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GM Stillborn Gen III V-10 - Perfect 10

The Unauthorized Biography Of GM's Stillborn Gen III V-10.

David Vizard Dec 1, 2005

The shot seen here shows the dense foam mockup that was produced by an enthusiast group of GM engineers who worked on it primarily from September 1994 to July 1995. Since it was never officially approved, the V10 project used funds siphoned off from other engine projects to hide its existence. The unofficial nature of the project caused a number of embarrassing political waves within the powertrain organization.

Both Chrysler (1994) and Ford (1996) have a V-10 powerplant in their engine lineup. So why doesn't GM? As you will see, GM looked into doing just that between September 1994 and July 1995--and came up in the end with a goose egg. In each of the aforementioned cases with Chrysler and Ford, the production V-10s were developed from existing V-8s. The move made here was to add two cylinders to an existing small-block V-8 to create a 90-degree V-10 that delivered the sought out increased displacement.

But, one may ask, why go this route instead of just designing a bigger V-8? After all, 10 cylinders means not only 25 percent more parts, but also 25 percent more complexity. Running smoothness might be an answer to throw into the argument here, but the bottom line is that a two-planed V-8 crank has perfect primary and secondary balance, so going to 10 cylinders is no big deal. In fact, some of the many possible V-10 crank/firing order configurations incur ether primary or secondary out-of-balance forces or uneven firing. Either way, V-10 engine smoothness is not a valid argument for its adoption. So why did Chrysler and Ford go with a V-10? Most likely, the decision was driven by a group of factors--lower emissions per cube from smaller cylinders tops the list. This gave a 10-cylinder engine the same size as a V-8 a distinct ecological advantage.

But hold on a sec--if the V-10 is such a good idea, why didn't GM take a look at going that route, especially since it has what is probably the best two-valve pushrod V-8 (the Gen III small-block) on the face of the planet to base it on? The engineers at GM are certainly not known for being technically tardy. This being the case, it probably comes as no surprise to find that as far back as 1994, a serious (if somewhat clandestine) Gen III-based V-10 feasibility study was instigated. Did it go anywhere? Well, if it had, insider sources indicate we would have been seeing an iron-block version in trucks and an aluminum one in the 2004 Corvette.


Figure 1
The proposed V-10's front-view silhouette is marginally narrower than a 454 big-block V-8 and...

Although we don't have the total inside scoop on the pros and cons involved, here are the advantages of a V-10 derivative of the Gen III based on what has leaked out from what is supposedly a closed-door project, plus some of our own thoughts:

1. A V-10 will satisfy marketing needs because it will be perceived by the buying public as a technically more advanced unit primarily because of the 10-cylinder configuration.
2. It would lower engineering overhead costs because of the parts commonality between the current V-8 and the proposed V-10.
3. A V-10 based on the Gen III presents a more optimal truck chassis packaging situation.
4. Going the V-10 route alleviates the need to spend money on the inevitable future upgrades required to keep the 454/502 big-block motor current in terms of emissions, fuel economy and customer satisfaction parameters.
5. From the end-product engineering standpoint, a V-10 would make use of the Gen III's considerable research and production tooling investment. This would produce--from an advanced V-8 design--an equally advanced V-10.

Let's go through and evaluate these topics. First, the subject of the perceived 'technologically more advanced' nature of the V-10 layout. No problem there. We talked to a dozen truck/sports car owners and although such a small number could produce statically flawed results, ten out of twelve said they would go for a 10-cylinder engine rather than an 8 if there was no major cost penalty.Point 2--no argument here. Any time the number of different required parts drops (the end-product being the same), so does cost.


...as can be seen from the plan view, only fractionally longer than the engine it was intended to replace.

On to point 3--As far as packaging is concerned, a V-10--at least at first sight--looks to be less optimal than a V-8 of the same displacement. A plan view of a big-block 454/502 and GM's Gen III V-10 shows the reality of the situation (see Fig. 1). The V-10 layout is generally about 1 1/2 to 2 inches narrower. As far as the expected increase in length is concerned, it just does not happen because of the Gen III's basically compact design. The only thing making the V-10 longer than a big-block 454/502 is the fact that the front pulleys protrude a little more and add about 1-inch. Plan view of GM's Gen III V-10 project shows that at least the center of gravity of the two units does not seem to differ by more than 1/2-inch. If we consider the side view, the situation favors the V-10 simply because the long motor is some 2 1/2 inches less in height. At a guess, this will lower the center of gravity of a V-10 compared with a 454/502 V-8 by about 2 inches. While this may not be a big deal when considering trucks, it is if we are looking to power a Corvette with this package.

