There are forged pistons commercially available that will work in the 300--I have them in mine. The TRW L2343 forged piston is for the 350 Buick (also fits the 231 V6 engines). Since the 350 has the same pin location as a 300 piston, it will work in the 300. Only thing is you have to bore the block .050" oversize and use standard bore 350 pistons and rings. A 350 piston gives the same compression height and everything as a 300 piston. 300 bore is 3.75" standard bore, and a 350 has a 3.80" standard bore.
56.0 cc chamber 14.0 cc piston dish 4.85 cc Gasket 3.72 cc deck (.020 deck clearance ) 794.00/78.54 = 10.1 : 1 C.R. actually a little less if you include volume above top ring and piston deck ( crown )
You are forgetting that we need a shorter piston with a more compact compression height so we can accomodate the longer stroke. Thanks! Hey this is outstanding! This opens up the possibility of using the stock 340/350 rods! Those are 6.387" for a rod ratio of 1.66. Much better! Let's see: 1.197 + 6.387 + 1.925 = 9.509. Now we can run regular, readily available head gaskets that are .040" thick. If you don't like that ever so slight positive deck clearance you can offset bush the small end of the rod since that Series II piston very likely has a smaller pin. We can be sure that this combo won't need any clearancing on the underside of the pistons since the longer rod will keep them further away from the counterweights. We can also be sure that those supercharger application pistons are stronger than those Olds 307 pistons are and I'm sure those pistons are lighter too! Plus we already know that the piston top's shape and valve notches are gonna be right. Lastly, since that supercharged engine has a lower compression ratio, we can be sure that there is a decent sized dish on it which will help keep our compression ratio from being too high with our increased displacement. Regards, Eric
Ok Eric, you got us on that one, a late model, Series 2 V-6 uses a slipper-skirt piston. This article was about vintage Buick V-8's, not late model, low deck V-6's. The 400 and 455 big block Buick's along with all the nailheads, plus the 215,300,340,and 350 small blocks, not to mention most of the V-6's, used NON-SLIPPER skirt pistons which, as the Hot Rod article points out, explains why all these engines have taller than normal deck heights relative to their stroke. The point of all this is, that you can use a relatively long rod with a long stroke crank in a 300 block, if you use a slipper-skirt piston. You seem to imply that we had a poor rod length to stroke ratio. Some people are big believers in long connecting rods or high rod length to stroke ratio's. There is even some disagreement among reputable engine builders on the benefits of rod length, both long and short. Very long connecting rods were common in old engines, especially in the 1920's and 30's, even some 40's and 50's designs, but is old school engineering when compaired to modern 4,6,8, and 12 cylinder engines of today. As an example, the newest performance V-8, the 2011 DOHC 5.0 Mustang motor, has a 3.653 stroke and a 5.933 rod length for a relatively low 1.62 to 1 ratio. This is not out of the ordinary for a late model engine. A rod length to stroke ratio of 1.548, as used in our 349 Stroker, is not a poor ratio and compairs favorably with typical street 383 Chevy and 347 Ford stroker motors as well as a 454 BBC and many late model OEM engines. This not to say that there is never a benefit in running a long rod, but changing to a longer 6.125 rod ( there is room to run a 6.125 or even longer rod in the 300 block ), would offer little, if any, performance gain at this H.P. and RPM level. Also, there are benefits to shorter rods, mostly related to torque in low RPM street motors. Running an aftermarket connecting rod designed for a high RPM race motor, or a forged piston intended for a motor with a power-adder, in a low RPM, 350 to 450 H.P., normally aspirated, street motor may make you sleep better at night, but that doesn't mean it is needed or that it is money well spent. David
Valve notches are not needed because of the shallow valve angle of the 300/340 head, even with over .500 lift, this is not theory but proven through actual experience, and the unique U shape dish ( shallow on the quench side, deep on the spark plug side) of the Olds piston worked excellent with the 300/340 combution chamber, as witnessed by the fact that the engine made best power with only 30 degrees to total timing. The cost to offset bush the small end of a connecting rod is a lot more expensive than you might think. If you use a 6.0 aftermarket Chevy 2 in. journal rod with the Olds piston it puts the piston just below the deck. Also, a virgin 300 block measures closer to 9.540 deck height. The chamber of a late model Series 2 or 3 V-6 is nothing like a 300/340 chamber, so how does that make the "piston's top shape and valve notches right". Dave
