two different headers on my first 305 project, I thought I'd make a set of headers that would feature different primary tube diameters. Cylinders 1,5,6,8 get the smaller (1 5/8") tubes, and cylinders 3,7,2,4 get the larger (1 3/4") tubes. Looking at the diagram below, you can see that if the two small tubes on each bank were linked with each other, and the two large tubes on each bank were linked with each other, they would mirror the old tri-y design, if the two adjoining collectors were then joined together. I'm still on the fence as to whether or not I want to link the tubes, or just run four sorta long open pipes on this motor, but the two different primary tube diameters comes from the basic idea Chuck and I discussed at length years ago when we spoke of designing a 305 to work as two overlapping four cylinder engines to create a motor with a very broad torque curve...being that torque accelerates the car. If I do link the tubes, it will be done in the cl***ic tri-y configuration, however. The diagram below illustrates what I'm talking about as far as header design. There will be more posts in this thread very soon, discussing the cylinder head mods, intake selection, cam specifics and all that good stuff, so stay tuned. I'm picking up the heads this weekend and getting in touch with my old cylinder head guy to see about getting the work I want done. I was hessitant to 'leak' this whole thing here, knowing that there's gonna be a clown or two out there arriving to compare apples and oranges...spouting off LS6 454 performance data and poo-poo'ing anything that goes against 'conventional wisdom', but the majority of y'all might find it interesting, so I'll post all my ideas, theories and mods here as I go. Ha Ha...the 285 Chevy will be the new 301 Chevy for today's crowd...using smog-era 'junk'!!! Just remember you read it here first!!
was it Smokey Yunick who was playing with headers that split the firing order like that, back in the 70s? although they were all one tube size. Interesting concept....having one half of the engine "help out" the other half. But looking at it another way, you're crippling both ends of the torque curve at the same time. Are you using power pack heads on the little motors?
Smokey was always an innovator when it came to small blocks, and I know he played with header design! I dodn't know everything he did, but it stands to reason that he'd come up with similar notions! (Here's some old SBC header pics, showing a tri-y type of design that splits the cylinders up by firing order, although with same-size pipes. Photos taken from a 1964 Hot Rod book.) I hear what you're saying about 'crippling' each end of the two torque curves to some degree, but I don't think it would really hurt...the amount that each curve would 'fall off' where the other overlapped it would be minimal, and I think the effect would spread the torque band out over a greater area. Being that this is a reduced stroke engine, it's my belief that this effect should be even more pronounced...helping it to pull harder through the mid range. The old 283 Power Pack heads would be ideal for this mill, with their small valves and small chambers to give back some of the compression that will be lost in the de-stroking process, but another aspect of this particular engine is that I want it to be able to run on the cheapes, sub-grade pump gas, and be affordable...so using small valve 267 'smog heads' with a few little mods to help 'em out is my answer this time around. This will be a LOW compression motor...something else that fights 'conventional wisdom'...but I ain't worried!
Interesting viewpoint Mr. Hack. Then again, we can always depend on you to take a little different look at things. Which is good. I think you're on the right track and it goes along with a little theory of mine that goes against the equal length primary header tubes. That being, it's better to have a flatter torque band than one that spikes all the cylinders at the same time for a shorter period of time and a slight increase in HP. Good too that you're dealing with a smaller displacement engine. It should be easier to see improvements there than it would be with a huge by large CID engine. Granted, subjective viewpoints are not the best, but the dragstrip is a good dyno for those without access to a real dyno. Not sure if it would apply here, but I always found Smokey's eight into one collector design interesting. Sort of a 180 degree header design simply by way of collector arrangement. Just to toss something different into the mix, I wonder how well it work if you had a venturi collector on the right bank. With the typical GM firing order of 1-8-4-3-6-5-7-2 it seems like running 1-3-5 into the top end of the collector and using a smaller primary pipe like you're doing and running that into the narrow part of the collectors venturi you may improve on the old 5 firing and then 7 firing right after inefficiencies. I understand - but haven't read it yet - that the new Hot Rod mag picked up about 10 HP by grinding a special cam for a BBC that required a different firing order which apparently spreads out the intake and exhaust pulses better than the original firing order does. I'll have to get the mag and read up on it. Only recently have I been getting Hot Rod, they seem to be doing a better job with it nowadays than a couple years back. Anyway, cool article, most interesting and like always, well written.
