Engine Build - Competitive Power Late Model Stocker

[DavidVizard-GFN]

Late Model Stocker Build

By

David Vizard

Theorizing what is needed to achieve a given goal is almost always far different from what may turn out to be a viable build proposition. From my feature discussing what it takes to build a winning restrictor motor ( Restricter Race Motors -make more power than your opposition ) we see that certain breathing issues need to be focused on somewhat intensely. The fact of the matter is that more often than not implementing characteristics needed to the point of building an invincible engine are too costly even for a reasonably well funded team. Sure our late model team has the engine building capability to put together a race winning combo but there would inevitably be a catch up phase that we did not want to go through. Don Losito, the teams owner (and boss at Ultra Pro Machining) has built some of the fastest stock block Indy cars on the planet so in-house capability is there. But what was needed was a successful engine program right now and at an affordable cost. What can inevitably prove less costly is to team up with an engine builder who already has successful experience with the type of engine needed. This means having a working knowledge of how, with reasonable dollar economics, to build an engine that will make the most from an engine with an artificially restricted induction. With the beginning of the season coming up we also needed a competitive engine right now! So with Don’s experience he should be able to recognize a good engine builder when he sees one. Billy Banks of Banks Racing Engines was seemingly just such a guy and so, when it came to the power plant for Nick Losito’s the Ultra Pro Machining late Model Stocker this is who we went to. He understands what is theoretically needed in the first place and has spent a lot of time fine tuning combinations that best approach the theoretical requirements in a cost effective and reliable manner. In other words he has made great progress applying pure theory into real world practice. Let’s see where this takes us.

The Foundations.

Every successful engine’s life starts with the selection of a block casting that is up to the job. Fortunately GM’s block casting techniques have got better over the years (and let’s face it they were never bad to start with) in as much as the cast iron used is better and the castings are more consistent. This makes the job of finding a good core easier. Couple that to the proliferation of sonic testers and the sorting of the best block to hand becomes a simple job of checking and selecting. Once that is done it all boils down to machining the block so that everything is sized as required for the job at hand. At Bank’s Racing Engines in Stoneville North Carolina, every critical machining op is done in house. A typical block prep involves letting the mains caps down a minimal amount and align honing the mains bores. This is then used as the datum line for every critical dimension such as deck height/squareness and bore location. That also goes for the lifter bores (machined with a BHJ fixture) and the front and rear faces of the block. After machining it’s very much a question of detailing. Here all the lifter bores are de-burred along with any sharp edges left from boring and align honing. As far as the block prep is concerned accuracy almost always equates to lower bottom end assembly friction and extended life. Both of these factors are of major importance. Any inadequacies in the block prep reflect negatively on the entire subsequent engine build. With the block done we move on.

The Crank and MOI Considerations.

With the block done we can now consider what is needed in the way of a rotating assembly. First the brand that Billy Banks favors here for crank and rods is Lunati. He reckons that for cost and quality they are hard to beat and the combination of component strength and lightness also justifies this as one of his principle choices.

Like many tracks the ones we’ll be racing Nick’s LMS on have rules calling for a minimum crank weight. In our case it is 50 lbs. and that might look like it is the end of any possible gains as far as crank Moment Of Inertia (MOI) goes. Well that is almost so but not quite. The rules call for stock bearing diameters but with the hollow big end journals used and the careful placement of mass in the counterbalance weights a little lower MOI than would otherwise be the case is achievable – and Lunati have done it.

The rules call for a non-aero counterweight 50 lb crank for the class. This is the Lunati crank Billy Banks advocates.

Rods and Pistons

We are stuck with a 50 lb crank so having the ultimate in piston and rod lightness can actually work against us when it comes to being able to balance the crank. Firstly let’s set the stage here. What we are looking for is a rod and piston combination that will easily allow the crank to be balanced at an ‘over balance’ factor of 5%. The main reason for picking that 5% is that it is very convenient in terms of producing it. With a 5% overbalance the 6.25 inch Lunati rod and the light piston used brings everything close enough to balance the crank without going under the 50 lbs limit yet delivers a reasonably light reciprocating assembly. Although it is not as easy to mentally picture as a flywheel that is lightened, the reduction of reciprocating mass also has a positive impact on the engines overall MOI. Added to that the Lunati rod selected is a really nice piece. We have had experience with such in a number of race engines over the last half dozen years and they have shown to be able to take one heck of a beating and come out looking like new.

This good looking 6.25 inch Lunati rod is, as we have found over the last 6 or so years, plenty stout.

