Any time you push the borders of engine output, you know there will should be some dyno testing, and also that"s precisely the instance here. We had some boundaries to work-related within, so that the end result was a sane build for the mean mid-budget warm rodder. These boundaries included pump gas, a minimum the 350 lb-ft in ~ 2,500 rpm, and also a near lope-free idle that no more than 850 rpm. Together for output, our goal was to watch if 600 hp native a 350 block to run on pump gas was even feasible. In the process, we would look in ~ some more recent speed parts, plus part tried-and-tested parts. Every this, it need to be said, will be attempted without the assist of a blower or nitrous.

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400 Cubes v A 350 Block! It"s doubtful any kind of of us should be reminded that an ext cubes method a stouter engine, yet it"s been part 35 years since GM do the 400-cube variation of the small-block. These had tendency to have actually an overheating and also cracking problem, which has actually resulted in a scarcity that usable ones. The very same cannot be stated of the 350 block. It"s about as trustworthy as a block can get and there are still millions easily accessible to the hot rodder. Stretching a 350 to 383 inches has been a common practice because that the best component of 20 years. The question below is, can we walk more? In regards to bore diameter, there is not much room to go more than 30 over, although a sonic tester can find blocks good for as much as 60 over. The mix to get a 383 is to boring 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 more rod clearance right into the bottom that the bores and also the political parties of the crankcase. The amount needed to carry out a 383 periodically compromises the block, and also the clearancing goes into the water jacket.

See all 22 photos
See all 22 photos

Going to 408 inch in an initiative to accomplish our 600hp goal can look favor a big expense, but a stock manufacturing facility crank at this power level will be fine on the means to the limit. This makes a stout aftermarket crank an ext or less essential to the engine"s can be fried survival. If a crank is needed, climate it may too be a stroker crank, together this will contribute to the output and beefing up the bottom end.

The piston demands to accomplish the needs of one engine such together this space a little more an important than normal. First, to ease the reciprocating tons brought around by a stroke boost of over half an inch, we have to go because that a challenging piston that is likewise light, and these two components are, for the most part, diametrically opposed. Fortunately, Mahle has a piston that fits the invoice really well. Not only is that light, but this high-tech piston functions thinner rings that are also narrower in setup view. This makes them able come seal up far better with less ring drag, and that"s an essential issue ~ above a stroker motor.

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

Cylinder Heads once AFR presented their 195cc port Eliminator heads, it was without any good fanfare, so fist from ours direction was somewhat limited. Yet rumors of an excellent results through these heads (typical street price under $1,500) kept cropping up, so that looked choose time to investigate. That was a year ago. Due to the fact that then, we have actually sat in ~ above dyno tests on four occasions and also the output figures achieved were strong. Because that an air-hungry 408, part top-notch heads would certainly be necessary if results were to reflect the invest of time and also money in the bottom end. These AFR heads looked favor they would fit the bill and do so at a an excellent price.

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

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

Along with good flow, the AFR entry ports likewise generated swirl number that commonly deliver great results. Additional probing showed good port velocities and velocity distribution. All this adds up to promising results on the dyno.

As great as every the gas dynamics of these heads were, it to be still brief of the amount total. Other choices could make a large difference, specifically if you intend to use them with a hydraulic roller cam. The valves, springs, and retainers we used have been selected to improve the rpm capacity of the top without going to a feather as heavy as would generally be used. Because that instance, the valves had an 8mm stem (a little under 5/16) through a lightweight head. This chops the load of the input valve from typically 129 grams come 105 grams with a commensurate save occurring on the exhaust. The valvesprings used for these heads are high-dollar item and additionally present a performance advantage. For our 408, we are going to need a many valve lift. To make a steady valvetrain, the spring must have low mass and a high organic resonant frequency. The AFR spring has actually both. It weighs a scant 92 grams (typical is 110) and delivers 160 lbs top top the seat, and 424 lbs in ~ .600-inch valve lift. Due to the fact that it is a much smaller diameter than most springs, it demands only a tiny retainer. This weighs a slim 17.5 grams, as opposed come a common retainer mass of 33.5 grams. Every this attention to information 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 typical the heads room ideally suitable to hydraulic roller cams, and also to high-lift solid street rollers-the latter is simply what we room going come use.

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Cam selection Probably the two top reasons why street engines use a hydraulic roller room the zero-service factor and the quiet operation. What this has actually done for many hot rodders is to exclude, the solid street roller indigenous consideration. We have actually run COMP"s heavy street rollers for plenty of years; our longest one in business has end 80,000 miles on it, and has yet to require a lash adjustment. Also, by do the lash adjustments through care, the valvetrain is much from noisy. The sound is more like a purr, and is far from objectionable. This is being lugged up due to the fact that a hard street roller to be a more appropriate choice; let"s look at this 408"s requirement. First, it has a the majority of inches, so that will need to have a high-lift valvetrain. Secondly, there is sufficient airflow v the top to make 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 service life. A COMP Xtreme energy street roller takes care of that. The profiles preferred were 286XSR for the intake, and 292XSR because that the exhaust. These profiles room 248 degrees and also 254 levels for the intake and also exhaust respectively. With COMP"s 1.65:1 rocker (PN 1006) on the intake and 1.5:1 (PN 1004) on the exhaust, network valve lift after lash was .620-inch and also .588-inch.

