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 even Chevy 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 they are 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 range have about a 1.7 or longer rod ratio. And, in general, Mopars tend to run on the longer side. I can't believe a Mopar guy wouldn't appreciate long rod ratios.

Yes, the 351M had a 1.88 ratio but that isn't why it had detonation issues, it was something else, probably something to do with it's being so heavily compromised for low emissions in the 70s. A lot of engines of that era were that way. And, for the record, I've been around more than a few 351Ms myself and never heard a peep of detonation out of any of them so I'm not buying this urban legend about 351M detonation issues. There are plenty of other engines that have long rod ratios like the 351M that don't have detonation issues either. The 352 FE had the same bore and stroke with a nearly identical 1.87 rod ratio and no detonation issues. The 350/361/383/400 "B" Mopar also comes in at 1.88 and even though, from 1968 onward, they too were flying with quenchless heads, had no detonation issues, with the possible exception of the later 400s that suffered from the same stringent emissions regulations as everybody else. All 318s, both "Poly" head "A"s and the later wedge head "LA"s, all 273s, and all 340s, also had a lengthy 1.85 ratio, most were also quenchless (it would be too lengthy to cover which ones had quench and which didn't, all LA "Magnums" do though), and again, no detonation issues until you get well into the 70s. No, the 351M's detonation issues, if there ever really were any, were smog related, not rod ratio related.
Regards, Eric

 

A little OT, but would someone please explain the obsession about rod ratios, please.

The cylinder, ring and piston wear issue is a non-starter because I have never, ever had to tear down an engine just because of that issue alone. Metallurgy and lubricants from the 1960's-on pretty much made the frequent re-ring job obsolete. Detonation is so complex a subject that there is no one single design feature that is going to explain it. Lets just say that current engines violate a lot of old rules and dont detonate on 87 AKI gasoline with 10.5:1 compression ratios and combustion chambers with very little quench.

 

When Ford created the 400, they spent BIG money to retool and raise the deck height so they could lengthen the rods (more tooling money) so they could maintain a good rod ratio. (About the same as the 351 Cleveland's.) Why spend all that money if rod ratios aren't important? They could have just done it the cheap, Chevy way and did it the way Chevy did by just saying "to heck with it" and stuffed their 400 into an existing block and saved a bunch of bread but they didn't. So I guess rod ratios are more important than people think they are. The 351C and the 351W both have taller deck heights than the SBC does so Ford definitely had the room available to throw a longer stroke crank into an existing block. Why didn't they just do it and save the money? Because maintaining a decent rod ratio is too important. Again, the SBC 400 has THE WORST rod ratio of ANY V8 EVER MADE! If short rod ratios worked well or there was some other benefit to them we would see other OEMs trotting out V8 engines with 1.48 to 1 rod ratios but no one has ever released a V8 with anything near that short of a ratio. Why? Because they know better. And clearly, even Chevy knows better too as evidenced by the fact that they lengthened the rods when they created the new LS based engines.

Real money was spent to assure that the Ford 400 would be a good engine. There wasn't anything done to assure the SBC 400 would be a good engine. It was just something thrown together to give Chevy a cheaper way of filling their 400 cube engine spot so they could kill the more expensive to build big block based 402 which they did do in 73. The 400 Chevy has short rods because it was cheaper to create it in the existing block rather than engineer and tool up a proper tall deck block like Ford did when they created their 400. And we are not OT cause we are talking about some of the reasons WHY the 400 Ford is the superior engine.

And folks can badmouth the 400's combustion chamber all they want, it's still better than that awful SBC chamber!

And has anybody here ever had to replace a GM starter from the 60s-70s? Did they ever dump that lame shim set-up? What a nightmare! They always have to be remeasured every time you replace a starter and then you have to add or subtract shims. How come I can just bolt in a new stater in a Ford and be done? Were Chevy's production tolerances so bad that they couldn't have a stater mounting system that didn't require shims? How come no Ford I ever worked on had shimmed starters? And how come the Ford starters last longer? O.T.? No, because 400 Chevys come with shimmed starters! Yet another reason why the 400 Ford is superior!

