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Slant four - Jeff Smith Technical Questions & Answers - Ask Anything

Half a Mouse - Slant Four

Wayne Woodrum; Madisonville, TN: I’ve been buying automotive magazines since 1965, and at times, I’ve run across special engines. The one that really got my attention was a small-block Chevy with the driver-side cylinder bank removed, making it an inline-four cylinder. Imagine a slant four cylinder Chevy. I plan on building one, but I don’t know much about it. Do you have any information on how to do this? I know I’ll need a special crank and camshaft, or can I use parts from an inline engine? I’m old-school so I don’t have any online capabilities. Can you help?

Jeff Smith: This engine was originally designed by Ron Hoettels, who owns Speed Engineering Service Co. (SESCO) in Colgate, Wisconsin. I talked with Speedway Motors’ museum curator Bob Mays, who says there are several SESCO engines in the museum located in Lincoln, Nebraska. Bob told me Hoettels designed the original SESCO engine as an inexpensive, alternative Midget engine for circle-track racing. Up until the SESCO engine, Midget racing had been dominated by the four-cylinder Offenhauser, which was a specific-built racing engine that could trace its roots back to Harry Miller’s ’20s Indianapolis race engines. I then spoke with Hoettels, who said the SESCO plan started with a 283ci Chevy block that was whittled down to just a 6-inch-tall portion of the right (passenger) side of the cylinder block. This machining completely eliminated the original main webbing as well. Hoettels then replaced the main webs with a two-piece aluminum crankcase assembly that then employed the crank from a Chevy II inline-four cylinder. Hoettels told me this worked because Chevrolet engineers pulled the Chevy II four-cylinder’s bore spacing and main web layout directly from the small-block Chevy. Combining a 0.030-inch overbore of the stock 3.875-inch bore with the Chevy II’s 3.25-inch stroke, the SESCO four-cylinder came out to 155 ci. In addition to being less expensive than the Offy, the slant four engine allowed racers to use a ported version of the production iron fuelie small-block Chevy head along with its entire valvetrain, making replacement parts both easier and less expensive to find. The engine did require Hoettels to make his own mechanical fuel injection manifold with 2.1875-inch throttle bores that fed methanol to the 13.5:1 compression engine. Spinning this engine 7,500 to 7,800 rpm would generally deliver around 225 hp, which computes to 1.45 hp/ci.

The SESCO engine was dominant in Midgets with racers like Mel Kenyon and Gary Bettenhausen between 1972 and 1973, but it was eventually supplanted by the aluminum, flat, four-cylinder VW engine. Hoettels then built his own opposed four-cylinder he called the “two by four,” using the center of a small-block Chevy with his own cast-aluminum cylinder heads and the small-block’s Chevy valvetrain. SESCO also built a few four-cylinder Mopar Midget engines using the same half-a-V8 idea, this time basing his four- cylinder on the 410ci Mopar Sprint Car V8. Measuring 165 ci, it made around 300 to 310 hp spinning to 8,500 rpm. This is very close to an impressive 2 hp/ci. Complete versions of all of the SESCO Midget engines can be found at the Museum of American Speed.

If you find yourself anywhere near Lincoln, Nebraska, and you call yourself a gearhead, you need to set aside an entire day to take in the Museum of American Speed. There you can immerse yourself in Speedy Bill Smith’s amazing collection of circle-track race cars and the 300-odd race and development engines on display. Among the plethora of internal combustion artwork are powerplants you never knew existed. This makes the museum literally an automotive pilgrimage for fans of racing history—especially if you think the smell of combusted methanol is just this side of true cologne.

Slant Four - More Info

Museum of American Speed; Lincoln, NE; 402/323-3166; MuseumOfAmericanSpeed.com
SESCO; Colgate, WI: 262/628-4040



CC Quickies
Big Gulp

The barrels on this PC Carburetors Dominator look like they could swallow magazine editors whole.



