Sometimes you need a HEMI

mhardy6647

Wow. I learned stuff today. Lots of stuff. Thanks Jstas!

mrbigbluelight

I'd say that was a pretty good nutshell, Jstas.

Emlyn

What the world needs is a 12 rotor wankel installed in a truck. May be a little impractical:

https://www.youtube.com/watch?v=Qcgg7w6TFQc

[Deleted User]

Jay Leno said his 426 Hemi Coronet shifted at 7200 rpm . The 440 six pack was quicker through the quarter mile but after that, her comes the Hemi! Never heard that the 426 didn't put out good power up top.

Jstas

I did not say that it didn't "put out good power up top". I said that the stock valvetrain and intake system are incapable of supporting high RPM performance. High being past 5500 RPM.

Neither Jay Leno's 426 in his Coronet or his 440 Six Pack are stock. Especially if they are running at 7000+ RPM. The only way he can get close to those RPM numbers is if he has a Super Commando HEMI and even then, they were good for a hair over 6000 RPM stock, not 7000+. Same goes for the 440. They might be able to get there but they are already losing power and getting close to if not at the valve float point. Hence the reason why both engines have redline ratings in the 5500-6000 RPM range at best from the factory.

Either engine can be made to handle high RPM performance and do it well but you need Jay Leno levels of money to do it reliably. You can get them close to 7000 RPM with just valve springs and bigger intake parts but they are unreliable at that point because the rotating assembly is being beat on like The Hulk is punching the pistons back down the cylinders on every rotation.

Racing engines like the 426 Super Commando which hit 425 HP at 6K RPM in 1964, were impressive at that time but much higher than that and you hit valve float problems in that too. But those engines were race only, not available in a production car. The "street" version still pumped out 425 HP but at 5000 RPM and firmly fell flat on it's face after that because of mechanical limitations and the fact that the street heads we deliberately choked down to boost low-end grunt. Also, the pinnacle of valvetrain tech at the time was solid lifters and beehive, progressive rate valve springs. Also, the cam-in-block/overhead valve design was relatively new still and they were focused on making it cheap so they could plug the engine in everything from a station wagon to a box truck. Now, that tech is arcane in comparison to a modern cam-in-block valve train.

But with 425 horsepower @5K RPM and 490 pound feet of torque available at just 4000 RPM and over 50% of your peak available just off idle, you didn't need to spin it to 6000+ RPM, you just needed gearing and lots of tire.

The first year the HEMI was out it wiped the floor in NASCAR finishing 1,2,3 and 4 at Daytona. Everyone else quickly caught up, though, and the 426's comparatively lazy engine was limited at the top end where it could breathe but the engine couldn't support those RPM levels without the high tech (read: expensive) race parts. They were strong but without that extra 500-1000 rpm range, it was lagging. It was a rockstar in drag racing, though, and the current Top Fuel spec is based around the 426 HEMI even if Ford, GM, Toyota and anyone else looking to compete in the class are running their own versions. It was a rockstar because of how easily it made power and you could run a 2-speed Powerglide with a tall 1st gear which let you peddle it out of the lights without turning your tires into smoke and slam 2nd gear right in the meat of the power band and walk away from your competitor. By the time you got to the point where your competitor could catch up and pass you, the race was over a 1/4 mile ago. So the shortcomings back then didn't matter in drag racing because you weren't running long enough to reach them. They still matter now but when your car runs on liquid dynamite, with a supercharger with more displacement than 4 Honda Civics combined and it's fuel pumps have higher pressure and flow ratings than your average fire truck, chamber pressures and intake system flow rates aren't really a problem on any displacement size.