The rationale of point 4 seems to be easy enough to see. If a Gen III V-10 is to replace GM's aging big-block V-8, money that might have been spent on any required V-8 upgrades can be put toward the development of the V-10. But we will hazard a guess here, an opinion based only on an outsider's view of the situation and a lot of big-block experience. The money saved by not having to revise the old big-block to make it current and bring it to production status won't cover the costs of morphing a Gen III V-8 into a V-10.

On to point 5--Here, we hit the real bones of the matter at hand. Namely, is it worthwhile (i.e., profitable) to build this proposed V-10? This will take a little longer to answer than the previous points. It will also be of more interest to us as GM product enthusiasts. This topic, at the end of the day, will be the clincher that decides--for us--whether we should be seeing V-10 sporty cars and trucks in GM's showrooms.


Figure 2
A crank with five pins, each shared by two cylinders such as seen here the easiest to produce but, in a 90-degree block, will deliver firing pulses spaced 54, 90, 54, 90 degrees, etc...

First, let's take a more serious look at the novelty of this proposal, namely the V-10 configuration and its pros and cons. Initially at least, it seems like a simple deal to just add two more cylinders and make a V-10. After all, Chrysler and Ford did it, so it can't be that difficult! The truth is, it isn't that difficult to do but unless some sound engineering decisions are made along the way, the quality of the end-product can be very questionable.

Let's consider the situation concerning firing intervals. With a conventional 90-degree banked V-8, firing intervals occur at 90 degree intervals (i.e., 720 degrees/8=90 degrees). To get even-firing intervals from a V-10 we need to have the space between firing to be 72 degrees (i.e., 720 degrees/10=72 degrees). When considering a V-10 derivative of a V-8, there are literally dozens of possible crank/block configurations. Of these, we can say that unless counter balance shafts are added (which increases friction and cost), only three primary configuration options are practical. First, design the block with 72 degrees between the banks and use common bank-to-bank pin journals (Fig. 2). Second, design the crank with split throws (Fig. 3) on each journal so the crank configuration compensates for the 90-degree block and produces 72-degree firing intervals. This is how Ford has done it for its V-10. Lastly, use a 90-degree block and a crank with common bank-to-bank pin journals and accept uneven-firing cylinders. This is the route Chrysler chose. This also was the way the proposed Gen III V-10 was to go. This allowed much of the Gen III production line manufacturing equipment to be adapted to produce the block and crank thus keeping costs down while only incurring minor penalties. The penalties in this case were a low secondary out balance (compared with zero for the V-8) and a low-frequency torque fluctuation due to the uneven firing (Fig. 4). How significant this may be for Corvette owners--who are used to even-firing pulses and the inherent perfect balance of a V-8--can best be judged by the fact that Viper owners don't seem to complain. Good, tuned engine mounts, big displacement performance and the distinct 10-cylinder exhaust note seem to more than compensate.


Figure 3
A crank with split big-end pins as seen here will deliver even 72* firing intervals but is more expensive to make and is likely to be weaker in torsion.

In addition to the uneven firing and slight imbalance produced by the proposed V-10 layout, there is the issue of the greater crank length. Putting more torque, especially with greater firing pulse fluctuations, means that crank torsional harmonics are increased in amplitude. Estimates indicate that such a crank would have strong torsional vibrations of the 3rd and 4th order at a little less than 5000 and 6000 rpm, respectively. Whereas these might not be an issue for a truck motor (which might never see the topside of 4500 rpm), they would be if the motor was intended to be used in the Corvette to make it an effective Viper-killer. This will place a greater emphasis on crank damper design than would be the case for a V-8. Nevertheless, it is nothing that a competent crankshaft damper design cannot effectively deal with, so in the end, it is unlikely to be a negative issue.

Power Production - 8 versus 10
Although we understand that GM did its V-10 feasibility study based on truck usage because that would be by far the largest sales area, we will also look at the potential for power and performance in relation to the use of the proposed V-10 in a Corvette and other performance application for which it was considered. This engine was a prime candidate for a 1500-series sport truck intended to be knockout competition for the Ford Lightning. [How ironic that seven years after the completion of GM's V-10 feasibility study, we're months from seeing a mass-produced 1/2-ton Dodge SRT-10 truck with the Viper's 500hp V-10! -Ed.


This diagram shows the uneven firing order that GM intended to give its V-10 engine. A dark arrow from one cylinder to the next indicates a 90-degree interval while a gray arrow indicates 54 degrees.