Oh, so NOW I exist! The article said "Buick never adopted slipper-skirt pistons in any of it's engines not any of it's V8s. It wasn't a personal attack, and I wasn't trying to "get" anyone. It was just a correction of an inaccurate statement. The funny thing is, that inaccurate statement is in fact what got me looking at the series II piston as a possibility for this engine. It also just seems better to use a Buick piston in the build. I also forgot to mention that the Series II Buick pistons already have the correct size ring lands so one can use modern low friction rings without having to resort to spacers. It's just a better deal all the way around. Sorry, you are not gonna convince me. I'm a long rod man, always will be. Even if you make the argument that there is no power to be gained with long rods, I still maintain that the decreased cylinder wall wear and piston side loading and the benefits of longer engine and even oil life make the long rods the better bet. There are still plenty of modern engines that have long rod ratios. The ones that don't usually have short rod ratios because of packaging or tooling reasons. (As in not wanting to spend the money to do it right and tool up a taller deck block and longer connecting rods.) This is a good example! A good example of an OEM not wanting to spend the money to do it right and raise the deck height and lengthen the rods! That 5.0 DOHC's rod length is the same as the 4.6 from which it sprang (despite what Ford says about this engine being "all new") the deck height of the block and it's bore spacing are the same too. That rod ratio isn't being used because Ford thinks it's the ideal, it's being used because that is simply what Ford ended up with when they were done cramming a bigger engine into the 4.6's package. (Ford had no choice when they created the 5.4 though, they HAD to raise the deck height.) Ironically, that 1.62 ratio is STILL closer to the 1.66 ratio of my combo than it is is to the 1.548 ratio of your combo. Good example there. [Edit: When using the unconverted metric dimensions of the new 5.0 Ford (it is after all a metric engine) it's ratio is actually 1.6257 which rounds to 1.63, not 1.62 (92.7 stroke and a 150.7 rod length). The "parent" 4.6's rod ratio is 1.68 to 1! Again, good example!] The 347 Ford (1.59) is tolerable. The 454 BBC (1.53), and 383/400 SBC (1.48-1.52) have the 2 WORST ROD LENGTH TO STROKE RATIOS OF ANY V8 engines EVER PRODUCED!!! No other OEM has EVER produced a V8 that comes close to being that bad. Short rods adversely affect everything from fuel economy to engine longevity to power and torque production. Short rod ratios suck!!! If short rod ratios were the hot ticket, more V8s would have them. THEY DON'T! Most OEMS hover in the 1.7 range. Short rods take their toll on cylinder wall wear, piston wear and ring wear. Even if the short rod engine wins the race (and again, I maintain that it won't) I'll still take the long rod engine cause it will live longer and that is the most important race of all! All this rod ratio stuff has been argued for years and will continue to be argued for years to come. All I can say is that now even Chevy, with the LS family, has lengthened their rod ratios to close to the 1.7 range which is where every body else has been all along. It seems that even Chevy is admitting, by their actions, that everybody else was right all along and they were wrong. Yes, there are still exceptions in cases where the OEM is trying to stuff a big displacement into a small package, but, for the most part, most all V8 engines in the 340 to 360 CID range have about a 1.7 or longer rod ratio. (BTW, I don't think we have a lot of Chevy lovers on this site. I'm certainly not one.) You've been spending too much time with Uncle Joe Sherman, he is a short rod man. David Vizard is a long rod man, so was Smokey Yunick. I'll go with what they believe. Um, we've actually already seen that there is actually room for a 6.387 rod. Um, my combo calls for a production series II piston and a cast 340/350 rod. I would like to have the option to upgrade both though so I can run copious amounts of N2O, not so I can sleep at night. I'm sure the series II piston has a dish that is just as good if not better since it is a more modern design and is for a chamber that is more closely related to the 300's chamber. The 300's deck height is actually 9.54? I thought is was an even 9.50. This is good news! This means my combo will fit WITHOUT offset bushing the small end! Problem solved! It's still more similar to the 300's chamber than the Olds chamber is. Still really wish you would post some pictures of the intake manifold mods. It would be the right thing to do. And it would be truly appreciated Regards, Eric
Not sure how far you could go in the 300 block, but in the 340 you can easily achieve a rod ratio of 1.818. This was done using 7" long light weight aftermarket Scat FHF rods and custom pistons without impacting the ring package. What it means is that there is no good reason to be limited by short rods, as there is obviously enough room to use a 6.356" length rod in the 300 with the same piston. That's .030 away from Eric's piston with the stock rod so I'd say he has found a darned good combination, especially if what you're looking for is an inexpensive street build. There is another excellent reason to stay away from short rods in the SBB. Thin cylinder walls. As a lightweight casting the block doesn't have excess metal in it anywhere and that includes the cylinders. For most blocks a .030 overbore is no problem but any more than that and you'll want to have it ultrasonically checked for core shift. Does this mean you're better off with the Olds pistons and a .030 overbore? Well the difference between .030 and .050 is ten thou at the cylinder wall so it's a judgement call, and a good machinist can shift it a little towards the off side, but it's something to think about. Still, pitting more stress on a cylinder wall that is thin to begin with can't be a good thing. I like the combo Eric has come up with right well. Like I said earlier, had I known some of this earlier I would have likely built a stroked 300. Eric, do you think you could come up with some more details as to calculated CR with this combo? TeamBuick gives the deck height as 9.543" JB