It’s All in the V

Larry Webb; Knoxville, TN: Thanks for the in-depth article about camshafts and turbos. The information is very helpful. Being a bit of a geek, I tried to reproduce the numbers you posted for the three cam examples. As I understand, each has a 106-degree intake centerline and an LSA of 110 degrees. If I understand correctly, the measurement of LSA is the difference between the intake and the exhaust at max lift. Since the cam rotates at half the speed of the crank, this value must be multiplied by two to match the two revolutions of the crank. This being the case, I get the following formula:

Intake open = intake centerline – 1/2(intake duration); Exhaust Close = intake centerline – 2(LSA) + 1/2(exhaust duration).

Doing this for the first cam gives me this IO = 106 – 1/2(218), so IO = – 3 or 3 degrees before TDC. EO = 10 – 220 + 1/2(224), so EO = 108 or 1 degree before TDC. This gives an overlap of only 2 degrees as opposed to the 53 degrees in the article. Using the same calculation for the other cams results in the expected 12-degree difference but at values of 13-degree overlap and 25 degrees. What am I missing from my equation?

Jeff Smith: You have a basic understanding of the concept—it just needs to be fine-tuned a little. The intake and exhaust centerlines establish the positions of the lobes, but to determine the amount of actual overlap (both intake and exhaust valves are open at the same time), we must use the opening and closing points as listed on the cam card. In the following example, we’ll use a Comp XR281 hydraulic roller small-block Chevy camshaft (PN 08-432-8) using the published specs on the cam card. Assuming a 1.5:1 rocker ratio and a checking spec of 0.006 inch of tappet lift, the valves are actually already open 0.009 inch. Measuring the true valve opening and closing points would require measuring exactly when the valves actually open (which is hard to determine—do you start with 0.001 or 0.00001 inch?), but those points would still be proportional to our 0.006-inch tappet-lift figure. For the purpose of this discussion, we’ll use the 0.006-inch opening spec because it’s easier. Here’s the formula for determining actual valve overlap:

Overlap = exhaust closing + intake opening

As a further point of reference, the formula for determining the lobe- separation angle is:

LSA = intake lobe centerline + exhaust lobe centerline/2
LSA = 106 + 114 = 220
LSA = 220/2 = 110 cam degrees

The XR282 cam specs are:
Advertised duration: 282/288 degrees
Duration at 0.050: 230/236 degrees
Lift: 0.510/0.520 inch
Intake centerline: 106 degrees
Exhaust centerline: 114 degrees
Lobe-separation angle: 110 degrees

Lobe opening and closing points at 0.006 inch of tappet lift:
Intake opens: 35 BTDC
Exhaust opens: 78 ATDC
Intake closes: 67 ABDC
Exhaust closes: 30 BBDC

Overlap = EC (30) + IO (35) = 65 degrees of overlap at 0.006-inch tappet lift with a 110-degree lobe- separation angle

If we were to widen the lobe- separation angle from 110 degrees to 114 degrees, it would decrease the overlap, and the small triangle in the illustration representing valve overlap would get smaller. To widen the lobe-separation angle, we must advance the exhaust opening and closing points 2 degrees while retarding the intake opening and closing points by the same number. Narrowing the lobe-separation angle would require the opposite movements of the intake and exhaust lobes. Of course, you can also move just one lobe or the other; there are no requirements to move both lobes an equal or unequal number of degrees. One way to double-check your opening and closing points is by adding the numbers together (plus 180 degrees) to ensure the duration hasn’t changed. You’ve simply moved the opening and closing points without changing the duration.

Keep in mind that on a pushrod V8 like the small-block Chevy, the only way these numbers can be moved like this is by grinding a new camshaft. You can move the intake centerline relative to the piston, but this also moves the exhaust. This discussion is aimed at pushrod engines. Now if you had a dual overhead cam (DOHC) engine with separate intake and exhaust lobe camshafts, you could move the intake and/or exhaust lobes separately, which means you could adjust the amount of overlap. That’s exactly what the late-model, variable-valve-timing engines are doing. Factory engineers widen the LSA at idle and low engine speeds to ensure a smooth idle and then generally tighten the LSA by retarding the exhaust lobes. This way, they don’t affect the intake closing point because the intake lobe must be advanced to tighten the LSA, and that is counterproductive for top-end power. It may seem complicated at first, but if you study the relationships for a bit, it will all make sense. Assuming that I’ve explained it properly, of course!

More Info

Comp Cams; Memphis, TN; 800/999-0853; CompCams.com

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