About how much extra HP would each of these mods add? My mill is a Buick 215 variant (Aussie Leyland 4.4 litre) but as a rule of thumb just approx % on a SBC would give me an idea... headers bigger exhaust pipes over stock aftermarket air cleaner - 350 Holley instead of smaller stock stromberg mild cam higher compression pistons Yeah I know there ar heaps of variables but ballpark? My engine was rated at 195hp in the original owners manual Thanks Steve
Think of the engine as a chain of components that all need to be matched. If you just do one or two of those modifications, you won't see much of an increase in HP. However, by upgrading the cam, headers, intake/carb and compression, each one of which is designed to operate in the same RPM range, you'll see a MUCH greater improvement. Good examples of this matched-set approach are the "Performer" and Performer RPM" packages offered by Edelbrock. My only hands-on experience is with a SBC, but achieving ~1.1-1.2 hp/cubic inch is quite reasonable in a street package. If you want much more than that in a normally aspirated, OHV, 2-valve/cylinder engine, you'll prolly have to sacrifice some amount of streetability.
Gary is right. You can actually hurt your performance if you don't take a package deal approach. I'll try to elaborate on each part of the system. headers - Not necessary if no changes made in overall breathing of the engine, i.e. Air filter, carb, intake cam, heads, in that order. One restricts the next. smaller engines benefit less than larger ones. Save this until you find that you are approaching 1 hp per cubic inch, then keep the tubes small to maximize torque. bigger exhaust pipes over stock - these fall behind headers and will affect performance to a lesser degree. Changes in pipes would be an intermediate step to adding headers. aftermarket air cleaner - 1st and most basic. ***uming the other parts are matched, the right air filter can help add 3 to 5 %. 350 Holley instead of smaller stock stromberg - This would be next in line after air filter, but really depends on intake/cam/heads. You won't see big gains here unless the engine wants more air. 350 cfm is the right choice for a 270 c.i. engine doing cruiser duty. mild cam - Best bang for the buck, but must match intake and exhaust flow. higher compression pistons - Best match to the right cam, good power gains. Don't go here unless you really mean business. Smaller engines with more weight will tend to max the capability of todays lowsy fuel. Unless you are prepared to run premium all the time, it should be left alone. Putting numbers to to these is tough since they each depend on one another. If you did all of the above without getting carried away, you could pull 250 hp overall out of that mill. That's serious in a light car. Consider that the Chevy Camaros from about 1978 to 1981 only made about 185 hp in Z28 trim. That's a near 4000 pound car that many of us really enjoyed in high school. Good luck!
hi been thinking about this all day..what you are planning takes a low tech (sorry) motor and turns it into "sports tune "such as an alfa romeo ,saab or bmw compared to mums little blue datsun. you arent going to double your power with these mods in fact i reckon about 20/25 percent (IF your motor is good now other wise the rebore for the pistons may get you that ) BUT the power will come on differently hi comp pistons are a h***le nowdays as there is no lead to stop them pinging id only do it to win a race in a cl*** where the other guys werent doing it yet. americans dont seem to go in for extractors ( id put them on my lawnmower!)any cast iron lumps with restrictive 90 deg bends you can remove will increase the efficiency of the vehicle (think air pump) lately i have been putting webbers off old abandoned xf falcons (RECONDITIONED FIRST)on my holden sixes (real good vacuum secondary so fuel only pours in when you need it unlike the holley where it pours in at idle ) your old strommie is probly so worn out by now a new carb would be a huge bonus i use a holley inlet manifold (about 25 bucks for a holden at swap meet !)and a webber/holley adapter plate (also 25 bucks )leaves a lot of money for a cool air cleaner compared to buying a holley and keeping fuel up to it. suggested books to read before you start paying for parts "fourstroke tuning in theory and practice" alexander graham bell ( the aussie mechanic not the light bulb guy) and" how to hotrod your datsun "(trust me)best book on modifying stuff lots of general info,the concept of establishing a base line so you can measure these improvements , and a chapter about handling that will wake up a few other options for you. good luck have fun and remember this is a recreational activty!
hi again thats the v8 with the alloy block not the huge six in the p76 isnt it ? pop ! foot removed from mouth stick the holley on and keep your eyes peeled for a little(450 ?) 4 barrel with vac secondarys. is this in a p76,hotrod or a motor bike ? cheers
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