> Short rod ratios suck! You really can't make a blanket statement like that. Engines with large ports (relative to displacement) tend to prefer shorter rod ratios and induction limited engines tend to respond to shorter ratios. Rod length alters the acceleration profile. Shorter rods have a higer acceleration near top dead center which is why they are preferred for large port engines. A longer rod reduces the rod angularity which reduces the cylinder wall loading and friction. The larger the ratio, the longer the piston dwells near TDC, allowing more power to be extracted from the combustion event. The more restrictive the induction system, the more benefit you'll see from increased rod length but the effect isn't very large. Since the piston speed profile is altered by changing rod length, engine tuning may also be affected so optimal cam timing or header dimensions may change. On the downside, longer dwell time at TDC requires deeper valve relief notches in the pistons for the same cam timing and is more prone to pre-detonation. > You've been spending too much time with Uncle Joe Sherman, he is a > short rod man. David Vizard is a long rod man, so was Smokey Yunick. Vizard likes longer rods but admitted the effect isn't all that much. Multiple Engine Masters Competition winner Jon Kaase's rule of thumb is the rods should be at least 2" longer than stroke. He says that rule has worked well on everything he's built from small port 289 Windsor Ford's to his large port Pro Stock 351C-4V Fords to the IHRA mountain motors. Like most things it's a trade-off and there's a point of rapidly diminishing returns. I wouldn't trade off piston stability for a longer rod and a stroke increase will show a larger torque increase than a rod length increase. The point is don't get too hung up on a single parameter. Just make sure everything plays nice together. Dan Jones
I don't know if this is completely correct. I'm in the midst of a 300 build and was able to bore it 0.070" over. Using custom Venolia pistons and narrowed SBC 6.0" rods. I'm under the impression that 300's can easily be bored up to .080 and some 0.100 over. So the thin block comment makes me wonder, is that mainly for the 340's and 350's?
Matt, did you have a sonic check done? There is a lot of difference in opinion on what is the minimum wall thickness you should have in the cylinder walls, but anything less than 1/8" is getting a little on the thin side. My understanding is that all the SBB engines share the thin wall characteristic, and core shift was common. In my 340 block (with .030 overbore) the walls ranged from .282" down to .116" with .160 on the thinnest thrust side. I'd like to stay over 3/16" there if possible just for reliability. My machinist took it out another .020 and minimized the material removal on the thin wall. (This was a fresh reman block.) Personally I'd try to avoid going any thinner than that. It might work fine, but if it doesn't it's a real bad trip. JB
Thank you! Coming from you that really means something! The Olds 307 and the Buick 231/3800 both have a 3.80" bore. So no difference there. They both require a .050" overbore which I'm not too thrilled about either but what can you do. Maybe there is an even better OEM style piston out there somewhere. I won't take it personally if somebody comes up with an even better piston/rod combo that doesn't require as big of an overbore and can be done as cheaply. I would need Timo to look in his trusty Silvolite catalog again so he can tell us what the CCs of the dish is. I know that piston has next to no crevice volume so we need to know what that is too. (Just how close is that top ring is to the piston deck?) I'll bet the dish's CCs will wind up being about the same as the 307 Olds piston's dish is so the compression will wind up being about the same too since we will use the more common .040" thick gasket to go with our near zero deck clearance set-up (after a minor clean-up) vs. the .020" down in the hole with a .020" gasket of the other set-up. The only wild card here is the decreased crevice volume of the more modern piston but that shouldn't change the final result too much. I'll address the other post soon (probably tomorrow night) when I have the time to give it the attention the rod length issue requires. (Short rods still suck.) Regards, Eric
Really nice to see the Buick build, that are few and far between in a mag I've read for 40 years. Pretty good numbers too on the lil 300 or should I say 349. Good article and nice work.:TU: Unfortunately....this is far from any type of "budget" build with the huge amount of machining that was done, let alone the over 100 hours on the flow bench. The article never mentioned what these costs were..... As was asked for in a prior post....would be nice to get a better idea what porting was done to achieve the results...
