Camshaft: Boat v. Auto

"Rusty Vandura - www.tinyurl.com/keepoppo" (rustyvandura) 07/28/2020 at 17:38 • Filed to: None

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So my brother-in-law is giving me an OMC 140, 153 CID GM-built four-cylinder from 1963. If I wanted to put this in a car, would I need a different camshaft? My understanding is that a typical marine engine has a cam that is sort of like an RV cam, bottom-end torque. I had a brief chat with a guy at Comp Cams, and there’s a matter of lobe separation... Here’s part of the chat transcript:

Matt: Looking for something off the shelf. I just put 268H out there as a comparison. I understand that 268H is an “RV” cam, torquey low end.

2020-07-28 14:03

Fred Jones: If it is a shelf that you are looking for, then the 14-123-5..

Fred Jones: 1200-5200...

Fred Jones: 212/212 duration @ .050" and .475/.475 lift with a LS of 110, but we would have to custom it for the reversion...to a LS of 112

I have a T-5 — mechanical tailshaft — transmission I could put behind it...

Here are !!!error: Indecipherable SUB-paragraph formatting!!! on the cam that the Old Guy recommended.

Can you educate me a little bit here, or refer me to a good reference material?

Thanks.

Maxima Speed > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 17:42

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This is the technical stuff that I absolutely love about oppo and have zero clue about. Im eagerly awaiting someones knowledgable answer.

Rusty Vandura - www.tinyurl.com/keepoppo > Maxima Speed 07/28/2020 at 17:43

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You and me both, and the people here are so enthusiastic that there will probably be someone eager to share their knowledge. There will also be numerous blokes with utterly pointless things that they will post. That’s the other good part about Oppo .

HammerheadFistpunch > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 17:44

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I hate that motor.  probably just ours but we had 2 (mercs not OMC, but same block) in a boat and the times that both of them worked was less than 50%

A Boy and His Longtail > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 17:47

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Don’t boat motors spin the other way? I could be wrong, but I was under that impression 

Sovande > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 17:48

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This help? 

Michael > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 17:52

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Boats are built for low rpm high torque, so a different cam would probably be appropriate for a car

Lobe separation is important in below -the-water exhausts, because with enough overlap to be efficient, there is actually a possibility of sucking water back into the engine if the exhaust baffles aren't in perfect shape. So they run almost no overlap (intake and exhaust valves open at the same time, which helps clear leftover exhaust from the combustion chamber)

Turbineguy: Nom de Zoom > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 17:52

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Besides the cam profile issue, you need to be sure the crank will accept a pilot bushing if you want to bolt up a manual trans . I assume the engine already has a flywheel (vs flexplate for auto trans)

mustangchris66 > HammerheadFistpunch 07/28/2020 at 17:54

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Our family boat had a motor that looked just like that too. I don’t disagree that it only worked ~ 50% of the time . It was such a chore to get it running every year. I never had any faith it would start even when it had been running fine all day.

Michael > Michael 07/28/2020 at 17:55

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https://www.amazon.com/dp/9332549494/ref=cm_sw_r_cp_apa_i_K6jiFbB7JM4EC

Good resource to understanding the fundamentals of combustion, valve sizing, etc

Michael > A Boy and His Longtail 07/28/2020 at 17:56

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Usually only one does, in twin engine applications

Snuze: Needs another Swede > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 18:01

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Lobe separation is one factor that determines overlap (the other being total duration). Think of it this way - given a cam with a set duration, a larger LSA gives less overlap. Overlap is important because it allows the exhaust to help draw in fresh intake air.

However, this effect only really works at high RPM. Racing engines typically run a lot of overlap, meaning the intake valve opens significantly before the exhaust closes. A t very high RPM the exhaust gases rushing out the exhaust create a vacuum/scavenging effect that helps draw in fresh air. However at low RPMs the there is less energy in the exhaust and the scavenging isn’t achieved so some of the exhaust hangs around in the cylinder, and dilutes the intake charge. This is why race engines often run like shit and sound like buckets of bolts at low revs and scream up top.

Conversely a wide LSA means little overlap. This means the intake barely cracks open before the exhaust closes, which prevents the exhaust from diluting the intake, which means more efficient running at low RPM and therefore more torque. But at high RPMs you don’t get that scavenging effect so you are giving up horsepower.  This is why "Truck/RV" cams make a lot of torque but wheeze up at high RPMs. 

If only EssExTee could be so grossly incandescent > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 18:09

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You could do it, but I think the work it would take to adapt it to automotive use would be not worth it. Boats don’t use transmissions as we know them. I t’s more just a box that does forward, nuetral, reverse. The block and crank will need to be adapted to hook up an automotive transmission, and for something that old it could mean having to m achine your own parts.

You also have to cobble together a cooling system from scratch. While the motor does have a water pump, boats usually just take in fresh or salt water from hull inlets and dump the hot water back out the stern. There’s no r adiator involved.