For pistons Billy favors a couple of brands and the ones used here were custom made for the job by Diamond. For any application that does not call for a stock piston to be used Billy has the pistons custom made to meet the particular parameters he feels are most important. The most obvious factor is weight but although it is important it is not the primary deal here. Remember that the rod/piston assembly must be such as to allow balancing to the 5% over balance factor (counterweights 5% too heavy). This means the ultimate in a light piston is not what is needed. Where Billy sees the greatest potential for more power is a well sorted ring pack placement along with a low drag set of rings. Here he moves away from conventional ‘D’ wall rings and goes for a less conventional ring geometry that Total Seal builds for him.

As you can see from the above shots of our Diamond pistons they are light and compact. The valve cutouts are minimal which helps compression and combustion but makes life more difficult in terms of the valve train – but we will get to that in a while. Check out the ring pack here. Note the high placement of the top ring (do not run this with a lean mixture) and the radial gas ports. Also, as is common practice since Grumpy Jenkins popularized it for drag racers some decades ago, a reservoir groove between the top and second ring is used. As for pin retention Billy favors the Cosworth style round wire snap ring with a removal slot in the piston’s pin bore. To make all these hi-tech ring choices work it is necessary to have the piston’s skirt design limit the piston rocking in the bore without introducing undesirable levels of friction. All these parameters means making the right choices in each area an important issue. In such a case just getting the piston optimal in terms of rings, skirt design and valve cutouts can mean as much as a 10 hp 10 lbs-ft advantage over a lesser specced engine.

Cam and Valve Train.

Let’s just check some of the key factors needed in terms of a valve train for a successful limited induction motor. First the flat tappet cam called for must have super rapid opening and closing of the valves. Getting cam profiles that deliver a fast opening/closing lift curve is not a problem in itself but when the requirement is to do so at 7000 rpm the picture changes dramatically. Consider this – the cam companies normally call for a static piston to valve clearance of a minimum of 0.100 inch and preferably 0.125. Why so much? It is to cover the situation at the point of rpm induced valve train crash when the driver misses a gear and the situation that can exist when the valve train combination is not quite right and spring surge at some rpm on the way up/down the rpm range causes a temporary loss of control. If the dynamics were perfect and the valve train could rpm to say 250 above what was needed then we could get away with a very minimal amount of valve to piston clearance.

I have seen well developed pushrod engine valve trains go to 11,000 rpm with only 0.030 static clearance and never touch – but that is the exception not the rule. It does however show it can be done. With the exception of a super light steel alloy lifter and a Cloys timing set Billy uses mostly Comp’s cam and valve train components. It is very much a tried and tested mix-n-match of parts he knows are dynamically compatible so that the required fast valve action can be had without having a dynamically unstable valve train. This means less valve pocket and less spring than might otherwise be the case. The valve train is a combination that he has spent a lot of time on and has asked that we not just hand out the results of his efforts – so we are respecting that request. If you want a valve train for your late model stocker you might just call up Billy and buy the parts from him – that’s everything from the valves in the heads through springs, pushrods, lifters to the cam itself.

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As you can see from the finished shots of the engine we used a billet Comp timing cover that allowed easy access to the cam. This can be the final frosting on the cake as it takes only a few moments to explore the last drop of power potential from at most a 1 degree swing of the cam.

Cylinder Heads.

Here we come to a critical point in our build. The rules call for stock heads in every respect other than we can re-cut the valves seats (the valves must remain 2.02/1.6 though). As it happens the stock valve seats in the Bow Tie heads called for can be improved upon and this is what is done here. Other than that the heads must pass a number of dimensional checks to establish that they conform to the original GM dimensions.

Induction and Ignition

The rules call for an Edelbrock 2101 Performer intake manifold and a 390 straight leg booster Holley carb. The maximum spacer thickness that can be used is one inch. First the intake manifold itself. We know from experience that given the carburetion the port runners are sufficiently flow efficient to support well over 500 hp. What we have though is carb that is a little too small for that kind of output even though an open spacer is allowed. What this means is that carb airflow as well as calibration are going to be critical. On top of that the straight leg booster has the least signal gain of any of Holley’s boosters. To make the most of everything here Billy blueprints the carb in terms of booster positioning and then redoes all the fuel circuits for more precise fuel air ratio’s over the range used while racing.