Induction The intent is come test 2 intakes. First, we want to see just how well one Edelbrock Air-Gap show RPM fared on one engine with a projected output of over 520 hp. Endure has displayed that top top engines in the 300 come 500hp range, this manifold yes, really delivers. Several of our previous experimentation has also shown that at around 530 hp, it shows up to be approaching a limit. But testing on our 408 should better define its already well-appreciated attributes for creating a really strong low finish with what is, because that a two-plane intake, a very creditable peak end. Following on the list to test is a Holley piece Dominator. This is a manifold which appears to be quick on credit for its an excellent power capabilities. Top top engines qualified of 500 or much more horsepower, ours previous endure has displayed it gets the project done in style. With the hot spec of this 408, the seemed favor a great idea come reacquaint ourselves v the piece Dominator"s strength potential. Both manifolds were checked for a harbor match. Both aligned quite well, so it was made decision that we would 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 v the lightest springs for the mechanical advance and fed the spark to the plugs via ACCEL 8.8mm plug cables. For this reason why the vacuum advance? with this coupled to manifold vacuum (not the ported vacuum source) us were may be to acquire the motor much much more street friendly. Not only did the vacuum development allow us to gain a far better and smoother idle, but also it consumed much less fuel at idle and component throttle cruise.

Our main push to be to check out if we could make 600 hp, and with just 6 hours of dyno time available to us, us did not invest too lot time v the Edelbrock Air-Gap demonstrate RPM tests. The allude was more to view what the "bulk" difference could be between the two-plane Performer and the single-plane Holley strip Dominator. Walking in, the was currently known that this combination would require a big cfm of carburetion. In ~ the exact same time, we did not want to weaken driveability, for this reason we determined to operation the Holley 750 equipped with the 850 baseplate. With its measure up 900-cfm capability, this looked to it is in a an excellent compromise ~ above what had actually to it is in a one-shot deal.

The tradition calibration on the carb verified to be right on the money, as any type of jet change up or down shed output. The results are in the graph on p. 92. Uneven you are acquainted with this type of result, this numbers space going to take it a small explaining for the true picture to be more clearly seen. First, keep in mind that the numbers are all rounded come the nearest whole lb-ft or hp. The fact is that this engine to let go the 550hp mark by simply 1.4 hp. That"s a very creditable number for a two-plane intake. But look in ~ the peak torque. The is only about 510 lb-ft. Normally, this would certainly be rather higher, but since the peak torque is at fairly high rpm, the manifold is already pushed close to its border in terms of ideal airflow per change of the engine. At the top torque figures, this combo is currently well over the 500hp mark that Edelbrock envisaged would certainly be around the limit of the use. What we have actually here is an example of a subtle parts mismatch. The need from large cubes and high rpm is being effectively communicated, via a collection of highly reliable heads, to the entry manifold and carb. However as the huge demand indigenous the cubes/rpm/heads combo is increasing, the flow capability of the intake/carb combo is close to being maxed out, even at 5,000 rpm. Result: since peak torque wants to occur so much up the rpm variety on this big-inch motor, the optimal torque worth is being endangered by absence of sufficient airflow. Don"t get me dorn here, the Edelbrock Air-Gap show is a good manifold. If, two decades ago, you had actually asked a agree engine builder whether a two-plane intake can be made come support also 500 hp, the price would have been, "not a chance." If we want to check out that 5 come 10 lb-ft the increase, then it"s a case of using a cam around 10-degrees much shorter to move the powerband down right into a range much more suited come the intake.

So, as an excellent as the Edelbrock two-plane may be, our following tests will present if over there is any kind of substance come our theory that this engine just needs much more induction capacity.

Single-Plane check The first move was to swap the end the two-plane intake because that the single-plane Holley Dominator. On peak of this walk the simple mildly-modified 750 through calibrations deemed vital for the single-plane setup. Back output below 4,500 rpm dropped, this 408 come on strong from there on up. Peak torque went as much as 516 lb-ft, and also peak hp to 572. That was good, however the carbohydrate capacity still looked a tiny on the weak side for this deep-breathing 408. To check and see if this was so, the 900-cfm 750 (with the 850 baseplate) was installed. Presto! 526 lb-ft and 579 hp. Us are beginning to look good here. Currently working top top the presumption that if part is good, and much more is better, the 930-cfm (modified 850) can be simply right, for this reason it was installed. Result: 534 lb-ft and 587 hp.

At this point, you can see us are carefully approaching our target 600 hp. The problem is, we have now supplied our best carb, however as frequently as not, a 2-inch spacer on an engine the this size deserve to make the carbohydrate look bigger, so that was the next move. This led to a finest of 541 lb-ft and 595.4 hp. Seeing as our 600hp target was so close, our next relocate would have actually been to do a tiny stagger jetting and adjust the oil for a great synthetic. That would have almost certainly offered us the 600 hp us were looking for, yet time was against us.

It"s worth looking at our graph compare the output through the two-plane against the output with the single-plane. In round terms, the Air-Gap Performer developed 45 lb-ft more down low, conversely, the piece Dominator produced 45 hp an ext at the peak end. As can be checked out from the graph, the crossover suggest was a shade over 4,500 rpm. As far as the valvetrain went, this COMP hard street roller ran prefer a 595hp Swiss clock at 6,800 rpm, and valvetrain noise at idle because that our diligently lashed device was right any more than a typical high-performance hydraulic. Together for the AFR heads, they proved to be qualified of feeding the 408 inches produced by the K1 crank and rods, and also Mahle pistons.

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See all 22 photosOur swirl and flow exam were performed on this SuperFlow flow bench appropriate after that is calibration was checked and also verified.
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