Any time you press the borders of engine output, you recognize there will need to be part dyno testing, and that"s exactly the situation here. We had some borders to work within, so that the end an outcome was a sane develop for the median mid-budget warm rodder. These limits included pump gas, a minimum the 350 lb-ft in ~ 2,500 rpm, and also a near lope-free idle the no more than 850 rpm. Together for output, our goal to be to watch if 600 hp from a 350 block running on pump gas was also feasible. In the process, we would look in ~ some newer speed parts, plus part tried-and-tested parts. Every this, it have to be said, will certainly be attempted there is no the help of a blower or nitrous.

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400 Cubes through A 350 Block! It"s doubtful any of us must be reminded that more cubes method a stouter engine, yet it"s been part 35 years because GM made the 400-cube variation of the small-block. These tended to have actually an overheating and also cracking problem, which has resulted in a scarcity of usable ones. The same cannot be stated of the 350 block. It"s around as dependable as a block can get and there space still millions available to the warm rodder. Extending a 350 come 383 inches has been a usual practice because that the best part of 20 years. The question below is, can we go more? In regards to bore diameter, over there is not lot room come go much more than 30 over, return a sonic tester can find blocks an excellent for as much as 60 over. The mix to get a 383 is to boring the block 30 end (to 4.030 inches) and use a 3.75-inch stroker crank. The stroke boost over stock is 0.27-inch. Crowding this into a 350 block normally way cutting an ext rod clearance right into the bottom the the bores and also the political parties of the crankcase. The amount needed to carry out a 383 occasionally compromises the block, and the clearancing goes right into the water jacket.


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Going to 408 inch in an effort to attain our 600hp goal can look favor a large expense, yet a stock factory crank at this strength level will be well on the method to its limit. This provides a stout aftermarket crank an ext or less vital to the engine"s can be fried survival. If a crank is needed, climate it may as well be a stroker crank, as this will add to the output and beefing increase the bottom end.


The piston demands to satisfy the demands of one engine such as this space a tiny more vital than normal. First, to lull the reciprocating lots brought about by a stroke rise of over fifty percent an inch, we have to go because that a challenging piston that is likewise light, and also these two factors are, for the many part, diametrically opposed. Fortunately, Mahle has actually a piston the fits the invoice really well. Not only is the light, but this high-tech piston features thinner rings that are also narrower in setup view. This makes them able come seal up far better with much less ring drag, and also that"s crucial issue ~ above a stroker motor.


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At this point, our 350 upgrade is feather good. We have 58 cubes more than stock, however that will certainly not it is in of much use if the heads can"t supply the air to feed those extra cubes.


Cylinder Heads as soon as AFR introduced their 195cc harbor Eliminator heads, it was without any an excellent fanfare, so fist from our direction was somewhat limited. Yet rumors of great results through these heads (typical street price under $1,500) kept cropping up, so the looked prefer time come investigate. The was a year ago. Since then, we have actually sat in on dyno exam on 4 occasions and also the output figures achieved were strong. For an air-hungry 408, part top-notch heads would be required if results were to reflect the invest of time and money in the bottom end. These AFR top looked favor they would certainly fit the bill and do so at a an excellent price.


The AFR Eliminator heads attribute 2.05-/1.60-inch valves and also are CNC ported. Together a pioneer in the field of both aftermarket cylinder heads and CNC porting, AFR has actually over a 4 minutes 1 century of endure to draw on. The Eliminator heads are a culmination of this experience, and represent some serious fine tuning the the 23-degree Chevy heads.


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AFR has constantly been very solid in the expense department. This is since they CNC harbor these heads to a end up that delivers the many cost-effective result. If the complete is make finer, the expense escalates dramatically, while power might only adjust marginally-and it could go either up or under here. If the complete were made coarser, the price would drop just minimally, when the flow and power would certainly drop measurably. But at the end of the day, end up is, in ~ best, a second-order effect. The primary aspect toward a practical head is port and also chamber shape. Fail here and also it matters small how great the surface complete is.


Along with an excellent flow, the AFR entry ports additionally generated swirl numbers that frequently deliver great results. Added probing showed good port velocities and also velocity distribution. Every this adds as much as promising outcomes on the dyno.


