View Full Version : more Horsepower for least $$$$ ?

02-18-2007, 01:29 PM
What makes the most extra HP ?

say you are stuck with a stock production lower end, stock crank , rods , pictons ,

you need to use a stock head, stock valve size,

What gives you the most bang for ther buck ?

header exhaust ?
cam ?
bigger carb / manifold like a side draft weber
porting the head ?

Just looking for ideas , not for any specific motor

thank for your thoughts


02-18-2007, 02:03 PM
Gasket-match Dremel porting is almost free, although time consuming. The time spent can be fairly rewarding if you know what you're doing.

02-18-2007, 02:19 PM
I've heard that a lightened flywheel gives you the most for the least.

Michael Oritt
02-18-2007, 05:27 PM

My friend Dave Porter in Albuquerque has a FIAT/OSCA race car that he was selling as of a few months ago. You can contact him at: frogeye@swcp.com or contact Taos Garage Annex (sorry, don't have number).

02-18-2007, 08:03 PM
A new cam, combined with rejetting the carbs and removing any smog controls can result in up to a 50% gain. On my SCCA ITS TR8, which has to keep all of the stock internals but allows many external mods, Ive gone from 137 stock HP to around 185. On a TR8 street car, you can install a four barrel carb, headers, and a cam and get 200HP very easily. The stock motor was absolutely strangled with emission controls. It's all about getting the engine to breath easier.

02-18-2007, 08:56 PM
Hp is an easy thing to make....
Just whack 1/10 inch off your head.

Keeping your engine in one piece, after you do that, is the tricky part. /bcforum/images/%%GRAEMLIN_URL%%/grin.gif

02-18-2007, 09:08 PM
This is virtually impossible to say what will make more power. All vehicles are different with different bottlenecks in different places. The total package must be kept in mind when building a motor. Most people don't seem to realize this. If you make the exhaust less restrictive, you now need a less restrictive intake to take advantage of this. The cylinder head can now be modified to take advantage of the new found breathing capabilities. The camshaft should be the last thing anyone changes on an engine, as its specs are dependent on everything else.

I'll echo what has been said above. If your car has emmision equipment, remove it (at least on older cars). Your car will then stand to make more power

I totally agree on the lighter flywheel.

You can also look at reducing parasitic drag. Get rid of that mechanical fan and go electric. If your car has power steering and / or A/C; ditch it! (make sure to have your A/C gas drained at a certfied dealer; help the environment a little.)

Also just try to reduce underhood tempatures. Getting cool air to the intake will do much.

02-18-2007, 11:44 PM

My friend Dave Porter in Albuquerque has a FIAT/OSCA race car that he was selling as of a few months ago. You can contact him at: frogeye@swcp.com or contact Taos Garage Annex (sorry, don't have number).


02-21-2007, 06:43 AM
There's no blanket "this works best" for all engines statement that can be made. Be cautious of those selling snakeoils with this claim.

But there are some general rules of thumb for performance that you can follow. The most basic being that an engine is an air pump, and anything that restricts its ability to pump air hurts performance.

Most cars restrict performance on the exhaust in pursuit of quiet and cost. Small diameter pipes and cheap mufflers usually restrict flow. Poorly designed exhaust manifolds can really hurt engine performance and efficiency.

On the intake side, many older cars have very restrictive inlet snorkels, and draw hot low pressure air from the engine bay. Cooler denser air drawn freely into an engine helps performance.

Camshafts define your engines personality. You balance peak numbers with usability. The more radical the lump stick, the harder it is to live with, but you get a higher peak number...usually...if you set the rest of the engine up to use the radical camshaft.

Porting and polishing are all about flow. Most stock engines are adequate on this department. A good valve job including a 3 angle or more cutting does gain you some flow. But all by itself, you wouldn't feel it in the seat of your pants. Narrowing down valve stems and such doesn't really help an essentially stock or even well warmed over engine. And it's expensive. This sort of work really shouldn't be done until the rest of the engine calls for it.

Compression increases are usually good, but beware of accidently restricting the flow through the combustion chamber! Many times you will do better to use a higher dome piston than to shave the head.

The next generic statement would be about fuel mixture, get it right. Many a carburetor upgrade merely has to do with getting the fuel mixture more correct, and nothing to do with enhanced flow. The SU doesn't flow any better than the ZS for example, but it's easier to get the fuel mixture right for performance with the SU for most folk.

And lastly is the tuning of the ignition timing. From where it starts, to where it ends, and how it gets from one to the other. Many an LBC has a good bit of power to be found here, particularly the later smogged ones. Merely advancing the base timing can gain appreciable performance increases, for free.

Simon TR4a
02-21-2007, 03:06 PM
I agree with Monkeywrench and Trapper that what gives the best result for the least money will vary from one car to another.
Most LBCs have a narrow bore to stroke ratio, which restricts valve sizes, so unshrouding the valves is worthwhile and just takes a bit of patience.

Being able to run the engine to higher revs is a sure way to increase power, so the ultimate limitation will be the stock bottom end, but for street use the improvements suggested will give a useful increase.

tony barnhill
02-24-2007, 07:23 AM
Boy, we need Hap to chime in on this one!

02-24-2007, 07:32 AM
Tony, I think Hap is staying out of it for the same reason I am! /bcforum/images/%%GRAEMLIN_URL%%/wall.gif

02-24-2007, 08:33 PM
The original question was what mod makes the most power.

This can't be answered except for specific cases and so it is a meaningless question. As a couple of people have pointed out, various engines have different bottlenecks.

02-24-2007, 11:43 PM
Dollar for horsepower, it's hard to be some good ol' NO2 /bcforum/images/%%GRAEMLIN_URL%%/driving.gif

(don't do it though, unless you like blowing motors up)

02-26-2007, 12:17 AM
If you believe the claims made by all those additive manufacturers, about $25 dollars worth of selected "miracle" elixirs should net a good extra 25-30 HP!
add some racing stripes and you will gain an additional 10 mph! /bcforum/images/%%GRAEMLIN_URL%%/jester.gif

02-26-2007, 05:43 PM
Hi all.....

I know there is no "real" answer to this question , but its a good discussion to have ,

I know with old VWs they strangled the motor so it would not rev , small carbs and narrow intakes,

Putting a 2 barrel carb and manifold and an extractor exhaust really changed those motors.....


02-27-2007, 11:47 AM
all the above is true. you have to look at YOUR package and find the largest bottle-neck. Your biggest bottle-neck is where you start.what we do here in race land is build a package of componenets that complements each other with a specific goal. ie we pick our rev range, torque, and hp range we need or want. by this we determine port sizes, valve sizes, cam, headers and exhaust, intake volume and length, strngth of components required and weights required for life span. more revs,more hp, more torque = less life.
more strength with less weight=more dollars . too much strength with more weight=less performance. its all a balancing act. too much power with too little strength=blown up motor.
look for a balanced package of components. an unbalanced package such as one thing too big for the rest of the package will COST power.

02-27-2007, 01:48 PM
That VW example you gave is a good example of air pump efficiency.

But the need varies tremendously, even in seemingly identical scenarios. The mid 80's Toyota trucks for example. 22R series engine. With a carburetor, they had a lousy exhaust manifold. So a header helped tremendously. If you had a fuel injected model, it came from the factory with an excellent exhaust manifold, so a header didn't help it at all. Both had tremendously restrictive mufflers, so both gained well from a muffler upgrade.

Ignition timing is another example. Bumping the ignition timing on that Toyota engine gains you nothing in power. Bump the ignition timing on a late Spitfire engine gains you tremendous amounts of power. Again, it's engine and vehicle specific.