As far as the ignition system goes an MSD distributor with the mechanical advance locked out is used. This might sound like it is an over simplification and an excused to not test for an optimal curve. The reality though is a lot different. Here is how it all falls into place. Over the 4000 to 7000 rpm range that is used for racing under WOT conditions the engine needs 38 degrees of advance so no ‘curve’ is needed here. For all practical purposes the engine is never at WOT at rpm below about 4000 so a ‘curve’ below that is not really needed. At part throttle below 4000 rpm the engine needs about between 38 and 50 degrees of advance so the fixed timing for that is close enough. At idle the engine needs about 45-45 degrees (this would correspond to a ‘regular’ engine requiring say 15 degrees of initial ‘mechanical’ advance plus about 30 degrees of vacuum advance). So with the fixed timing we find that the advance is right on for power and close enough for all other practical purposes. The only hang up is that with 38 degrees of advance back rotating at starting can be an issue. This is overcome by the use of a Quarter Master heavy duty high torque/rpm starter.

Dyno Time.

To test the engine we used Billy banks in-house dyno rather than our own as it was a lot more convenient. On Billy’s dyno we expected to see right around 450 hp which is a competitive number and would serve our needs well as we did have time constraints on the engine first time around. The plan was to get a good engine in the car quick and let Billy build a no compromise engine in his own good time as a replacement.

The targets for such were 450 hp for the first engine and 460 for the second. At this point it was time to let the dyno do the talking so our ‘primary’ engine was installed on Billy’s dyno. As functional as it was the Bank’s dyno room was not the best for photography but since all of us were impressed with Billy’s engine building we persuaded him to ‘decorate’ out the dyno cell for future features.

Here Nick (center) and Billy (right) got with the program of loading the engine on the dyno ready to test. Dusty (left) took on what for him was the unusual role as interested spectator.

It may not look that sophisticated but the Bank’s dyno does have all the data acquisition capabilities to make it a highly functional piece of equipment. That, and regular calibration, ensure accurate results so the numbers you see in this feature are ones you can have total confidence in.

Break in and the actual dyno testing was undramatic in the full sense of the word so I may as well get right to the results. After the post break in service the engine was put through it’s paces and delivered the curve shown below.

Here we see the results from the Banks dyno when out late model stockers engine was put through it’s paces. The blue curve is torque and the red horsepower.

In round numbers that amounted to 453.1 lbs-ft at 5000 rpm and 452.3 hp at 6100 rpm. Numbers that obviously met our initial goals with some to spare. But dyno numbers are one thing – what happens on the track is the real issue.

What with the light grey chassis and engine bay the Bank’s engine looked good installed in out late model stocker.

With these good numbers Nick was anxious to get to the track and test. That happened soon after the engine was installed. Although we had some chassis issues at the track Nick was really impressed with the engine. His comment here is well worth repeating ‘Best engine I ever had” – I suppose that about say’s it all!

In the shot above you see Nick and dad, Don Losito, ready for the first track session. Nick was very pleased with this engine but a few days later Billy called to say the ‘back-up’ engine with just a little more fine tuning in the component department just cranked out 458 hp.

If you are interested in having Billy Banks build you a race engine (circle track or otherwise) give him a call on 336-573-2461.

For more info on Nick’s racing activities go to http://www.gofastnews.com/board/tech...sitoracing.com and for info on the Ultra Pro lubes hit their website at http://www.gofastnews.com/board/tech...omachining.net


Now for the final question - how well did out theory on what it takes to make best output from a restricted motor pan out? As you can see the rules prevented anything overly drastic being done. What was applied was done so as far as the rules would allow. Probably the most margin to maneuver here was within the valve train. Opening and closing the valves at the right time and as fast as possible in a well controlled manner may have been the real key issue here toward solidly competitive power.

David Vizard

[roygoodwin]

Would conturing the crankshaft counterweights to reduce drag be worth the effort ?

roy

[DavidVizard-GFN]

Roy,

I did a back-to-back about 20 or so years ago with a flat face crank and a fully detailed aero crank. I would have to look up the exact figures here but I do seem to remember that at 7500 rpm it was worth at least 7 hp.

A story on aero cranks might be something worth doing here so this would force me to delve through 50 million power curves (not quite - it just seems that way) to see what exactly happened here. Let's say at this point that a real race engine should have an aero crank.

Your comment here actually brings to mind a little incident about 18 years back I was looking at an F1 crank done by a well known company who shall remain nameless to avoid embarrassment. The gist of the matter is they had windaged the crank the wrong way and no one had noticed it. The crank pushed the oil into the rod path instead of away!
Just goes to show even the top guys in the business can sometimes screw up!
DV