Maybe this 'splains why the Astro Van I usta have came with a cast manifold on one bank and a tube header on the other? Wasn't for space saving, that's for sure. If it was they would have been switched right to left.
Please keep us updated, this is all very interesting. I can't help but think of the article I read not to long ago in Rodders Journal I think about Stu Hilborn and how when he first showed his " fuel injection" Everyone told him it would never work, etc... untill every car that ran it started kickin the **** out of everyone. Good luck and Kudo's for thinking outside the box.
Hmmm, I wonder if this would apply to the 292 Y block which has always had a reputation as a torquer and similar size Chevy eater! Bore 3.75 & 3.30 stroke
305 rods & pistons on a stock 307 crank in a stock 305 block... ...simple, cheap and widely available!!
But if you shorten the stroke won't the factory pistons end up down in the hole too far!?!? I'm not really well versed in bore and stroke stuff, but if you shorten the swing and use the same rods, wouldn't you need to compensate with the piston...or can you just use a higher compression stock type piston and modify the dome or something? Or maybe High comp pistons will work as is and just not give the rated compression result? I dunno! Not being a naysayer...just trying to figure this stuff out a little better. Engines aren't really my favorite part of car building, but it is interesting as I have several 305 blocks to mess with and I always liked the small Chevy engines! Not likely to find a good 283 around here anymore...
Good thinking, C9! One of the things Chuck always worked to correct on his full-tilt 400 based engines was the way that cylinder 5 tended to rob cylinder 7 of some of it's intake charge. In stock or very mild engines with dual plane intakes, it's almost a non issue, but in higher rpm engines featuring single plane intakes with short runners off a common plenum, the effect is more pronounced. Chuck was an advocate of solid lifter cams and cylinder specific tuning, and he used valve lash settings, spark plugs and carb tuning to try and equalize the cylinders to the best of his ability. (His talks on spark plugs lead me to trying two different heat ranges on that old 305...one on the right bank and another on the left bank...the car responded by knocking nearly two tenths off the ET. It was a painfull experiment...pulling into the pits and quickly swapping spark plugs after every two p***es...starting with the same heat range on both sides in two different tests, then mixing them up to see what yielded the best results...burned my hands a bunch of times, but Chuck's theory proved valid! He always repeated "You don't have a V8...you have two FOUR cylinders...treat it like that and you'll go faster!". He was even MORE fanaticasl with his car...treating it more like eight ONE cyliner engines! After that day at the track, I always ran R42TS plugs on one side and R45TS plugs on the other!) I heard that there was an article in the new issue of HOT ROD relating to a firing order change on a Chevy motor accomplished through a cam swap...but I haven't read it yet. Seems very sensible...Ford did that YEARS ago on their V8s to solve the same problems! On my 285 motor, I'm running a single plane intake...I wanted an old Holley Strip Dominator, but I think those (the OLD ones) are long out of production. The Edelbrock Torker II is priced under a hundred bucks new through Jegs, and I ran one on another 305 with excellent results, so I'll likely run one on this mill. If you look at the header design I illustrated at the top of this thread, you'll see that cylinder 7 has a larger pipe diameter than cylinder 5, which should help balance them somewhat. I was also initially considering a hydraulic 'cheater' cam in this motor (stock lift, long duration), but I think a solid lifter cam is the way to go for this animal. That will allow finer cylinder-specific tuning and I found a grind by Crower that I really REALLY like for this engine. (Chuck always advocated solid lifter cams for any serious performance motor, and me being one to lean towards daily driven, milder performance cars, I opted for hydraulics, but this motor is a prime candidate for some experimentation in the solid lifter realm!)
