[pdq67]

What's everybody's take on his article on page 98 in the new, (June, 2005), issue of HR Mag??

I thought it was interesting that he tried to hold the two R/S ratio's as close as he could, b/c I would have done it just backwards and ran as long a rod on the short stroke motor as possible and a stock length one on the stroker motor!!

Plus, the comment of 111 LCA's was interesting b/c ERSON has a bunch of older BB cams spec'ed 111/111...

The first thing I did when I picked up my copy of D2K was to run two motors through it that were the same size, but that one was a large bore, short stroke and the other was a SMAAALL bore with a LOOONG stroke and held eveything else constant and it spit out the same thing he said their results were!!

Let the jaw-boning begin!!!

pdq67

[77 cruiser]

I was going to post the same ? should be interesting.

[TJ1967SS]

I've been told that if I build a 383 and use a 6" rod that clearance gets so tight that a small base circle cam is necessary to avoid rod interference. In light of what this article says, I'll stay with a 5.7" rod. Everything else was just gravy.

What exactly is your gripe? I think I missed it? Are you supporting his findings or implying that he just did some desktop dyno work and published it?

[Motor Martyr]

i have a 385" with a 6.0" rod, and i'm not using a small base circle cam. Nothing interfered.

[GRN69CHV]

I think what he is saying is 400 cubes is 400 cubes whether you get there by bore or by stroke. Up to a point the deviation is probably smaller for us street guys. At the extremes of performance where they are building large bore short stroke motors to really rev, there should be a difference. THe one difference is going to be undersuare motors, [bore smaller than stroke], these always wind up RPM limited - except in blower motors.

[Eric68]

Interesting idea . . . you know 400 cubes is 400 cubes BUT there is one issue that will give the bigger bore engine an advatage in a high performance 2 valve motor . . . valve shrouding. Case in point -- the Chevy 305 vs the Chevy 302.

But if you look at the route the OEM 4 & 6 banger engines are going these days you can see that with 4 valve heads there is enough flow to overcome the valve shrouding problem you would have with a 2 valve head on these engines. The bores are very small with relatively long strokes and great HP / cid numbers.

There are some other advantages to a small bore . . . since the flame front have less distance to travel you can build a real fast (and clean) burning combustion chamber. Fast burn means less timing advance and less reverse torque.

My opinion is that unless you can go with a multi-valve head that flows good you are better off with the larger bore if sheer HP is your goal.

[pdq67]

TJ1967SS,

No gripe at all.. Just trying to get a dialog started so that we can mull it over and hopefully learn more among ourselves is all.

When the Honda S2000 came out, I had a problem with it being an 8,000+ red-line engine b/c it is undersquare, (i.e., smaller bore then stroke is long), but after checking out it's R/S ratio, it is fine.

Please keep it coming...

And I hope Harold chimes in here and add's his knowledge too....

pdq67

[UDHarold]

pdq67,

You may not like what I have to say........

To me the article was trying to prove his pre-conceived notions.

If you look at the last 50 years of Gran Prix racing engine development, small bore/long stroke engines are conspicous by their absence. Everything, from English BRMs through Italian Ferraris to Japanese Hondas, have gone the big bore/short stroke route. You have to, if you want to have 4 or 5 valves/cylinder.
OTOH, all V-12 tank engines are small bore/long stroke. They seem to need a lot of bottom-end torque.
Of the 120,000-some odd cams that UltraDyne made, many, in the thousands, were for racers who switched their 5.7" rods in their 355s for some 6.00" ones, and noticed the lack of bottom-end power. They came to us, wanting bottom-end back. A simple LSA change was often all it took. If they had also added some big-port heads, it would also take a little shortening of the cam, as well as the LSA change.
In drag racing, 292-cid(3.935"X3.000") SBCs with 5.7" rods and 4-speeds gave way to 296-cid(4.030"X2.900") with 6.00" to 6.125" rods and 5-speeds. They used to dump the clutch about 10,000........
There is something about all those racers, whether dirt-track or 1/4 mile drag, that doesn't agree with the article.
Remember that cam company who ran an article showing that theiur hydraulics, solids, hydraulic rollers, and solid rollers all made about the same BHP?
That doesn't happen the way I design them.
The article was to prove a point of view, and it did.
The real world cares about what works, rather than your point-of-view.