Michael > Snuze: Needs another Swede 07/28/2020 at 18:27

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What’s your background?  Very knowledgeable 

Exage03040 @ opposite-lock.com > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 18:30

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Would you need it? Not really . It might be nice to have though, it might feel sluggish .

It depends on what you’re throwing this in and what you’re going to be doing Rusty. That comp cam is going to have more punch for sure than the specs Fred stated for that cam. It has higher valve lift and greater duration (opening) so it will have a sharper cam profile and allow the engine to breath better.

More air allows, more fuel, allows more power to be developed with correct spark timing. By making more power you now run dip into longevity of components if it was ran like a marine engine .

Marine engines are typically used at deeper throttle and continous operation so the cam is designed with a high load and high rpm operation and with longevity in mind; sacrificing power output that you’d find in a street car where we don’t typically drive with a heavy foot.

The exceptions being on-ramps or racing. W ith regards to racing usually they’re pushed for power and response as long as the engine lasts the season, not say + 1 0,000hrs and many years of run time .

A Boy and His Longtail > Michael 07/28/2020 at 18:43

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Of course. This counters the rotational moment caused by the propeller

Urambo Tauro > Sovande 07/28/2020 at 18:55

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I’ve had this stuck in my head all day. Thank you for giving me an excuse to share it. (I guess that counts as being helpful after all?)

Rusty Vandura - www.tinyurl.com/keepoppo > If only EssExTee could be so grossly incandescent 07/28/2020 at 19:21

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I am under the assumption, until I learn that I am mistaken, that this block would be identical in every way to the 153 block. The head could be different, but I doubt that as well. Pilot bushing in the crankshaft could be an issue, but I bet that’s the same as well. But you know what they say: assume = ass + u + me

What I learn, I will report.

I’ve got a guy who would know the answer to this in intimate detail, but first I would have to endure being excoriated for even wanting to try it, then I would have to endure a bunch of grumpy right wing trolling about Democrats and Commiefornia and frankly, I’m tired of that.

I need to read up on the internets.

Rusty Vandura - www.tinyurl.com/keepoppo > Sovande 07/28/2020 at 19:22

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But why it’s gotta be a black dude?

Rusty Vandura - www.tinyurl.com/keepoppo > Urambo Tauro 07/28/2020 at 19:23

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Nice recording though.

Rusty Vandura - www.tinyurl.com/keepoppo > HammerheadFistpunch 07/28/2020 at 19:24

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But the problem probably wasn’t the engine, but the application thereof.

Did you see my Bronco post?

Rusty Vandura - www.tinyurl.com/keepoppo > A Boy and His Longtail 07/28/2020 at 19:25

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Some of them do, if they have rotating engine mounts. They spin longitudinally.

Rusty Vandura - www.tinyurl.com/keepoppo > Turbineguy: Nom de Zoom 07/28/2020 at 19:26

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Good point. I’ll see about that.

Rusty Vandura - www.tinyurl.com/keepoppo > Michael 07/28/2020 at 19:27

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Very intriguing. Thank you for the tip.

Rusty Vandura - www.tinyurl.com/keepoppo > Exage03040 @ opposite-lock.com 07/28/2020 at 19:32

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There are some fundamentals here that I do not understand. But let me back up:

I am operating under the assumption that this engine is basically a 2.5L/153CID Chevy II four-cylinder. My friend had a 68 Nova with one of those engines. I have a T-5 transmission sitting here that will probably go unused or sold* . I thought some little fiberglass T-bucket with this engine might make a fun project. The engine is in my brother-in-law’s houseboat and has been superceded by a slick Honda outboard. I’d have to go and retrieve the engine from the houseboat, which would be a very interesting project in itself. Just hate to see the thing go to waste, which it surely otherwise will.

My van has a three-on-the-tree, so I want to look for one of the 3-speeds with Borg Warner electric overdrive and keep the column shift because few people alive have ever seen one.

ITA97, now with more Jag @ opposite-lock.com > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 19:52

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There’s no reason that marine cam won’t work throwing the engine in a car. They’re usually spec’d similar to an “RV” cam from back in the day biased to a lower rpm output and less to top-end power at higher rpms. Probably won’t be ideal in a performance application, but otherwise should be good enough.

The bigger thing you may need to ensure is that the intake manifold has some provisions for the big vaccum port you’ll need for the brake booster. It’s likely on the casting and plugged, but if not you’d need a different intake manifold for automotive use. You may also need to fabricate some brackets for the throttle cable and return spring for automotive use. The boat’s throttle cable is going to be a bit different setup. Will also obviously need an automotive exhaust manifold, too, unless you’re looking to run it out the top of the hood.  

Exage03040 @ opposite-lock.com > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 20:03

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With a T-Bucket for a fun run around I’d probably go with a street cam over what’s in it, if you willing to spend the money.