I'll say it again. the port work and flow bench work make this motor a poor choice when looking at cost vs hp made. even if the labor rate were only 50.00 per hour you would have 5000.00 in head work alone,( i'd love to find a professional head porter who only charges 50.00 per hour) then toss in the standard machine work and grinding the crank to fit the 300 block. i bet this motor would cost the average guy as much to build as JW gets for a level 2 455.
What I'd like to know (and I am sure I am not alone), is what the cost would be for everything below the heads- sourcing a 340 crank, all the machining, boring, balancing +pistons and rods. In other words- the cost involved for the short block, if you already have a 300 block to work with. I was considering a 340 build, but the stroker build allows me to keep my original numbers matching block and make it a real sleeper... Any idea what a short block build like this would cost?
Using the Buick series II piston should be cheaper because you don't need to have the bottom of the pistons clearanced and you don't need ring spacers. You also don't need to weaken the small end of the rod by boring it for the Old's unnecessarily large pins. Just use the rods from the same 340/350 that is donating the crank! (We do need to bush the rod's small end though but that still leaves us a stronger rod than boring it does.) Also, let's don't forget that the SBB 350 got a fairly decent "capscrew" design rod in, what was it, 1975? Much better design, much stronger (but still cast unfortunately). So not only do we get a better rod ratio with this package, we also get a stronger rod too! AND that capscrew rod will very likely clear everything without the need for the clearancing that the bolt and nut rod requires! More savings! Also, looking into the future, it doesn't take a rocket scientist to deduce that the availability of pistons for supercharged 3800s will far surpass the availability of pistons for the Olds 307. In other words, the supply of pistons for the Olds will begin to dry up. (There aren't a whole lot of folks building Olds 307s. I see supercharged 3800s at my track all the time. I NEVER see Olds 307 powered cars.) This will also effect pricing, with the Olds piston getting the raw end of the deal (if it isn't already.) Still probably not gonna be the cheapest engine you ever built though. Regards, Eric
I can, have, do, and will continue to do just that. First part of that statement is true, second part is not. I believe you meant to say that induction limited engines tend to respond to longer ratios. You mean "lazy" low velocity port engines. It's much better to have a high flow, high velocity port that doesn't need to be crutched with a shorter rod. Very true. Long rods are the greatest! And since this thread is about building the 300 SBB, it makes sense to be talking about stuffing longer rods in it. If there ever was an engine that was/is induction limited and could benefit from a longer rod ratio for the reason stated above, the 300/340 is it. When you add in the other benefits of longer rods and then you factor in the fact that it doesn't cost us any more to build this engine as a longer rod engine, it makes the choice a no brainer. Let's also please keep in mind that at 1.66 to 1, this combo is still only an AVERAGE rod ratio engine, not a long rod ratio engine. We are simply putting the rod ratio BACK to where Buick put it when they created the 340/350 by stroking the 300! We are just using a more modern Buick piston to do it! With the stock 300's rod ratio being 1.75, even my longer rod ratio combo still winds up with a shorter ratio than the stock 300! The LS based Chevys are 1.68-1.69, the 4.6 Ford is 1.67, the new 5.0 Ford is 1.6257 (which rounds to 1.63, not 1.62, I need to correct somebody's earlier post), and the new Hemi is 1.75. The 360 Mopar, 360 AMC, 302 and 351W Ford are all 1.70-1.71, the 260/307/330/350(gas)/403 Olds is 1.77, the 318 Mopar is 1.85, heck, even my 92, 93, 94 and 95 32 valve 4.2L Mercedes V8s are 1.89! So contrary to what others would have you believe, rod ratios are not getting shorter, piston C.H.s are! http://users.erols.com/srweiss/tablersn.htm#Buick With SO MANY divergent OEMs from such divergent eras all having rod ratios above 1.66 (yes, even Chevy now too), I'm gonna go with a longer ratio too! Very true, so build the long rod engine and then tune to that! That's