UDHarold

[Busted Knuckles]

I was very anxious to read this article since this is a decision I've been struggling with. I surely expected more difference than he found, particularly with peak points, both hp and tq. I think that one thing that they apparently didn't measure is how long it took each engine to climb from 4000 to 7000 rpm's. I think that the short stroke engine should recover faster from a shift and that has a lot to do with the popularity of shorter strokes in many facets of motorsports.
Most heads I've measured don't have combustion chambers that are affected by shrouding past about 4.500 anyway - the chambers stop well short of the cylinder wall, so the last .100 of overbore does nothing for breathing other than act as a factor in volume. IF you further unshrouded the valves by enlarging the chambers to very near the edge of the bore in the big bore engine, then cut the decks down to equalize compression ratios, it might pick up a couple of hp and foot pounts. Unshrouding by notching the tops of the bores has been proven to help, so there are a few tricks available that they didn't go into for the smaller bore engine as well.
They dang sure labelled their cams correctly - the small hydraulic roller had shorter lift than hydraulic flat tappet cams of similar duration (218/224, .501/.501 at .050) and is small by pretty much everyone's standards for an engine of that displacement. The bigger solid roller (.253/.260, .734/.732) would be a handful on the street and require faithful periodic inspection and maintenance. Not saying it can't be done, Jim, just that you have to really want one to make it worth the effort. My gurus have advised me that .700 is pretty doable on the street without a tremendous amount of maintenance.
Even though the numbers didn't really back it up, I agreed with their choice - the short stroke engine has slower piston speed, better rod:stroke ratio and lets the heads breathe easier.
Shoot, as long as you have both blocks and cranks, whip up a 565 and get the best of both worlds as long as you have a drivetrain that can take it!

[Slowpoke70]

Just some food for thought about the 302 vs 307/305 comparison. This stuff just popped into my mind today.

Everyone knows the 302 is the superior engine among Chevy's 5 Liter Small Blocks. But there's some stuff never taken into account when comparing the 302 to the other two 5L engines.

Compression Ratio. The 302, as far as I know, came in a 11:1 flavor and that was it. The 307 had 8:1 on a lucky day. The 305 had a high record of 9.3:1 in its final years.

Intake valves. The 302 came with a healthy set of heads equipped with a 2.02 intake vavle. The 307 was bastardized with a 1.72 intake valve when a bigger valve would've easily fit. My proof? The 305, with a smaller bore, used a 1.84 valve. But even then, the 305 can swallow 1.94 valves quite easily, just ask the third gen camaro guys.

Head design. The 302 enjoyed the power-making head design at the time. The 307, produced during the same years, got a weaker semi-open chamber head. The 305 briefly enjoyed heads similar to those of the 302, but that was during the years the 305 was 8.5:1 CR. By the time the CR was upped to 9.3, the 305, for the most part, was using the "torque swirl" TBI truck heads, no good for HP.

Cams. The 302 came with one cam and was usually upgraded to another GM cam. Both intended for hi-perf use, both mechanical lifter cams. The 307 had a hydraulic cam the whole time it was produced, tiny one too. The 305 first shared the 307-style cam then got a good boost in 1987 when they went to hydraulic rollers.

Intake systems. The 302 either used a high-rise dual plane topped with a Holley 4bbl or an optional Cross-Ram topped with two 4bbls! The 307 was always topped by a one or 2bbl carb from the factory. The 305 had a fighting chance because it was available with a Qjet. And of course, got a GREAT boost with the TPI option in the late 80s and early 90s.

With all that taken into account, lets look at the GM-provided top HP ratings for each engine.

