Any time you press the boundaries of engine output, you understand there will must be part dyno testing, and also that"s precisely the situation here. We had some borders to occupational within, so the the end result was a sane construct for the average mid-budget hot rodder. These boundaries included pump gas, a minimum that 350 lb-ft in ~ 2,500 rpm, and also a close to lope-free idle of no an ext than 850 rpm. Together for output, our goal to be to watch if 600 hp indigenous a 350 block running on pump gas was also feasible. In the process, we would look in ~ some more recent speed parts, plus part tried-and-tested parts. Every this, it have to be said, will be attempted there is no the aid of a blower or nitrous.
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400 Cubes with A 350 Block! It"s doubtful any of us have to be reminded that much more cubes means a stouter engine, however it"s been part 35 years since GM made the 400-cube variation of the small-block. These often tended to have actually an overheating and also cracking problem, which has actually resulted in a scarcity the usable ones. The very same cannot be claimed of the 350 block. It"s around as dependable as a block have the right to get and also there room still millions accessible to the hot rodder. Stretching a 350 come 383 inches has actually been a typical practice because that the best component of 20 years. The question here is, have the right to we walk more? In terms of bore diameter, there is not much room to go an ext than 30 over, back a sonic tester can discover blocks good for as much as 60 over. The combination to get a 383 is to bore the block 30 end (to 4.030 inches) and also use a 3.75-inch stroker crank. The stroke boost over share is 0.27-inch. Crowding this into a 350 block normally method cutting an ext rod clearance into the bottom of the bores and also the political parties of the crankcase. The amount needed to carry out a 383 sometimes compromises the block, and also the clearancing goes right into the water jacket.
Going to 408 customs in an effort to accomplish our 600hp goal could look favor a huge expense, but a stock factory crank at this power level will certainly be fine on the means to the limit. This makes a stout aftermarket crank an ext or less important to the engine"s ultimate survival. If a crank is needed, climate it may also be a stroker crank, together this will contribute to the output as well as beefing increase the bottom end.
The piston needs to accomplish the demands of an engine such as this room a small more an important than normal. First, to ease the reciprocating loads brought about by a stroke boost of over half an inch, we should go for a tough piston the is additionally light, and these two factors are, because that the most part, diametrically opposed. Fortunately, Mahle has actually a piston that fits the invoice really well. Not only is the light, but this high-tech piston attributes thinner rings the are also narrower in arrangement view. This makes them able to seal up better with much less ring drag, and also that"s vital issue on a stroker motor.
At this point, our 350 upgrade is feather good. We have 58 cubes an ext than stock, however that will certainly not be of much use if the heads can"t it is provided the waiting to feed those extra cubes.
Cylinder Heads when AFR introduced their 195cc harbor Eliminator heads, it was without any an excellent fanfare, so fist from our direction was rather limited. But rumors of great results through these heads (typical street price under $1,500) retained cropping up, so it looked like time to investigate. That was a year ago. Because then, we have sat in ~ above dyno tests on four occasions and the output figures achieved were strong. Because that an air-hungry 408, some top-notch heads would be essential if results were come reflect the investment of time and money in the bottom end. This AFR top looked like they would certainly fit the bill and also do so in ~ a an excellent price.
The AFR Eliminator heads feature 2.05-/1.60-inch valves and also are CNC ported. As a pioneer in the ar of both aftermarket cylinder heads and CNC porting, AFR has over a quarter century of experience to attract on. The Eliminator heads room a culmination that this experience, and also represent some severe fine tuning of the 23-degree Chevy heads.
AFR has constantly been very solid in the price department. This is due to the fact that they CNC port these heads to a finish that it is intended the most cost-effective result. If the finish is make finer, the cost escalates dramatically, if power might only change marginally-and it might go either up or down here. If the complete were do coarser, the price would certainly drop only minimally, if the flow and power would drop measurably. Yet at the end of the day, end up is, at best, a second-order effect. The primary factor toward a functional head is port and also chamber shape. Failure here and it matters small how good the surface end up is.
Along with great flow, the AFR entry ports likewise generated swirl numbers that typically deliver good results. Extr probing showed good port velocities and also velocity distribution. Every this adds approximately promising results on the dyno.
