Any time you push the borders of engine output, you recognize there will need to be part dyno testing, and also that"s exactly the situation here. We had actually some limits to occupational within, so the the end an outcome was a sane develop for the average mid-budget hot rodder. These borders 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. As for output, ours goal was to view if 600 hp indigenous a 350 block running on pump gas was even feasible. In the process, we would look at some newer speed parts, plus part tried-and-tested parts. All this, it have to be said, will certainly be attempted there is no the assist of a blower or nitrous.

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400 Cubes with A 350 Block! It"s doubtful any of us should be reminded that more cubes way a stouter engine, but it"s been some 35 years due to the fact that GM make the 400-cube variation of the small-block. These had tendency to have an overheating and cracking problem, which has resulted in a scarcity the usable ones. The exact same cannot be said of the 350 block. It"s about as reputable as a block deserve to get and there are still millions easily accessible to the warm rodder. Stretching a 350 come 383 inches has actually been a typical practice for the best part of 20 years. The question here is, deserve to we walk more? In terms of bore diameter, over there is not much room come go much more than 30 over, although a sonic tester can discover blocks great for as much as 60 over. The mix to obtain a 383 is to bore the block 30 end (to 4.030 inches) and also use a 3.75-inch stroker crank. The stroke increase over share is 0.27-inch. Crowding this right into a 350 block normally way cutting more rod clearance into the bottom that the bores and the political parties of the crankcase. The amount needed to perform a 383 sometimes compromises the block, and the clearancing goes right into the water jacket.

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See all 22 photos

Going to 408 inch in an initiative to achieve our 600hp goal can look choose a huge expense, however a stock manufacturing facility crank in ~ this strength level will be fine on the way to that limit. This renders a stout aftermarket crank much more or less essential to the engine"s ultimate survival. If a crank is needed, then it may as well be a stroker crank, as this will add to the output and beefing increase the bottom end.

The piston requirements to fulfill the needs of an engine such together this room a little more an essential than normal. First, to lull the reciprocating loads brought around by a stroke boost of over fifty percent an inch, we should go for a difficult piston the is likewise light, and also these two determinants are, for the most part, diametrically opposed. Fortunately, Mahle has actually a piston that fits the invoice really well. Not only is it light, but this high-tech piston attributes thinner rings that are also narrower in arrangement view. This makes them able to seal up better with less ring drag, and that"s an essential issue on a stroker motor.

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At this point, ours 350 upgrade is looking good. We have actually 58 cubes an ext than stock, however that will not it is in of lot use if the top can"t supply the wait to feeding those extra cubes.

Cylinder Heads when AFR presented their 195cc harbor Eliminator heads, it was without any great fanfare, so attention from our direction was somewhat limited. However rumors of great results v these top (typical street price under $1,500) retained cropping up, so the looked choose time to investigate. That was a year ago. Since then, we have actually sat in ~ above dyno exam on 4 occasions and also the calculation figures completed were strong. Because that an air-hungry 408, part top-notch heads would certainly be needed if results were come reflect the investment of time and also money in the bottom end. This AFR top looked prefer they would certainly fit the bill and also do so at a good price.

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

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AFR has always been very solid in the cost department. This is because they CNC port these top to a finish that delivers the many cost-effective result. If the finish is make finer, the price escalates dramatically, if power may only readjust marginally-and it could go either up or down here. If the complete were do coarser, the price would drop just minimally, when the flow and power would certainly drop measurably. But at the finish of the day, end up is, in ~ best, a second-order effect. The primary variable toward a practical head is port and also chamber shape. Fail here and it matters little how an excellent the surface finish is.