First, a Gen III-based V-10 at exactly the same displacement as a V-8 will produce more power, since a greater number of small cylinders are better than a lesser number of large ones. Additionally, it's possible to turn more rpm with smaller cylinders before reaching piston speed and acceleration limits. The same goes for the valvetrain--a greater number of smaller valves brings about a dynamic advantage. Also, all other things being equal, smaller cylinders reach their detonation limit at a higher compression ratio than larger ones. Probably the biggest advantage of more cylinders is that such an engine delivers more piston area for the same overall displacement and bore/stroke proportions. Even allowing identical bore/stroke ratios (this removes the stroke length as a factor), the V-10 would sport 125.7 square inches of piston area against a

V-8's 116.7. But the V-10 has a more performance-oriented bore/stroke ratio than the 454, so the advantage here at 125.7 to 113.5 is even greater. Based on this alone, the V-10 should produce almost 8 percent more torque and power.The advantages of the Gen III bottom-end configuration doesn't stop at just piston area. It also has the advantage of having a bigger bore/stroke ratio at 1.1 compared to the big-block V-8's 1.06, and a rod/stroke ratio of 1.822 versus only 1.533 for the big-block V-8. Apart from reducing piston-to-bore friction and peak piston accelerations, the longer rod/stroke ratio delays the point at which peak piston speed occurs. This in turn delays induction demand on the intake valve until it is open slightly further, thus increasing the engine's breathing (volumetric efficiency) capability. This could account for a 1.5 to 2 percent increase in VE. This may not sound like much, but because of some knock-on domino effects, it could account for as much as a 4-5 percent advantage in output.


By any standards a big-block Chevy head is an effective design, but when compared to...

Power Production - Cylinder Heads
Since we have now touched on the subject of engine breathing, let us look at it in greater depth. For a Corvette application, the cylinder head design would almost certainly have been a five-cylinder version of an LS6 head. The first point of comparison we need to look at is the intake valve area in relation to the cubic inches that must be supplied. Current production big-block Chevys typically have an intake valve of 2.19 inches diameter, max. Assuming the bottom end is a 454, this means every square inch of intake valve must support the demand of 15.06 cubes of displacement. A similar comparison for the V-10 shows that the ten 2-inch valves and 455 ci result in a more favorable 14.49 cubes, making a demand on each square inch of intake valve. Still, comparing what the factory may put in for stock valve sizes and what a set of race-prepped heads may could paint a different picture. A look at such a scenario shows a big-block 454 Chevy head will take a 2.3-inch intake valve. An LS6 can accommodate a 2.06-inch intake. If we run the numbers again with these bigger valve sizes, the Gen III V-10 still comes out on top, though by a narrower margin.

Although valve sizes are a factor, we must take into account that a cylinder responds not to valve size but to airflow. Although production 454 heads can be effectively ported, the LS6 head has even more potential. Based on some current numbers, the LS6 head can deliver better than 5 percent more airflow per cube than a set of ported factory big-block castings. All this is achieved with almost 20 percent less valve lift, so the valvetrain of the V10 would be significantly more reliable.


...LS1/LS6 heads, it has to take second place. These heads have airflow potential that, a dozen years ago, would have rivaled Winston Cup race heads.

As far as the exhaust is concerned, the LS6 has an excellent port in stock form and in modified form, second only--and marginally at that--to a Winston Cup head. So dumping spent gases is not an issue, although developing headers as effective as current V-8 ones for a five-cylinder-per-bank configuration may take some time.

Power Production - Induction and Exhaust Systems
Even with this writer's limited experience dyno testing intake manifolds for the LS6 engine, it is apparent that the factory plastic unit is an excellent design for the stock application. The bottom line here is that the aftermarket is going to be hard pushed to produce an intake that will show any increase over a stock LS6 on otherwise stock or near stock engines. The same cannot be said for the big-block Chevy and although the factory has produced some good designs, they are not in the same league as the LS6 intake--or any other Gen III truck intake manifold for that matter. It appears the factory had every intention of using the LS6-style intake so on that score the V-8 is on a par with the V-10. On the 346-inch LS6 V-8, the intake throttle body ultimately becomes a limiting factor. To avoid an overly restrictive throttle body, the V-10 would need one with at least a proportionate increase in flow potential.As far as exhaust is concerned, unlike a truck, packaging has always presented some problems when it comes to the Corvette. Still, as personal experience shows, it can be done without the loss of any significant amount of hp. However, it is doubtful the factory will go to the extremes that a racer will to achieve such goals. As ever, costs and emissions are primary factors. But regardless of this, we can still expect a better-than-average production type exhaust system that won't cost an arm and a leg in terms of power loss.