As an excellent as all the gas dynamics of this heads were, it to be still short of the sum total. Other alternatives could do a big difference, especially if you intend to usage them through a hydraulic roller cam. The valves, springs, and also retainers we used have actually been selected to enhance the rpm capability of the top without going come a spring as heavy as would usually be used. For instance, the valves had actually an 8mm stem (a small under 5/16) through a lightweight head. This chops the load of the input valve from typically 129 grams to 105 grams through a commensurate save occurring on the exhaust. The valvesprings provided for this heads space high-dollar item and also present a power advantage. For our 408, we room going to need a the majority of valve lift. To do a stable valvetrain, the feather must have actually low mass and also a high herbal resonant frequency. The AFR spring has both. It weighs a scant 92 grams (typical is 110) and also delivers 160 lbs top top the seat, and 424 lbs at .600-inch valve lift. Due to the fact that it is a lot smaller diameter than many springs, it needs only a tiny retainer. This weighs a slim 17.5 grams, as opposed to a typical retainer fixed of 33.5 grams. All this attention to detail chops a worthwhile lot of mass the end of one of the many mass-critical locations of the valvetrain. AFR"s initiatives in this direction mean the heads space ideally suited to hydraulic roller cams, and also to high-lift heavy street rollers-the latter is simply what we are going come use.


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Cam choice Probably the two height reasons why street engines usage a hydraulic roller space the zero-service factor and also the quiet operation. What this has actually done for plenty of hot rodders is exclude, the hard street roller from consideration. We have actually run COMP"s solid street rollers for many years; ours longest one in organization has over 80,000 mile on it, and has yet to need a lash adjustment. Also, by make the lash adjustments through care, the valvetrain is much from noisy. The sound is an ext like a purr, and also is much from objectionable. This is being lugged up because a hard street roller to be a an ext appropriate choice; let"s look in ~ this 408"s requirement. First, it has actually a most inches, so the will require to have a high-lift valvetrain. Secondly, there is enough airflow through the top to do power as much as 7,000 rpm. This means we have actually to attend to two contradictory situations: high lift and high rpm. Included to that, we necessary a long and also reliable company life. A COMP Xtreme power street roller takes care of that. The profiles liked 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. With COMP"s 1.65:1 rocker (PN 1006) ~ above the intake and 1.5:1 (PN 1004) ~ above the exhaust, net valve lift ~ lash was .620-inch and .588-inch.


Induction The intent is come test two intakes. First, we want to see just how well one Edelbrock Air-Gap show RPM fared on one engine with a projected output of end 520 hp. Suffer has displayed that ~ above engines in the 300 to 500hp range, this manifold really delivers. Some of our previous testing has likewise shown that at around 530 hp, it shows up to be approaching a limit. Yet testing on our 408 should far better define its currently well-appreciated qualities for developing a really solid low finish with what is, because that a two-plane intake, a an extremely creditable height end. Following on the perform to test is a Holley piece Dominator. This is a manifold which seems to be quick on credit for its great power capabilities. On engines capable of 500 or more horsepower, our previous suffer has shown it gets the job done in style. V the warm spec of this 408, the seemed favor a an excellent idea to reacquaint ourselves through the strip Dominator"s strength potential. Both manifolds were confirm for a harbor match. Both aligned quite well, so the was made decision that we would certainly run both join in out-of-the-box form.


Spark Generation because that ignition, we supplied a Pertronix HEI-style distributor through vacuum advance. This was equipped through the lightest springs because that the mechanical advancement and fed the spark come the plugs via ACCEL 8.8mm plug cables. For this reason why the vacuum advance? v this combination to manifold vacuum (not the ported vacuum source) us were able to acquire the engine much much more street friendly. Not just did the vacuum development allow us to get a far better and smoother idle, but likewise it consumed less fuel in ~ idle and part throttle cruise.


