Pent v Hemi.

[Jack Gifford]

... Few prettier sounds than the Mopar Hydrocarbon Octet...

So... you can tell by its sound if a particular hemi V8 is a Mopar? I can't. But Mickey's Pontiac hemi sounded quite "pretty" to me when I watched it take Top Eliminator at the '62 drag nationals- which included beating Garlits' Mopar hemi. [And then there's the sound of my M/T hemi at 9,000 RPM, haulin' a 14,000 lb. transfer sled... ]

Moral of story: please don't use terms 'hemi' and 'Mopar' interchangeably...

Back to topic: Regarding Rex's ignition timing comment- my hemi never liked more than 30.5 degrees advance (blown alky).

[Robin UK]

Jack - has anybody (you for instance) ever written up the full story of the Pontiac M/T Hemi? I've got a couple of period Hot Rod magazines with some detail but the full story must be worth telling. Apologies if you already have and I've missed it.

Take your point about Mopars and Hemis but I reckon its now a generic term much like Hoover for vacuum cleaner. I too have a Hemi that is not a Mopar  It's 1.8 litre twin cam cross flow Lea-Francis that will go in my early 50's sports racer. Over here in Europe you can pick up LeaF engines for very little money, while the vintage racing people pay silly money Riley stuff without ever realising that Hugh Rose designed both engines. They are very similar. He worked as chief designer for Louis Coatalen at Sunbeam on - amongst other things - the Silver Bullet so even has LSR form of a sort.

Here's a pic of the LeaF head

Robin

[fordboy628]

Take your point about Mopars and Hemis but I reckon its now a generic term much like Hoover for vacuum cleaner. I too have a Hemi that is not a Mopar  It's 1.8 litre twin cam cross flow Lea-Francis that will go in my early 50's sports racer. Over here in Europe you can pick up LeaF engines for very little money, while the vintage racing people pay silly money Riley stuff without ever realising that Hugh Rose designed both engines. They are very similar. He worked as chief designer for Louis Coatalen at Sunbeam on - amongst other things - the Silver Bullet so even has LSR form of a sort.

Here's a pic of the LeaF head

Robin

Sort of off topic but very interesting is the fact that there is pretty much a DIRECT connection from all of the high performance British engine manufacturers/constructors and their engineering staffs, all the way from the Brooklands racing of the '30's to Ilmor Eng Ltd. of today, and no doubt beyond.  Many of the most influential individuals had proteges who spun off their own companies, or did design work on the side.   Also of interest are the connections of these folks and their small companies to LARGE manufacturers with huge resources and support possibilities.  It would be very interesting to build a "connection tree" of all these folks.   I suspect it would get out of hand, quickly.

And I'm sure there are connections I am NOT aware of . . . . . .

Sorry for the thread hi-jack.
 
Fordboy

[Dynoroom]

As a side note to the side note......
Mopar/Chrysler owns the name "Hemi". Ask Nick Arias, he sells a hemi head conversion for big block Chevys, LS-Chevys, & now the Ford Windsor engine not to mention his own 8.3 & 10 liter hemi engines. Anyway he now calls them "Hemispherical" cylinder head conversions in print as he has received several cease and dissect letters from the parent company.



The last picture is the 10 liter engine use in the Arias lakester before it was sold.

[Rex Schimmer]

My good friend, Steve Nelson, is replacing the V4, DOHC Ford B block in his  lakester with one of the Arias four cylinder setups with his new design hemi head. He is looking for the F fuel lakester record.

Jack, regarding your blown alky motor, one of the possible reasons that it liked 30 degrees could be that you probably didn't have a big pop up on the piston to make compression. The pop up gets in the way of the incoming charge and typically requires more ignition lead. Just thought.

Rex

[Dynoroom]

Another thing I've noticed on the dyno regarding engine timing is the combustion chamber type, even for hemi engines. The "shallow" early 392 type chamber required less timing than the later "deep" chambers on the 426 type engines. The deep chambers seem to work well with blown fuel but the shallow chambers better blown or unblown on gas. Just saying I noticed the big chambers didn't respond as well on gasoline as the small. On fuel in a blown application all bets are off!

And Rex, I know about Steve's engine. Going to be an interesting season in 2015.

[John Burk]

Flame travel is slow till the mixture is compressed . A fellow I know put the mag in a couple of teeth off in his top fueler . 150* advance and it didn't hurt anything .

[wobblywalrus]

The fuel/air mixture was set rich, between 12.5 to 13.5 to 1 when I started to tune the pentroof Triumph.  The old hemispherical chamber Triumphs liked that rich mixture.  The new engine ran bad.  The mixture was leaned out to stoichometric ratio and it produced the best power at this setting.  An old Triumph would burn up at stoich ratio.  The timing advance is less than with the old style engines, too.  The best way to tune these engines is to put them on a dyno and to try different fuel/air mixtures and advance curve settings.  The motor will tell you what it likes best.

One amazing thing is, when this pentroof engine is tuned very well, it has relatively low brake specific fuel consumption.  The old hemi style ones tended to produce power in proportion to fuel use.  This modern Triumph engine does not do that.  It is a strange beast.

 

[Peter Jack]

Nay Wobbly, the old one's the strange beast!  

Pete

[Jack Gifford]

Robin- Pontiac Enthusiast Magazine did a good feature on my M/T hemi (Mar/Apr '99) in which I tried to share most of what I've learned about it (article titled "Great Mickey's Ghost!", by John McCarthy). There's a copy of the article on the wallaceracing.com website (go to bottom of home page, click 'search wallace racing site', search for "Gifford").

The Lea-Francis head is interesting- never saw one before.

Rex- My hemi V8 pistons have the traditional shape of any early Chrysler hemi race piston. The dome is somewhat truncated, to get the 10:1 compression ratio I wanted.

[Seldom Seen Slim]

Peter, are you calling Bo a strange beast?

[Peter Jack]

Peter, are you calling Bo a strange beast?

There are a lot of us fall into that category. Old English motorcycles fit the description even better. 

Pete

[Jack Gifford]

I apologize in advance for slightly "detouring" this thread:

In Honda ads from about 1980, I see a trademark symbol (TM) by the word "pentroof"- and I assume Honda was claiming ownership of the trademark. How could that be? I thought the word went all the way back to the nineteen-twenties when some Indy roadster engines used four-valve pentroof chambers?

[Dynoroom]

Interesting. In the early 2000's Shelby TM'd 427, FE, Shelby, Shelby American, any many more. Never could figure out how 427 could be trade marked? So I'm not surprised Honda got pent roof.