dohc hemi

brightb · Post by **brightb** » Sat Jun 18, 2005 5:49 pm

Why isn't there or can't there be a dohc hemi engine?

YWROADRUNNER · Post by **YWROADRUNNER** » Sat Jun 18, 2005 9:04 pm

Actually, there were one or two prototypes made in the mid 60s to compete in NASCAR. The rumer is the cam bosses cracked in early testing and before any other development proceded NASCAR had outlawed the use of overhead cam engines. At least this is the information I ran across several years ago. Also mysteriously the prototypes disapeared.

OldIron · Post by **OldIron** » Mon Jun 20, 2005 6:53 am

I wish I still had the article on it. There was a write-up about the A925 project in a major car magazine in the late 80's (i think). The cam bosses cracked as mentioned while the engine was spun by an electric motor. The engine never ran under its own power. A guy ended up with one of them and it was never fully known how the engine even left the corner of the shop where it was stored.

I can't remember if it was a 2 valve or a 4 valve per cylinder engine. If it was 4 valve (and i think it was) then of course it wouldn't be a Hemi at all but rather a pentroof combustion chamber. The new "Hemi" doesn't have a hemispherical chamber though so I imagine it wouldn't stop DC from sticking the name on it for marketing purposes.

OldIron · Post by **OldIron** » Mon Jun 20, 2005 7:08 am

I guess to better answer the question posted instead of rambling like i did...

....

There "CAN'T" be a 4 valve per cylinder Hemi DOHC due to the valve angles. Each cylinder would look like a porcupine.

There "COULD" be a DOHC 2 valver per cylinder Hemi.

The reason for the current engine being "cam in the block and pushrod" is cost effectiveness. OHC engine cost more to make due to the extra camshafts etc. The current engine offers a better performance to cost ratio. While not performing as well it's alot cheaper to build.

HEMICharger/Durango · Post by **HEMICharger/Durango** » Mon Jun 20, 2005 4:47 pm

One reason I heard for the new HEMI being OHV and not OHC was to make the engine have a lower profile.

brightb · Post by **brightb** » Mon Jun 20, 2005 8:56 pm

do you think it is possible for there to be a 4 valve hemi though ,dohc?

OldIron · Post by **OldIron** » Tue Jun 21, 2005 5:40 am

To quote myself (not a good idea at times...

)

"There "CAN'T" be a 4 valve per cylinder Hemi DOHC due to the valve angles. Each cylinder would look like a porcupine"

Get a softball and some of those little suction cup darts that those little kiddy guns shoot...stick 4 of the darts on there....and the try to imagine getting it to work with the camshafts.

OldIron · Post by **OldIron** » Tue Jun 21, 2005 5:44 am

Hey HEMICharger,
If you can run across the article again on the engine height deal stick it on here. I'm a little curious. I'm thinking there shouldn't be much of a difference between an OHV and an OHC but I may be missing something.

Checked your website out... thanks for the link ! very nice.

HEMICharger/Durango · Post by **HEMICharger/Durango** » Tue Jun 21, 2005 6:31 pm

Oldiron,

thanks for the comment about my site. I have been unable to find where I read about the lower profile but I may have come across another reason for the new engine not being OHC. The MDS was part of the design from the beginning. It works by deactivating the lifters. Not sure if this would or could work on an OHC. Here is the link where I found this.

http://www.allpar.com/mopar/new-mopar-hemi.html

Maybe if this system was all above the head it would raise the overall height of the engine.

freebird12345687 · Post by **freebird12345687** » Wed Jun 22, 2005 5:15 am

DOHC Hemi i think this is about the 2nd or 3rd time this topic has been discussed. It was quite a unique idea, twin cams, 32 valves, 16-branch intake manifold. Theoretical ouput i believe was around 950 horsepower with a single 4 bbl and the theoretical maximum RPM was in the 8000-9000 rpm band. Unfortunately Ford OHC 427 was so dangerous that NASCAR shut the OHC engine concept down. Now, had Ford used there heads and had some help from Cosworth as they so often dealt with anyway, I'm sure Cosworth could have come up with a gear drive setup for the cams. We all know that upon seeing this Chrysler could have engineered a gear driven 32 valve DOHC, (pentroof)Hemi. Turns me on thinking about it. On the pentroof side of things, ideally a pentroof design is not a Hemi as the shape up the combustion chambers gave the hemi its name, but the #1 best characteristic of the Hemi is still retained and thats the flow through head design, yes you can throw quench effect and those sorts of things in there too, but letsface it without the laterally opposed valves the hemi would have never been what it was. The pentroof design is often referred to as a pentroof hemi for that very reason, but blah it doesn't matter anyway i suppose. Just thought i'd ad a little more to this thread, have a good one fellas.