a bit of a case of splitting hairs, as you would say "the effect isn't very large." Plus, as has already accurately been pointed out, we have an engine here with a very flat valve angle so this issue isn't much of a concern. Even if there was no effect at all, the lower wear issue makes longer rods worth it to me. Who wants an engine that is beating itself to death? I would love to ask ole Jon what his rule of thumb is for engines that are gonna be abused on the streets for 200,000 miles. Neither would I nor are we. We are using an OEM production based piston for a supercharged production engine that meets demanding longevity requirements. There is no doubt that that supercharged Buick piston is designed and built to take more abuse than that 307 Olds piston is. Don't forget, it is a lot lighter too. That carries all kinds of performance and longevity benefits with it. I agree. Yes, a longer stroke will give you a better return (power wise) than using that available space for a longer rod will (longevity WILL suffer though) but that is only because we are increasing the displacement. Since we don't have any more room in the bottom end to increase the stroke any further than we already are (to 3.85", remember how close that camshaft is), we might as well put the remaining available deck height space to good use by lengthening the rod. Reducing rod angularity is a GREAT way to "make sure everything plays nice together". Regards, Eric
Regarding “ Uncle Joe “ ( Joe Sherman ) For those of you who do not know of Joe Sherman or anything about his accomplishments or reputation, the following is a brief summary. Joe has been building race and street performance engines for over 40 years and is well know and respected in the industry not only in the U.S. but also Canada, Europe, and <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-comU.S.</st1:country-region>, but also in <st1:country-region w:st=" /><st1:country-region w:st="on"><st1lace w:st="on">Australia</st1lace></st1:country-region>. He worked for Edelbrock for 14 years and was involved in product testing and development. He was credited by Hot Rod Mag as being one of the first to put the new Gen 1 Camaro ( in 1968 ) into the 10’s with a normally aspirated , 350 SBC He is also credited as one of the first engine builders ( very early 70’s ) to put a modified ( reduced mains ) 400 SBC 3.75 stroke crank into a 350 SBC there-by creating one of the most popular stroker combo’s ever, the 383 SBC. During the late 80’s, Nostalgic Drag Racing became very popular across the country. The NDRA ( Nostalgic Drag Racing Association ) had several classes including Super Stock. In <st1:State w:st="on">California</st1:State>, a fairly large group of NDRA Super Stock racers developed a series of races that toured several strips up and down <st1:State w:st="on">California</st1:State> and also <st1lace w:st="on"><st1:State w:st="on">Arizona</st1:State></st1lace>.. This series became so popular, that some of the top running cars were paid to show up and race at several strips. The two fastest cars were a1963 426 ( wedge ) cross-ram Super Stock Plymouth and a 409 powered 62 Bubble-Top Bel-Air Chevy ( heavy ). The Chevy usually out ran the <st1:City w:st="on"><st1lace w:st="on">Plymouth</st1lace></st1:City> and was a solid mid 10 second car. Joe was the engine builder and tuner and toured for 3 years with the car owner. Joe won the inaugural Popular Hot Rodding ENGINE MASTER CONTEST and was awarded the first prize of $75000.00. His winning engine, a normally aspirated, 364 c.i. SBC made 604 H.P. at a street friendly 6500 RPM, using a single Demon carb on a modified Edelbrock Victor manifold, hand ported ( intake only ) AFR heads, an Isky Hydraulic Roller Cam,( mechanical rollers and sheet metal manifolds were not allowed ), and on pump gas and through mufflers. There were a number of well respected engine builders that participated including: Ron Shaver ( noted Sprint Car Engine Builder ) Dan Crower ( Son of Bruce Crower of Crower Cams ) John Beck of Pro-Machine ( Builder of the engine that powered the first roadster to 300 MPH at Bonneville – March 2011 issue of Hot Rod ) Tom Nelson, Nelson Racing Engines ( noted turbo specialist ) and Keith Dorton of Nascar fame to mention a few. More recently: 816 H.P from a normally aspirated, 302 based, 374 in. SBF ( Hot Rod -Jul 06 ) 650 H.P. from a normally aspirated, 348 based 437 in Chevy W motor on pump gas with old school duel in-line four barrel carbs ( Hot Rod - Nov, 09 ) 500 H.P. for $5000.00 dollars ( 383 Chevy, single four barrel, pump gas Hot Rod – Sept. 06 ). Currently, his son Steve runs a box Nova with one of Joe’s SBC at two So. <st1lace w:st="on"><st1:State w:st="on">Cal.</st1:State></st1lace> 1/8 mi. drag strips, Barrona in San Diego Cnty and Irwindale in L.A. Cnty. With a normally aspirated, 434 c.i. SBC , toped off with AFR heads, a modified Eldelbrock tunnel ram and two big Demon Carbs and backed by a Powerglide the car has run a best of 5.70 and a 121 MPH in the 1/8 th. ( 8.90/ 150 mph mi )