As an excellent as every the gas dynamics of this heads were, it was still short of the amount total. Other choices could make a big difference, specifically if you intended to usage them through a hydraulic roller cam. The valves, springs, and also retainers we used have been selected to enhance the rpm capacity of the top without going come a spring as hefty as would normally be used. Because that instance, the valves had an 8mm stem (a tiny under 5/16) through a lightweight head. This chops the weight of the input valve from generally 129 grams to 105 grams v a commensurate save ensuing on the exhaust. The valvesprings provided for this heads room high-dollar items and additionally present a performance advantage. Because that our 408, we are going to require a many valve lift. To do a secure valvetrain, the feather must have actually low mass and a high natural resonant frequency. The AFR spring has both. That weighs a scant 92 grams (typical is 110) and delivers 160 lbs ~ above the seat, and also 424 lbs in ~ .600-inch valve lift. Because it is a much smaller diameter than most springs, it demands only a small retainer. This weighs a slim 17.5 grams, as opposed to a usual retainer fixed of 33.5 grams. Every this attention to detail chops a worthwhile quantity of mass the end of one of the most mass-critical locations of the valvetrain. AFR"s efforts in this direction mean the heads are ideally suitable to hydraulic roller cams, and also to high-lift heavy street rollers-the latter is simply what we room going come use.
Cam an option Probably the two top reasons why street engines usage a hydraulic roller space the zero-service factor and also the quiet operation. What this has actually done for numerous hot rodders is exclude, the solid street roller indigenous consideration. We have run COMP"s solid street rollers for numerous years; ours longest one in business has over 80,000 miles on it, and also has however to require a lash adjustment. Also, by make the lash adjustments through care, the valvetrain is far from noisy. The sound is an ext like a purr, and is much from objectionable. This is being brought up because a solid street roller was a an ext appropriate choice; let"s look in ~ this 408"s requirement. First, it has a lot of inches, so that will need to have actually a high-lift valvetrain. Secondly, there is sufficient airflow v the heads to make power up to 7,000 rpm. This method we have actually to attend to two contradictory situations: high lift and high rpm. Added to that, we essential a long and also reliable business life. A COMP Xtreme power street roller takes treatment of that. The profiles favored were 286XSR for the intake, and 292XSR for the exhaust. This profiles space 248 degrees and also 254 levels for the intake and exhaust respectively. V COMP"s 1.65:1 rocker (PN 1006) on the intake and 1.5:1 (PN 1004) ~ above the exhaust, network valve lift after lash was .620-inch and .588-inch.
Induction The will is come test two intakes. First, we wanted to see exactly how well one Edelbrock Air-Gap performer RPM fared on an engine v a projected calculation of end 520 hp. Endure has presented that on engines in the 300 come 500hp range, this manifold really delivers. Several of our previous testing has also shown that at about 530 hp, it shows up to it is in approaching a limit. However testing on our 408 should better define its already well-appreciated characteristics for producing a really strong low end with what is, because that a two-plane intake, a very creditable height end. Next on the list to check is a Holley strip Dominator. This is a manifold which seems to be short on credit transaction for its great power capabilities. ~ above engines qualified of 500 or much more horsepower, ours previous experience has presented it gets the project done in style. V the hot spec the this 408, it seemed like a great idea come reacquaint ourselves with the piece Dominator"s strength potential. Both manifolds were confirm for a harbor match. Both aligned pretty well, so that was made decision that we would certainly run both join in out-of-the-box form.
Spark Generation for ignition, we supplied a Pertronix HEI-style distributor with vacuum advance. This was equipped v the lightest springs for the mechanical advancement and fed the spark come the plugs via ACCEL 8.8mm plug cables. So why the vacuum advance? with this coupled to manifold vacuum (not the porting vacuum source) we were able to acquire the engine much an ext street friendly. Not only did the vacuum advancement allow us to obtain a far better and smoother idle, but also it consumed much less fuel at idle and part throttle cruise.
