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Ask Away! with Jeff Smith: The Pros and Cons of the Chevy Inline Six for Old-School Hot Rods

 

I was at my local car show the other day and I talked with a guy who built an inline Chevy 6 for his street rod. I was interested in the engine because it’s different. I’m getting tired of seeing small-block Chevys and LS engines everywhere. I don’t know much about these engines. Are they worth building for a mild rat rod?

J.L.

Jeff Smith: There is a whole subculture of hot rods out there running around with “alternative” engines. While most street rods built before WWII were Flathead-powered inline fours and later V8 Fords, Chevrolet was always considered a very conservative company with inline six-cylinder engines with overhead valves. The biggest drawback to an inline six is its physical length and it will be smaller in displacement because it only has six cylinders. But for a lightweight street rod with an open engine bay, a Chevy six could be a great engine. We’ll go over some material for the Chevy 6 as it’s the most popular– but the AMC, Ford, Pontiac OHC 6, Mopar slant six, and Jeep engines are other obvious candidates.

ASK-11-02If you’re into a dramatic-looking engine, consider the Pontiac Overhead Cam (OHC) inline six that came in the 1966-67 Tempest and 1967 Firebirds. These engines are very modern looking with the factory ribbed cam and front timing belt covers. There was power with this engine as well–in 1967 the 230-cubic-inch Pontiac OHC 6 was rated at 215 horsepower with 240 ft.-lbs. of torque, a Rochester Q-jet four-barrel carb, and 10.5:1 compression. There are parts available for these engines, although usable core engines are becoming scarce.

As we mentioned earlier, Chevy has built overhead valve inline sixes since 1929, but we will deal with only the later model engines used from 1962. This lineage of Chevy inline six came in four different bore/stroke/displacement combinations: 194, 230, 250, and 292 cubic inches. The largest was used only in Chevy pickups because of its taller deck height. The deck height allowed a very long 4.12-inch stroke compared to 3.25 for the 230, which is probably the most common of the Chevy sixes that you’ll find. The 230-cubic-inch engine came in mid-1960s passenger cars like the Chevy II, Camaro, Chevelle, and some full-size cars as well. It was rated at 140 horsepower with a one-barrel and 155 horsepower with a two-barrel carburetor and 8.5:1 compression.

All early Chevy six engines place the intake and exhaust manifolds on the driver side of the engine. This is not the optimal placement for the intake since the exhaust puts lots of heat directly into the intake manifold, which hurts power. But the good news is there are lots of parts available for these engines. Offenhauser offers a single four-barrel intake manifold, several companies grind cams, and there are headers available. Keep in mind that most headers will be designed for pickups and it’s probable that they may need tweaking to fit other chassis.

One odd thing about the Chevy six is its paired intake ports. Three common ports feed all six cylinders. Worse yet, a head bolt boss intrudes into these ports, restricting flow. We discovered a small company in Iowa called AutoWerks (12bolt.com), owned by Tom Lowe. Lowe has spent several decades working on these little six cylinders. He has developed a part called The Lump. Its name is descriptive, if not necessarily attractive. Lowe’s approach was to remove the large cast iron boss that surrounds the stock head bolt. He then spot faces the bottom of the port for an Allen head bolt and places an aluminum cover (The Lump) over the Allen bolt head to improve airflow. The conversion can be done on your workbench and the increase in airflow is significant enough to reward the effort. You can check out an installation video and all the particulars on Lowe’s website 12bolt.com. Lowe also offers a new intake called the P.E.S. Ram that is about the best looking Chevy inline intake I’ve seen.

For power, a mild street V8 will make roughly 1.1 hp per cubic inch with stock heads. The heads on these older Chevy six cylinders are not very good so making 1.1 is about the most you can expect. With a 230-cubic-inch inline six with a mild cam, headers, and the cylinder head work we’ve described, you could expect to make around 250 to perhaps 260 horsepower. Because the inline six crankshaft is so long, even with 7 main bearings it’s probably not a good idea to spin these engines much beyond 6,000 rpm.

Overall, internal parts are readily available and they’re not overly expensive so you could assemble a decent performance street inline Chevy six without draining your bank account. It might be a fun adventure and surely one to garner more attention than just another small-block.

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34 Comments

  1. paul ruliffson says:

    If I remember correctly, the Pontiac OHC was based on the Chevy 6 cyl; plus I’m pretty sure they also had a 250 cid version rated at 250 hp with the 4 barrel and split exh manifold.

    • ed nowaski says:

      the four bbl Pontiac OHC 230’s had 207 hp, the later 250 versions had 215 hp for the automatic cars and 230 hp for the stick shift cars

  2. PES, -Precision Engine Service – created the 1st bolt in Port plates -or lumps as many say. He created the intake manifold as you mentioned also. Tom Lowe has only copied what PES started years ago. Please let Clyde Norwood – owner of PES and Inventor of the port plates (lumps ) and mentioned intake manifold get the Honor of his work .