You are absolutely right, Bill! The piston WILL end up further down in the hole due to the shorter stroke, but we're only talking about a .23" reduction in stroke, about a quarter inch, which means that the piston will only really end up less than an eighth inch lower in the bore than it would be stock. Any lost compression could be made up through reduced combustion chamber volume (head swap) or running 305 pistons with a thicker (taller) compression height. I'm interested in seeing how a LOW compression performance motor acts in this configuration, so I'm willing to start off with a low static ratio here! (A little something I learned playing with mini-bikes...which have VERY low compression ratios...I ran super cheap-o sub-grade fuel in them and they ran great. I thought it would be cool to put some Turbo Blue racing high octane leaded fuel in the tank, and found the engine would hardly even start, much less run! Low octane fuel actually burns FASTER...so, coupling that characteristic with a low compression engine, it seems to me that it could be a benficial condition in an engine where fast revving and higher rpms are desired...the low octane fuel ignites and burns QUICKER, which should work in concert with a fast spinning motor by completing the combustion event quickly, while the low static compression ratio should stave off 'spark knock' or pre-ignition.) I could be way wrong...but since this is essentially a very low buck engine using cast off 'junk' parts (in the eyes of most!), I figure it's worth a shot...not much to lose!!
BUT.... ideally, you want to keep "quench distance" down to .040-.060"... you will have .125"+.025" deck (oem ***umption)+ .039" gasket. Way too much, IMO... you will have really low C.R., and poor combustion efficiency. HOWEVER... here is a thought: GM used a 5.9x rod in the 94-96 265 ci LT1 style engine (used in Caprices). Maybe you could use these rods, and mill the tops of std 305 pistons to get deck height to an acceptable range?
This post blew my mind. just as a side note. the latest HotRod magazine has an article about changing the firing order. I think it wasa 4-7 swap or something like that (at work now, mag is home). May be something to add.
I think it would be fun to see what happens with the piston down in the hole an eight of an inch. Although I have heard about it....I have a nice set of 454 forged pistons that someone had installed in a 427, it really ran bad, and not just because they had the 454 damper and flywheel on it (making it shake like crazy)
Excellent points, Novadude...and something indeed to consider. Glenn (AHotRod here on the HAMB) found a set of 305 pistons with a raised compression height that would put the compression ratio back a little closer to stock at least. (Anyone considering piston swaps and such owes it to themselves to talk to Glenn...he listened to what I wanted and made excellent suggestions while looking through what he has available to come up with a piston to suit my needs. Top Shelf guy all the way! ) I thought of a connecting rod swap as well, but I want to see how it works with the stock 305 rod first. I have a feeling this motor will be tampered with quite a bit down the road a ways!
the compression height difference will only make the effective combustion chamber 21cc bigger, according to my quick calculation. Shoud be able to run it on turpentine....
Make that left bank . . . geez . . . I musta had Ford on the brain. 1-2-3-4 Ford, right bank. 1-3-5-7 GM, left bank. Oncet upon a time we swapped a Rocket motor into a very nice 29 RPU. Had fenders and everything. No matter what we did, we couldn't get it to light off and all we got for our troubles was a loud bang now and then. You guessed it, me bein a flathead guy and all had wired the Rocket motor Ford style....
Ha Ha...that's about what sub-grade unleaded fuel is these days! Your calculations are close to my own su****ions...the drop in compression won't be that drastic, and could be made up with the pistons Glenn suggested or with early style 265 or 283 heads with the small valves and small chambers if desired.
I remember reading something about the Ramchargers "High and Mighty" using different length exhaust and intake runners on their radiator hose tunnel ram. It mentioned going down the strip and hearing 4 cylinders detonating, then as rpm increased it would stop, then the other 4 would start detonating.
Entirely possible, although it could have probably been corrected through various tuning methods, such as different spark plug heat ranges, valve timing, etc like I was talking about earlier. 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!
