Any time you push the limits of engine output, you recognize tbelow will need to be some dyno testing, and also that"s exactly the instance below. We had actually some borders to occupational within, so that the end outcome was a sane develop for the average mid-budacquire hot rodder. These limits included pump gas, a minimum of 350 lb-ft at 2,500 rpm, and a near lope-totally free idle of no even more than 850 rpm. As for output, our goal was to watch if 600 hp from a 350 block running on pump gas was also feasible. In the procedure, we would certainly look at some more recent speed parts, plus some tried-and-tested parts. All this, it have to be said, will certainly be attempted without the help of a breduced or nitrous.
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400 Cubes With A 350 Block! It"s doubtful any of us need to be reminded that more cubes indicates a stouter engine, but it"s been some 35 years given that GM made the 400-cube version of the small-block. These tended to have actually an overheating and cracking difficulty, which has actually resulted in a scarcity of usable ones. The same cannot be sassist of the 350 block. It"s around as reliable as a block can acquire and also tright here are still millions easily accessible to the warm rodder. Stretching a 350 to 383 inches has been a common practice for the ideal component of 20 years. The question below is, have the right to we go more? In terms of bore diameter, tbelow is not a lot room to go even more than 30 over, although a sonic tester can find blocks excellent for as much as 60 over. The combicountry to gain a 383 is to bore the block 30 over (to 4.030 inches) and usage a 3.75-inch stroker crank. The stroke rise over stock is 0.27-inch. Crowding this into a 350 block normally indicates cutting even more rod clearance into the bottom of the bores and also the sides of the crankinstance. The amount necessary to do a 383 periodically compromises the block, and the clearancing goes into the water jacket.
Going to 408 inches in an effort to accomplish our 600hp goal could look like a big expense, however a stock factory crank at this power level will certainly be well on the means to its limit. This makes a stout aftermarket crank even more or much less vital to the engine"s ultimate survival. If a crank is essential, then it may as well be a stroker crank, as this will certainly add to the output and also beefing up the bottom finish.
The piston demands to fulfill the needs of an engine such as this are a small more crucial than normal. First, to ease the reciprocating loads lugged about by a stroke increase of over half an inch, we must go for a hard piston that is also light, and these two components are, for the a lot of part, diametrically opposed. Fortunately, Mahle has actually a piston that fits the bill really well. Not only is it light, however this high-technology piston attributes thinner rings that are likewise narrower in setup view. This renders them able to seal up better through less ring drag, and also that"s an important issue on a stroker motor.
At this allude, our 350 upgrade is looking excellent. We have 58 cubes more than stock, however that will not be of much usage if the heads can"t supply the air to feed those extra cubes.
Cylinder Heads When AFR introduced their 195cc port Eliminator heads, it was without any great fanfare, so attention from our direction was somewhat limited. But rumors of good results through these heads (typical street price under $1,500) maintained cropping up, so it looked prefer time to investigate. That was a year ago. Due to the fact that then, we have sat in on dyno tests on 4 occasions and also the output figures accomplished were solid. For an air-hungry 408, some top-notch heads would certainly be necessary if outcomes were to reflect the investment of time and money in the bottom end. These AFR heads looked prefer they would fit the bill and do so at a good price.
The AFR Eliminator heads feature 2.05-/1.60-inch valves and also are CNC ported. As a pioneer in the area of both aftermarket cylinder heads and CNC porting, AFR has over a quarter century of endure to draw on. The Eliminator heads are a culmination of this endure, and also represent some significant fine tuning of the 23-level Chevy heads.
AFR has actually always been exceptionally strong in the cost department. This is bereason they CNC port these heads to a finish that delivers the a lot of cost-reliable outcome. If the end up is made finer, the expense escalates substantially, while power might just adjust marginally-and it might go either up or down right here. If the complete were made coarser, the price would drop only minimally, while the flow and also power would certainly drop measurably. But at the finish of the day, complete is, at finest, a second-order impact. The main variable towards a functional head is port and chamber form. Fail right here and it matters bit how great the surconfront complete is.
Alengthy via excellent circulation, the AFR intake ports likewise created swirl numbers that commonly deliver good outcomes. More probing confirmed good port velocities and velocity distribution. All this adds as much as promising results on the dyno.
