Packard Forum Index » Pre-War (1899-1942)

Thanks Bruce,

I have sorted out the problem, the fuel pump was drawing oil into the inlet manifold.

Pat.

Quote:


Phil,

Allow me to explain a little. An engine of this nature has a relatively low cruise rpm (revolutions per minute) My guess is (only a guess)that optimum cruise rpm is around 1900 - 2100

This combined with the incredibly low axle ratios (4.39 to 4.69 :1) that were standard equipment gave very low highway speeds. As O_D said in a prior post, these cars were geared (in most cases) for 50 mph cruise. While going flat out balls to the wall you might pinch 80ish out of one, sustaining this speed for any period will result in parts exiting the block at warp 9.

The absolutely amazing thing is, I can't seem to find anyone that has much of an opinion to offer on safe cruising rpm. When I say cruising rpm, I mean what engine rpm is safe for cruising all day long.

For a car equipped with 4.39:1 gears, and 30 inch diameter tires at 50 mph is turning about 2441 rpm. That is about wound out. So depending on your tire size, and rear axle ratio, I guess it is somewhere in that neighborhood. You can imagine my excitement when you reported cruising at 65, that is very impressive.

I originally asked my question (both in this thread, and another here in the forum) because I am working on setting my car up with the optimum gearing for optimum cruise at the optimum cruise rpm. Unfortunately, so far, no one can answer my question on safe max. rpm and max sustained cruise rpm. I am totally shocked that others far more experienced in these earlier engines than I have not had these same questions, or fooled with gearing combinations more. So, I will venture out, do the math, do the work, and know for myself.

Unfortunately, so far, no one can answer my question on safe max. rpm and max sustained cruise rpm

I thought I had answered the sustained cruise, at least as best I can. I limit myself to 50 mph, very rarely 55 and only then for short periods, these were my limits for about 45,000 miles with babbitt bearings in my 34 320 engine, 4.69 rear before I finally got a hint of a rod knock. Tire size is 7:00 x 17, do you want me to calculate the corresponding rpm? Probably about 2400 or so.

39super8.

I am not familiar any of the Packard streight 8's.

However, A good general rule of thumb for nearly all engines manufacatured prior to the HP revolution of 1955 is about 2400-2700 rpm as u and Owen have already pointed out.

Converting to insert bearings is certainly a good idea especialy for quick service replacement. So worring about the bearings (converted to inserts) is not a major issue to any one willing to crawl under the car and replace them on relatively short intervals.

The problem is the RODS!!!! I have no idea about the rods in a Packard streight 8. But it mite stand to reason that the rods are no better for exceeding 2700+ rpm than the babbit bearings would be.

Wearing out bearings prematurely is one thing. Just replace them on short intervals if that's what i comes down too. THE RODS are a different story!!!! Break a rod and it can ruin a block or a crank.

So, youir original question really boils down to:
1. What is max sustained rpm range for the RODS.
2. Does Carillo or some other aftermarket mfg'er (past or present) supply racing rods????
3. Availability of pistons that won't break at higher rpm.
4. is the crank strong enuf???? I'm guessing yes.

SInce i am not familiar with the rods,crank or replacment pistons for the streight 8 then my efforts would be toward researching any period aftermarket or factory available racing or heavy duty rods that were ever available. OR to put it another way, What did the racing or hot rodding crowd use during the 30's and 40's?????

Contact Carillo industried of California about rods. 10 years ago i paid $500 for 2wo Indian rods from Carillo. Long storyshort: 10 years ago ONLY stock or Carillo's were available. Now there is a mid range rod available for about $250. BUT, there was one other alternative for the EOM rods invloving a skeletal reinforcement.

Bottom line: If u can not get the speed out of the gearing then research the racing or even perhaps any truck or industrial applications that the Packard 8 mite have been used in to see what changes they made to the 8.

Super8:

I went over to AACA where u asked the question about the upper rpm range for sustained speed operation. Someone indicated 2500 rpm.

Based on my limited experience with various long stroke low compression engines of the pre 1955 era the 2500 rpm should be about rite. Maybe even 2700 rpm.

Note that one post over at AACA indicated 100mph but also note the continued reference to using overdrive.

The person running 100mph with the Over drive mite be a good one to ask about how many rods he broke or other engine failures and what kind of mods were made to the engines for HiPo applications.

O_D,

I deeply appreciate your answer to my question about rpm with your nominal cruise rpm. It seems there is a reliable consensus beginning to evolve citing around 2500 (I really lean more towards 2400 myself).

PackardV8,

You make some great points. The straight 8 Packards have a plethora of bore and stroke relationships. This particular family of engine is way longer stroke than any of the latter engines. I really think your thoughts on 2500 are likely the high end of the range.

I think your thoughts on the 11 inch long rods being the weak link are spot on. As far as making new ones, that is a tough one. They are longer than any available blanks. They are gun drilled to pressure feed the small ends. I have been to the mountain top and back on the rod deal, and feel confident that the stock rods with modern inserts (what Pat and I have in our engines) is the best compromise.

The truth is, these engines make loads of torque, and really do not need to be turned at max safe rpm for cruise speed if satisfactory gearing can be obtained through whatever means (rear gears and or overdrive).

Guys,
This is great food for thought. I really appreciate the feedback. This is a fun process, mulling over all the how's and what's of these old engines, and figuring out how to get the most out of the car, gearing, and engine design. It is truly uplifting to hear of how many miles Pat and Owen have put on their 320 powered cars. Some day I will be able to report miles of smiles as well (I hope!)

Jim

My concern about connecting rods is not because they are 11 inches. My concern is that it was designed as a 2500 (sustainable) rpm engine and many rods of that era were not strong enuf for much over 2500 rpm.

Have u determined the gear ratios and wheel diameters that u will need for the sustained speeds u want????

Wouldn't the endurance test Packard did in 1935 when they switched over to insert bearings indicate the rods were pretty durable (at least when new)?

"insert bearings indicate the rods were pretty durable (at least when new)?"

Probably so. WHAT SUSTAINED rpm range and for how long???? Were they testing rods or bearings???

Was it strictly an insert bearing test????
If they were only trying to prove the inserts were superior then maybe the rods were beefed up especialy if exceeding the 2500 rpm range. I don't know the specifcations of the test.

How many engines did they blow before they got one to hang together long enuf to make their claim??? It's not like they didn't have 1000's of engines setting around to blow up at will for testing or marketing purposes.


Don't get me wrong. I'm not trying to be argumnetative.
If the prewar Packard 8 experts say the rods are strong enuf to sustain engine speeds significantly higher than say 2500 rpm then Super8 and i can most likely take their word for it.

Super8 raised the question. My opinion is based strictly on general experience and no personal fact finding based specifically on the Packard 8.