OldIron · Post by **OldIron** » Wed Jun 22, 2005 6:35 am

Thanks for the thoughts freebird. Yep. I thought of mentioning that this topic has been around for some time. NASCAR didn't want "showroom" parts but production engines. The 427 that Ford came up with sneaked out the doors in a few Galaxies and Mercuries but was never an "official" production engine. They were an over-the-counter race engine that ended up in Gas FX cars etc. Some of the engines had the timing chain replaced with a belt drive which was reliable at high rpm's. 616hp with one 4 barrel and 657 with 2 if I remember the rating correctly.

It would have nice if NASCAR has let Ford and Chrysler at least develop smaller cube OHC engines. I think engine evolution in passenger cars woudln't have taken near as long as what it has although the computer controlled ignitions are as much as factor.

You are right on with the flow through-head / valve angle being the most important feature of either a Hemi or a Pentroof chamber. Peugot was making these things in 1913 but American car companies didn't seem to follow suit with most of their engines...I imagine due to the cost issue again.

peace !

freebird12345687 · Post by **freebird12345687** » Wed Jun 22, 2005 10:28 pm

I thought there was an american car manufacturer even that early that had a hemi headed engine. I think it was only a single cylinder chain drive deal, but i think there was one at around that time. I could be mistaken, probably am, but i think the engine which i speak of has been discussed on here before

OldIron · Post by **OldIron** » Thu Jun 23, 2005 5:59 am

I think there were a few other configurations but I've forgotten so much stuff that I've read it's unreal.

Pontiac had an SOHC inline six that was a really cool mill in the 60's.

http://www.highperformancepontiac.com/f ... _overhead/

Some history on the Peugeot cars (just realized I spelled it wrong earlier!)

http://peugeot.posiklan.com/hist08.shtml

The M26 Pershing used an engine built by ford which produced 500hp at 2600rpm and 1040ft lb of torque. OHC it appears to be from the pics...I seem to be having a problem reading Itailian too

http://www.ferreamole.it/images/pershin ... engine.htm

Alot of this old stuff is interesting. I didn't mean that American car comanies NEVER builld OHC or hemi headed engine...they just didn't for the most part.

freebird12345687 · Post by **freebird12345687** » Thu Jun 23, 2005 11:47 am

yeah you're right hemi heads just weren't as popular as they should have been. I found something intriguing however, is anyone aware of the "Hemi" inline sixes of Australia and New Zealand. 265 cubes pushing 302 horsepower with 3 2bbl carbs. This little 6 pot screamer is capable of 500 horse easy, but not a Hemi at ALL. It was a straight wedge head that is about 85% identical to the Jeep 4.0L HO engine. Weird, why'd they call it a Hemi? shi*s and giggles? why isn't my jeep a hemi? just more thoughts from someone who smokes a little too much dope and spends too much time under hoods.

dodgedifferent2 · Post by **dodgedifferent2** » Thu Jun 23, 2005 6:40 pm

i have heard of the hemi inline 6's from australia. Never heard 500 HP out of them. I think that is just a little far fetched.

freebird12345687 · Post by **freebird12345687** » Fri Jun 24, 2005 12:38 am

Not farfetched at all, 302 horse stock, 400 easy, only limitation was cylinder heads Mopar Performance makes an aluminum head that flows enough air for 500 horsepower. Ofcourse its gonna take a nasty cam and high compression but ya know whatever.

OldIron · Post by **OldIron** » Fri Jun 24, 2005 6:42 am

I heard of the Aussie 265's a long time ago but haven't seen but maybe one pic of one. I thought they were a Hemi also... strange. I'll see what I can find on them and post a link up. I agree it's kinda strange to stick the Hemi name on something that isn't. Makes me feel like they think we are so dumb we won't notice and go mindlessly buy something.

500hp isn't far fetched to me either. I think their 72 Charger E49 was rated at 325hp but don't quote me on that. An inline 6 engine has great low and midrange torque characteristics and you can make some serious power with them.

A cousin has an old Ford F150 with a carbed 300 ci 6 that he has ported the head on. He added a slightly hotter cam, offenhauser intake and 4bbl carb too. (secondaries aren't hooked up right now) The thing will eat the back tires off. Probably doesn't have an insane amount of horsepower with the mild mods but the torque is unreal. He can lug it down to 15mph in 4th gear on some pretty good inclines.

Inline 6's are a nice powerplant ! Just ask BMW...hehe.

freebird12345687 · Post by **freebird12345687** » Sat Jun 25, 2005 2:16 am

The 265 tri-power is reffered to as the "Bathurst Special" was stock at 302 horsepower. I found a picture of the head once and the valves are inline parallel to the crank centerline like a 4.0L head. Its straight wedge, if you can find a picture compare it to a picture of a 4.0L HO head you'll be surprised at the similarities, visual mostly. Naturally one would have to compare them in person side by side to be sure.

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