How much power do engine mods yield?
The same logic that leads them to cut off 80,000 lbs semi's.
The original poster of this thread asked about the viability of add-on hop up hardware such as increased carburetion, compression, exhaust capability and camshaft chacteristics as regards how effective they would be in a naturally-aspirated street engine. This discussion has, as online discussion threads are prone to do, drifted far afield of that, and, I am probably one of ther worst offenders when it comes to hijacking threads, with all my turbo-this and turbo-that prattle.
I would like to take this opportunity to apologize to the O.P. for that. It's probably VERY frustrating to ask a question and, in just a few posts, read the answers to a whole bevy of questions you DIDN'T ask, while NOT getting the answers to the ones you DID ask.... In his original post, he asked:
"I pulled this posting from the forum and was wondering how much extra power you're going to get with mods like this...
See if he will recurve the distributor for you too. That is a low cost high gain improvement.
I would do this in this order:
Cam and head work (dutra cam/shaved head)
Distributor recurve
2 bbl Supersix with the next $200-$300 you can invest.
Better throttle response and better pull up through the rpm's
Dual exhaust with the next $500-$600
Better mid to high rpm power
Is it a noticeable difference or just a slight bump up. My car is going to be a '65 Valiant 2 door and I'm wondering how much of a difference these mods would make along with adding a manual trans and better rear end gears...
I don't want to swap the engine, I really dig the slant 6!"
Let's start over and see if we can give him some answers to these questions:
I'll start...
To begin, the headwork is critically-important on a naturally-aspirated engine, but is unduly expensive because it's a cast iron head and has long ports that have places that are hard to get the grinder to. Bost is Uuusally in the neighborhood of $1,200.00-$1,400.00 for a profesiional job. But, the OEM valves and ports are restrictive on the stock head; it's pretty much a necessity if you are ever going to make a significant improvement in the engine's output. The additional, add-on parts like manifolds (both intake and exhaust,) will be seriously hamstrung if you try to make those improvements with a stock head.I think a 500cfm two bbl carb on a Super Six manifold would flow suffucuent air/fuel to feed a 225 that was redlined at 5,500 rpm, a reasonable redline with moderate aspirations (225 horsepower.) That's one horsepower per cubic inch... not anything to scoff at... The 2bbl setup should be reasonable in terms of money-spent...
I'll leave the rest of the mechanical parameters to someone more knowledgable than me... shouldn't be too hard to find dozens of guys like that , here,(and, probably, a few girls. too!)