Power outputs

[Mike Costigan]

...  I cant imagine a '22-'34 engine topping out so early, especially given Mike's response.

If I was to change up from second to top at 2,400 rpm, that would be around 20mph; at that speed the engine is only just getting into its stride, and by the time top gear is engaged the engine doesn't have enough power to pull the skin off the proverbial rice pudding!

Edit: I should add that the engine is to entirely standard 1931 specification.

[David Stepney]

Interesting to note that the early RP handbook for the crash gearbox cars (Publication 972B) quotes the HP as 10.5 at 2400, while the later handbook for the 2 synchro cars (Publication 1095) quotes the HP as 12 at 2600.There appears to be no discernible difference between the engines, unless, as Ian Williams says, there is some subtle difference in the cylinder heads. My car will also do just about 50 mph on the flat (it was actually recorded at 51.6 mph along the A494 past Bala Lake) so I suspect my engine produces more that the claimed 10.5 horse power too.

[Colin Morgan]

It takes a lot more power to go faster.  If it is assumed that the power required goes up with the cube of the speed (square law for air resistance and linear for rolling resistance), then if 9 bhp is needed to reach 40mph, about 12.5 bhp is required for 45mph, and 17 bhp for 50mph.  As my Ruby seems happy to do a maximum of about 45mph, this might suggest it is currently putting out about 12.5 bhp rather than the 17 bhp Austin originally intended?

[Robert Leigh]

Publication 1095 refers to synchro on 3rd and top only. The box labelled 2 SYN only arrived in 1936.

[David Stepney]

Publication 1095 refers to synchro on 3rd and top only. The box labelled 2 SYN only arrived in 1936.

Robert. When I said '2 synchro' in my post, I was thinking of synchro only on third and top. I forgot that the '2 Synchro'  labeled boxes had synchro on second. Sorry for the confusion. At least I knew what I meant.

[Robert Leigh]

Sorry, I am a grumpy old (past 80) pedant. I suspected I knew your reasoning, but thought some might not.

[andrew34ruby]

HI All,
I would like to know the TORQUE Figures and at what RPM it levels off at with these Engines,
For me Quoting  Hp is Irrelevant.

Colin
NZ
.

Colin, it's bhp that matters, but if you want torque it's easy to work it out......   torque x revs = bhp

so.......  torque = bhp/revs

This would give you torque at the revs of max bhp, not max torque, but might be useful.

---

Looking at the technical specifications published in sales brochures over the years, the official power output of the Seven is given as follows:

1922-23 10bhp at 2,400 rpm (696cc engine)
1923-32 10.5bhp at 2,400 rpm (747.5cc engine, up-draught carb)
1933-35 10.5bhp at 2,400 rpm (side-draught carb and revised exhaust manifold)
1935-36 13.5bhp at 3,000 rpm (presumably higher-comp 1A684 cylinder head)
1936-38 17bhp at 3,800 rpm (3-bearing engine with high-comp cylinder head)

Which raises a few interesting questions (well, it does to me!).

Did the 7.5% increase in engine capacity in 1923 really only provided a 5% increase in power?
Doesn't the 1933 side-draught carb and associated manifold not provide a bit more power?
If the earlier engines are rev'd to 3,000rpm as quoted for 1935-36, how much more power is achieved?
Similarly, if revs are increased to the 3,800rpm used for the 3-bearing engine, how much more power do the earlier engines produce?

Thoughts, anyone?

I would expect all of those figures to be maximum bhp.  So if an earlier engine was rev'd to 3,000 I would expect the bhp to drop below the quoted 10.5.
Similarly the bhp would drop further if revd to 3,800.

Increasing revs leads to a proportional increase in power if torque stays the same. But torque would be at a maximum at lower revs, maybe 2,000. So increasing revs from say 2,400 to 3,000 would lead to a big decrease in torque, an increase in revs, and a resultant moderate reduction in bhp.

With any engine, what really matters is the bhp at the revs you actually use.

[Bob Culver]

Several years ago Alan unearthed a 1935 iMechE paper from Austin Co giving bhp. At 2200, 2400,2600,3000,3200,3500 11,12,12.5,13.5, 13.7, 13.4.(calc torque 26,26,25,23 1/2, 22 1/2, 20 lbsft.)

 For a 1937 Thetis marine with possibly similar manifold but water cowled, 12.1,13,14, 15.4, 15.8,16.3
Further, the Thetis 800 3.8,1200 6.2, 1600 8.8, 2000 11.1 ,3600, 3800 16.4
Thetis torque 800 26, 1200 27.5 1600 28.5, 2000 29.5, 2200 29, 2400 29, 2600 28, 3000 27, 3200 26, 3500 25, 3600 24, 3800 22.5
By way of comparison A30 at 2400 40 ibs ft and 18bhp, at 3200 37, 23 at 3600 36, 25 at 4800 30lbsft 27.5bhp.
. OHV and high comp.
(As hp is torque x revs and torque is hp /revs can draw own curves
HP/revs X 5252)) 
My stock RP speedo read slower than other cars so was probably accurate. On dead level in dead calm would attain 50 mph but fell off rapidly as carbon formed. Removed and instantly recovered. Suggests breathing restriction so the earlier low comp head may have had more top end hp. Incidentally I drove 60 miles most weekends to my home town. Most would assess the road as about 50% flat; in fact only about 4 miles were! (Wellington-Levin. The Paekak waterfront level)
The top speed was little improved with later head and SU but hill climbing in 3rd hugely improved (at rate where wind resiatance less dominating)
 

Note the 4.9 3 speed cars in 2nd closely match the 5.25 in 3rd

Amended to correct tThetis torque figures (graph very small and my eyes old)

[Ian McGowan]

"If I was to change up from second to top at 2,400 rpm, that would be around 20mph; at that speed the engine is only just getting into its stride, and by the time top gear is engaged the engine doesn't have enough power to pull the skin off the proverbial rice pudding!"

Perhaps this coincidence with 20 MPH in top with the quoted power RPM is intentional given that when the 7 was introduced the blanket speed limit on ALL UK roads was 20 MPH and remained so until 1930??

[AustinWood]

Our 1929 fabric saloon runs happily at 20mph in top on the level. Just as well really as The Borders Council have recently dropped 30mph speed limits to 20mph.
We have an 'Andes' 2nd gear which allows 40mph in 2nd easily and removes the otherwise huge gap between 2nd & 3rd.
The car goes very well on it's bronze updraught and I think it must be producing more than the nominal 10-1/2 bhp. It's happy at 50mph. The head I believe is the later low compression one and I think it's been skimmed though not in my time.