The intake ports of the LS1/LS6 head may look a little unconventional but with a 320-cfm flow capability they certainly do produce the goods. Using these heads, 346-inch endurance race engines are making 600-plus hp.

Power and performance predictions
As one might expect, GM Powertrain's undercover V-10 project group did some power and performance predictions. These were all for a truck application because this is where the greatest production volume would be. If they could justify a V-10 here then a Corvette project would almost certainly ride on its coat tails. First, the factory power and performance figures. In Figure 5, we see the results of a dyno test of a '96 454 L-29 big-block versus an LS6-style motor scaled up from eight to ten cylinders. Although this looks impressive enough, the impact on the performance of a heavy-duty truck is even more startling.

The reason is that not only is there a higher output throughout the rev range (duplicating that of the 454 big-block V-8) but also an increase of some 1500 rpm of usable rev range. This means the vehicle can hang on to a lower gear for longer. More output and more rpm really does add up to a big performance increase, as GM's predicted numbers in the adjacent chart show. For a truck tipping the scales at over 3 tons, the performance with the 454 V-8 is not bad, but with the V-10 it is positively sports-car-like. In case you feel that some measure of poetic license has been invoked here, just check the 0-60 times of some of the import sports cars and you will find they can't match the estimated 7.1 seconds of a 3/4-ton V-10 truck--and look at the quarter-mile times and speeds. At 15.6 seconds and 84 mph, we are talking sports sedan performance at a minimum. To put these numbers in perspective, the performance of the big-block V-8, with the aid of a typical nitrous kit, would still fall short of the V-10.

Corvette V-10 Application
So far, for our power and performance predictions, we have relied mostly on the info gleaned from our secret GM sources. To get an idea what such a motor would do in a Corvette, we will need to make some of our own predictions. Here, use was made of Performance Trends Engine Analyzer Pro and Drag Strip Analyzer (for details, call 248/473-9230). First the baseline big-block. Here it would have been tempting to simply put in an existing GM spec but if they were to ever consider again using a big-block motor in a Corvette, it would be one with a spec inline with current requirements in all areas. What we did here was to try and second guess what the most likely improvements would be and then add a little so as not to make the comparison lopsided in favor of the V-10. This being the case, a 454 was spec'd out using an intake system of the same style as an LS6 with an 800-cfm throttle body. Head flow was taken from the best production figures and then improved by about 5 percent. A typically moderate factory-style cam spec was also chosen. This was 208/210 degree at 50 thousandths intake/exhaust and was on a 110-degree LCA. Usually, GM puts such cams on 112 degrees, but 110 degrees produces better results. The only area in question might be the compression ratio. The factory has not used ratios over 10:1 since the musclecar era of the late '60s. It's doubtful they would use 10:1 with the 454's big cylinders, but they may use 9.5:1 instead of the current, commonly used, 8.75:1. We elected to plug in 9:1 in our simulation and figured it could cover up to 9.5:1 (as we had been generous with the cylinder head airflow and a more appropriate cam spec). As for the exhaust, a typical emission-style exhaust was modeled.


This is what a GM Powertrain computer model produced for power and torque figures for a 454 V-8 versus a 455 V-10. (The original is not being shown in order to protect the source.) The big thing to note here is the improved output and significantly more rpm capability.

For the V-10, the same LS6-style intake was used for our computer model. The throttle body flow at 800 cfm was the same as used for the 454 V-8 big-block computer model. As for cylinder heads, the flow numbers for an LS6 were entered into the computer. The CR used is 10.5:1, the same as for the GM-model truck motor. Cam events used were as per the 454 big-block even though they might not be optimal for the V-10 configuration. The only significant change made was in the rocker ratio, with the V-10 at 1.6 instead of the 1.7 used for the 454 engine. The spent gases leaving the V-10 had to pass out an emission-type exhaust of the same flow capability as the 454 V-8.

Entering all the data into Performance Trends Professional Engine Analyzer Pro program produced the curves shown in Figure 6. Bear in mind that this is a slightly optimistic 454 V-8 versus a slightly pessimistic 455 V-10. In spite of this, the V-10 wins handsomely by delivering some 50 lb-ft more torque, 64 more horsepower, a superior curve throughout the rpm range and 500 more usable rpm.


What we see here is a computer model of a slightly optimistic 454 V8 output versus a slightly pessimistic 455 V10 (generated by a Performance Trends Engine Analyzer Pro). As with GM Powertrain's truck simulation, this simulation shows how the hotter sports car spec version of the V10 still outperforms the V8 throughout the rpm range.