EFFECTS OF LONG RODS PRO: provides longer piston dwell time at & near TDC, which maintains a longer state of compression by keeping the chamber volume small. This has obvious benefits: better combustion, higher cylinder pressure after the first few degrees of rotation past TDC, and higher temperatures within the combustion chamber. This type of rod will produce very good mid to upper RPM torque. The longer rod will reduce friction within the engine, due to the reduced angle which will place less stress at the thrust surface of the piston during combustion. Thiese rods work well with numerically high gear ratios and lighter vehicles. CON: They do not promote good cylinder filling (volumetric effieiency) at low to moderate engine speeds due to reduced air flow velocity. After the few few degrees beyond TDC, the piston speed will increase in proportion to crank rotation, but will be based by the connecting rod length. The piston will descend at a reduced rate and gain its maximum speed a a later point in the crankshafts rotation. Longer rods have a greater interference with the cylinder bottom & water jacket area, pan rails, pan and camshaft. EFFECTS OF SHORT RODS Pro: Provides very good intake and exhaust velocities at low to moderate engine speeds causing the engine to produce good low end torque, mostly due to the higher vacuum at the begining of the intake cycle. The faster piston movement away from TDC of the intake stroke provides more displacement under the valve at every point of crank rotation, increasing vacuum. High intake velocities also create a more homogenous ( uniform) air/fuel misture within the combustion chamber. This will product greater power ouput due to this effect.The increase in piston speed away from TDC on the power stroke causes the chamber volume to increase more rapidly than in a long-rod motor - this delays the point of maximum cylinder pressure for best effect with supercharger or turbo boost and/ or nitrous oxide. Cam timing ( especially intake valve closing ) can be more radical than in a long rod engine. Con: Causes an increase in piston speed away from TDC which, at HIGH RPM, will out run the flame front, causing a decreas in total cylinder pressure ( Breake Mean Effect Pressure ) at the end of the combustion cycle. Due to the reduced dwell time of the piston a TDC, the piston will descend at a faster rate with a reduction in cylinder pressure and temperature as compaired to a long-rod motor. This will reduce total combustion. Not one word of the above summery on connecting rod length is mine. They were written by John Erb, Chief engineer, Keith Black Pistons. Considering the source, I think it is safe to say, that his summery is more conclusive than Short Rods Suck. Does this mean that short rods are better than long rods? No, nor does it mean that long rods are better than short. What you should conclude is that both combinations have benefits and draw backs. It is also interesting to note that according to John Erb and also SAE, the range of rod length to stroke ratio that denotes short rods is from 1.45 to 1.75 and long rods are from 1.76 to 2.2. It is true that using a 350 rod would improve rod angularity over the shorter 300 rod, but there would be little, if any performance gain, on a low RPM (Below 6000 RPM )street motor and low to mid range torque might be less. The reduced rod angularity of the 350 rod would probably reduce cylinder wear, but would likely not be significant until the motor accumulated over 100,000 miles. The bases for this assumption is the fact that a Big Block 454 Chevy has a 1.53 rod to stroke ratio and the 400 SBC had a 1.45 ratio and both engines had to pass the same G.M. durability standards ( 100,000 in the 60s and 70s ) as engines from the other divisions.
