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Old 01-02-2003, 01:39 AM
E.T. divided by $ spent= Speed
 
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Post Stock eliminator

I've been thinking for a long time about making a legal stock eliminator car outta mine.I haven't done any figureing or evan looked to see if my car is a listed car or not,but I've always liked class racing and am interested.
My car came with a 305 2bbl as the "Big motor".Now from what I know and have read,the rules basically restrict engine mods to headers,any ignition,any cam duration with stock lift,blueprinting and balancing(???).What kinda times do ya think would be possible with such limited mods on this little motor,assuming a optimal rear gear and converter.
Pretty much if I'm right I could be run heads up against another car in the same HP-weight evan though the other car came factory with say a 350 4bbl or evan larger(which would respond better to these limited mods than my little 305 2bbl).
Now befor someone says a backyard mech can't compete with these big dollar guys,your probably right but it seems it would be alot more fun to try than just plain old brackets.I just love the whole idea.Anyway its a long way off evan if I do decide to go the route.I'll have to find a #s block and heads.

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Old 01-02-2003, 02:18 AM
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Here is a copy paste compilation of whats involved..

Rules.
To set the scene lets first look at the basic rules these cars must be built to. Essentially they are stock but with a number of liberal area's. In the main the air filter case is free but cannot be routed to pick up air at a significantly different location to stock. The carb/fuel injection and manifold must be stock and in no way modified other than what ever it takes to calibrate the mixture.

The heads for a particular motor are listed and must be stock other than machining to raise the CR. The valves, springs, rockers etc must be stock appearing and the valve lift no more than that of the production vehicle. The duration of the cam however is free but it's type, solid or hydraulic, is not. Exhaust is also free. Such things as pistons, rods crank etc must be of stock origin, or an approved, stock pattern replacement.

A stock origin or an approved, stock pattern replacement also goes for much of the transmission and suspension. Shocks, as long as they bolt up to the existing location points are free and simple traction bars are OK but the width of the slick tire is limited.

To give you an idea of just how fast it is possible to go with all these constraints let's take a look at the mid sixties Chevy Nova 327 inch 275 hp (factory rated) cars of Jim Parsons (F/Stock) and John Hladky (G/Stock). Both parties are considered highly competitive and John, a past record holder, has run an 11.12 @118.6 mph in his car. When the limited areas of modification are taken into account these performances start to look really creditable. To understand just how creditable it helps to appreciate just what we are dealing with here in terms of a mid sixties small block Chevy and what it will take to maximize output. Like most things understanding the nature of the beast is critical taming it or for that matter making it wild.

Limitations.
The stock Quadra Jet 4 barrel carb with it's small primary and large secondary throttle bores is capable of about 800 cfm which is enough to meet the demands of a stock type race motor. Were we see the first impediment to performance is the intake manifold. While this is not a problem on a 225 hp motor it certainly starts to become one when the potential is around 400. The manifold however must remain stock although some competitors will do some acid porting on it. However if the sharp edges, which are a principle restriction to flow, are not there tech inspection may throw it out.

From the indifferent manifold the air passes into heads with intake ports of equally indifferent flow. The charge is burned in a classic wedge shape chamber that burns well so long as there is not an intrusive piston crown present. This, plus the use of a flat top piston and a limited amount of chamber reduction leaves the CR at about 11/1. This is an important factor as the poor breathing capability of the head makes the requirement for the highest compression possible a prime consideration. When it comes time to empty the cylinder the exhaust must pass out an exhaust port equally as indifferent to flow as the intake. With the valve lift limited to about 400 thousandths the problem of poor flow is compounded further yet. An initial reaction here is to use a cam with very long duration but that can be a problem also. In fact just one of many.

Consequences.
Because the intake ports, right from the base of the carb, are less than free flowing there will be an obvious problem filling the cylinders. The low lift of the stock valve train means even the limited potential of the stock port is never fully realized. Because the valves can only be lifted to 400 thousandths the need to produce effective flowing seats becomes paramount. Fortunately there is a reasonable amount of leeway with seats so the first step toward prepping a motor like this will be to maximize the low lift flow capability of the valve and seat combinations.

The problem of poor intake flow is further compounded by the fact that the exhaust has minimal, if any, real scavenging effect, mainly because of it's own limited flow. This can produce not only higher than normal pumping losses but also tends to damp pressure wave tuning effects from pipe length. Limited compression and poor flow bring about chamber residuals far high than we would expect on a normal race motor. With it's poor intake and exhaust this motor's character is one of overlap flow reversion throughout most of its rpm range. As a result it will respond positively to increased cam duration right up to a certain point where it will suddenly fall flat on it's face so to speak.

Where Do We Start?
Regardless of all the other points of restriction the first place to start in the search for power is the cylinder head and within that, the valve seats. The rules allow a three-angle valve job of which the proportions are more or less free so long as the machining down into the throat (bowl) still appears stock. This work is critical as the production seat works well in the 0-200 thousandths range. The key here is to develop the seat form to enhance the flow between 200 to 400 thousandths lift without sacrificing any low lift flow. This was achieved as is shown by the graph Fig 1.

Next the heads where milled to reduce the chamber volume as much as possible. With a wedge chamber design this is best done by angle milling the head face and then milling the manifold face to restore the correct angle for intake manifold gasket sealing. With the block decked to the minimum allowed the CR can be raised from about 9 -9.5/1 to 11/1.

Before we leave the cylinder heads a point concerning the practice of acid porting where rules call for an untouched port. Basically acid porting involves filling the ports with acid to enlarge them in an effort to increase flow. Strictly speaking the rules don't allow this but it is hard to detect it has been done. It is, it seems, a fairly common practice and can take a great deal of time. However, past cleaning the casting of corrosion it seems to achieve very minimal results to the point that both Jim and John feel time is better spent refining other aspects of the motor.

