This is the 3.25" stroke X 4.125" bore motor, with 6.2 rods.
I'm planning one of these projects, partly because I have the crank and block already on hand. And the AFR article I read left an impression, so why not?
So this is all kind of premature, since I won't be working on it til next year anyway, but has anyone on the boards actually tried out this combo? The 11:1 CR with the 58cc AFR heads, 87 octane ... and actually road tested it?
If so, did you go with the 6.2" rods, or the more commonly available 6.125" or 6.250" and matching pistons?
It's just something to think about for now, but I'd like to hear about it if someone's tried it.

 

seems like a severe waste of cubic inchs to me. If you have a 400 block, build a 406.

yes it does make more power than a 4" bore 350, but it won't make the power a similar equiped 406 would. And the 406 would be cheaper.

 

I'm am smack dab right in the middle of such a motor. Here is the link I started on the subject.

https://www.thirdgen.org/techbb2/sho...4&goto=newpost

Progress has been slow for various reasons but the motor was assembled this past week and waiting for a break in the weather for installation and dyno time.

PM me for exact details.

 

Excuse me, but Chevrolet DID build such an engine. It was called a "348", and was/is a fornicating dog. The 327 was a far superior engine with a smaller bore.

 

It'd actually be a 353 (352.5).

You'd make the a little more HP with a 406 built similar, but TONS more torque (with the 406)....so whats the point...?

 

It might seem like a waste of a block , but I've had this LJ 3.25" stroke forged crank sitting around and I can't let THAT go to waste. So it's waste a block or waste a crank... one or the other.
I'll build both a 406 and a 352. That way everyone will be

 

Waste the crank.
That block is turning into something valued more and more like gold each day.

 

A few have built it. Many will argue against it. I havent built one, but my father did.

400 block, 327 steel crank, 6.125" eagle h beams, SRP pistons 12.5:1, mechanical roller 255 @ .050 .575 lift on 110lca, Iron Eagle 215s... yada yada...

Hasent been in a vehicle yet, Im planning on putting it in this summer since he is bound to a wheelchair 50% of the time now from extreme arthritis , and cant do this kind of work anymore, but he still enjoys putting engines together and cruizing town.

 

I actually could do that, couldn't I? (Build both a 406 and a 355)
Get a set of 6.25" rods to go with the 3.25" stroke crank and a set of 6" rods to go with the 3.75" crank. And keep the same pistons.
Try em both and then make up my mind which club to join.
...Excuse me ...But my life's mission just became crystal clear to me ...I have work to do!

 

Yea its a neat idea, too much trouble to actually do well for me anyway. I'd rather sink some time into a SB 454.

 

depends, does a 406 with 6" rods take the same compression height pistons as a 352 with does?

even if it did the 352 would have less compression so it wouldnt be apples to apples

EDIT: You would lose 1.5 points of compression.

 

The point is often missed on gear heads because the bottom line is strictly power. This motor as built by the article is for people interested in motor efficiency. That was the point of the article....to achieve relatively good numbers with a motor using high compression and still using a short duration cam running on pump gas. Low octane pump gas to boot. All in a useable rpm range. A huge contrast to the conventional streetable high compression motor that must bleed off the compression with a long duration cam. Power exercises like this allow a "have cake and eat it too" appeal. Sure you can get more power from a 406. That's not the point.

Long rod motors like the one mentioned have seen brake specific fuel consumption figures that suggest they would be great for reaching high mpg figures, as well.

If you can expand your mind a little, it lends itself to some big possibilities. Applying your 406 to this would be unrealistic because of the cost and/or packaging restraints of a typical SBC with a 9.025" deck height but if you look at the possibilities with a big block, you might have something. How about a 3.75" stroke in a 454 block (a 427, for those who don't remember) with a reasonably affordable aftermarket 6.8" long rod. Now you have a rod/stroke ratio of 1.81 and can start seeing the benefits of a long rod motor especially if it is coupled with the newer generation big block heads that are coming out. Now you have a relatively large displacement motor that is very efficient in it's ability to convert pump gas to power.

 

Yes, the comp. height for a 6" rod 406 is the same as the comp. ht for a 6.25" rod 352.
I guess you'd have to get some different heads to compensate for the CR diff.