6000 RPM might seem "high RPM" for something as big as a 426 HEMI but in the racing world it's low. The problem with it being that low is that it needs another gear more to be able to attain the same level of performance as it's competitors that are running around 7000 RPM. The higher strung engines can stay in gears longer and accelerate more in each gear. For example, that means that when a 426 powered car is trying to get to 200 MPH with a 4 speed transmission, it's going to take longer to get there. If the 427 Cammer next to him is winding it out to 7000 RPM in every gear, he's hanging on to each gear for half a second longer and picking up 5-10 more MPH in each gear. So with 3 shifts, the 427 is about 3/10ths of a second faster in a full acceleration run and is getting 15-30 more MPH than the 426 with all of those shifts. So the 427 is entering top gear at an advantage that doesn't seem big but drive down the highway at 60 MPH and have a friend pass you at 90 MPH. That's a big difference at that speed. It's not as pronounced at ~200 MPH vs ~215 but if you are running at those speeds for 500 laps...the difference is immense.

By the end of the run, even if the 426 is pumping out 425 horsepower, the Cammer, at the same power level or slightly lower is going to be ahead of the 426 at 200 MPH in both time and distance. Not only is that because the 427 could stay in each gear longer and pick up more speed than the 426 but, if the 200 MPH mark comes right around the 3-4 shift, the 427 likely doesn't need that last shift to get to 200 MPH and doesn't bleed off a couple tenths of a second making the shift. Also, it means that the 427 starts out in the last gear at the meat of it's power band where the 426 is already into it when it finally gets to 200 MPH. Also, the 427 has headroom over it because when the 426 hits redline in 4th, the 427 is still accelerating.

It doesn't seem like much but, here's the math:
- 1 shift costs an average manual driver 1-2 10ths of a second. 4 gears means 3 shifts and that's 3-6 tenths of a second
- 1 tenth of a second is about half a car length to a full car length in drag racing.
- 1 tenth of a second means that if you are ahead of the guy in the other lane by 1/10th of a second in a drag race, you are likely looking across his hood when you look at him, or farther forward, he might not even be in your immediate view. 6/10ths, there is significant daylight between your rear bumper and his front bumper in a profile view. 10/10ths (1 second) or more and you blew the other guy's doors off.
- on a road race or circle track, 1/10th isn't a big deal. It's usually about a bumper to a fender length. But, you are doing multiple laps and if your 1/10th deficiency has 1/10 added to it on every lap because you are 1,000 RPM down on power band range then after 10 laps, you're 1 second behind. After 100 laps, you're solidly in the middle of the field and unless you can find a drafting partner to make your car more aerodynamically efficient and thereby faster, you are not going to win, place or show in that race.

That's why 5000-6000 RPM is a low-rpm engine. On the street, it's fine, it's even cool. In a race, it's like bringing a knife to a gun fight. You might be able to do some damage with a lucky stab or somebody else making a mistake but your chances of winning are slim to none barring extremely exceptional talent. But we're talking Aryton Senna or Juan Manuel Fangio levels of talent.

dromunds

Got to ride in a classmate's Charge RT Hemi this weekend at a reunion golf outing. He opened it up a "bit" for me, it was a "go-er"

[Deleted User]

I was surprised to at the 7000 plus . He says it is stock and he also commented that the 66s were higher tune than the later years. But, what does he know ?

motorhead43026

The 426 HEMI max horsepower was made @ 5000-5200, rpm. Anything above that is just RPM.

[Deleted User]

motorhead43026 wrote: »

The 426 HEMI max horsepower was made @ 5000-5200, rpm. Anything above that is just RPM.

That was true with almost all the old big blocks.The 426 Hemi, according to old dyno readings peaked at 6000.

http://www.allpar.com/mopar/hemi/dyno-test.html

ZLTFUL

BTW, Dan...I'll just leave this here for you...

(Ignore the year listing as it is the same for the 2017s per my buddy who orders them for one of our local Jeep dealers for installs)
https://rippmods.com/collections/dodge-durango/products/2015-dodge-durango-5-7-ripp-supercharger-kit

It is on the short list of mods for mine...but the basement comes first so I have to wait another year.

motorhead43026

TForan wrote: »

motorhead43026 wrote: »

The 426 HEMI max horsepower was made @ 5000-5200, rpm. Anything above that is just RPM.