Induction System.
As was mentioned earlier the carb has more than enough flow potential to satisfy the needs of this motor. The carb can be equipped with or without an air filter. Many drag racers run without a filter but when one is used a 360 degree 12 x 3 K&N is recommended for an application such as we are dealing with here.

Although carb flow may be up to scratch the intake manifold could be better. Fortunately the low valve lift means the effect of its restriction is not fully realized. However there are small but measurably beneficial moves that can be made to improve manifold flow. For instance the type of carb gasket used (it must be stock or stock replacement) not only influences the carbs operating temperature but also the flow of the carb/manifold combination. Flow bench and dyno testing revealed one particular brand to be worth some extra cfm and a couple of hp.

The Valve Train.
Since the valve springs must be stock or stock appearing and need to deliver no more force than is needed to get the job done valve train mass is important. As it happens some of the later model Corvette valves are hollow and can be turned down to the correct 1.94/1.5 inch head sizes required. These valves are about 20 grams lighter than even a lightened stock valve.

The springs need to have the minimum mass consistent with enough delivered force. This means a spring with as high a natural resonant frequency as possible. This involves searching for the right spring with a spring tester and a set of scales. A substantial amount of extra rpm capability is needed over and above the peak power rpm as the start line performance can be measurably helped by absorbing the flywheel momentum from a 7500 rpm or more launch. Once under way the shifts through the gears are made at 6800-rpm max.

The rockers used must be stock pattern and over the years many brands of replacement stamped steel Chevrolet rockers have been produced. Though intended for the same purpose they are far from equal. The ratio from best to worst varies by over a point. Where breathing is limited the intake valve accelerations become much more important. The trick here is to select components that deliver the highest rocker ratio then have a cam ground with a lobe lift giving the maximum allowed valve lift.

Pushrod selection is another area of potential power increase. By selecting a pushrod with the right flexibility characteristics in relation to the spring it is possible to get the valve train to launch off the nose of the cam and actually achieve higher valve lift.

The Camshaft.
The selection of the cam events and profile parameters is critically important. As I have already mentioned, too much cam, mostly in terms of duration and overlap, will spell disaster. The difference between success and failure may be less than 5 degrees. John Hladky had arrived at his current cam by virtue of dyno testing a number of cams. An interesting point was that he had just about found the limit of duration and overlap with the current valve train and a conventional cam profile (I mention this because I intend to talk of an unconventional one in a moment) by dyno testing. When suitably sophisticated software was used to model the motor the limit predicted was almost identical to that indicated by John's testing. One of the problems with the valve events is that if the low lift flow, lifter acceleration or the rocker ratio changes then the optimum valve events also change.

At this point John really was intent on moving on from where he was with the cam and valve train. Because hydraulic followers tend to collapse the way to maximize lift is to internally limit their range of motion. A certain amount of hydraulic motion must be present or the tech inspectors will disallow their use. However I did manage to come up with a different approach to the profile design that promised results superior to a regular solid lifter thereby bypassing the problems of a hydraulic cam. Using the MotorTec Cam Master program I computed the valve events that this motor would require using the rather unconventional profiles proposed. After that I made a call to Dema Elgin of Elgin Cams (Redwood City, California - 650-364-2187) to check whether or not the concept in mind could be done. Well it could so profile masters were started and a new cam was put in the works. Now I really would like to tell you about this but the deal is that John gets to use the concept until he has gained sufficient advantage this season to achieve his goals. Then I get to tell.

Exhaust System.
A first impression would be that the exhaust is critical to the performance of this motor. While it certainly cannot be below par it is not as critical as it first appears. The biggest issue is that there be no backpressure for the poor flowing exhaust port to combat. Because of this, and the close chassis constraints, the exhaust on these cars exits via the wheel wells thereby avoiding unnecessary tight bends. After this if diameter and length are about right, and these are easily computed for the rpm range involved, then you are in business.

go to <a href="http://www.motortecmag.com/archives/2001/jun/JUN01-02/imageset.html" target="_blank">http://www.motortecmag.com/archives/2001/jun/JUN01-02/imageset.html</a> for graphs.

[ January 02, 2003: Message edited by: deuce_454 ]</p>
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Old 01-02-2003, 04:20 AM
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This is the best post I have seen to date!! Makes me feel very humble. Even tho I'm not into the drag racing, still extremely interesting. Thanks!!

Trees
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Old 01-02-2003, 04:59 AM
E.T. divided by $ spent= Speed
 
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Thanks for the article.I dunno why,its like asking to get my *** kicked,but I wanna try it.If I do commit to this idea I'll have to just go one piece at a time till its a complete car.I still got alotta readin and researching to do befor I start sinkin money into this whole thing.But for now just gatherin info.Hollow valves and acid porting are getting way beyond my basic grasp of hipo SBCs.
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Old 01-02-2003, 05:07 AM
E.T. divided by $ spent= Speed
 
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By the way do you have calouses on your typeing fingers?? Thanks
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Old 01-02-2003, 05:10 AM
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Having built several stock eliminator engines, one of which held the E/SA record back in 2000 all I can say is that you could fill a book with what's needed in order to be competitive in stock eliminator. Finding the right combination to run (carwise) is very important. There are some cars that no matter how much money is thrown at them won't be competitive. Others, are so unique that it takes far less effort to run under the index. Before diving into it I would recommend lots of research to see just how competitive your combination is. A good place to start is by going to <a href="http://www.classracer.com" target="_blank">www.classracer.com</a> they have a couple of bulletin boards to ask the right questions. I'm sure someone there probably already runs that combination and would be a great help.
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