Thread: Need some advice

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Well cash flo is always the finial way to hp huh? ahhh as long as i can keep it under 2000.00 i guess . im not looking to race this truck . its going to be a daily driver . I will be towing a boat (runabout) but when i put my foot in it i want to feel it if you know what i mean . the old 290 hp is getting a little to weak for me now .

Originally Posted by my77chevy

Well cash flo is always the finial way to hp huh? ahhh as long as i can keep it under 2000.00 i guess . im not looking to race this truck . its going to be a daily driver . I will be towing a boat (runabout) but when i put my foot in it i want to feel it if you know what i mean . the old 290 hp is getting a little to weak for me now .

It wouldn't be very hard to spend twice 2 grand for a good top haft.I suggest you look for heads for a 350 to have intake runners no more than 185cc's.

HP ratings isn't what makes a street driven vehicle whatever it is.Those HP ratings generally have a peak in RPM's that are not generally used in daily driving.As you said torque is the focus you need to look at.The lower the torque curve,the better off you are.

Yes,I read where you said you didn't want to stroke it.But for the shortest path to your goal and the budget you stated,that is within the range of possibility.Just by the nature of C.I.'s,torque in bigger C.I. engines happens in normally driven RPM ranges.Well the torque curve begins at a lower RPM in bigger C.I. engines.And hopefully without getting into a debate of longer connecting rods VS shorter ones,the longest connecting rod you can fit into it helps aid in building a lower torque curve because of the longer the pistons dwell at TDC.So a very mile 383 would easily get you to your goal.Oh yeah,the thing is for the people closest to you when they want to know why your 383 is so much stronger than theirs,well you can just leave out the fact of the longer rods.It will make you look like a pro engine builder.

One last thing-for a 383,your looking to intake runners at 195cc.You want to maintain the volume of the intake charge at lower RPM ranges.But try to keep in mind you can always do a update with a set of heads at any point.The stroke and at cost of 2 grand is another matter.That is a building block that needs to be done first.

In the interest of giving equal time on the subject of connecting rod length, I will submit a tutorial from Iskenderian....

Tech Tip - 2005
Rod Lengths/Ratios: Much ado about almost nothing.

Why do people change connecting rod lengths or alter their rod length to stroke ratios? I know why, they think they are changing them. They expect to gain (usually based upon the hype of some magazine article or the sales pitch of someone in the parts business) Torque or Horsepower here or there in rather significant "chunks". Well, they will experience some gains and losses here or there in torque and or H.P., but unfortunately these "chunks" everyone talks about are more like "chips".

To hear the hype about running a longer Rod and making more Torque @ low to mid RPM or mid to high RPM (yes, it is, believe it or not actually pitched both ways) you'd think that there must be a tremendous potential for gain, otherwise, why would anyone even bother? Good question. Let's begin with the basics. The manufacture's (Chevy, Ford, Chrysler etc.) employ automotive engineers and designers to do their best (especially today) in creating engine packages that are both powerful and efficient. They of course, must also consider longevity, for what good would come form designing an engine with say 5% more power at a price of one half the life factor? Obviously none. You usually don't get something for nothing - everything usually has its price. For example: I can design a cam with tremendous high RPM/H.P. potential, but it would be silly of me (not to mention the height of arrogance) to criticize the engineer who designed the stock camshaft. For this engine when I know how poorly this cam would perform at the lower operating RPM range in which this engineer was concerned with as his design objective!

Yet, I read of and hear about people who do this all the time with Rod lengths. They actually speak of the automotive engine designer responsible for running "such a short Rod" as a "stupid SOB." Well, folks I am here to tell you that those who spew such garbage should be ashamed of themselves - and not just because the original designer had different design criteria and objectives. I may shock some of you, but in your wildest dreams you are never going to achieve the level of power increase by changing your connecting rod lengths that you would, say in increasing compression ratio, cam duration or cylinder head flow capacity. To illustrate my point, take a look at the chart below. I have illustrated the crank angles and relative piston positions of today's most popular racing engine, the 3.48" stroke small block 350 V8 Chevy in standard 5.7", 6.00", 6.125" and 6.250" long rod lengths in 5 degree increments. Notice the infinitesimal (look it up in the dictionary) change in piston position for a given crank angle with the 4 different length rods. Not much here folks, but "oh, there must be a big difference in piston velocity, right?" Wrong! Again it's a marginal difference (check the source yourself - its performance calculator).

To hear all this hype about rod lengths I'm sure you were prepared for a nice 30, 40, or 50 HP increase, weren't you? Well its more like a 5-7 HP increase at best, and guess what? It comes at a price. The longer the rod, the closer your wrist pin boss will be to your ring lands. In extreme situations, 6.125" & 6.250" lengths for example, both ring and piston life are affected. The rings get a double whammy affect. First, with the pin boss crowding the rings, the normally designed space between the lands must be reduced to accommodate the higher wrist pin boss. Second, the rings wobble more and lose the seal of their fine edge as the piston rocks. A longer Rod influences the piston to dwell a bit longer at TDC than a shorter rod would and conversely, to dwell somewhat less at BDC. This is another area where people often get the information backwards.

In fact, this may surprise you, but I know of a gentleman who runs a 5.5" Rod in a 350 Small Block Chevy who makes more horsepower (we're talking top end here) than he would with a longer rod. Why? Because with a longer dwell time at BDC the short rod will actually allow you a slightly later intake closing point (about 1 or 2 degrees) in terms of crank angle, with the same piston rise in the cylinder. So in terms of the engines sensitivity to "reversion" with the shorter rod lengths you can run about 2-4 degrees more duration (1-2 degrees on both the opening & closing sides) without suffering this adverse affect! So much for the belief that longer rod's always enhance top end power!

Now to the subject of rod to stroke ratios. People are always looking for the "magic number" here - as if like Pythagoras they could possibly discover a mathematical relationship which would secure them a place in history. Rod to stroke ratios are for the most part the naturally occurring result of other engine design criteria. In other-words, much like with ignition timing (spark advance) they are what they are. In regards to the later, the actual number is not as important as finding the right point for a given engine. Why worry for example that a Chrysler "hemi" needs less spark advance that a Chevrolet "wedge" combustion chamber? The number in and of itself is not important and it is much the same with rod to stroke ratios. Unless you want to completely redesign the engine (including your block deck height etc.) leave your rod lengths alone. Let's not forget after all, most of us are not racing at the Indy 500 but rather are hot rodding stock blocks.

Only professional engine builders who have exhausted every other possible avenue of performance should ever consider a rod length change and even they should exercise care so as not to get caught up in the hype.

http://www.iskycams.com/ART/techinfo/ncrank1.pdf

Actually Ed and us had the same discussion over dinner after a auction that John Lingerfelter(sp) was holding selling off 25 yrs of collected hot rod parts.We met Ed originally at a Indy Drag Racers auction 2 yrs before.It was John's operations and business that convinced me of the longer rod theory.At that time John's builds included 5.85 length rods with comparative dyno results.Hands down the 5.85 produced a great torque curve and a broader torque ban at a lower RPM.On the cheap-there was a method of using Buick rods that where 5.85.Currently John's company uses 6.0 rods.Now I know Ed Has been around forever,but John was and his company is the innovator on the cutting edge for a long time as well.From what I have seen from Linerfelter's(sp) and used in a drag race operation where E.T. gains where found with longer rods,well I am a believer.Well the other question is why then are stoker kits universally using 5.7 rods and not the shorter 400 rods??.Humm,must be something to that.

Oh yeah,God Rest John's soul.He was one of the good guys for sure.