That was true with almost all the old big blocks.The 426 Hemi, according to old dyno readings peaked at 6000.

http://www.allpar.com/mopar/hemi/dyno-test.html

It states this is not necessarily from a production engine. Sounds like something they found just laying around.

mrbigbluelight

Be careful about driving that mod through Kalifornia, Zltful:

PENDING: Legal for use in California

Of course, they'd have to catch you first.

[Deleted User]

motorhead43026 wrote: »

TForan wrote: »

motorhead43026 wrote: »

The 426 HEMI max horsepower was made @ 5000-5200, rpm. Anything above that is just RPM.

That was true with almost all the old big blocks.The 426 Hemi, according to old dyno readings peaked at 6000.

http://www.allpar.com/mopar/hemi/dyno-test.html

It states this is not necessarily from a production engine. Sounds like something they found just laying around.

It was very common back in the to see people rev their motors beyond peak HP. Most big blocks were all done at 4800-5000. Most big blocks would have valve float much over 5000 RPMs but the Hemis with the proper cams will rev far beyond that without float.

Jstas

TForan wrote: »

but the Hemis with the proper cams will rev far beyond that without float.

That would then make them not stock.

[Deleted User]

Jstas wrote: »

TForan wrote: »

but the Hemis with the proper cams will rev far beyond that without float.

That would then make them not stock.

Right, just pointing out the rev capability.

vmaxer

TForan wrote: »

Jstas wrote: »

TForan wrote: »

but the Hemis with the proper cams will rev far beyond that without float.

That would then make them not stock.

Right, just pointing out the rev capability.

It's the valve springs that stop float, not the cam.

[Deleted User]

vmaxer wrote: »

TForan wrote: »

Jstas wrote: »

TForan wrote: »

but the Hemis with the proper cams will rev far beyond that without float.

That would then make them not stock.

Right, just pointing out the rev capability.

It's the valve springs that stop float, not the cam.

Of course. I was pointing out that the Hemi will put out more power with proper camming at higher RPMs. Jeez.

mantis

ZLTFUL wrote: »

BTW, Dan...I'll just leave this here for you...

(Ignore the year listing as it is the same for the 2017s per my buddy who orders them for one of our local Jeep dealers for installs)
https://rippmods.com/collections/dodge-durango/products/2015-dodge-durango-5-7-ripp-supercharger-kit

It is on the short list of mods for mine...but the basement comes first so I have to wait another year.

I saw these videos before. I'm so in!!!! Adding a Supercharger is absolutely on my list of things I want to do.
Ask your buddy if you have to replace the computer in order to tune a 2017 R/T. A local Speed shop told me you have to in order to do a full tune. I didn't think that was right but I've been out of the Performance realm for a very long time and I'm re learning.
They use a Dyno to test the vehicle before during and after a tune. They sold me that the factory computer is setup for all states and is a standard of all different areas. They tune it to your area and make sure you get the most out of it. They also talked about doing Modifications before a tune so they can "Tune" it for max performance.

steveinaz

My Granny (Bev's Mom) has a Hemi, and I'm not joking! How cool is that? Ram 1500 Hemi.

pitdogg2

mantis wrote: »

ZLTFUL wrote: »

BTW, Dan...I'll just leave this here for you...

(Ignore the year listing as it is the same for the 2017s per my buddy who orders them for one of our local Jeep dealers for installs)
https://rippmods.com/collections/dodge-durango/products/2015-dodge-durango-5-7-ripp-supercharger-kit

It is on the short list of mods for mine...but the basement comes first so I have to wait another year.

I saw these videos before. I'm so in!!!! Adding a Supercharger is absolutely on my list of things I want to do.
Ask your buddy if you have to replace the computer in order to tune a 2017 R/T. A local Speed shop told me you have to in order to do a full tune. I didn't think that was right but I've been out of the Performance realm for a very long time and I'm re learning.
They use a Dyno to test the vehicle before during and after a tune. They sold me that the factory computer is setup for all states and is a standard of all different areas. They tune it to your area and make sure you get the most out of it. They also talked about doing Modifications before a tune so they can "Tune" it for max performance.