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

As good as all the gas dynamics of these heads were, it to be still short of the amount total. Other choices could do a huge difference, specifically if you intend to usage them v a hydraulic roller cam. The valves, springs, and retainers us used have been selected to improve the rpm capability of the heads without going to a spring as heavy as would typically be used. For instance, the valves had actually an 8mm stem (a little under 5/16) through a lightweight head. This chops the load of the intake valve from commonly 129 grams come 105 grams through a commensurate save taking place on the exhaust. The valvesprings used for these heads space high-dollar items and additionally present a power advantage. Because that our 408, we are going to require a the majority of valve lift. To make a stable valvetrain, the feather must have actually low mass and a high natural resonant frequency. The AFR spring has actually both. It weighs a scant 92 grams (typical is 110) and delivers 160 lbs ~ above the seat, and 424 lbs in ~ .600-inch valve lift. Because it is a lot smaller diameter than most springs, it needs only a tiny retainer. This weighs a slim 17.5 grams, as opposed come a usual retainer massive of 33.5 grams. Every this attention to detail chops a worthwhile amount of mass the end of among the most mass-critical areas of the valvetrain. AFR"s initiatives in this direction average the heads are ideally suitable to hydraulic roller cams, and to high-lift solid street rollers-the latter is just what we are going to use.

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Cam choice Probably the two optimal reasons why street engines usage a hydraulic roller space the zero-service factor and also the quiet operation. What this has done for countless hot rodders is exclude the solid street roller native consideration. We have run COMP"s heavy street rollers for numerous years; our longest one in business has over 80,000 mile on it, and also has however to need a lash adjustment. Also, by making the lash adjustments v care, the valvetrain is much from noisy. The sound is an ext like a purr, and is far from objectionable. This is being brought up because a hard street roller was a more appropriate choice; let"s look at this 408"s requirement. First, it has a most inches, so it will require to have a high-lift valvetrain. Secondly, over there is sufficient airflow through the top to do power as much as 7,000 rpm. This method we have actually to address two inconsistent situations: high lift and also high rpm. Included to that, we necessary a long and reliable company life. A COMP Xtreme energy street roller takes treatment of that. The profiles liked were 286XSR for the intake, and 292XSR for the exhaust. This profiles are 248 degrees and 254 degrees for the intake and exhaust respectively. With COMP"s 1.65:1 rocker (PN 1006) on the intake and also 1.5:1 (PN 1004) on the exhaust, net valve lift ~ lash to be .620-inch and .588-inch.

Induction The intent is to test 2 intakes. First, we want to see exactly how well an Edelbrock Air-Gap show RPM fared on one engine v a projected calculation of end 520 hp. Endure has shown that ~ above engines in the 300 come 500hp range, this manifold yes, really delivers. Several of our previous experimentation has likewise shown that at around 530 hp, it appears to it is in approaching a limit. However testing on our 408 should far better define its already well-appreciated features for developing a really solid low finish with what is, because that a two-plane intake, a really creditable optimal end. Following on the perform to test is a Holley piece Dominator. This is a manifold which seems to be short on credit transaction for its an excellent power capabilities. ~ above engines capable of 500 or more horsepower, our previous experience has shown it gets the task done in style. Through the hot spec that this 408, it seemed favor a an excellent idea come reacquaint ourselves with the piece Dominator"s power potential. Both manifolds were confirm for a port match. Both aligned nice well, so it was chose that we would certainly run both intakes in out-of-the-box form.

Spark Generation for ignition, we provided a Pertronix HEI-style distributor through vacuum advance. This was equipped with the lightest springs because that the mechanical breakthrough and fed the spark to the plugs via ACCEL 8.8mm plug cables. Therefore why the vacuum advance? through this coupled to manifold vacuum (not the porting vacuum source) us were maybe to acquire the motor much much more street friendly. Not only did the vacuum advance allow us to gain a better and smoother idle, but additionally it consumed less fuel at idle and part throttle cruise.

Our main push to be to see if we could make 600 hp, and with only 6 hours of dyno time accessible to us, us did not invest too much time through the Edelbrock Air-Gap show RPM tests. The allude was much more to see what the "bulk" difference can be between the two-plane Performer and also the single-plane Holley piece Dominator. Going in, it was currently known that this mix would need a large cfm of carburetion. In ~ the exact same time, us did not want to compromise driveability, for this reason we made decision to operation the Holley 750 equipped with the 850 baseplate. V its measure up 900-cfm capability, this looked to be a an excellent compromise on what had actually to it is in a one-shot deal.