As excellent as all the gas dynamics of these heads were, it was still brief of the amount total. Other options could make a large difference, especially if you intend to use them through a hydraulic roller video camera. The valves, springs, and also retainers we provided have actually been selected to improve the rpm capability of the heads without going to a spring as heavy as would generally be offered. For circumstances, the valves had an 8mm stem (a tiny under 5/16) with a lightweight head. This chops the weight of the intake valve from generally 129 grams to 105 grams via a commensurate save taking place on the exhaust. The valvesprings offered for these heads are high-dollar items and also also existing a performance benefit. For our 408, we are going to need most valve lift. To make a stable valvetrain, the spring need to have actually low mass and also a high organic resonant frequency. The AFR spring has actually both. It weighs a scant 92 grams (typical is 110) and delivers 160 lbs on the seat, and 424 lbs at .600-inch valve lift. Since it is a a lot smaller sized diameter than most springs, it requirements just a little retainer. This weighs a slim 17.5 grams, as opposed to a typical retainer mass of 33.5 grams. All this attention to detail chops a worthwhile amount of mass out of one of the the majority of mass-crucial areas of the valvetrain. AFR"s initiatives in this direction mean the heads are ideally suited to hydraulic roller cams, and to high-lift solid street rollers-the last is just what we are going to usage.
Cam Selection Probably the two height factors why street engines usage a hydraulic roller are the zero-business element and the quiet operation. What this has done for many kind of hot rodders is exclude the solid street roller from consideration. We have run COMP"s solid street rollers for many years; our longest one in business has actually over 80,000 miles on it, and has yet to need a lash adjustment. Also, by making the lash adjustments via treatment, the valvetrain is much from noisy. The sound is even more prefer a purr, and is much from objectionable. This is being brought up because a solid street roller was a much more correct choice; let"s look at this 408"s need. First, it has the majority of inches, so it will certainly have to have a high-lift valvetrain. Secondly, there is sufficient aircirculation through the heads to make power approximately 7,000 rpm. This indicates we have to resolve 2 contradictory situations: high lift and also high rpm. Added to that, we required a lengthy and trusted business life. A COMP Xtreme Energy street roller takes treatment of that. The propapers chosen were 286XSR for the intake, and also 292XSR for the exhaust. These prorecords are 248 degrees and also 254 degrees for the intake and exhaust respectively. With COMP"s 1.65:1 rocker (PN 1006) on the intake and 1.5:1 (PN 1004) on the exhaust, net valve lift after lash was .620-inch and also .588-inch.
Induction The intent is to test two intakes. First, we wanted to check out just how well an Edelbrock Air-Void Performer RPM fared on an engine with a projected output of over 520 hp. Experience has displayed that on engines in the 300 to 500hp range, this manifold really delivers. Several of our previous testing has likewise shown that at about 530 hp, it shows up to be approaching a limit. But experimentation on our 408 have to better specify its currently well-appreciated features for producing a really solid low finish through what is, for a two-plane intake, a very creditable top end. Next on the list to test is a Holley Sexpedition Dominator. This is a manifold which appears to be short on credit for its excellent power capabilities. On engines qualified of 500 or more horsepower, our previous experience has actually shown it gets the job done in style. With the warm spec of this 408, it appeared favor an excellent concept to reacquaint ourselves via the Strip Dominator"s power potential. Both manifolds were checked for a port match. Both aligned pretty well, so it was chose that we would run both inabsorbs out-of-the-box develop.
Spark Generation For ignition, we supplied a Pertronix HEI-style distributor via vacuum advancement. This was equipped through the lightest springs for the mechanical breakthrough and also fed the spark to the plugs by means of ACCEL 8.8mm plug cables. So why the vacuum advance? With this coupcaused manifold vacuum (not the ported vacuum source) we were able to gain the motor a lot more street friendly. Not just did the vacuum advancement enable us to acquire a far better and smovarious other idle, yet likewise it consumed much less fuel at idle and also part throttle cruise.
