"Modified"

I made some nasty comments in my F&F blog about modifications to imports.  I suppose it might be more appropriate to revisit the issue in general.

As I mentioned earlier, traditionally the cars most likely to be modified were Firebirds, Camaros, Mustangs, etc., but people have been modifying cars since they were invented: the Model T has aftermarket parts listed for it in 1920s Sears and Montgomery Ward catalogs.

 Here are some of the more popular modifications.

 Intake.  The theory is that cars make power by adding fuel to air and igniting it correctly.  Since the fuel added is dependent on the amount of air, and there’s only so much spark you can give it, ultimately the way to maximize power is to maximize air.  The crudest and most obvious way is simply displacement: a larger engine.  Leaving aside complete engine swaps, and assuming you simply want to optimize the performance of the engine already sitting under the hood of your car, here is how you do it.

            Performance intake manifolds and K&N air filters are the most popular modifications.  The former are usually aluminum and the aftermarket manufacturers claim to use CAD/CAM designing to ensure better airflow and better performance.   So they claim.  There are several catches to this.

            First, the intake system is only as efficient as its least restrictive element.  Opening up a part which was not the bottleneck in the first place will have no effect.

            Second, depending on the compression ratio and cylinder heads, the engine can only ingest a limited quantity of air.  Opening the intake larger than that not only won’t help, but if it decreases the velocity of the incoming air, will actually hurt performance.  This is why K&N filters, despite their claims of higher air flow than the stock air filter, usually don’t deliver noticeable performance gains because the engine doesn’t need any more air than the stock filter can deliver.

            Having said that, I do have a TPIS Big Mouth lower intake and SLP runners, plus an SLP throttle body with an airfoil.  I can’t say I’ve noticed a huge difference with the Big Mouth (which is Edelbrock’s model ported out a bit more); the main benefit is theoretically increased top end.  The OEM TPI baseplate was designed for a 305, and I have a 350.  Whether that makes a difference at streetable RPMs is something I’ve yet to hear explained.

 Camshaft.  Rodders love to replace the camshaft, which is what controls how the valves open and close – how far open (lift) and for how long (duration).  A hot cam gives the car a nasty, lopey idle – close to what we think of when we hear a Harley engine - but kills the low-end torque.  I haven’t replaced my cam yet, though I have the new cam in my possession (Crane with 214/220 @ 050” duration).  A bad cam will make the car fail emissions and make it unpleasant to drive on the street, a high price to pay for a lopey idle.

 Carburetor/chip.  Older cars can sometimes see a benefit with a carb change, mainly 2 barrel models upgraded to 4 barrels with the appropriate intake manifold.  Notice that NASCAR still uses ONE carburetor, so a dual quad on a street car may well be overkill; best to use a reasonably sized and properly tuned 4 barrel carburetor (Rochester Quadrajet, Holley, Carter AFB/Edelbrock).   Late model EFI cars can benefit from a performance chip; these remap the fuel curve for more power and a more aggressive ignition curve while still keeping emissions compliance.  I replaced the chip on my base Firebird (5.0L TBI) and my Formula has the SLP chip for its 5.7L TPI V8.

            I found out the hard way that TPI systems prefer working injectors and fuel pressure regulator, which you would think would be common sense.  I was thrown off by a speed shop and two dealers claiming my engine was worn out.  Another speed shop correctly diagnosed the fuel system as the real problem, and now that these parts have been replaced – without a new engine – the car passed emissions and accelerates as it hasn’t done in years.

 Cylinder Heads.  Expensive, but since this is the heart of the intake/exhaust system (along with the camshaft) it pays to pay attention here.  I have yet to be able to afford aftermarket heads, or even to have my cast iron heads ported with a 3 angle valve job, but I’d definitely upgrade when the money allowed. 

 Ignition.  Here is one mod that is way overrated.  The aftermarket companies claim huge horsepower gains, when the reality is that even their heavily touted systems really give practically no benefit over the OEM system.  The most that can be said is that a properly set up ignition system – plugs, wires, cap & rotor – are essential, but the difference between a properly set up OEM system vs. an aftermarket system is almost impossible to tell.