  3. Jerald Knudson says:

    I had one in a 1955 2 door chevy, The cam was wild, with 3 2barrel stomberg 97 carbs, but gas mileage was horrible around 6 mpg. It ran 6000 rpm’s to get horsepower, but rings don’t last long and constant setting the carbs so don’t backfire… Then we didn’t have ignition system we do now, but betting that would help a lot.

  4. Terry Milford says:

    do i own the only 85 hp chev 6 cyl in the world?? (1953) panel truck

  5. I have a inline 6 with a 3915 bore can anyone tell me what I have

    • ed nowaski says:

      A .040″ over 230, 250, of 292 Chevy — if the opening for the water pump is about 3/8″ to 1/2″ or so from the top of the block, then it’s one of the smaller two,,if it’s maybe an inch or more then it’s the 292….if the piston is dished then it can only be a 250 or the 292…230’s are the lower deck height blocks with flat top pistons. The 250 is the lower deck height block with dished pistons,,, and the 292 is the only raised deck height block, and it has dished pistons–all of this is assuming the pistons are standard replacement configuration, not hotrod parts.

  6. Chris hall says:

    Could it be possible to drop a straight 6 into a 2001 dodge ram 1500?

    • Robert B Marshall says:

      When i was a young boy my father & i would stick 392’s, 413,& 426 Hemi big block Chrysler’s in First Gen Camaro’s & FirdFird’s,1967-70,just to be different,and these were only F-body car’s,i’m a Gm man all the way,and have built some wild engines,SBC-283,327,305,350’S,400,BB-396,409,427,454,even a old Buick Nail head 425,Chrysler 273 Commando,340,383,392,413,426,440,some pretty cool Ford engines,my last was a 1971 400 SBC-done to a 406 with all the right goodies,About 450 HP,My son and i put it in our 1984 3rd Gen Camaro,Anything is possible if you put your mind to it,why not go BB Chevy in your Dodge?Something really cool like a 396,409,427 that will turn heads,if your going to go with your s-6 Chevy,do you want fuel injection or carbed?good luck on your project.

  7. Frank Hutto says:

    Jeff do your homework, there are 250 sixes out there making 450 hp turning 8000 rpm all day

  8. Paul Fuller says:

    I have a chevy 6 #FO53ISG. want it to be a 250. Is it?

  9. Somebody told me that street six engines were the only ones you could balance perfectly. I don’t know much about balancing other than the obvious. That somebody was from England and he loves his jaguars

    • ed nowaski says:

      ask your buddy how did his perfectly balanced “street six” like life at 6000 rpm? due part to inherent inline design balancing can be dead on, but with the longer inline’s crankshafts they will experience “torsional vibrations” as these long cranks see themselves being twisted by the firing cylinders along their length and rebounding from it. old Jags, other British sixes, and earlier American sixes “enjoyed” this “phenomenon” by vibrating flywheel bolts loose and harmonic balancers OFF….longer the crank-less the main bearing count…the more crank vibes–the Chevy 292’s and Ford 300’shave real problems at 6 grand–some Brit motors have them at lower AND multiple rpm ranges and sometimes while on the highway a gear change is required or just a simple speed change to solve this damaging situation.

  10. 20 years ago, I bought a 1940 Chevy Coupe. It was stock with the 215 Babbit six. Duel carbs and split headers helped but it was still pitiful. I ended up building a mild 292, bored .030, crank .010, Ported & Polished, CompCams rockers, 270 duel duration Wolverine cam, Split Cast headers, 3×2 Offy intake with 5100 Holley/Weber. This motor really woke up the Coupe. coupled with a T-5 from a Camaro and 10 nova rear, it makes close to 300hp and a lot of fun!

  11. Funny he didn’t mention the 250 & 292 much. Seems like there are plenty of them out on the market too. I have a 250 in my C10 which runs great and there are lots of parts available. I also recently purchased a 292, which I hope to build some day. Ford also made a big 300 six. I think those were mainly used in trucks.

  12. My understanding of the six is that they were used mainly in trucks. So in 1974 I bought a 1966 Chev belaire and the motor was a 292. I knew original owner and he had never changed engine. My question is would that have been factory or special order? I never knew the HP but I raced 283’s that never had a chance.

    Thanks

  13. Dan Schuhmacher says:

    How much horsepower does a typical 250 6cyl GM engine have from 1965?

    • Hey Dan, Do you mean the Chevy 250? It was introduced in 1966 and made about 150 gross (e.g. at the crank) horsepower and 125 net (at the wheels). Now, GMC had a 270 six available in the early 1960s, and it made between 130-140 (gross) hp. We found this website that’ll have more specs on the Chevy I-sixes.