Our major push wregarding see if we can make 600 hp, and via just 6 hrs of dyno time available to us, we did not spend also a lot time via the Edelbrock Air-Void Performer RPM tests. The suggest was more to watch what the "bulk" difference might be in between the two-plane Perprevious and the single-plane Holley Strip Dominator. Going in, it was currently well-known that this combination would need a large cfm of carburetion. At the exact same time, we did not desire to compromise driveability, so we determined to run the Holley 750 equipped with the 850 baseplate. With its measured 900-cfm capability, this looked to be a great compromise on what had actually to be a one-swarm deal.
The custom calibration on the carb showed to be best on the money, as any jet change up or dvery own shed output. The outcomes are in the chart on p. 92. Unless you are familiar through this sort of result, these numbers are going to take a small explaining for the true photo to be more plainly seen. First, note that the numbers are all rounded to the nearemainder entirety lb-ft or hp. The fact is that this engine missed the 550hp note by just 1.4 hp. That"s a really creditable number for a two-aircraft intake. But look at the top torque. That is only around 510 lb-ft. Generally, this would be somewhat higher, however because the optimal torque is at reasonably high rpm, the manifold is currently pumelted near its limit in regards to ideal airflow per rdevelopment of the engine. At the top torque figures, this combo is currently well over the 500hp note that Edelbrock envisaged would be about the limit of its usage. What we have right here is an instance of a subtle components miscomplement. The demand from big cubes and also high rpm is being successfully interacted, by means of a set of very reliable heads, to the intake manifold and carb. But as the big demand also from the cubes/rpm/heads combo is raising, the flow capcapability of the intake/carb combo is close to being maxed out, also at 5,000 rpm. Result: Since peak torque desires to happen so far up the rpm range on this big-inch motor, the peak torque worth is being endangered by lack of adequate airflow. Don"t get me wrong here, the Edelbrock Air-Void Perprevious is an excellent manifold. If, 20 years back, you had asked a pro engine builder whether a two-aircraft intake can be made to support also 500 hp, the answer would certainly have been, "not a chance." If we desire to see that 5 to 10 lb-ft of rise, then it"s a instance of utilizing a video camera around 10-levels shorter to relocate the powerband dvery own right into a selection even more suited to the intake.
So, as excellent as the Edelbrock two-plane might be, our following tests will display if tbelow is any kind of substance to our concept that this engine simply needs more induction capacity.
Single-Plane Test The first relocate wregarding swap out the two-airplane intake for the single-airplane Holley Dominator. On optimal of this went the fundamental mildly-modified 750 with calibrations reputed necessary for the single-plane setup. Although output below 4,500 rpm dropped, this 408 came on solid from tright here on up. Peak torque went approximately 516 lb-ft, and also peak hp to 572. That was good, but the carb capacity still looked a little on the weak side for this deep-breathing 408. To examine and view if this was so, the 900-cfm 750 (with the 850 baseplate) was mounted. Presto! 526 lb-ft and also 579 hp. We are starting to look excellent here. Now functioning on the presumption that if some is good, and also more is better, the 930-cfm (modified 850) could be simply appropriate, so it was set up. Result: 534 lb-ft and also 587 hp.
At this allude, you can see we are closely approaching our taracquire 600 hp. The problem is, we have actually currently offered our biggest carb, however as regularly as not, a 2-inch spacer on an engine of this dimension have the right to make the carb look bigger, so that was the next move. This caused a best of 541 lb-ft and 595.4 hp. Seeing as our 600hp tarobtain was so close, our next move would have been to execute a tiny stagger jetting and readjust the oil for a great fabricated. That would certainly have almost absolutely given us the 600 hp we were in search of, but time was versus us.
It"s worth looking at our graph comparing the output with the two-plane versus the output with the single-plane. In round terms, the Air-Gap Perprevious developed 45 lb-ft even more down low, whereas the Spilgrimage Dominator produced 45 hp even more at the peak finish. As have the right to be seen 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 favor a 595hp Swiss watch at 6,800 rpm, and valvetrain noise at idle for our diligently laburned mechanism was barely any kind of even more than a typical high-performance hydraulic. As for the AFR heads, they proved to be capable of feeding the 408 inches produced by the K1 crank and also rods, and also Mahle pislots.
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