Best overall SBF combo for a street/strip Cobra

[Streetwize]

I've built a lot of engines over my lifetime and a fair number of stroker motors, certainly nowhere near the number Professional Builders like Mr. Brent Lykins, who's opinions I highly respect and who's contributions to this site keep me coming back again and again.

I was trying to decide in terms of streetable 500-ish HP and the broadest torque curve, with very high TQ/CI and HP/CI..so taking what I've learned from many bore stroke ratios and head flows...What combination would I like to put in another Cobra?

I certainly wouldn't replace my 427 Windsor, it's a solid 500/500 combo that accelerates at the slightest hint of throttle, will pull hard from ~2400 to 5600 in any gear and chugs along effortlessly at only 1800 rpm at 70MPH in 5th gear. It does all I can ask of it and the highest compliment I think I ever received was from a few people that either owned or driven Several original 427 S/C's , they told me the powerband and tractability from behind the wheel this one feels very close to the "real deal". The wall to wall torque from the long stroke and light weight (450-ish pound carb to pan) is really fun.

For me it very tempting to 'overbuild' a 427 W, which in my view would be something like a CHI headed 408 Cleveland (Clevor) for 600+ hp (which is very easy to do) ,but to me basically becomes untenable in a Cobra bodied car because it's accelerating so hard combined with the fact that you really have no aerodynamics to keep the tires and the car itself planted at higher speeds.

I've driven some serious firepower and I can tell you even with my "measly" 500 HP it feels like a sprint car without a wing at 90-120 going into a corner.

However...I would think the BEST overall combo (I'm looking to do next) would be an 8.2" deck big bore 302 block with at least a 4.125" bore and a 3.25" stroke for 347" combined with a big but not huge 205 CC head like the AFR Renegade or Trick flow 11R with a Ported Victor Jr type manifold (keep the carb height under the hood without a bigger scoop) built for ~10.75:1-11.25:1 with a small endurance type solid roller like the Bullet/Ultradyne .4033 lobe with 251/259 @.050 and 171/178 @ .200 Durations on a 109 lobe spread and a 107 intake centerline. With 1.6:1 rockers the lift would be .645 (~.620 with lash compensation) on both valves.

(I've used this lobe on several engines including a 440" (360 based) Mopar stroker with ported W2 heads.) I think this would be a great balance between streetability/endurance and easy revving spring rates and checked the lash yearly but it stays the same (this one I only rev to 5800 though).

I think this motors powerband would be "just about" perfect with a Close Ratio Tremec and ~3.70-3.90 Rear gears with a 28" tire in a Light independent rear axle car like a Factory 5 that was built for a road race handling. I think this would be a near perfect motor combination for a 289 FIA style car.

I think this combo would give a very nice tractable cruise range throttle response and a predictable roll-on power with great upper bottom but not Excessive torque through the middle, and when you romp on it, it would pull violently from about 3600 RPM up and over 7200 RPM.

I actually prefer the 3.25" stroke to the 3.40" with the 5.400" rod length for High RPM, but the same combo would obviously work at 363 as well. With the light weight of the Cobra, there is a 'sweet spot', just the right amount of torque to keep the car balanced, the tires planted and tractable, without either breaking the tires loose from excessive torque or bogging it from not having enough.


I would expect this combo to fairly easily make in excess of 530 HP which is a very efficient (1.4-ish HP/Cube) power and torque.

Curious to hear your comments and other opinions of what you would build and why.

[mrmustang]

347 stroker, compression under 9:8:1 to run pump gas, a solid 350-375hp with 375-400 ft/lbs of torque. This for a street driven car. Anything more for a street driven car is a waste of time and money, also a waste of the potential for more HP/TQ as it will never get used unless the owners ego gets the better of them, in which case, see the other popular post here at the moment.




Bill S.

[Mark IV]

Originally Posted by mrmustang

347 stroker, compression under 9:8:1 to run pump gas, a solid 350-375hp with 375-400 ft/lbs of torque. This for a street driven car. Anything more for a street driven car is a waste of time and money, also a waste of the potential for more HP/TQ as it will never get used unless the owners ego gets the better of them, in which case, see the other popular post here at the moment.




Bill S.

Bill,

Like the guy with 500 HP 347 on an SPF MK II Street Roadster.....on 205/70 tires! I gaurantee I can go as fast with my 306/345 HP on my 205/70s!

[Streetwize]

Yeah, you see this is where this gets a little interesting.

My approach to this is if you have a 400 HP 9.8:1 347 that makes ~400 hp @ somewhere around 5800-6200 rpm. The motor I describe would have nearly identical power and torque up to your RPM peak...the Difference is that this motor would rev and continue to make power for another 1000 rpm.