 Exhaust.  The flip side of the intake is the exhaust.  This usually means headers and mufflers, with a catalytic converter (cat) in between on any car made from 1975 onward.  By now they’ve developed cats which flow enough not to compromise performance, so there’s really no excuse for removing the cat and losing emissions compliance.  The muffler has no emissions role and simply reduces the sound.  A good muffler can improve performance and give a bad-ass sound, so this is one area where the money is well spent.  The main caveat here is that a muffler that’s too loud will get annoying (particularly for female passengers) and attract unwanted police attention.

 Transmission.  On an automatic, the best mods are shift kits which bump up the shift points and firm up the shifts.  A firmer shift improves the longevity of the transmission, and may even cause the tires to “chirp” on gear changes.  A properly modified A/T can frequently push the car to competitive performance with a similarly-equipped manual transmission car.  Also, a higher stall converter can improve the car’s speed if picked correctly.  Of course, you can replace the transmission itself for an upgrade: swap out your Turbo 350 for a 400, your C4 for a C6, your Torqueflite 904 for a 727, or replace any of these with the modern, electronically controlled, overdrive variants for better fuel economy and reliability with no loss in torque capacity or performance.

            For manual transmission cars, the better mods are better clutches and even full trans upgrades.  Although I’ve always preferred and owned automatic cars, my choice for a manual would be a Richmond Six Speed.  This has a 1:1 fifth gear with the sixth gear being overdrive. 

 Rear Gears.  Stock cars tend to have rear axle ratios in the neighborhood of 2.73-3.55.  Some rare cars have 4.11 or 4.33 gears from the factory.  My own Formula came with 3.23 gears in the back, which I upgraded to 3.73.  A higher numerical gear ratio will improve the low-end acceleration but limit the top end, but since we never drive at 120 mph we’d never notice the latter part of the tradeoff but certainly notice the former part, i.e. the benefit.  Warning:  Richmond gears are VERY noisy – and annoyingly so.  I went with Precision Gears, which were much quieter.  When you replace the rear gears you definitely have to replace the speedometer gears, or the speedometer will be way off, like 10-15 mph.

 Suspension.  The best mods here are upgrading shocks to performance varieties and adding sway bars to cars that didn’t already have them.  Stiffer springs usually don’t help nearly enough to justify the far harsher ride quality they inflict.  A car that handles well is more fun to drive, and suspension mods have no emissions impact.  I even put a rear bar on my Neon – Neons have excellent aftermarket support as they were popular in some SCCA classes – and it did much better.

 Wheels/Tires.  Usually this means larger wheels with lower aspect ratios.  I was lucky that my Formula already had 16x8” wheels fitting a 245/50ZR16 tire.  The OEM Gatorbacks were never that good, and over the years I’ve upgraded to Dunlop SP4000s, Goodyear Eagle F1 GS, and most recently Firestone Firehawk Indy 500s.  The tire selection in this size has shrunk dramatically since I bought my car back in 1995. 

            Do NOT cheap out on tires.  Crappy tires are terrible: the car feels uncontrollable in the rain, a real terror to drive.  Good tires grip the road and keep the car ON the road when it rains.  Pay the money to get the good tires.  It’s worth it.

 Brakes.  No one really cares about this much, and I haven’t upgraded my brakes except to slotted rotors in front and keeping with OEM GM pads on all 4 wheels, which are MUCH quieter than aftermarket pads.  Here’s one area I leave well enough alone and stick with GM stuff.  Besides which, I haven’t modified the car enough to make an upgrade necessary.

 Nitrous.  Made famous in the F&F movies.  Nitrous oxide – yes, the same stuff we used for general anesthesia back in the 70s – gets injected with fuel and gives a huge bump in HP…while the bottle lasts, activated at wide open throttle, and IF the engine doesn’t grenade in the process.  Hot Rod (or was it Car Craft) even did an article where they juiced a stock engine just to see how much it could endure before blowing up.  Nitrous kits are far cheaper than superchargers or turbos, but have those important drawbacks. 

