How to Tune Your Carbureted Car for Conditions – Part 2

Wayne Scraba

12 Jul 2018

Click Here to Begin Slideshow In our last issue, we examined different ways to tune your car for varying conditions, particularly those we all experience in the shift from Spring to Summer. If you recall, we looked at carb jetting, ignition timing and valve lash as ways to pick up performance that goes missing when ambient temperatures rise and the relative humidity goes right off the scale. This time around, we’ll devote space to driving changes, as well as look at some other relatively simple changes you can make to your car to compensate for Mother Nature’s conditions. Check it out: Shift Points... Making a change in the shift points for your car can also prove positive, particularly when there are changes in barometric pressure. Huh – that sounds complex? Let’s look at this in a cut down manner: If the barometer drops, the engine becomes less efficient. Makes sense, but how do you compensate? Dropping barometer = increased RPM at the shift point. But keep in mind this is a seriously huge (and I mean huge) oversimplification. In the case of something basic such as a Powerglide-equipped car, it's all very easy. Try increasing the shift point by one hundred RPM increments. If the car picks up, add another 100 RPM to the shift point. Obviously, the sky isn’t the limit here - roughly 300-400 RPM more on the shift point is all most camshaft and valve springs will tolerate, but it should be enough to improve performance. If your car is equipped with something like a five-speed manual transmission, you might have to open a big can of worms. The car might like an extended shift point on the 1-2 shift and nothing more. On the other hand, it might like an extended shift point on the 2-3 and 3-4, but not on the 1-2 or 4-5. It all depends upon the car, and you can only find the perfect setup by experimenting. In the end, when you play with extended shift points, keep in mind that inertia is working in your favor, particularly when the engine is down on power. In this case, the engine is operating higher on the torque band, and it doesn't drop down as low (in terms of RPM) on the gear change. More Ways to Compensate… Although the big three tuning tools used to deal with weather include jetting, timing and valve lash, there are several other ways to deal with our pal Mother Nature. Keeping your fuel cool is one of them. And this doesn't only mean that you should keep the fuel cool while it's in the car (fuel line insulation, cool cans, etc.). If you’re a racer, think about how and where your store the race fuel you carry with you. Allowing your spare fuel jugs to bake in the afternoon sun isn’t such a “hot” idea. The best situation is to store fuel in a tightly sealed proper fuel jug that's kept in a cool spot (for example, inside the trailer or under an awning). One item you might want to consider is a carb spacer. Carburetor spacers accomplish a couple of things: They increase the plenum volume, and at the same time, good examples (particularly those manufactured from plastic or wood) tend to insulate the carburetor from the hot intake manifold. Remember, too, that because of the increased distance between the manifold plenum floor and the carburetor, the carburetor signal is weakened. When the signal is weakened, a larger jet or jets in the carburetor will likely be required. Carburetor spacers manufactured with four separate holes tend to recapture the velocity of the mixture stream, which has been lost when an open carburetor spacer is installed. That means more exit velocity in the mixture stream creates a stronger carburetor signal than that found with an open spacer. Typically jetting will still have to be increased when a four-hole spacer is used, but not as much as with an open spacer. Rear axle and transmission gear swaps are beyond the scope of this article, but for some combinations, they can prove beneficial when the time comes to deal with the weather. In some examples, a car just “likes” more rear axle gear in the heat (and/or steeper gearbox ratios). That's why you'll often find drag racers from the East will typically use a little bit more rear axle ratio in their class cars in comparison to similar (identical) race cars campaigned almost exclusively in the West. What’s with that? It’s easy to answer: The high summer humidity experienced east of the Rockies plague racecars. In the end, don’t ignore little things when dealing with heat. Carburetor heat shields are still viable pieces. The same applies to lifter valley trays that help to isolate the bottom of the intake from hot oil (working somewhat like an air-gap intake). Blocked intake heat risers are helpful too. Wrapping carburetor fuel lines with air conditioning hose insulation is an easy fix. Coated headers often allow engines to run cooler. If you’re a racer, consider back-flushing the engine. It’s much more common in some parts of the country than it is in others. The reason is engine temperature. Some cars respond very well to a consistent intake manifold temperature. That's why some racers routinely ice the manifold. Others don't. Some racers even concern themselves with car color (obviously white is cooler than black). Others don't worry about it. The bottom line here is to do everything you can to get rid of excess heat - engine generated or otherwise. We all know we can’t control the weather. Mother Nature does that. However, you can offset the effects of weather with a series of simple changes, tuning and otherwise. And just a final reminder: Be vigilant with spark plugs when making tuning changes. There’s a fine line between performance and detonation.