Cams on naturally aspirated   engines are a major dictation of power development and drivability.

If you had said it was going in like an old S10 to make Lowe’s runs , I’d have said don’t bother.

Sovande > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 20:09

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That’s the only Cam  I could think of.

If only EssExTee could be so grossly incandescent > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 20:22

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I think it's totally possibly, the only question is why?

Rusty Vandura - www.tinyurl.com/keepoppo > ITA97, now with more Jag @ opposite-lock.com 07/28/2020 at 20:24

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Now we’re talking. I am assuming — and remember that assume = ass + u + me — that apart from little things like you describe, this is basically a Chevy II engine with an RV-ish cam. From the reports I’ve received here, there’s NO WAY it would run any less dependably in a car than it would in a boat. IOW, not dependable in boats, but that is owed to poopy carburetors and such.

Put the T-5 behind it and we might have something interesting. 

Rusty Vandura - www.tinyurl.com/keepoppo > Sovande 07/28/2020 at 20:25

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Dude’s name is Cam? (I was purely trolling with the identity politics part.)

If Dude’s name is Cam, then I am watching the perfect amount of NFL because I had zero idea.

Rusty Vandura - www.tinyurl.com/keepoppo > Exage03040 @ opposite-lock.com 07/28/2020 at 20:27

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No, it would be in some kind of runaround cart because of the novelty of the engine. Something very light. (I’d want nothing to do with an S-10 of any description.)

Rusty Vandura - www.tinyurl.com/keepoppo > If only EssExTee could be so grossly incandescent 07/28/2020 at 20:29

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I’ve been told that answering a question with another question is bad form, so I won’t reply, “Why not?”

I knew a guy who had a ‘68 Nova with the street version of one of these four-bangers. I thought it might be fun to put a 5-speed behind it and run it around in a fiberglass T-bucket. 

Rusty Vandura - www.tinyurl.com/keepoppo > If only EssExTee could be so grossly incandescent 07/28/2020 at 20:30

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And I’m a hoarder and I’d hate to see this thing just rust to death in the engine pod of my brother-in-law’s houseboat while I’m still alive and could possibly do something with it.

Sovande > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 21:09

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That's Cam Newton. He is a football player of great renown. 

Snuze: Needs another Swede > Michael 07/28/2020 at 21:11

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Thank you.

I studied mechanical engineering in college with a focus in automotive engineering.  Though ultimate thats not what I ended up doing, but it was a good background and I still like reading technical articles and things related to automotive engineering.  

Rusty Vandura - www.tinyurl.com/keepoppo > Sovande 07/28/2020 at 21:28

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To me, he is of great unknown.

Michael > Snuze: Needs another Swede 07/28/2020 at 21:47

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Oh hey I’m BS in mechanical engineering and  internal combustion engines was one of my electives, and my highest grade while I was in school. Same here career wise, now I design boxes to ship powersports equipment, not what I had in mind but it’s where life led me.

ITA97, now with more Jag @ opposite-lock.com > Rusty Vandura - www.tinyurl.com/keepoppo 07/28/2020 at 22:08

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That would be my assumption, too.  

Rusty Vandura - www.tinyurl.com/keepoppo > ITA97, now with more Jag @ opposite-lock.com 07/28/2020 at 22:48

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I am a nostalgic hoarder. I think in the right buggy, like a fiberglass T-bucket or something, it could be fun. Get the engine, put some oil in the cylinders and what not so it’s decently preserved, and prowl the swap meets for an appropriate glider. Some kind of headers would give it a cool sound, too. Engine is in my Brother-in-law’s houseboat and I can’t bear to think of it just rusting into oblivion. Not while I’m still alive to at least dream of what I might do with it.

Rusty Vandura - www.tinyurl.com/keepoppo > ITA97, now with more Jag @ opposite-lock.com 07/28/2020 at 22:49

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And not only that, if it really does make 140 hp, as OMC claims, that’s not too shabby.

MiniGTI - now with XJ6 > Rusty Vandura - www.tinyurl.com/keepoppo 07/29/2020 at 01:14

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My mom was more Jalop than she realized back in the day — drove Fiats and SAABs in the 70s and I remember her once borrowing a 3 on the tree Chevy van about 1986. 10 year old me though it was cool; I’ve hardly even seen a picture let alone in real life since.

Rusty Vandura - www.tinyurl.com/keepoppo > MiniGTI - now with XJ6 07/29/2020 at 08:18

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Some Mercedes sedans from the 60s had four-speed column shifters.

Snuze: Needs another Swede > Michael 07/29/2020 at 12:31

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I was in the Navy for 6 years as an electrician on a nuclear submarine. After college I ended up working for a ship designer for a few years. Now Im back working for the Navy doing acoustics. Its interesting work, for sure, but not what I really imagined doing.  

Rusty Vandura - www.tinyurl.com/keepoppo > Snuze: Needs another Swede 07/29/2020 at 23:35

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