'36 Terraplane with high compression report

terraplane8 · November 2009

I've finally got the engine back together after what started out as a valve grind and ended up 18 months later with a complete new valve train including valves, guides, springs, followers and a better used cam, plus a later model Hudson 112 head, and a new timing gear. The bottom end and rings seemed fine so I adhered to the "if it ain't broke don't fix it" school of thought. I did clean out the sump though and checked that the big-end nuts were tight.

I realized late on that the head is supposed to be 2" thick, but when I measured it it was 1.4mm thinner than it should be - I'm a bit frightened to re-calculate the compression as it was already going to be around 7.3:1 with the 112 head. It's probably in the 7.6 region now. Once I find my data on measured chamber volume I can work it out approximately. I measured the valve to head clearance at full lift and there is plenty of room.

Also researched a bit on plugs as all my cars seem to have the short-reach plugs such as Champion J8 or NGK B6S which end up with the plug recessed. The correct plug appears to be NGK B6HS which is 1/2" reach.

Anyway, it is now running extremely well and has lots of power. There's no pinking that I can hear on standard 91 octane and it's pulling slightly over 21" vacuum at idle at 1,635' altitude. I timed it using the vacuum gauge, advancing until the gauge peaked out and started fluttering then backed off a little (nearly 1lb) until it steadied up. Pickup in top is very strong and it doesn't seem a lot slower than my '36 H8 127" car (it is a bit slower for sure but not by much). There's plenty of power at 60mph when you put your foot down whereas before there was hardly anything there with the slogged out valves, guides and followers which had a trough cut in them by the cam through wear.

It took a lot of hours to do the job, I'm glad I wasn't paying someone to do the work or the bill would have been high. Hudsons are definitely not easy to work on with accessibility very poor on the "busy" side of the engine. But it's all worth it when you get a result like this.

So it should be rated at least 100hp now as this is what Hudson quoted with the optional higher compression which I think was 7.0:1. The standard horsepower was 88 on 6.0:1.

It should be noted that Terraplanes had a fine reputation for performance back in the day, the 1937 records were 87mph or so for 24 hours and just pipped by the Eight.

Next on the list is a better exhaust manifold, I could go for a split one or just get a custom set of headers made to go up and over the engine. Although it's a small port block, I don't think that matters too much as revs are lowish <4,000 and in fact the ports aren't that small anyway for fairly small 575cc cylinders where velocity is what matters.

Richard E. · November 2009

The '36T crowd thanks you for your thoughtful report!

Browniepetersen · November 2009

I am expecting that you are talking about an 8 cyl engine because of the small port block comment?

Richard E. · November 2009

The 1936 6 cylinder engine was a small port engine. It will only run a single barrel carb. The 1937 6 cylinder is a big port 6 because the block was re-ported to accept a 2 barrel carb intake manifold This later 6 was used until they redesigned the engine for the Stepdowns.

terraplane8 · November 2009

Richard E. wrote:

The 1936 6 cylinder engine was a small port engine. It will only run a single barrel carb. The 1937 6 cylinder is a big port 6 because the block was re-ported to accept a 2 barrel carb intake manifold This later 6 was used until they redesigned the engine for the Stepdowns.

The 37'-on big port 212's didn't really have much extra horsepower on paper compared to the earlier engines (on the same compression ratio), it would only be a few horsepower, maybe 4-5. I'd like to see a comparison between the two, on the same compression ratio.

From what I can see, the exhaust manifold is a big restrictor with dreadful flow past the inlet manifold heating valve in the centre of the manifold. Pat McDonald of the Railton Club makes a free-flow manifold for the Eights but not the sixes as far as I know. I'm keen to try a set of extractors over the top of the engine as there is no room at all on RHD cars to install more or bigger exhaust on that side of the engine.

terraplane8 · November 2009

I've now done a few good drives and have some times for the top gear increments.

30-50 in 7.4 seconds

40-60 in 8.5 seconds.

It's easy to be accurate as the speedo is large and with each mph marked.

As a comparison I have looked at the old road tests with the average Hudson 6 from 1938-39 doing 30-50 in 8.2 secs. at best and 40-60 in 10 secs at best.

The 1938 Hudson 8 did 7.6 secs and 8.6 secs respectively.

The 1936 Railton Light Sports Saloon did 6.5 secs and 7.0 secs respectively.

The 1933 Terraplane Eight did 30-50 in 6 secs. A really quick car!! And that would be on low compression of 6.0: 1 too. It would have to be 5.5 or better on 7.5:1 which is a pretty good figure even today.