Corvette V-10 Performance
We are all aware that GM does not make a big-block 'Vette, but if it had an emission-legal engine of 518 lb-ft and 414 hp it would, even at the 3,450 pounds modeled, be a potent production vehicle indeed. If you want to think in terms of a slightly more practical vehicle, then a 1500 series V-10-powered truck would be more competition than a 13-second, 108-mph Ford Lightning owner would want to go up against. Indeed, we could see a truck that could be almost as quick down the quarter as a current Corvette!

Exciting though it may be, let's put the truck application aside and consider Corvette performance. Assuming good street tires and a 3.08 rearend, the biggest problem shown by the model computed using Performance Trends Drag Strip Analyzer is traction. As can be seen from the computed numbers in the adjacent chart the V-10 'Vette shows no advantage over a V-8 one until 60 mph is reached. Even the 0-100 only shows a scant 6/10-second advantage for the V-10. It is not until we start talking in terms of very high speeds that the performance-robbing effect of traction limitations starts to diminish. For instance, the V-10's 70-120 time is 1.1 seconds better while the time for the quarter-mile is 0.26 seconds better. This may not sound like much but the faster the speeds and the shorter the times involved, the smaller the gains appear to be even if the performance increase is substantial. Along with the .25-second ET reduction, the V-10 'Vette is going almost 5 mph quicker. If we want to talk about top speed, then the V-10 could put anyone with the desire into the 200-mph club. The computed Bonneville speeds are 192 mph for the V-8 and 203 mph for the V-10.


A rear view of the V-10 mockup clearly exposes it as a foam model, but two prototype iron blocks were actually poured from molds created for the engineering exercise. The mockup alone cost $35,000, but documents show actual prototype cope and drag tooling was ordered in September of 1994 at a cost of $310,000. The two V-10 iron blocks are presumably still floating around in the bowels of Powertrain Advanced Engineering in Pontiac, MI.

With so much less difference in performance than is seen with the truck usage, it might not seem worth the effort to go the V-10 route but for one important factor: tire technology is advancing rapidly. Such advances in tire technology will cause the performance gap between these numbers to get wider. A V-10 Corvette with tires of the sort we can envisage by, say, even 2004, would be the way to go. It would also be a serious challenge to the Dodge Viper's position as the premier super car as far as outright performance is concerned. Certainly the power of a V-10 together with the Corvette's greater chassis sophistication would produce a world-class performance sports car likely to be second to none.

If we want to talk about the V-10 in terms of a racecar then some simple scaling up of the output of a race LS6 engine will serve to give a realistic gauge as to the possible potency of the V-10. A race LS6, for an endurance-type event such as Daytona, can deliver well in excess of 600 hp. This indicates that a 10-cylinder version of such an engine should be good for some 790-800 hp. Bearing in mind just how competitive a Corvette is with an LS6 V-8, we should see something close to unbeatable if it were endowed with what amounts to another two hundred hp.


This GM document is a proposed cost/time schedule of a prototype build-out of twenty V-10 test engines--half of them with aluminum blocks! The engines were never built, but you can see GM Powertrain was very serious about it in the fall of 1994.

The V-10 - Where Is It?
With all that it appears to have going for it, one would certainly wonder where this Lightning-quenching, snake-devouring V-10 is. As good as it seems, there are some stumbling blocks impeding its path to production. At first, such arguments against the production of a GM V-10 might seem to hold little water simply because we can see that both Chrysler and Ford have successfully brought a V-10 to market. The bottom line here is that both Chrysler and Ford had relatively mundane and indifferent big-block V-8s that were replaced. On the other hand, GM's big-block, though it has been around since 1965, is still the big-block by which others are judged. It was good in '65 and it is still good in '02. At least one of the existing V-10s would fail to produce the results of Chevy's big-block V-8, if push came to shove. Also, all the tooling and research costs for Chevy's big-block have been more than recouped, so it is (relatively speaking) cheap to produce. If GM had not done such a good job with the its engine back in the early '60s, we may well have seen the V-10 trucks and Corvettes that we are all probably drooling over now. The only factors we see that might push this project into being are tighter emissions and public demand. If you want one, then our advice is to start demanding right now!GMHTP would like to extend its sincerest thanks to those GM Powertrain insiders who helped bring this story to fruition. We acknowledge that some have put their careers and financial well-being at grave risk in doing so. As much as we would love to give credit to these true gearheads within the Powertrain organization, we realize that it would be detrimental to do so.



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