The Unauthorized Biography Of GM's Stillborn Gen III V10.
Both Chrysler (1994) and Ford (1996) have a V10 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 V10s were developed from existing V8s. The move made here was to add two cylinders to an existing small-block V8 to create a 90 V10 that delivered the sought out increased displacement.
But, one may ask, why go this route instead of just designing a bigger V8? 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 V8 crank has perfect primary and secondary balance so going to 10 cylinders is no big deal. In fact some of the many possible V10 crank/firing order configurations incur ether primary or secondary out-of-balance forces or uneven firing. Either way, V10 engine smoothness is not a valid argument for its adoption. So why did Chrysler and Ford go with a V10? 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 V8 a distinct ecological advantage.
But hold on a sec-if the V10 is such a good idea, why didn't GM take a look at going that route, especially as it has what is probably the best two-valve pushrod V8 (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 V10 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.
JustificationsAlthough we don't have the total inside scoop on the pros and cons involved, here are the advantages of a V10 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 V10 will satisfy marketing needs as 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 V8 and the proposed V10.
3. A V10 based on the Gen III presents a more optimal truck chassis packaging situation.
4. Going the V10 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 V10 would make use of the Gen III's considerable research and production tooling investment. This would produce-from an advanced V8 design-an equally advanced V10.
Let's go through and evaluate these topics. First, the subject of the perceived 'technologically more advanced' nature of the V10 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 were 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.
On to point 3. As far as packaging is concerned, a V10-at least at first sight-looks to be less optimal than a V8 of the same displacement. A plan view of a big-block 454/502 and GM's Gen III V10 shows the reality of the situation (see Fig. 1). The V10 layout is generally about 1 1/2 inches 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 V10 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 V10 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 V10 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 V10 compared with a 454/502 V8 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 V10 is to replace GM's aging big-block V8, money that might have been spent on any required V8 upgrades can be put toward the development of the V10. 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 V8 into a V10.
On to point 5. Here we hit the real bones of the matter at hand. Namely, is it worthwhile (i.e., profitable) building this proposed V10? 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 V10 sporty cars and trucks in GM's showrooms.
First, let's take a more serious look at the novelty of this proposal, namely the V10 configuration and its pros and cons. Initially at least, it seems like a simple deal to just add 2 more cylinders and make a V10. 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 banked V8, firing intervals occur at 90 intervals (i.e., 720/8=90). To get even-firing intervals from a V10 we need to have the space between firing to be 72 (i.e., 720/10=72). When considering a V10 derivative of a V8, 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 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 block and produces 72 firing intervals. This is how Ford has done it for its V10. Lastly, use a 90 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 V10 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 V8) 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 V8-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.
In addition to the uneven firing and slight imbalance produced by the proposed V10 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 V8. 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 10Although we understand that GM did its V10 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 V10 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 V10 feasibility study, we're months from seeing a mass-produced half-ton Dodge SRT-10 truck with the Viper's 500-hp V10! -Ed.]
First, a Gen III-based V10 at exactly the same displacement as a V8 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 valve train-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.