I agree whole heartedly with your assessment of "most peoples" driving capability, and tractabilty. But if you put a 6000 RPM rev limiter on my motor it would feel very much the same as far as how it puts power to the ground....it's just this motor, by comparison, (to borrow from Spinal Tap) "goes to 11" , for guys like me that Rode a Yamaha V-max (Remember the Cycle World V-max vs Cobra article from 1985?) for years.

As for my mild 427 W, I control the tractability very easily because I simply shift to a higher gear. My motors torque curve feels more like a 455 Buick Stage 1 (shove in the back) in terms of driving. As I said the guys that drove the real deal 427's said mine feels "as close as it gets" to ones they drove on the street. They also said the 428's Shelby slipped into the later cars, were way slower than the Medium riser S/C 's

[Gaz64]

Is there another longer rod option above 5.4?
Other than that, I like all of your ideas, numbers, and thinking.
347 came straight to me at the start of your post. Similar compression, heads, solid roller, transmission, diff gears.
Gary

[Streetwize]

Thanks for the kind words.

I really do think about the specific parameters I'm working with and have gotten pretty good at building motors that really feel exactly like what I'm wanting behind the wheel.

As for the longer rod, the only standard size I think could work would be a 5.565" 400 Chevy small block which I'm not sure it anyone makes an H beam rod for that app. the short 8.2 deck doesn't give you much Compression height to work with and there's always a balance between pin position in the bore and skirt design to maintain stability.

These 3.25" / 5.400" have been around for years and years in 331"s and turning a LOT higher than the 7200-7500 MAX I'm looking for. but 1.66 is a pretty nice Rod Ratio for the advantages of low 8.2 deck height though. a 327 Chevy is ~1.75 with the same 3.25" stroke and the standard 5.7" rod

I'm a big believer in low bobweights, Even my 4.17" stroke 427" and 4.25" Stroke mopar Small block are around 1850 which offsets at least a bit of the horrible 1.47 rod ratio.

I'd like to see piston MFGs start building slugs around the modern hemi .866" pin instead of the more common SBC .927". it would give us just a bit more meat before we get up in the ring packs.

[eschaider]

I think it would be interesting if you built it with four short rods and four long rods. That way, you could work both ends of the power band. And while you are at it, stroke four of the cylinders to get a 427-ish cylinder displacement and then build the remaining four as a 347 but, and here is the secret sauce, on the four 347 holes. Do two as big bore 347 cylinders and two as smaller std bore 347 cylinders.

This visionary, modestly unique configuration checks all the boxes for all the most desirable engine types/displacements and manages to do it all inside of one block and one car. The crank might be a little challenging, but it is nothing that a good billet crank shop would not be up to

My modest expectations would be that you have never driven anything like it previously and will never drive anything like it going forward — and it checks all the boxes you have identified as either important or interesting to you!

[eschaider]

I think it would be interesting to see you build it with four short rods and four long rods. That way you could work both ends of the power band. And while you are at it, stroke four of the cylinders to get a 427stly cylinder displacement and then build the remaining four as a 347 buuut, and this is the secret sauce on the four 347 holes do two as big bore 347 cylinders and two as smaller std bore cylinders.

This modestly unique configuration checks all the boxes for all the most desirable engine types/displacements and manages to do it all inside of one block and one car.

My modest expectations would be that you have never drive anything like it previously and will not drive anything like it going forward.

[Streetwize]

OK, wow, yeah I get it!

But should I put the big 427 cylinders on the outside cylinders to dissipate more heat?

[eschaider]

Nah...

You want the 427 cylinders in the middle four. That way, the heat they radiate is relatively uniform in all directions, allowing the engine to do a better job of avoiding hot spots. Annnd, an extra added attraction available at no additional cost would be the reduced longitudinal couple in the crank balance attributable to the center placement of the potentially heavier 427 rotating assembly components ...

The short-rod 347 cylinders would potentially have more torque than the long-rod 347 cylinders, so they could be placed at the rear of the block closer to the flywheel, improving low-speed performance.

The more I think about this configuration, the more impressed I become! This technique puts the best of every engine in one engine, and the displacement should work out to be ((427-347)/2)+347 or 387 inches — this might just be the ultimate engine recipe.

[blykins]

It took me an hour to just get logged in so I could post.

You guys that have only been here for a few years don't understand how awesome this website was back in the early 2000's. It's now a steaming, stinking shell of what it was.

The only advice I'll give is this:

1. Go for displacement. I've built exactly one 331 since I've been building engines. I've built countless 347's. IMO, unless you have a displacement rule or something, there's no need for a 3.250" stroke crankshaft. Why pass up on displacement?