      • ed nowaski says:

        I never knew they ever used the GMC 270 engine after ’62. GMC immediately went into using the Chevy 230 and 292 as pickup engines in 1963–I went to that site and as you can see by its dismal hp/torque numbers that it was the old design engine — not everything found on the Internet is always the truth

  14. ed nowaski says:

    Hey Jeff, that 155 hp/230 with the “two-barrel” carb, I think that was only a larger single bbl Rochester like was standard on the 292 truck six–the camshaft did carry a different part number than the standard 140 hp/230, and they all had 8.5:1 comp. ratio

  15. Anthony M. says:

    I have the 78 C-10. It came with 250-4.1, with the integrated head. that head is gone. I have collected the new head, and manifolds for the top… As I live In California, and our smog laws are a mess. I must pass the test. All I need are the smog air tubes… Any help?

    • OnAllCylinders Staff says:

      Hey Anthony, unfortunately we couldn’t find an exact match, but maybe this will help: Here’s a list of Air Tubes made by a company called Standard Motor Products. You can filter it down in the lefthand column to find a few listed for the 1975+ Chevy C10, and a few for the Chevy 250 I6, but we’re not experts on exactly which years got which head–integrated or traditional. Perhaps one on this list will fit the bill?

      • Anthony M. says:

        Thank you for the fast reply. The tubes shown there are for the 300 ford I6’s. Which I may have to modify, not sure yet!
        I just wonder why they are available for that motor ‘NEW’ and not the chevy 250 I6.

  16. Norman Shiflett says:

    I have a 71 C10 with a 292. I’m looking for the stock power steering pump bracket. If anyone has one or knows where I could fine one for sale I would greatly appreciate.

    • Hey Norman–after some research, it looks like there were some variations of that bracket between all the iterations of the I6 and its respective cylinder heads–so make sure you know which one you’ll exactly need. That said, there’s a company in Wisconsin called Davis Speed Equipment. Check out their website–they’ll probably be able to steer you (pun intended!) in the right direction.

  17. Anthony M. says:

    Ok , I think I have the air tube problem fixed… I’ll make one! Another question I have is… You have the intake/exhaust manifold bolts. But on top of those are small “keepers” sort of horseshoe shape that hold the intake/exhaust on at the end of the bolts. What are those called, and where do you find them? TY

  18. Mike Logan says:

    I have a 1936 chevy coupe stock car with a 250 chevy. The series we race in will not allow any intake manifold or head modification, and we can only use a one barrel carb. I want to build a new engine this winter and want to know what the best components to use to get the maximum horsepower. We. can. use any stock 235, 250, or 292 head but it cannot be modified. The short. block has no restrictions. Can you advise me on what I should use to build a high horsepower engine?

    • Chuck Spaeth says:

      Mercruiser sold marine 250 ci i6 engines which were made by chev. They are built for performance to run all day at 4200 rpm, and my stock 1974 165 hp has an intake that can accept a 4 barrel, boosts hp to 190 – 200 hp With a lump head modification probably close to 230 hp, and still have plenty of room for more hp mods. These boat engines can be had all day long and the beauty is boat engines usually have very low hours on them.

  19. Jeff Smith says:

    This is a little bit out of my area of knowledge, but essentially you are building a restrictor plate engine. I would do research around that, but right off the start, I’d run as much compression as you can – assuming that you are allowed a fuel that will not detonate. Compression adds power everywhere. I would also choose the thinnest rings I can afford – thinner is better – they seal better and drastically reduce friction – which is free horsepower. Since the 1 bbl carb will limit ariflow, I would look at maximizing cam timing within the rpm limit – probably 5,000 rpm. If for example, the engine speed is from 3,000 to 5,000 then obviously that’s where you would concentrate with cam timing. I would also flow test the head to see where maximum flow is attained and then place valve lift above that to maximize the time the valve is flowing. Also check for valvetrain deflection – how much lift are you losing. Check lift with a solid lifter and checking spring and compare that to the actual lift with the actual spring. The inline 6 uses a very long pushrod – almost 10 inches. Long pushrods tend to bend easily – so its’ worth investing in at least a 5/1`6 pushrod with a 0.105-inch wall thickness. That alone might be worth 0.010-inch of reclaimed valve lift – perhaps more. This also means running good rockers if they are legal and optimizing pushrod length for ideal geometry. These are just a few ideas to get you started. I would also spend a lot of time blueprinting the shortblock to create optimal clearances.

  20. i was thinking of using a 250 straight six for an industrial engine ..i was wondering if they make a cam for these engines that would be all low end torque and not rev past about 3000 rpm

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