Why would you need to replace the computer?
There is this tool that some of the Ford guys use that pulls off the old program saves it. Then rewrites a new program into the computer. You can make a stock mustang do some awesome stuff just with a predator module which is basically what I'm refering to.
Do they not have something like that for mopars.
He hot rodded his car then told the module what he did it rewote codes for the product with shift points, fuel ect. You can then when you take said product off restore back to factory with the saved info on the module.

mantis

pitdogg2 wrote: »

mantis wrote: »

ZLTFUL wrote: »

BTW, Dan...I'll just leave this here for you...

(Ignore the year listing as it is the same for the 2017s per my buddy who orders them for one of our local Jeep dealers for installs)
https://rippmods.com/collections/dodge-durango/products/2015-dodge-durango-5-7-ripp-supercharger-kit

It is on the short list of mods for mine...but the basement comes first so I have to wait another year.

I saw these videos before. I'm so in!!!! Adding a Supercharger is absolutely on my list of things I want to do.
Ask your buddy if you have to replace the computer in order to tune a 2017 R/T. A local Speed shop told me you have to in order to do a full tune. I didn't think that was right but I've been out of the Performance realm for a very long time and I'm re learning.
They use a Dyno to test the vehicle before during and after a tune. They sold me that the factory computer is setup for all states and is a standard of all different areas. They tune it to your area and make sure you get the most out of it. They also talked about doing Modifications before a tune so they can "Tune" it for max performance.

Why would you need to replace the computer?
There is this tool that some of the Ford guys use that pulls off the old program saves it. Then rewrites a new program into the computer. You can make a stock mustang do some awesome stuff just with a predator module which is basically what I'm refering to.
Do they not have something like that for mopars.
He hot rodded his car then told the module what he did it rewote codes for the product with shift points, fuel ect. You can then when you take said product off restore back to factory with the saved info on the module.

So far from what I know you need to swap out the computer.

ZLTFUL

Negative. You use a programmer that rewrites the flash memory of the stock ECU.

Diablo Tune is one example. You can get piggy back ECUs like Hypertech but the mapping is static and not adjustable like the programmers are.

mantis

I went to a local Speed shop and they told me I would have to get another ECU. I found that strange but they said they are locked and you have to get a unlocked one.
Chain pulling here?

ZLTFUL

Chain pulling.

RIPP sends you their supercharger tunes via emailed zip file that you then load via a programmer like the hemifever or diablotune tuners.

mantis

Thats what I was thinking. After I was told that I told them I would get back to them with a list of things I wanted to do. I'm gonna take my list elsewhere.

mikeyb128

Some VW and Audi ECMs are locked from factory. this prevents tunes from being flashed through the OBD port. The ECMs need to be removed from the car and cracked open, they are then modified to be able to accept software flashes through the OBD port. What is weird is this is some models and not all. They really don’t want their cars to have unauthorized flashes/tunes!

pitdogg2

mikeyb128 wrote: »

Some VW and Audi ECMs are locked from factory. this prevents tunes from being flashed through the OBD port. The ECMs need to be removed from the car and cracked open, they are then modified to be able to accept software flashes through the OBD port. What is weird is this is some models and not all. They really don’t want their cars to have unauthorized flashes/tunes!

Or it could be they do not want someone knowing they have suspicious software on it to begin with..

mikeyb128

pitdogg2 wrote: »

mikeyb128 wrote: »

Some VW and Audi ECMs are locked from factory. this prevents tunes from being flashed through the OBD port. The ECMs need to be removed from the car and cracked open, they are then modified to be able to accept software flashes through the OBD port. What is weird is this is some models and not all. They really don’t want their cars to have unauthorized flashes/tunes!

Or it could be they do not want someone knowing they have suspicious software on it to begin with..

Hahahaha that’s true!