2. There are many wives tales that seem to be circulated around the internet by people who don't know what they're talking about. The first one is that longer stroke engines won't rev. That's foolishness. The second one is that pistons with the oil rings intersecting the wrist pin bore causes issues. That's another strong bout of internet stupidity.

3. Rod ratios don't mean squat. Make a light piston, then use the rod length you need to connect the piston to the crankshaft.

4. If the car is set up for a 9.500" deck block, I'd go back with a tall deck engine. A 4.100" stroke crank in a 9.500" Dart block (438-445 cubes) will rev as high as you want it to rev and will not only make a ton more peak hp, but will also have an extremely high average horsepower/torque curve.

5. For everyone whining that you can only use so much horsepower. That may be so, but every car I've driven thus far has had a gas pedal in it. You can control how much fuel you give the engine.

[cycleguy55]

Great advice from Brent, as usual.


IMO, for given HP / torque goals, a 438-445 CID engine is going to be far more docile than a 331-347 CID engine. Would you rather have the smaller displacement running on the 'ragged edge', or a larger displacement engine that's easier to live with?

Originally Posted by blykins

It took me an hour to just get logged in so I could post.

You guys that have only been here for a few years don't understand how awesome this website was back in the early 2000's. It's now a steaming, stinking shell of what it was.

The only advice I'll give is this:

1. Go for displacement. I've built exactly one 331 since I've been building engines. I've built countless 347's. IMO, unless you have a displacement rule or something, there's no need for a 3.250" stroke crankshaft. Why pass up on displacement?

2. There are many wives tales that seem to be circulated around the internet by people who don't know what they're talking about. The first one is that longer stroke engines won't rev. That's foolishness. The second one is that pistons with the oil rings intersecting the wrist pin bore causes issues. That's another strong bout of internet stupidity.

3. Rod ratios don't mean squat. Make a light piston, then use the rod length you need to connect the piston to the crankshaft.

4. If the car is set up for a 9.500" deck block, I'd go back with a tall deck engine. A 4.100" stroke crank in a 9.500" Dart block (438-445 cubes) will rev as high as you want it to rev and will not only make a ton more peak hp, but will also have an extremely high average horsepower/torque curve.

5. For everyone whining that you can only use so much horsepower. That may be so, but every car I've driven thus far has had a gas pedal in it. You can control how much fuel you give the engine.

[Streetwize]

Brent,

Don't get me wrong I agree with your "go for cubes' and 600HP or more is great, but for MOST cobras even with 450 hp puts the power to weight ratio of a 1000cc Sport bike.

My whole thing is what (TO ME) would be the best overall motor combination for a Cobra.

the ~ 3.25" stroke in any small block, Ford, 327 Chevy, 340 Mopar is just a great balance of "just right" torque for a light car and it makes a very linear and predictable and very "fun to drive" power curve, which for I think a lot of people might be "just right". The torque stays flat and the power curve, even with a very docile and streetable cam, just goes up and to the right, all the way past 7000; so the HP gain per 500 rpm is not violent, like a "light switch" or a nitrous shot, but it is "predictable" and the part throttle roll-on makes the cobra feel more like a High torque 289 FIA car.

That's why I picked this combo around this stroke. It's not about the peak hp its about the drivability and fun...specific to a street driven (or even an occassional track day road race) Cobra.


I love the 427 Windsor in my Midstates cobra, to me it feels "perfect" with the 500/500 wall to wall torque and a Tremec and 3.50 gears. BTW my Rotating kit was the very first one Coast High Performance sold over the counter, with bushed 340 Mopar Rods that needed a good bit of rod shoulder massaging just to clear the cam lobes.

But when my friends all say "can I drive it?" I have to tell them "Hell No!" because as any of us know, most people cant jump into a 500hp 2500 pound car with big block torque at 2500RPM and then romp on it and not get sideways or do a 360 going around a corner.

Yeah my whole point of this thread was looking for the Cobra specific "ideal" 4.125 x 3.25 302 block 347 (Again, to me) would be a perfect all-around motor for a Cobra; combine the 289 tractability at part throttle along with the sports car 7500 redline, along with FE 427 S/C 500 ish HP power up top. So it's not the HP really, it's how you want to apply it, and that could be "tuned" simply by how you gear the transmission and rear axle.

Maybe not what everyone would build for themselves, but one that ANY Experienced Cobra driver could drive and be happy with and respect.

The thread was also to encourage what others what They think is the perfect combo.

[blykins]

By itself, the stroke doesn’t make the torque, it doesn’t shape the curve, it doesn’t control the rpm limits, it doesn’t control the smoothness. All of that is attributed to other parts of the engine. You could literally substitute any other number into that sentence and say the exact thing.