How to Tune Your Carbureted Car for Conditions - Part 2 — Click Here to Begin Slideshow In our last issue, we examined different ways to tune your car for varying conditions, particularly those we all experience in the shift from Spring to Summer. If you recall, we looked at carb jetting, ignition timing and valve lash as ways to pick up performance that goes missing when ambient temperatures rise and the relative humidity goes right off the scale. This time around, we’ll devote space to driving changes, as well as look at some other relatively simple changes you can make to your car to compensate for Mother Nature’s conditions. Check it out: Shift Points... Making a change in the shift points for your car can also prove positive, particularly when there are changes in barometric pressure. Huh – that sounds complex? Let’s look at this in a cut down manner: If the barometer drops, the engine becomes less efficient. Makes sense, but how do you compensate? Dropping barometer = increased RPM at the shift point. But keep in mind this is a seriously huge (and I mean huge) oversimplification. In the case of something basic such as a Powerglide-equipped car, it's all very easy. Try increasing the shift point by one hundred RPM increments. If the car picks up, add another 100 RPM to the shift point. Obviously, the sky isn’t the limit here - roughly 300-400 RPM more on the shift point is all most camshaft and valve springs will tolerate, but it should be enough to improve performance. If your car is equipped with something like a five-speed manual transmission, you might have to open a big can of worms. The car might like an extended shift point on the 1-2 shift and nothing more. On the other hand, it might like an extended shift point on the 2-3 and 3-4, but not on the 1-2 or 4-5. It all depends upon the car, and you can only find the perfect setup by experimenting. In the end, when you play with extended shift points, keep in mind that inertia is working in your favor, particularly when the engine is down on power. In this case, the engine is operating higher on the torque band, and it doesn't drop down as low (in terms of RPM) on the gear change. More Ways to Compensate… Although the big three tuning tools used to deal with weather include jetting, timing and valve lash, there are several other ways to deal with our pal Mother Nature. Keeping your fuel cool is one of them. And this doesn't only mean that you should keep the fuel cool while it's in the car (fuel line insulation, cool cans, etc.). If you’re a racer, think about how and where your store the race fuel you carry with you. Allowing your spare fuel jugs to bake in the afternoon sun isn’t such a “hot” idea. The best situation is to store fuel in a tightly sealed proper fuel jug that's kept in a cool spot (for example, inside the trailer or under an awning). One item you might want to consider is a carb spacer. Carburetor spacers accomplish a couple of things: They increase the plenum volume, and at the same time, good examples (particularly those manufactured from plastic or wood) tend to insulate the carburetor from the hot intake manifold. Remember, too, that because of the increased distance between the manifold plenum floor and the carburetor, the carburetor signal is weakened. When the signal is weakened, a larger jet or jets in the carburetor will likely be required. Carburetor spacers manufactured with four separate holes tend to recapture the velocity of the mixture stream, which has been lost when an open carburetor spacer is installed. That means more exit velocity in the mixture stream creates a stronger carburetor signal than that found with an open spacer. Typically jetting will still have to be increased when a four-hole spacer is used, but not as much as with an open spacer. Rear axle and transmission gear swaps are beyond the scope of this article, but for some combinations, they can prove beneficial when the time comes to deal with the weather. In some examples, a car just “likes” more rear axle gear in the heat (and/or steeper gearbox ratios). That's why you'll often find drag racers from the East will typically use a little bit more rear axle ratio in their class cars in comparison to similar (identical) race cars campaigned almost exclusively in the West. What’s with that? It’s easy to answer: The high summer humidity experienced east of the Rockies plague racecars. In the end, don’t ignore little things when dealing with heat. Carburetor heat shields are still viable pieces. The same applies to lifter valley trays that help to isolate the bottom of the intake from hot oil (working somewhat like an air-gap intake). Blocked intake heat risers are helpful too. Wrapping carburetor fuel lines with air conditioning hose insulation is an easy fix. Coated headers often allow engines to run cooler. If you’re a racer, consider back-flushing the engine. It’s much more common in some parts of the country than it is in others. The reason is engine temperature. Some cars respond very well to a consistent intake manifold temperature. That's why some racers routinely ice the manifold. Others don't. Some racers even concern themselves with car color (obviously white is cooler than black). Others don't worry about it. The bottom line here is to do everything you can to get rid of excess heat - engine generated or otherwise. We all know we can’t control the weather. Mother Nature does that. However, you can offset the effects of weather with a series of simple changes, tuning and otherwise. And just a final reminder: Be vigilant with spark plugs when making tuning changes. There’s a fine line between performance and detonation.

A change in shift points can go a long way toward improving performance of your car when the weather changes. The text offers more info.

Carb spacers help in several ways: Not only do they provide another tuning tool (see the text), they also help to isolate the carburetor from a hot intake manifold.

Don’t discount old-school ideas such as carburetor heat shields, insulated fuel lines and other ideas to keep the engine cool.

Note that the fuel jug is under the awning alongside the shady side of the trailer.

Keeping your fuel cool is important!

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