Ask Away! with Jeff Smith: Engine-Building Strategies for 700 HP in a ’71 El Camino

LSA engine swap photo


I’m asking this for a friend and I know you will have suggestions. He’s building a ’71 El Camino and has decided on an LS swap. He wants 650-700 hp with an automatic. The LS9 is 635hp to start but no auto is recommended. As a crate engine, the LS9 would cost about $21,000 plus the transmission and harness. The next idea is an LS7 for about $13,000 plus trans and harness. What would be your suggestion for a cost-effective way to get to 650-700 hp? What about an LS3 for about $12,000, plus trans and harness and throw on a Magnuson supercharger for about $6,000? Would that be a more cost-effective way to go? – R.L.


Jeff Smith: Let’s first look at why he thinks he needs 700 hp in an El Camino.

It will be near impossible to plant this kind of power with street tires and especially in an El Camino since there is minimal weight over the rear tires.

Even at 500 hp, this would be difficult—at 700 hp, he will likely need slicks just to keep the tires from spinning at any speed below 60 mph.

This will make the car extremely difficult to drive.

If it has $10,000 worth of suspension, perhaps traction will be slightly better.

But with a near-stock suspension it will be a dangerous handful unless he’s a very skilled driver. Emphasis here on driver skill.

Much of this horsepower push is coming from the magazines. They rarely talk about 500 hp engines anymore. The problem with 650- to 700-hp engines is there are parallel issues which are never discussed, yet are critical to creating reliable performance.

You mentioned transmissions. Let’s limit our discussion to automatics since they are easier to drive. At 750 hp, we are at the top of the heap for a 4L75E from GM, and it’s probably better to go with a 4L80E. This is a big transmission, but in a ’71 probably won’t require floor pan mods.

A strong 4L80E will cost between $3,500 and $4,000 and will then demand a custom driveshaft and something stronger than an 8.5-inch 10-bolt rear end.

We’re looking at another $3,500 for all those pieces. And don’t forget that you will need some monster tires to hook all that power.

The best way to get to that power level is probably with a supercharger—either a centrifugal like a Vortech, or a positive displacement blower like the Magunson you mentioned. These add-on kits will also drive up the price of the entire package. If we include the previously discussed drivetrain parts—we’re looking at numbers approaching $20,000.

Don’t Sleep on the Supercharged LSA

6.2L supercharged LSA


One supercharged Chevrolet Performance package I like is the one that garners very little attention. The LSA (PN 19331507) is the engine used in the older supercharged Cadillac CTS-V before the conversion to the LT4. The LSA is a docile package, yet delivers excellent power at 550 hp and is essentially an LS3 with different heads, a small 1.9L TVS blower, and an ultra-conservative cam.

This engine never makes less than 400 foot-pounds of torque from 2,000 to 6,300 rpm with a peak torque of 551 ft.-lbs.

That would feel like a mild big-block in the car and yet is only 6.2L or 376 c.i.d. Remember, these are conservative horsepower ratings—at least 5 percent under the normal hot-rod-style correction factor.

Adding 5 percent means closer to 575 hp.

Add headers and a mild tune (the engines are always soft on timing and rich in the air-fuel calibration) and the power could jump to 625 hp. This is a far better choice in terms of power per dollar.

The engine is still expensive at slightly less than $12,000 and it will need additional parts.

Among the required add-ons is a controller kit as well as a complete intercooler since it is plumbed to employ this advantage. That will mean an external reservoir, lines, and a separate radiator. All this keeps the inlet air temperature manageable so that the engine doesn’t detonate.

It’s a chore to find a spot for all the plumbing although a ’71 El Camino probably has the room. But much of that real estate will be eaten up pretty quickly when you start adding an ECU, intercooler, and all that plumbing. Plus, you will also need a complete accessory drive, which GM also can supply and is highly recommended

Consider a Junkyard Pull for the Most Cost-Effective Build

LS junkyard engine pull

(Image/Hot Rod)

For a slightly different approach, I just finished a junkyard 6.0L truck engine for Car Craft Magazine with a small cam (it idles at 14 inches of vacuum), mildly ported 5.3L heads, and EFI using a stock Trailblazer SS intake.

That engine made 496 hp at roughly 6,000 rpm.

Duplicating this package probably wouldn’t cost more than $6,000 including the Holley HP ECU.

With better heads and slightly more camshaft, we think this engine will make 550 hp but the price begins to climb with better parts.

NOTE: LS car engines and LS-based Vortec truck engines are abundant in scrapyards everywhere, and a good low-cost option for LS swap projects. You can use these articles to help you locate the engine you want to work with.

If your friend wants a new engine with a warranty, he can’t go wrong with an LS3.

Put headers and a mild cam in it and that will make close to 550 hp and I’ll bet he will be thrilled—unless he is used to more power. If his previous ride had less than 450 hp—the added power will astonish him. It’s not a bad idea to go conservative at first and then build from there.

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One Comment

  1. FWIW…as a 70 ElCamino owner I wish to take issue with your statement about El Camino’s having minimal weight over the rear tires, if you would check the specs, El Camino’s actually have a little more weight over the rear than the coupe. I believe it is between 20 and 40 lbs rear weight bias for the El Camino, not a whole lot, but I wish to lay to rest a common misconception. Thank you

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