302 - 290HP
307 - 200HP
305 - 230HP "LB9"

Note that the LB9 was rated with the NET ratings and not the Gross rating system used in hte days of the 302/307. The LB9 was also only a 9.3:1

I'm pretty sure the 302 would win, but I want to see all the engines built like the Z28 engine was and then tested against each other both on a dyno and on the drag strip. All built with 11:1 CR, all with the biggest factory-valves that'll fit (2.02 for the 302, 1.94 for the other two.), all using the same Duntov cam, all using the 302's double-hump heads, all either using the Z28 manifold with a Holley or the Cross-Ram intake, same typical 1 5/8" headers. I know the 302 will have the advantage of the big bore, but I want to see just how superior the little 5L Chevy is against its slightly larger brothers.

[LXS]

I know this might sound pretty dumb, but, I'd like to see how Chevy's 302 does against Ford's 302. I know I'm coming waaay outta left field here, but, I'd like to see those engines built with specs as close as possible...then having a dyno shoot out

[Ron454]

I'd have liked to have seen them take this to the next level. And that would have been to optimize each combination. Granted, this would have taken a BUNCH more time and parts.

I spoke to my builder about this article, because we are building my 498.

He has done a bunch of dyno testing on just this subject with SB chev engines. Granted, the rat is a different animal. But his testing has shown that the two engines will want totally different cam profiles. And in the end, the big bore, long rod (not tested in the article), short stroke engine is better.

He says that big inch rats almost can't get enough cylinder head on them, can't run a long enough rod unless it's a tall deck, and need way more camshaft than one would think.

The article is good from the standpoint of the average builder, but doesn't tell the whole story.

I guess for me, at least I know my 498 has decent potential. And because I didn't have a 502 block to start with, it will still be good bang for the buck. I don't however, now think I'll make my desired HP level. Not enough head, cam or CR.
If I had it to do it over, I'd go with a 502 block and make it a 540.

I also think they could have spoken about notching the tops of the bores on the 454 block to help with the airflow. The AFR CNC head chambers do indeed hang outside the bores on a 454.

And, I think they should have run a bigger carb and manifold.........

In fact, since they have these two engines kicking around......how about a carb and manifold shootout?

More than a few of us would like to know........

Ron

[-SS454-]

Originally Posted by LXS

I know this might sound pretty dumb, but, I'd like to see how Chevy's 302 does against Ford's 302. I know I'm coming waaay outta left field here, but, I'd like to see those engines built with specs as close as possible...then having a dyno shoot out

I'd likely put my money on the Ford. Take something like AFR SBC heads vs AFR SBF heads, to keep the heads equal as possible, and the Ford would likely come out on top.

[Slowpoke70]

Alex, I'm thinking the Chevy would win unless you're talking the Boss 302s that were used in SCCA racing back in the late 60s and early 70s. They were modified to accept the Cleaveland style heads which are pretty much Big Blocks as far as Fords go. So that's a small block ford with a bb head.

Both the Chevy 302 and Ford 302 have a 4.00 x 3.00 bore/stroke dimension. But I think the Ford uses shorter rods. But that's easy enough to change.

If we're talking small block headed combos, the Chevy has the advantage. Every mustang guy I've talked to says the week point in the Ford motors is their exhuast port design.

The Ford does have an advantage in the wider lifter though. More degrees of duration per lift value are possible with the bigger Ford lifters.

Induction also matters. We talking EFI 5.0 Ford vs. Carb'd 302 Chevy or? I think it'd be best to run them with a similar intake and carb.

Firing order? The 5.0HO uses the same firing order as the LS1 (just looks different on paper, same thing though if you number the cylinders the same on both motors). And the regular Ford 302 uses the same firing order as the conventional Chevy V8. So take your pick there.

In the end I think they'd be pretty darn close.

[Slowpoke70]

Hmm, the AFR thing is true, haven't they been working with the Ford casting longer though?

Now that I'm looking at the ford head design a little closer, I think some of the ford guys I know were lying to me. It looks like the SBF layout is better than the SBC. Maybe stock vs. stock heads the SBC has the advantage? I've seen some tiny looking exhaust ports on Ford 302s before.