 Supercharger/Turbocharger.  As mentioned earlier, the engine can only take in so much air by itself.  To add more air than the pistons can draw in on their own, an air pump can be used.  Either it’s run off a belt from the crank pulley – a supercharger – or uses exhaust gases to spool a turbine, which is linked to another turbine on the intake side, i.e. a turbocharger.  Turbos need a bit of time for the gases to spool up the turbine – turbo lag – while superchargers come on right away.  Centrifugal superchargers can fit under the hood, whereas Roots style typically tend to stick way up out of the hood – although in recent years they’ve begun designing extremely low-profile models which will fit under the stock hood.  None of these kits are cheap, but they do make some serious horsepower.

 Stroker Kits.  These replace the stock crankshaft with one with a larger stroke, which typically increases torque while limiting top RPM.  The kit includes new pistons, the full reciprocating assembly, i.e. crank, connecting rods, pistons, and piston rings.  One of the more popular stroker kits is a 383 combo for the 350 small block Chevy V8 – the crank from a 400 in a 350 block.

 Crate Engines.  These range from short blocks (the block and reciprocating assembly minus the heads), long block (same, but with heads), all the way to turnkey motors ready to be dropped into a car.  The ZZ4 has been a popular Chevy 350 crate engine, and GM has upgraded its 454 HO (LS6) with 502, 540, and 572 cubic inch big blocks, plus crate versions of highly sophisticated late model EFI engines; as you can imagine, they aren’t cheap.  Mopar Performance has reissued the 426 Hemi as a crate engine, and upped the ante with a 528 cubic inch version of the same engine.  The V10 Viper engine is also available in crate form for those with a wallet large enough to pay for it.

 Top Aftermarket Companies.  The most popular are:  Edelbrock (intakes, cylinder heads, carbs, cams, and more recently crate engines and suspension products), Crane (camshafts), Lunati (cams, stroker kits), Holley (carburetors), AFR (cylinder heads), Hooker (headers), Flowmaster (exhaust), SLP (late model EFI cars), Lingenfelter (late model EFI cars), MSD (ignition), Paxton & Vortech (superchargers), Gale Banks (turbo), NOS (nitrous), B&M (automatic transmissions), Richmond Gear (rear gears and manual transmissions) just to name a few.   GM Performance Parts, Ford Motorsports, and Mopar Performance also make aftermarket parts for their brands and a wide and impressive array of crate engines.

            While they can be very expensive, crate engines come with extended warranties, are put together intelligently with mutually compatible parts for a specific intended purpose (stock replacement, high performance street/strip, or full race), and are brand new.  When replacing like with like (e.g. one-piece rear main seal late model small block Chevy V8) it’s simply a matter of pulling one engine and replacing it with another.

 Warnings.  By now we’ve learned to take the aftermarket suppliers’ claims of horsepower gains with a grain of salt.  They typically diss the OEM engineers as incompetent hacks diligently trading off HP to satisfy federal emissions and fuel economy standards, whereas their own wizards know how to unlock obscene amounts of horsepower.  The reality is that the car companies hire smart engineering students and spend $$$ trying to figure out the best system before an engine is even stuffed into a prototype, much less put into a production car sold to the public.  I’ve read an article which showed absolutely no HP gains from various aftermarket intake manifolds over the OEM Pontiac 4 barrel cast iron intake; the stock Pontiac cam grinds, all the way up to the Ram Air IV cam, were likewise intelligently designed and do well when properly selected.

            The major problem is that the fiduciaries we “trust” - Hot Rod, Car Craft, and the local speed shop – all have a vested interest in maintaining the fiction that the aftermarket products are better than what came on your car from the factory.  The car magazines can’t afford to alienate their advertisers; their installations invariably occur with no snafus or missing parts, and the aftermarket part ALWAYS performs as promised, which we know almost never happens in real life.  Unfortunately, there is no Consumer Reports for the automobile aftermarket.  The speed shop makes its money selling you these parts and installing them for you, so they naturally want to sell you the most expensive upgrade, e.g. a custom-built, balanced and blueprinted engine, when your stock engine just needs new injectors and a fuel pressure regulator and it will be on its way.