The average Hudson 112 did 30-50 in 12.6-13.5 secs with the smaller 6 cylinder engine. And that was with a 4.55: 1 axle, not the 4.1:1 used otherwise.

So it's pretty pleasing overall. A long steep test hill that used to result in speed dropping from 50mph to 38 mph on the old low compression and worn out valves can now be taken without dropping a single mph. The engine is very responsive in its working range.

Regarding the bottom end and concern about only 3 mains, the 1936 Hudson salesman's booklet indicates that the total bearing area is pretty large compared to the average 4-bearing 6, and also pointed out that on any one power stroke there are 2 mains either side of that particular cylinder whether you have a 3 or 4 bearing crank. With the firing order 153624 the power strokes are alterating between one end of the engine and the other. So I'm not worried about that now.

The next task to to get a nice set of headers made up with correct primary sizes and lengths, and an anti-reversion step at the flange. They'll be two sets of three each going into their own tri-collector, then those two pipes going into a dual collector and tailpipe. The routing will be over the top and down the left side of the engine, as with RHD there's nothing really on that side except the generator, starter and dipstick. That should help quite a bit, as the standard exhaust manifold is dreadfully restrictive. I recall Park noted that he found the manifold on his H8 that he raced back in the day made a very big difference to the power. I think he had a split one, and then changed back to the standard one and noticed a big drop in power.

Once that's done, I may need to look at the carburettor and put a slightly more modern one on that has a better capacity. I'm mindful not to lose the flexibilty of the engine. The idea is to have full flexibility and really excellent top gear power over a wide range. That's why I'm not too worried about the small port block as I suspect the key for what I want is good velocity rather than massive ports that don't flow nicely on light throttle or lower speeds.

Park_W · November 2009

Now you've got to figure out how to post an audio recording of that thing when you get the headers on it! Here's pic of my '47 C8 with duals. Sounds quite healthy.

terraplane8 · November 2009

Park W wrote:

Now you've got to figure out how to post an audio recording of that thing when you get the headers on it! Here's pic of my '47 C8 with duals. Sounds quite healthy.

I see you've got a lot of space there to place extra exhausts with the wider body, not like the very tight '36 engine compartment. Nice job on the dual outlet manifold.

[Deleted User] · November 2009

Park W wrote:

Now you've got to figure out how to post an audio recording of that thing when you get the headers on it! Here's pic of my '47 C8 with duals. Sounds quite healthy.

So who makes a dual exhaust manifold for a 175 or 212 6? Has anyone fabed headers or a manifold for these engines?

Craig

terraplane8 · November 2009

HotrodHR wrote:

So who makes a dual exhaust manifold for a 175 or 212 6? Has anyone fabed headers or a manifold for these engines?

Craig

http://classiccar.com/index.php?option=com_jfusion&Itemid=62&jfile=showthread.php&t=12483&highlight=split+manifold

also check out posts by members here denverslim who has done a split manifold on his Terraplane and splitz1983 who is the guy who does the splitting of the manifolds to a high standard from what I have read.

fabbed headers have been done, but it's hard to get specifics for the 212. I'm going to just use the correct size pipe for the primaries which would likely be 1 1/2" and a nice long 45-50" length unlike the high rpm shorty headers you see used on the 308, and through to a free-flow system. These would be routed over the top of the engine and down the left side as has been done many times previously in racing applications, Railtons etc.

Aaron D. IL · November 2009

I can vouch for the '33 T8 being a really quick car, I've seen it. I read it had a better power to weight ratio than the Ford v8 of the same year and was one of the fastest US domestic regular production cars in its time. I haven't seen a lot pre-war performance 6's though and look forward to hearing what results you get with more optimization of the engine.

terraplane8 · December 2012

An update on the car. We're now living at sea-level instead of 1630' which necessitated adjusting the fuel mixture a little. The car is going exceptionally well and clicking off the 30-50 increment in top in 7 seconds flat. And that is with the standard exhaust manifold. The search is now on for someone who can make me a set of over the top headers and down the left side. These will be small-bore and reasonably long to keep up the gas velocity and I'll probably wrap them for the same reason and to damp the noise and heat down.

On RHD cars there is no space to drop down with six primary pipes as the steering box is in the way. It may be possible to take them out under the mudguard. There's plenty of room on the left side though. They'll just be 6-3-2 style with a balance pipe and free-flow mufflers.

'36 Terraplane with high compression report

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