Just look at the 2 engines: the Ford 400 with it's modern even by today's standards compound valve angle symmetrical port heads, the Chebby with it's cheap simple inline valve paired intake and exhaust port 50s based wedge heads, the 400 Ford's beautiful spot faced rod bolt 6.58 inch rods, compared to the Chebby's broached rod bolt 5.565 inch rods, The Ford's front mounted distributor which gives us ignition events which are immune to camshaft flex and is easier to access vs. the Chebby's rear mounted dizzy which IS NOT immune to camshaft flex and is HARDER to access, and then add in the fact that it is the 400 Ford, not ANY Chevy, that has won more Engine Masters championships than any other engine, my God do I need to continue? The Ford 400 is the better engine! Pure and simple!
Regards, Eric

 

Not a Chebby fan, but Ive known many that had 400 small blocks and had good luck with them. One of my inlaws bought a Caprice new in '71 with one and sold it in the middle 80s with well over 150,000 miles on it and never opened it up. They were very torquey and major gas guzzlers, though.
Quite a few guys in circle track racing swear by them. That short rod to stroke ration gives you instant torque.
I like the Ford 400, but it seems its weak point is its a bit hard on the bearings. As far as horsepower potential: its starting to get noticed !
Imagine if they made a factory 400 with 3514V style heads and the whole 351 boss package could have been. Maybe as quick as a 429 ?

 

Im well aware that the Chevy 400 was done on the cheap and am not defending it. But, I asked a simple question. Explain the importance of rod ratios.

 

400 ford 4" stroke 4" bore 6.580 rod length. 6.58 divide into 4"= 1.645. chevy 350 5.7 rod into 3.5 stroke=1.62. chevy 350 with same stroke and longer rod, 6"= 1.71 rod ratio. One of advanages of longer rods is piston dwell time. meaning staying at Top dead center longer. Not a big deal at lower rpm's but important at high rpm's. Also piston side load. Piston pushing on cylinder walls sideways. shorter the rod steeper the rod angle and harder on componets and friction on cylinder walls. wasting energy in friction and creating heat internal. but one of the advantages with short rods within reason is low rpm it works well and helps in the less time at top dead center and less time for the combustion chamber to pre ignite. Their are many different situations to consider but short rod ratio's are hard on componets at high rpm's. bearings and cylinder walls are the big factor when running a short rod. long rods keep things straighter in bore and easier on componets. but the question what is you application and what is the sweet spot for you. I know their is more to discuss but these are the major factors when I'm building a engine and rod ratio is a issue.

 

Jim, the problem is it isn't a simple question. It goes beyond the scope of this thread and could fill a whole book. I've got a feeling you already know that and you're just trying to suss me out. Here, read this thread and it's links: The long-threatened Engine Geometry discussion. - Turbobricks Forums Starting at post #18, it get's heavily into rod ratios. If, after reading all 5 pages and the links, you still want to want to discuss it, start a new thread on the topic and link it here. I promise I will weigh in there. I will say this though: When EVERYBODY except Chevy builds their V8 engines in this size range with rod ratios in the 1.60 to 1.88 range and NOW EVEN Chevy DOES TOO. THAT SAYS MORE THAN A WHOLE THREAD OR WHOLE BOOK ON THE TOPIC DOES. Not one OEM has EVER built a normal production V8 with rod ratios as low as the 400 SBC. NOT ONE. Only another knappy Chevy V8 engine, the 454, comes anywhere near close to being as bad. Ford spent real money to give their 400 a decent rod ratio. There must be some pretty good, valid reasons. Maybe even some that us mere mortals don't know about. So while folks will be arguing the long rod/short rod debate for the rest of time, I've already seen all the proof I need to see.

I will also say this: Even short rod fans concede that short rod ratios do cause increased side loading which leads to increased piston, ring, and cylinder wall wear, and increased oil temperatures. THAT is the issue that I personally have with short rod ratios. Yes, some SBC 400s still make it past 150,000 miles but that doesn't impress me. Just about ANY engine can do that. (Except for another Chevy: the Vega 2.3 4 cylinder.) I feel totally ripped off if I don't get at least 200,000 miles out of an engine! I have an 85 Volvo Turbo Diesel that's still humming at 304,000 miles! And I had a 560SEL that made it past 302,000 miles!