Our key push was to check out if we can make 600 hp, and with only 6 hrs of dyno time easily accessible to us, we did not invest too much time with the Edelbrock Air-Gap demonstrate RPM tests. The suggest was an ext to check out what the "bulk" difference might be between the two-plane Performer and also the single-plane Holley strip Dominator. Walking in, the was currently known that this combination would need a big cfm the carburetion. In ~ the same time, we did not want to compromise driveability, for this reason we chose to run the Holley 750 equipped v the 850 baseplate. Through its measure 900-cfm capability, this looked to be a great compromise ~ above what had to it is in a one-shot deal.


The practice calibration top top the carb showed to be ideal on the money, as any kind of jet change up or down lost output. The outcomes are in the chart on p. 92. Unless you are acquainted with this type of result, these numbers space going to take a tiny explaining because that the true photo to be more plainly seen. First, keep in mind that the numbers room all rounded come the nearest totality lb-ft or hp. The fact is that this engine to let go the 550hp mark by simply 1.4 hp. That"s a really creditable number because that a two-plane intake. Yet look in ~ the peak torque. The is only about 510 lb-ft. Normally, this would be somewhat higher, but because the peak torque is at fairly high rpm, the manifold is already pushed near its border in state of best airflow per revolution of the engine. In ~ the optimal torque figures, this combo is already well end the 500hp mark that Edelbrock envisaged would be about the limit of the use. What we have actually here is an instance of a subtle components mismatch. The need from big cubes and also high rpm is being successfully communicated, via a collection of highly efficient heads, come the input manifold and also carb. Yet as the large demand native the cubes/rpm/heads combo is increasing, the flow capability of the intake/carb combo is near to gift maxed out, even at 5,000 rpm. Result: because peak torque desires to occur so much up the rpm range on this big-inch motor, the peak torque worth is being endangered by lack of sufficient airflow. Don"t gain me wrong here, the Edelbrock Air-Gap show is a good manifold. If, two decades ago, you had asked a agree engine builder whether a two-plane intake can be made to support even 500 hp, the answer would have actually been, "not a chance." If we want to check out that 5 to 10 lb-ft the increase, climate it"s a instance of using a cam around 10-degrees shorter to relocate the powerband down into a range much more suited come the intake.


So, as an excellent as the Edelbrock two-plane might be, our next tests will show if over there is any type of substance come our concept that this engine just needs more induction capacity.


Single-Plane check The first move was to swap the end the two-plane intake for the single-plane Holley Dominator. On peak of this went the simple mildly-modified 750 v calibrations deemed vital for the single-plane setup. Return output below 4,500 rpm dropped, this 408 come on strong from over there on up. Top torque went approximately 516 lb-ft, and also peak hp come 572. That was good, but the carbohydrate capacity quiet looked a little on the weak side for this deep-breathing 408. To check and also see if this to be so, the 900-cfm 750 (with the 850 baseplate) to be installed. Presto! 526 lb-ft and 579 hp. We are starting to look great here. Now working top top the presumption that if some is good, and more is better, the 930-cfm (modified 850) could be just right, for this reason it to be installed. Result: 534 lb-ft and also 587 hp.


At this point, you deserve to see us are very closely approaching our target 600 hp. The trouble is, we have now used our greatest carb, yet as regularly as not, a 2-inch spacer on an engine that this size have the right to make the carbohydrate look bigger, so the was the next move. This caused a best of 541 lb-ft and also 595.4 hp. Seeing as our 600hp target to be so close, our next move would have been to perform a little stagger jetting and adjust the oil because that a great synthetic. That would have almost certainly given us the 600 hp we were looking for, however time was against us.


It"s worth looking at our graph comparing the output v the two-plane against the output with the single-plane. In ring terms, the Air-Gap Performer produced 45 lb-ft more down low, conversely, the strip Dominator created 45 hp more at the height end. As can be watched from the graph, the crossover allude was a the shade over 4,500 rpm. As much as the valvetrain went, this COMP solid street roller ran favor a 595hp Swiss watch at 6,800 rpm, and also valvetrain noise at idle for our diligently lashed device was proper any more than a typical high-performance hydraulic. Together for the AFR heads, they confirmed to be capable of feeding the 408 inches created by the K1 crank and rods, and also Mahle pistons.

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See every 22 photosOur swirl and also flow tests were carried out on this SuperFlow flow bench appropriate after that is calibration was checked and also verified.
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