It does sound like a lot of work doing all that parts swapping, doesn't it? I guess the point is, it isn't a waste of a block. If the 352 isn't what it claims to be, put a different crank in it, and use the 327 crank for a 327.

 

I built mine with exactly that attitude. First, since the 6" 406 shares the same compression height, I could purchase off the shelf pistons. Then, as you suggest, I could easily go back to a 406 if I wanted to with just a change to crank, rods, and a good 76cc combustion chambered head minimizing the cost.

For supposedly being so limited, the forged 327 cranks has been easy for me to find. Someone told me the school buses from that era (60's) used the steel crank that is plentiful.

 

got any times with these motors? how do you like them?

I cant wait to get my fathers into his car. Since Ill drive it as much or more than him, and I live in OH and the car and father are in MI.

 

Yeah, I'm interested in finding out how the short stroke 350 road tests too.
I kind of like that have your cake and eat it too concept.
Like you were saying with a smaller cam to help keep the fuel consumption low, and the high revving abilities inherent to the short stroke/ long rod motor, it could be a promising combo for those of us who are satisfied to run in the 12's.
And if it isn't good enough, stroke it or supercharge it.
This forged crank cost me $65 at a swap meet, why not use it ??
BTW Last month I saw two 327 steel cranks bring in about $225 each on ebay.
Could it be that some guys have been following your posts, Wes?

 

check this post.... Click here

 

I saw the same eBay lot for those cranks. Couldn't believe two forged cranks in one lot. Tried to make a play for just one and got blown off.

I will be hitting the dyno soon. That will be my only means of comparison because to be honest, I consider myself an autocross/road guy. The extent of my drag racing experience is a V-8 Vega drag car with a strong running 400 backed by a Clutch Turbo 400 that I bet a trained seal could have knocked off consistent 13 flats in. In other words, it will take me awhile to learn how to run well with no experience in a true stick car (I'm running a Hanlon T5).

Don't believe the $2999 price tag on the Hot Rod article. Just by reading it, you will wonder who the heck does math for them. My Proline Vortec headed motor has hit me for just under $4000 from carb to pan. Add in their recommended AFR's would have easily hit me for an additional $700. Don't get me wrong. If it was a sin to "Covet thy Neighbors AFR's", I would be set right there in the bowels of hell but my pockets are empty enough with the Prolines.

Incidentally, I want to run a 350 TPI in my truck this coming fall. Be patient because plans are to bolt EVERYTHING on the standard 350 that the long rod 350 has to get a real apples to apples comparo.

 

I say more power to you guys. I often dream up off the wall combos at work based on what production parts will yield if put together correctly. However, due to lack of everything, I can't experiment with them myself.

So go on, do something orginal.

Don't get me wrong 383, 406, and 427 cid small blocks are really cool, but having something that no ones else and in some cases no one else has even heard of such a combo, now thats COOL!!

Later

 

ok i'll play devils advocate on this one.

magazine articles are very very tricky.

they say that this is the 350 that chevy "should" have built.

the engine in that article is equipped with a pair of just about the best aftermarket cylinder heads you can buy.

had chevy built this engine, they wouldn't have put heads on it that can even be metioned in the same sentence as AFR's ( i know i just did )

so had they slapped on a set of heads like say.... LT1 heads (which were a GREAT! factory head, pretty much only the vortec could be claimed better, and only on the intake side) and the cam they installed is a lot hotter than a stock LT1 cam, like the claim it closely matchs.

a stock 96 lt1 cam:
duration @ 0.050=205/207
valve lift: .447/.459 "
lobe seperation: 117 !!

comp cams HR270:
duration @ 0.050=215/215
valve lift: .500/.500"
lobe seperation: 110 !!

that is BIG difference.

also they used full roller rockers @ 1.6 ratio.

that boosts the cam lift to .533/.533" which works nicely with the AFR flow numbers.