Edit: While I spent over three hours looking for that link, plus some time-outs to take some calls, plus this site seriously messing up by inexplicably dropping half my post so I had to do it again, Wyoming4x4 made his post in which he elaborates a bit more on what I have been saying. While I agree with most of the post I disagree with the assertion that the increased wear issues of short rod ratios only manifest themselves in the upper RPM reaches and I also disagree with the assertion that short rod ratios are better for low RPM torque. From it's beginning of production in 1971 to it's end of production in 1981, the 400 Ford was nothing but a 2bbl low RPM torque engine and yet Ford still spent big money to tool up a taller deck height block, longer connecting rods, longer push rods, and a wider intake manifold, all just so they could maintain the 351 Cleveland's 1.65 to 1 rod ratio (OK, 1.6450 vs. 1.6531 but both of those numbers do round to 1.65). Why bother? Because even in the lower RPM ranges, longer rod ratios are still better. Why else would they spend all that money, time and effort on an engine that was never anything other than a low RPM torque powerplant? Ford could have very easily thrown together a 351W based 400 using the existing 351W block and rods and ended up with a very realistic 1.547 compression height piston and a 1.489 rod ratio that still bettered the SBC 400's 1.484! But Ford wanted to build a better engine than that. One with better breathing heads, better wear characteristics, and better fuel economy. That they did in spades.

Also, it is important to be accurate: The SBC 350 stroke is actually 3.484 inches so that means the math works out like this: 3.484 stroke divided by 5.700 = a 1.6361 rod ratio.
Regards, Eric

 

Absolutely not true. A degree in mechanical engineering (1975) and working with mostly aircraft, motorcycle and import car, but never racing or hot rod, engines, the topic never came up. In school we did an analysis of a theoretical piston engine and came to the conclusion that the less piston and rod mass the better. That goes against long rods. I didnt study combustion events in detail until way after graduation.

What I did yesterday is Google "rod ratio" and got a wealth of discussions on the matter. In a few minutes of study, I realized this is a very controversial subject among racing engineers and shade tree racers as well. It is interesting that modern 7000rpm Honda street engines have rod ratios close to 1.5. Side loadings are apparently a non-issue with extremely small bore sizes with very low mass pistons. So, I get your argument about a big-bore engine, especially at high rpms. Aircraft engines that I am familiar with have huge bores, but with redlines below 3000rpm it doesnt matter. Sorry, I cant find rod length for this engine.

Lycoming IO-390-X

* Type: 4-cylinder fuel-injected horizontally opposed aircraft engine
* Bore: 5.319" (135mm)
* Stroke: 4.375" (111mm)
* Displacement: 389 in³ (6.37 litres)
* Length: 30.70 in (78.0 cm)
* Width: 34.25 in (87.00 cm)
* Height: 19.35 in (49.1 cm)
* Dry weight: 308 lb (140.1 kg)
* Power output: 210 hp (157 kW) at 2700 rpm
* Compression ratio: 8.70:1
* Fuel consumption: 11.1 gallons per hour (42 litres per hour) at 65 percent power


As far as this thread is concerned, these 1970's 400's were never intended by the manufacturers to be race engines. The mission was low rpm torque only to move heavy vehicles on the street. Short rods do that quite fine, but when pushed to race duty, I can see the problem. Ford may have had more plans for the 400 when it was first designed, while GM looked at the SBC 400 as a cheap way to accomplish one mission.

 

Even the Ford 300 6 cylinder, which most definitely was always intended to be nothing more than a low RPM truck engine, still has a better rod ratio than the SBC 400. It's 1.5603 is even better than the BBC 454's 1.5338. Also worthy of note: the 300 Ford has almost exactly the same bore and stroke as the 400 Ford.

Another very noteworthy fact: the 292 Chevy, which is most definitely a low RPM torque truck engine has a 1.6422 ratio! In a very strange twist, it was Chevy that did the right thing and raised the deck height and lengthened the connecting rods when they created the 292 off of the 194/230/250 block. (That was something that Ford DIDN'T do when they stretched the 240 into a 300.) So I still maintain that the fact that these OEMs spent good money to raise the deck heights so they could lengthen the rods so they could maintain decent rod ratios is proof that, even in low RPM applications, rod ratios of 1.60 and above are best.

