Roush 427 IR

[olddog]

Your choice of engine manufacture has a big name in the performance world, there is no doubt. There have been many threads on this site with tales of woe. Mostly oil burning. Mostly valve seals. They have been less than eager to make these problems right, based on these threads, therefore I have concluded they are not customer oriented. To be fair, I do not recall any problems with assembly. The problem's all seem to be they choose to use a 3rd party part that wasn't up to par.

The top notch small builders seem to only use quality parts and stand behind their engines a lot better. I think better engines can be purchased for the same or less money.

As for carbs verses EFI, first not all carbs nor all EFI are alike. In the older crowds eyes (who grew up with carbs and do not understand EFI) carbs are the pick. Simpler easier seem to be the opinions. The violent acceleration that a Cobra is capable of can slosh gas in the fuel bowls causing issues. Finding mechanics that have worked on carbs is going to be near impossible in the next 20 yrs. They are retiring and thinning out right now.

Some of the aftermarket EFI is geared toward drag racing. They run great at WOT. Drive-ability not so much. Throttle plate injectors are a step up over a carb, but not a lot better. IMO multi port injection is best.

EFI strategies are alpha-N, Speed Density, and Mass Air Flow. Alpha-N is very basic it mostly uses the throttle position and RPM to calculate everything. It is not very accurate, but it is fast. It also can always make a decent guess of what the engine needs under rapidly changing engine conditions. It is usually included in Speed Density and Mass Air Flow systems, as a sanity check and to handle rapid changes.

Speed Density uses a map sensor and throttle position to calculate and estimate what the mass flow of air into the engine is. On factory engines with mild cams this is pretty darn good. However you change anything and it needs re-tuned. Put a radical cam in it and it is very difficult to get a decent tune.

Mass Air Flow is the best technology, at least in theory. It actually measures the mass of the air flow into the engine directly with a heated wire. It doesn't matter what you change short of cid as long as you don't impact the accuracy of the mass meter. This is in my opinion the best strategy.

However when you get to very radical cams, you have all types of ugly things happening. Reversion flow into the intake, for one. The mass meter doesn't know which way air is flowing and can measure it twice (I believe there is a new meter now that addresses this). Exhaust gasses can carbon up the mass meter wires. Therefore there needs to be enough pipe to even out these pulses.

During the overlap (both valves open) un-burned air fuel can go into the exhaust. If it is not burned in the exhaust, it causes the O2 sensor to falsely read lean.

The most important improvement of EFI is a better control of timing. Timing is what makes the power. It also allows the CPU to better control the idle speed using timing. By setting the timing about half way to maximum torque at an idle, the CPU can pull timing out to slow the rpm or add more timing in to increase the rpm. At 600 rpm timing can respond in 10 milliseconds.

To sum this all up, a good EFI properly designed for the engine and properly tuned is much more accurate on fuel delivery, timing control, and idle control. You will never have to fight vapor lock, fuel bowls boiling over, and all the issues that come with a carb. EFI starts better, where carbs washes your cylinders down with gasoline wearing rings and contaminating oil. Hands down EFI beats a carb when it comes to drive-ability.

Is EFI worth the cost? Maybe not. Most of these cars do not have enough miles put on them to value a lot of this. However if you like the drive-ability improvements, it may be worth it to you.