Another way to split up the header tubes might look like the second drawing here, shown with the dual plane intake manifold. If I were running a dual plane, I'd make the headers as shown in that diagram, and that's how they SHOULD have been done on my old Malibu (which ran an Edelbrock Performer dual plane), but for this 285 motor with a single plane, I like the set-up in the first diagram better. In either case, the general theory is the same... For the Dual Plane design, you follow the firing order , 1-8-4-3-6-5-7-2, with a small tube on cylinder one, big tube on cylinder 8, etc. This pattern also conforms to how the planes of the intake are configured. The cylinders with the smaller tubes should exhibit a tourque curve that peaks slightly lower than the torque curve on the cylinders with the larger diameter tubes...thus, with the torque curves overlapped, the cylinder with the smaller tube "leads" the cylinder firing right behind it with the larger tube...if you follow my thinking here. With the longer runners in a dual plane engine designed more for lower rpm use, this one small-one big pattern should work well. For the Single Plane design, however...on an engine with shorter runners designed to run at higher rpms, my thinking with the original header layout was to do the same thing as mentioned above on the Dual Plane design, but to go in a pattern with two small tube cylinders leading two large tube cylinders. With the engine turning more revs faster, I thought it made more sense to double them up. (Not to confuse y'all more...just trying to explain my thinking here a little more clearly.)
You know...some of the 305's had a dished piston. I wonder would it work out to run the longer rods from the late model LT1 and just sand off the dish lip from the piston? ( I belive NOVADUDE mentioned the same thing.) Make a jig and do it yourself kinda stuff seeings its just the raised ring! wonder would that give you the required deck height??? That would be really cool. Not sure if the small valve diameter and short required lobe lift would allow for no valve relief in the piston or not... Maybe use an old head and valve create a poor man's flycutter! What do you have to lose? Some old, stock 305 pistons and a dead head? I'm getting way into this! LoL I like it...it's man against the world/ outside the box sorta stuff! There's a variety of chamber sizes and port flow rates in 305 heads just like in the old "Camel humps", but the 305 heads are naturally smaller and thus undesireable...for a 350. BUT, given the small size of your engine, it would be fun to play "find and swap" just like in the bad ol' days! Might be some killer combinations just waiting for the right little engine. 416's and 601's seem to be the ones the short track guys go for. Check this out! (Mortec...) 14022601...80-86...267/305......1.72"/1.5" or 1.84"/1.5" valves, 53cc chambers 53cc Chamber + hardened valve seats. An early 283 only had a 60cc chamber and soft seats! The 416's have 58cc's BTW. Seems you don't need to go back to the real early stuff to get better compression! Question...why run a single plane if you want to treat the engine as "2-4 cylinder" engines? Wouldn't that just take away a degree of separate tuning ability? With a dual plane you can jet both engine halfs separately, but not with an open plenum manifold...and won't torque and response drop off with a big runner manifold like that on a small engine, considering it was sized to fit the more popular 350?
As Fat-Hack and I discussed, If he has the block decked to 9.000" crank center distance, the effective compression ratio will be where he wants it to be. The 305 cylinder head flows very well, as evident in the performance achieved by NHRA stock cl*** engines, of which I have personally been involved with. This cylinder head on a 285 CID engine will in effect be a 'ported' unit out of the box. With the choice of intake manifold he has made, and a Q-Jet or vacuum secoundary carb set up correctly and a 1 1/2"-1 5/8" primary tube exhaust header, the combination should run very well. One of the important keys will be camshaft selection, where a stock 300 HP 327 cam could be just the ticket for the 285 CID combination. Personally, I would want my camshaft to have a 106 centerline, as to ***ist the rotating ***embly in m*** acceleration. In my 'stockers', we used these and shorter, some were on a 102. It should be a little screamer........
Bill, you're ahead of the cl*** here!!! I'm getting a set of 267 heads from Aaron51 for this engine, for some of the same reasons you just pointed out...small valves (desireable in a small bore) and hardened valve seats (being from the smog era)!! My plan for the heads, is to have them rebuilt with oversized exhaust valves. My buddy did this to a set of 1.94 heads on a 350 years ago, having the 1.60 exhaust valves from the 2.02 heads installed and it worked out really well. I'm buying a set of good 1.60 exhaust valves to go into the 267 heads in place of the stock 1.50 exhaust valves. You can run 1.84 intake valves in a 305 bore, but valve shrouding may become an issue. I'll just get that little 1.72 ****er open a little more, and keep it open longer to accomplish cylinder filling goals! With the 1.60 exhaust valves installed, the difference between the intake and exhaust valve diameters will be reduced. This would negate the need for a dual pattern cam to some degree, but I still like dual pattern grinds. (Racefab often makes reference to a comment I once made about single pattern cams only being good for dump trucks...it's a little joke we share...I know single pattern cams work okay in race engines with open headers, and in a motor with oversized exhaust valves, but stock intake valves, they'd work out pretty well, too I believe.) The only other head mods I'm considering at this point is a little clean-up work, a fresh valve job, new seals and the recommended springs for the chosen cam...nothing fancy or high dollar!