That thread that I linked talks about the Honda ratios too but like you said, that's a different animal with other variables.

I really hear what you are saying about Ford maybe having broader plans for the 400, I've wondered about that myself but the 429 was only 3 years old when the 400 came out and I can't imagine Ford already thinking to replace it. That would really be the only reason to bring out a performance version of the 400 so I'm thinking a performance version of the 400 wasn't part of their long term plans but who knows. Then they went and killed the 429 anyway just two years after the 400 came out in 71. Anyway I think the 400 was just simply a replacement for the 390 FE, nothing more.

Wasn't there also a six cylinder version of that flat four Lycoming or am I thinking of a Continental engine family? Either way, a 6 cylinder version would be a beast in a truck! (Don't know how we could attach a transmission to it though. I guess that might pose a problem.)

One more thing while still on this 400 Ford vs 400 Chevy topic: this may seem petty to some but anybody who has ever had to pull a transmission just to replace a rotten freeze plug will appreciate the fact that while the 400 Chevy has freeze plugs on the back of the block, the 400 Ford does not. Yet another good reason to avoid the knappy Chevy!

Oh! One more: the 400 Ford has screw in plugs on the ends of ALL of it's oil galleys while the 400 Chevy has them only in some locations while the rest are only pressed in plugs. While blown oil galley plugs aren't too terribly common, it has and does happen. Why not just make a tiny bit extra effort, maybe spend an extra nickel per engine and do it right like Ford did?
Regards, Eric

 

Continental, Lycoming (and Franklin) have plenty of six cylinder engines. The Lycoming IO-720 is an opposed eight! I used the IO-390 as an example because it has the biggest bore. The reason these are so low rpm is the lack of any kind of gearbox. Direct drive means that the propeller is bolted directly to the crankshaft flange, so attaching a transmission would not be easy.

Mopar LA's also have freeze plugs inside the belhousing. I had to wrestle a big Torqueflite off the back of a 273 in the tight confines of a Plymouth Valiant.

 

Yes, I am very aware of that. Where do you think I got the first hand knowledge and experience of the misery that is the rear freeze plug? The LA's predecessor, the A engine (AKA the "Polyhead"), also has freeze plugs on the back of the block. Pure misery!
Regards, Eric

 

Looked up the specs for 1972 ford and chevy 400s SAE specs to make it fair as possible. Chevy was 185 hp and 300 ft lbs. And ford was 172 hp and 298 ft lbs. We can most likely chalk that up to the heads.13 horsepower and 2 ft lbs is not very noticable in a heavy truck. And even if it was different gearing can compensate

 

The numbers you quoted are actually for the 75-78 4bbl Chevy 400. It has the advantage of having a 4 bbl, that is why it's numbers are better, NOT because it's heads are better. The 400 Ford actually has the vastly superior heads complete with much larger valves (2.04/1.66 vs. 1.94/1.50).
Regards, Eric

 

Lol just posted what came up when I googled ill dust off the chiltons later

 

I'm having a heck of a time finding power ratings myself. I'm focusing on 75-77 era trucks because trucks didn't have to have cats until 78-79 while cars had to have them starting in 75. Prior to 75 the Chevy 400 was only available in cars and prior to 74 it was only available with a 2bbl. I did find these numbers for the 76 AMC Jeep 360 and 401 4BBLs which puts those 185 hp/300 tq Chevy 400 numbers in perspective:
360-4BBL 180 @ 4400, 280 @ 2800 8.25:1
401-4BBL 215 @ 4200, 320 @ 2800 8.25:1
The AMC 360 nearly equals the much larger 400 Chevy and the AMC 401 (remember the Chevy "400" is really a 401 too) flat spanks it! Just more proof that the Chevy 400 ain't all that, and never has been. Sure wish we had some 400 Ford truck numbers from the 75-77 era too to show up the Chevy with. Anybody?
Regards, Eric