So what i am getting at is. Slap the cam above, in a 4" bore 350, bear in mind its a roller cam, with AFR 190cc heads, a compression ration of 10:1, full roller rockers, forged lightweight pistons (like they used in the article) A performer RPM intake, and a dyno tuned carb.

and it will easily match the power numbers they came up with.

especially running in an air conditioned dyno room, with no accessories hooked up, and long tube headers. 412hp isn't that much for magazine horsepower.

and the 11:1 compression they are running on 87 octane gas, i'd love to see how well that works out here in the arizona heat, running on our absolutly SHI**Y special "phoenix blend" gasoline, about 10,000 miles down the road. sure while it is brand new it can run octane that low, but once carbon deposits form, and all that good stuff, see how well it runs.

articles like that one on the 352 just **** me off because of how well the obscure the truth. fact is, they just but a 412 gross horsepower with a nicely built SBC, nothing new, nothing exciting.

did anyone notice the guy in the popular hot rodding engine masters challenge that ran 16:1 compression on 92 octane gas.
once again, only in a dyno room, and only on a brand new motor.

stick with the tried and true, if you want a 350, build a 4" bore 350.

if you have a 400 block build a 400 or something bigger, you'll lose 3 miles a gallon with it, and make 50 more horsepower, ghee, thats a hard trade off.

if i wanted good mileage, i would buy an import.

but if i drop 4K plus on an engine, im for damn sure not going to have gas mileage as my primary goal, you can guess what it would be.

the word starts with a "P" and ends with an "R"

 

So basically your saying anyone who has a 400 block and doesnt build 400+ ci is wasting the block? And your assuming we destroke for gas milage reasons????

 

You are right about magazine engine build ups that tend to be obscure and seemingly unduplicatable. They have access to the latest and greatest parts, dedicated pros to machine, build, and tune. And then they can talk about how much power and gas mileage a high compression small block will get all while sniffing low octane gasoline. Sure they are silly sometimes, but they are fun to read, and in many cases they can get readers thinking about a new engine build up. Which is precisely what they want you to do. Buy from mag advertisers.

So there ya go...

 

Ok, one would tend to believe I would defend the article because I have 4000 more reasons to do so than the next guy. I can't deny that fact but I know enough about piston engines to recognize that two of the biggest areas to gain power are in combustion efficiency and the other is friction load. You don't need to go far to see that. Power numbers jumped in a big way when aftermarket companies discovered the benefits of the kidney shaped combustion chambers. Chevy went one step further in a push to increase torque and gas mileage for it's truck program in developing the Vortec head. Combustion chamber design is just one part of the combustion process. The long rod theory addresses cylinder pressure, piston dwell, and other processes to lengthy to get into here.

As far as friction goes, it is fact that the biggest area of friction in a motor is in the piston and ring pack. Long rods reduce side loading and relieve ring drag to a some degree. This reduction of friction has great benefits in helping the motor live longer too.

Long rod motors offer a chance for a builder to gain power by pure efficiency. "Free horsepower" , if you will, where it didn't compromise some other process to get that power. I think if we settle for the tried and true then what we end up with is point where there is nothing more to gain. Just 15 years ago, the bench mark for a daily driver was 300 hp...now look. There is still things to learn and we should embrace some degree of pioneering so we can all benefit.

 

I might as well ad to that, at the start of this thread my original question was, has anyone tried this combo(?).
Sure those magazine articles make some extrordinary claims, I think it's a good thing that there are guys out here who are willing to put those concepts to the test in a real world application. Especially in a side by side test such as the one Wes is planning.
I've heard repeatedly, from different sources, all of them experienced, that long rods make a better motor. A 6.25" 350 next to a 5.7" 350 sounds like a perfectly valid experiment to me. I plan on trying it myself and when I do I'll know first hand.
Also some guys just like the way a particular combo feels, the way the power curve comes on... Personally, I appreciate an engine that redlines at 6500, and I'm looking for different ways to broaden the powerband. It isn't always something that can be quantified with timeslips, but that doesn't make it a waste of time.
So let us fart around with the driveability issues of our little smallblocks, might as well...
I'm sure there's someone out there with a big block who will tell you that building a 406 is a waste of time. And when/ if I do build my 406, I'll probably have to answer to him, and explain why it isn't a waste of time.
Cause I'm havin fun!

 

VERY VERY well said Scottland.... and very true.

Increasing rod length and therefore piston dwell time as well does have a slight advantage in requiring a little bit less spark advance to make maximum power, and that's just in theory because everything else has to be in order as well. Several other factors play a part in the fuel's burn rate. Overall, even in ideal conditions the actual difference in rod length makes VERY little difference in the spark requirement by itself.
In actual practice you'd have to have a pretty low running temperature to keep it out of detonation with 87 octane. Also in actual practice, a very slow burning fuel like methanol is a better match for a long rod engine, but still with a rod length change being that small the difference is not significant.