The tradition calibration ~ above the carb showed to be ideal on the money, as any jet readjust up or down lost output. The results are in the graph on p. 92. Uneven you are familiar with this sort of result, these numbers are going to take a tiny explaining for the true photo to it is in more plainly seen. First, note that the numbers room all rounded come the nearest totality lb-ft or hp. The truth is the this engine to let go the 550hp mark by just 1.4 hp. That"s a really creditable number because that a two-plane intake. However look at the peak torque. That is only about 510 lb-ft. Normally, this would certainly be rather higher, but due to the fact that the height torque is at fairly high rpm, the manifold is currently pushed near its limit in state of finest airflow per transformation of the engine. At the optimal torque figures, this combo is currently well end the 500hp mark that Edelbrock envisaged would be about the limit of its use. What we have actually here is an example of a subtle parts mismatch. The demand from huge cubes and high rpm is being efficiently communicated, via a set of highly reliable heads, to the intake manifold and also carb. Yet as the big demand native the cubes/rpm/heads combo is increasing, the flow capability of the intake/carb combo is near to gift maxed out, also at 5,000 rpm. Result: due to the fact that peak torque desires to happen so much up the rpm selection on this big-inch motor, the height torque value is being compromised by absence of enough airflow. Don"t get me wrong here, the Edelbrock Air-Gap show is a an excellent manifold. If, 20 years ago, you had actually asked a pro engine builder whether a two-plane intake could be made to support also 500 hp, the prize would have been, "not a chance." If we want to check out that 5 come 10 lb-ft of increase, then it"s a case of making use of a cam about 10-degrees shorter to move the powerband down right into a range more suited to the intake.

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

Single-Plane test The an initial move was to swap out the two-plane intake for the single-plane Holley Dominator. On peak of this walk the an easy mildly-modified 750 through calibrations deemed crucial for the single-plane setup. Back output below 4,500 rpm dropped, this 408 came on solid from there on up. Top torque went up to 516 lb-ft, and also peak hp to 572. That was good, yet the carbohydrate capacity still looked a tiny on the weak side for this deep-breathing 408. Come check and also see if this to be so, the 900-cfm 750 (with the 850 baseplate) was installed. Presto! 526 lb-ft and also 579 hp. Us are starting to look good here. Now working on the assumption that if part is good, and much more is better, the 930-cfm (modified 850) might be just right, for this reason it was installed. Result: 534 lb-ft and 587 hp.

At this point, you deserve to see us are very closely approaching ours target 600 hp. The trouble is, we have now provided our greatest carb, yet as regularly as not, a 2-inch spacer on one engine that this size deserve to make the carb look bigger, so the was the following move. This led to a ideal of 541 lb-ft and 595.4 hp. Seeing as our 600hp target to be so close, our next move would have been to execute a tiny stagger jetting and readjust the oil because that a an excellent synthetic. That would certainly have practically certainly given us the 600 hp we were spring for, but time was against us.

It"s worth looking at our graph compare the output through the two-plane versus the output v the single-plane. In round terms, the Air-Gap Performer created 45 lb-ft more down low, vice versa, the piece Dominator created 45 hp much more at the optimal end. As can be checked out from the graph, the crossover point was a shade over 4,500 rpm. As far as the valvetrain went, this COMP hard street roller ran like a 595hp Swiss clock at 6,800 rpm, and also valvetrain noise in ~ idle for our diligently lashed system was barely any an ext than a typical high-performance hydraulic. As for the AFR heads, they confirmed to be capable of feeding the 408 inches developed by the K1 crank and also rods, and Mahle pistons.

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See all 22 photosOur swirl and flow tests were performed on this SuperFlow circulation bench ideal after the calibration was checked and verified.
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