Do you think an engine with a 4.400” bore and a 3.25” stroke would behave the same way as an engine with a 3” bore and 3.25” stroke? Nope! It’s not about the stroke number!

[blykins]

Originally Posted by Streetwize

As for the longer rod, the only standard size I think could work would be a 5.565" 400 Chevy small block which I'm not sure it anyone makes an H beam rod for that app.

One other note that I'll mention here: Just because it's an H-beam doesn't make it inherently stronger, nor does the opposite hold true for an I-beam. In most cases, I do not elect to run an H-beam rod because they're usually heavier. If I do run an H-beam, it's something like a Molnar rod, which is extremely light due to a narrower beam.

One of the strongest rods that you can use is an I-beam (Oliver)!

[Streetwize]

Originally Posted by blykins

By itself, the stroke doesn’t make the torque, it doesn’t shape the curve, it doesn’t control the rpm limits, it doesn’t control the smoothness. All of that is attributed to other parts of the engine. You could literally substitute any other number into that sentence and say the exact thing.

Do you think an engine with a 4.400” bore and a 3.25” stroke would behave the same way as an engine with a 3” bore and 3.25” stroke? Nope! It’s not about the stroke number!

That’s not apples to apples so I’m not sure what point you’re trying to make

but there is definately a correlation between stroke and torque. Step on a 1 speed bicycle pedal, one with a 3.25 stroke and the other with a 4.25 stroke. The longer one gets going faster initially but the smaller one uses less energy to pedal faster once it gets moving.

Piston speed is also a factor…a shorter stroke will have less friction at any given rpm, and Peak torque is the RPK point at which ring and bearing Friction starts acting like a brake and overcoming the rate of acceleration under load. And that is generally why shorter stroke engines tend to carry more rpm between peak torque and peak hp RPM where long strokes tend to flatten out at a faster rate. All else being equal.

That’s true of any 4 cycle engine that have enough airflow and combustion efficiency to reach that point.

And with full respect….The whole point of this thread really wasn’t anything to do with engine theory, it had to do with what engine cubic inch combination might produce the best powerband might be in a 90” wheelbase Cobra.

[blykins]

I'm sorry, but a lot of the statements that you're making are just basic internet-based misapplications that I see on various forums. They are unfortunately passed around and around and are never corrected.

Let me try to be more apples to apples...

Displacement makes torque. Not the stroke. A 4.030"x3.250" engine is a 331. A 4.125"x3.250" engine is a 347. They will not have equal amounts of torque because the stroke is the same. You chose the 3.250" stroke because you stated that it's the 3.250" crankshaft that makes an engine docile, linear, predictable, non-violent, etc. I could build an engine exactly like that with a 4" stroke, or a 4.250" stroke. I could also build a 331 that would be more "violent" than your 427 and would make you poop your pants if one of your friends hopped in and did a 360 around a corner...

I understand that this thread is not about engine theory, but your fascination with a 3.250" stroke prompted me to explain that the stroke is not a magical number. It's the combination of *every* part that's in an engine that makes/breaks a combination.

Nice to see that I'm highly respected until I disagree.

[blykins]

That's a 363 SBF. 4.125"x3.400". It made 464 lb-ft of torque.



That's a 357 Cleveland. 4.030" x 3.500". It made 430 lb-ft of torque.

There is no correlation between stroke and torque.

[My427stang]

I have to back Brent here. Displacement makes power and torque, if a longer stroke for a given displacement was to make anything different, it would only go down in HP and TQ assuming a valve shrouding problem due to the smaller bore.

As far as the bike pedal comparison, yes, there is leverage with the longer pedal, but there is a fatter rider with the bigger bore. More surface area pushing down seems to equalize the leverage advantage if there is one

It is very wild, I used to think the same thing, but as long as they both breathe the same, a given setup will make almost identical HP and TQ per CID.

I also agree that rod length has been over-hyped, a nice stable piston with a good weight for the RPM desired and enough room to not hit the counterweights...after that, just connect them.

[My427stang]

I have to back Brent here. Displacement makes power and torque, if a longer stroke for a given displacement was to make anything different, it would only go down in HP and TQ assuming a valve shrouding problem due to the smaller bore.

As far as the bike pedal comparison, yes, there is leverage with the longer pedal, but there is a fatter rider with the bigger bore. More surface area pushing down seems to equalize the leverage advantage if there is one

It is very wild, I used to think the same thing, but as long as they both breathe the same, a given setup will make almost identical HP and TQ per CID.

I also agree that rod length has been over-hyped, a nice stable piston with a good weight for the RPM desired and enough room to not hit the counterweights...after that, just connect them.