Glenn...whats the head of choice for those stock cl*** cars? I'm likeing this whole idea. I'm not fully "into" the dual 4 cyl thing...gotta think about that for a while...but this whole "little" engine deal seems to put FUN back into the equation! So your saying that the required milder cam will keep the cylinder pressure up...a high compression "number" isn't really important? Cool. This is an owner input style build. You won't see this on the POWER BLOCK! What you lose in outright performance, you gain back in the ability to maximize on a budget...with even cast off parts. You gain some rev-ability over the 305, a great cam is just the stock cam from a bigger engine, heads are carefully chosen stocker cast offs...modified with cast-off larger exhaust valves. Cheap Holley or Quad carb...I'm lovin' it. Very cool. Like a trip back in time...to fun Hot Rodding.
Bill, In NHRA Stock Cl*** racing, the engine has to have stock type pistons, stock rods, stock crank, stock heads, rockers, pushrods,factory intake and carb..... Stock. We are allowed headers, blueprinting the engine, and the camshaft must have the stock lift, but in the duration and lobe centerline areas, we can go wild. A good 'stockerized' 305 will make the same HP as a 'stockerized' 350 in allot of cases, the difference being what the original 350 started at, ie: 350HP motors of course make more. For example: Start with a '82 Camaro 305 175HP engine, zero deck the block, bore it .030, new forged stock pistons, a trick Speed Pro ring combination, stock oil pump, true-roller timing set, a Bullet Cams camshaft with stock .410 lift, but with 300 degrees (250 @ .050) duration on intake, 322 degress (272 @ .050) on exhaust, on a 106 lobe center, installed around 102-104 depending on the gearing. The stock heads are blueprinted, milled to the minimum cc per NHRA rules, factory diameter valves that we 'back cut', factory looking valvesprings, factory rocker arms, the carbs are internally modified, Jacobs or MSD ignition, .....the finished product will produce 420HP @ 6200 RPM ! My '74 Vette Stocker 350 195HP engine, with the #882 heads, my camprofile was less due to the 350 has .390 intake and .410 lift, anyway......mine made 392HP @ 5400 RPM. My car had to weigh 3610#'s PLUS me @ 210, ran a Turbo 200 and 8" convertor, 4.88 gears w/9"x 28"tall Goodyear radial drag slicks,.....in good air I ran 11.60's with the front tires 2 feet in the air leaving the starting line. If folks would just spend the time making the factory combinations the best they can be, they would be astonished with the results.
Interesting ideas. I'm not 100% sold on the small-cube choice, as the easiest way to gain power is through displacement. Why not work to maximize power on another big bore / short stroke engine configuration? Maybe an Olds 403? From what I see, it fits all your criteria, especially the notoriety as a junk smog-era engine, and would put another 120ish cubes on the plate. It is 4.351 x 3.385 and those small valve heads generate some serious port velocity and GRUNT. And I'm with some of the other guys that make it sound like you're giving up some at both ends of the spectrum. A friend I know built a 350 Chevy with nice pieces, but one side ran 11:1 compression and the other was at 9.5:1 while running equivalent World Products heads on each, but an aluminum casting on the high compression side and iron on the other. He did it while his other alum head was being repaired. When he took it to the track, it lost nearly a half-second in ET and a few mph over the same engine in its normal high comp/alum headed configuration. And it was soggy on the street from what he said. Your results may vary. Anyway, cool concept, keep us posted.
The Jalopy Journal