There is a local guy here that ran a long rod smallblock in his race-car with methanol and turned some very high RPM somewhere between 8000 and 9000. He made surprisingly good power with methanol at that high of RPM, so the advantages of the longer rods seem to increase at the high RPM. He also ran his carburator much leaner than most people do with methanol. I can't remember what size carb he ran but I may be able to find out.

I don't think the long rod has a significant advantage with a street engine myself, and definately nowhere near the advantage a longer stroke crank has at streetable engine speeds.

 

Speaking of having fun... SweetS10v8's pics of the engine test stand got me thinking last nite. I wanna build an engine test stand mounted in a motorcycle frame, just to raise some eyebrows

 

its funny..

all this talk about theory... and none of it happens in the real world.

no matter how efficent you make your sub 400 SBC, i will match your power per displacement, have a milder motor and make more power.

as far as BSFC, while i may APPEAR lower on paper, i can also run more of a overdrive, and still match or beat your MPG.

so SweetS10v8 if it isnt for fuel miliage, what is it for? when you come down to it, theres no reason.


theres only 2 reasons people have been able to tell me that made any sence.

1. you're in a Displacment VS weight class
2. they have the parts sitting there and dont have the money to go buy everything else again to make a bigger motor.

 

MrDude, you're right and I think they understand about the power output issue. I wouldn't criticize them for wanting to be different and experiment with other combinations because it's an opportunity to learn. I'm pretty sure everyone understands that the longer stroke/more cube combinations make more power.

I can tell you that the rod change you're debating will not prove to show any significant advantage by itself. If you're going for an experiment in efficiency you will need to address several other areas of improvement to get the gains. To do it right will take a lot of work and cost quite a bit too. Most people wouldn't go to such an effort for a street engine, but many do to build a race engine.

To get a significant increase in rod/stroke ratio I'd go for the aftermarket block with a taller deck and maybe look for a 3" stroke crank that will fit the mains. Many aftermarket blocks can bore out to 4.2"
I think you can get custom pistons with an offset pin position to get further efficiency increases by changing the rod angle slightly.
Also I believe you can get a crank offset ground to decrease the stroke to give slightly more room for rod length.
You can also run your piston above the deck for positive deck height and keep your top ring near the piston deck to give you a little more room for rod length.
These increases all add up in the end and could actually show some significant advantages if you run the right fuel.

Once you get the rod ratio problem solved then you have to look at other areas like thermal efficiency, controlling the intake charge temperatures, and matching your valve events to the piston position & rod angles you've created with this engine.
I'm not sure on which way the specs will go but a long rod engine will want a different overlap period and will allow you to extend the intake opening and exhaust closing events for longer effective durations ( I think ). Again I think this seems to be a better match for very high RPM and a slower burning fuel.

I myself would never consider building a street engine of this kind, but that's just me.




Obviously it's way too much trouble & money for a street motor and most of us can't afford to experiment like that.

 

Again this is my fathers motor, and he built it because he doesnt like externally balanced motors, he had a 327(and 350's, but wanted to be different) crank, but i would take a 377 over a 406 if I were drag racing only. With that know that I am currently building a 406, not a destroker.

The post asked if people had done them....my answer to that is yes...

have i gotten to drive it yet and tell you about it? Not yet...

 

one of his stories is how he was building 302s before chevy did, and how they could rev to the moon.... hes just doing the same thing but on a bigger scale.

All my motors have been 350s, and my 400 is the first time I am straying...somthing inside of me want to buy an internally balance crank though.

 

if you dont already have a crank, do it.
it'll save money and even out when it comes time for the flywheel...(assuming its a manual)

if you already have the crank i wouldnt bother..

 

I have 2 gm cast 400 cranks, and ive seen a lot of people go fast on them, but I think it might be worth $400-500 or whatever for peice of mind, because after i get done and keep upgrading in say 5 years, I think I will kick myself for mot doing it right the first time.

 

While rod length is important when you talk about dwell time so is stroke. I believe the shorter stroke of 3.25 vs 3.484 had a much bigger impact on dwell time than the rod length in that article. The stroke of the engine also plays a bigger part when it comes to dynamic compression. I would think rod length is more important when it comes to rod angularity and the resulting side load.