Our key push to be to see if we might make 600 hp, and also with only 6 hrs of dyno time obtainable to us, us did not spend too much time with the Edelbrock Air-Gap performer RPM tests. The allude was more to watch what the "bulk" difference might be between the two-plane Performer and also the single-plane Holley piece Dominator. Walk in, it was already known the this combination would require a big cfm that carburetion. In ~ the very same time, us did not desire to deteriorate driveability, therefore we decided to run the Holley 750 equipped v the 850 baseplate. Through its measured 900-cfm capability, this looked to be a an excellent compromise on what had to be a one-shot deal.
The custom calibration ~ above the carb proved to be appropriate on the money, as any type of jet adjust up or down shed output. The outcomes are in the chart on p. 92. Uneven you are familiar with this type of result, this numbers space going to take a little explaining because that the true photo to it is in more clearly seen. First, keep in mind that the numbers are all rounded to the nearest totality lb-ft or hp. The reality is that this engine missed the 550hp note by simply 1.4 hp. That"s a an extremely creditable number because that a two-plane intake. But look at the optimal torque. That is only about 510 lb-ft. Normally, this would be somewhat higher, but due to the fact that the height torque is at relatively high rpm, the manifold is currently pushed close to its border in terms of finest airflow per transformation of the engine. In ~ the top torque figures, this combo is currently well over the 500hp note that Edelbrock envisaged would be around the limit of that is use. What we have actually here is an instance of a subtle parts mismatch. The demand from huge cubes and high rpm is being successfully communicated, via a collection of highly effective heads, come the entry manifold and carb. However as the large demand from the cubes/rpm/heads combo is increasing, the flow capacity of the intake/carb combo is nearby to being maxed out, also at 5,000 rpm. Result: due to the fact that peak torque desires to take place so far up the rpm range on this big-inch motor, the height torque worth is being compromised by lack of adequate airflow. Don"t gain me wrong here, the Edelbrock Air-Gap demonstrate is a good manifold. If, 20 years ago, you had asked a agree engine builder even if it is a two-plane intake might be made come support even 500 hp, the prize would have been, "not a chance." If we want to view that 5 come 10 lb-ft the increase, then it"s a situation of using a cam around 10-degrees shorter to move the powerband down into a range more suited come the intake.
So, as good as the Edelbrock two-plane may be, our following tests will present if over there is any kind of substance come our concept that this engine simply needs much more induction capacity.
Single-Plane check The first move to be to swap the end the two-plane intake because that the single-plane Holley Dominator. On optimal of this go the simple mildly-modified 750 through calibrations deemed vital for the single-plane setup. Although output below 4,500 rpm dropped, this 408 come on strong from there on up. Height torque went approximately 516 lb-ft, and also peak hp come 572. That was good, but the carb capacity quiet looked a small on the weak side for this deep-breathing 408. Come check and see if this was so, the 900-cfm 750 (with the 850 baseplate) was installed. Presto! 526 lb-ft and also 579 hp. Us are beginning to look good here. Now working top top the presumption that if part is good, and more is better, the 930-cfm (modified 850) might be just right, so it to be installed. Result: 534 lb-ft and 587 hp.
At this point, you have the right to see us are closely approaching our target 600 hp. The problem is, we have actually now used our best carb, however as frequently as not, a 2-inch spacer on one engine the this size deserve to make the carb look bigger, so that was the next move. This brought about a best of 541 lb-ft and also 595.4 hp. Seeing as our 600hp target to be so close, ours next move would have been to carry out a tiny stagger jetting and adjust the oil because that a good synthetic. That would have practically certainly given us the 600 hp us were spring for, but time was against us.
It"s worth looking at our graph compare the output v the two-plane versus the output through the single-plane. In ring terms, the Air-Gap Performer developed 45 lb-ft an ext down low, vice versa, the strip Dominator produced 45 hp an ext at the optimal end. As have the right to be checked out from the graph, the crossover allude was a shade over 4,500 rpm. As far as the valvetrain went, this COMP solid street roller ran prefer a 595hp Swiss clock at 6,800 rpm, and also valvetrain noise in ~ idle for our diligently lashed mechanism was proper any much more than a common high-performance hydraulic. Together for the AFR heads, they proved to be capable of feeding the 408 inches created by the K1 crank and rods, and also Mahle pistons.
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