540 RAT

Tech author David Vizard has another tech article in the new June '09 issue of Popular Hotrodding Magazine. On page 52 of that issue he shows one of his dyno graphs, comparing the results of a 106* LSA cam vs a 112* LSA cam in a 505ci, 700 hp BBC. He doesn't make clear any other build specs on the motor, but the accompanying text, as well as the graph, indicate that the 106* LSA cam made 21 more hp, and 30 more ft lbs peak, than the 112* LSA cam. The graph also shows that the 106* cam made more hp and torque than the 112* cam throughout the entire rpm range, which is the same thing we saw in that SBC LSA cam comparison article in the May '09 issue of Chevy High Performance magazine, awhile back, which was also discussed here.

Anyway, here is what Vizard said was the reason for the narrow LSA being clearly superior to the wider LSA in a big block:

"The most important factor in making hp is the circumference of the intake valve in relation to the cylinder's displacement. In a typical 350 SBC, each intake valve circumference has to feed 6.9 ci. But, a 454 BBC with stock 2.19 intake valves, has to feed 8.3 ci for every inch of valve circumference. So, even a 454 is air starved.

Because air demand on a BB cylinder can so easily outpace the flow capability of the intake valve until high lift, it needs a greater head start than would normally be the case. This puts the valve at a higher lift earlier in the intake event so that the valve reaches high lift (and consequently high flow) sooner. Because the cylinder can draw earlier, the port velocity in the first half of the opening event is higher. As a result, the ramming effect in the second half of the opening event is increased. We find from port and cylinder pressure measurements, that success in the first half of the induction, dictates the success in the second half. If the first half is not optimal, there is nothing that can be done in the second half to rectify the problem.

What this means is that the opening point of the intake valve for any given overall duration, needs to be sooner than for an equivalent cam in a SB. This translates into having cams with a "TIGHTER LSA" than we traditionally see."

Vizard may have a point here. Because if you recall, the winner of PHR's Big Block Engine Masters Challenge, 2 or 3 years ago also used a narrow 107* or 108* LSA. And of course he could have used anything he wanted in the pursuit of best average as well as best peak numbers. So, let the kicking and screaming begin…………..

Guru_4_hire

He wrote a similiar article on small blocks awhile ago. When I get home from work I will post it.

I have done a lot of thought into small blocks and the engine masters, it will take me awhile to dig up my old thoughts and what not so I will deal with it after work.

TheSkunkWorks

I just knew you'd start this up again when I saw that article. Rather than rehashing all of the reasons this is NOT prudent for every type of build...

http://forums.corvetteforum.com/c3-t...omparison.html

Viewers should be aware that there are many other factors which must be taken into account when spec'ing out a build in order to achieve results which match the needs of their specific application. Yes, there are specialized applications where it may be warranted, but in many cases (especially on the street) simply building for max peak numbers is IMCO a rookie mistake. Before following this tight LSA, very early intake valve closing, never mind idle vacuum or DCR approach, novice builders would be well advised to wrap their heads around this fact. 'Nough said. If you can't or refuse to understand that, you'll just have to learn this lesson the hard way...


TSW

gerry72

Well, it works for that engine on a dyno. Unless this engine is going into a race car, it has to be driven on the street in slow and stop and go traffic. The price has to be paid somewhere since engines -good engines, anyway- are a compromise.

540 RAT

Maybe some of you guys missed this part from above, "The graph also shows that the 106* cam made more hp and torque than the 112* cam throughout the entire rpm range". Other than idle vacuum, the big downside you talk about is ???

zwede

That would be throttle response, idle quality, fuel economy... All improve as LSA increases.

540 RAT

Idle quality, true if you want your car to sound like a grocery getter rather than a Hotrod. Fuel mileage, probably true, though anyone worrying about fuel mileage should not own a Hotrod, instead they should buy a Honda Civic. Throttle response, absolutely false. You obviously don't know what you are talking about. That is one of the commonly known strong points of a narrow LSA cam. And this comes from the earlier intake closing point, and the subsequent higher cylinder pressures. My 540 with its 108* LSA cam, is the quickest revving motor I've ever owned. You need to go do some more reading Markus. Or maybe actually drive a good running narrow LSA motor.

540 RAT

I'm not starting anything up AGAIN. That earlier magazine LSA comparison test discussion awhile back, was regarding small blocks, while this one is regarding big blocks. Since Vizard made a distintion between the two, I figured there might be some folks who'd like to see it. But you on the other hand, didn't have to click on it, did you? It sounds like you are all sour grapes because you've realized that you left some performance on the table. And for the record, it is NOT engraved in stone that anyone, including novices, HAVE to run a wide LSA. Vizard and the Big Block Engine Masters Challenge, beg to differ. To think that a wide LSA is the only way to go, is to bury your head in the sand. And it may shock you to know that quite a few guys out there do in fact run narrow LSA's, yes even on the street. Not only do they run good, but they SOUND like real Hotrods, rather than grocery getters. Oh, and feel free to share any big block back to back LSA comparisons that you've personally done to back up your position. We'll all be waiting………...

gkull

IMO - advancing or retarding a cam has a greater effect than lobe center angle

Way to much going on in port flow, ramp rate, total lift to make a general statement

MotorHead

As an engineering type myself the above is quite true, there is no free lunch you gain something here and lose something there.

63mako

The dyno charts start @ 2500 RPM. Cruising, off idle and low rpm throttle response, vacuum, ability to safely run pump fuel in real world driving conditions, part throttle operation and street manners below 2500 RPM are not even considered or encountered on the dyno. Try comparing a 106 LSA cam with big duration in a 700 HP car with an OD trans at part throttle cruise and in traffic to a 112 LSA. I have had both wide and narrow LSA cams in different engines and have run both on the strip and the street. Explained all the other downsides in your other post and here you are again spewing the same crap. You have knowlegable people with real world experience all telling you the same thing on both threads and presenting facts to back it up. You continually ignore anybody elses experience and the facts posted in the other thread and now this one. Peak power production is your only concern and the only real advantage to that 106 lsa. I, and many others will gladly give up 3% peak power or less from 2500 to redline with a 700 HP engine to have a much more streetable combination that is a pleasure to drive on the street not a chore. You just don't get it and never will.

I sold a 548 CI, 10.25 to 1 compression street engine for my buddy Randy right here on the forum about a year ago to a friend of Jim Moore with Ported Iron Dart 308 heads and a 110 LSA solid roller cam. 778 HP @ 7000 RPM and 680 Ft Lbs of torque on the dyno and it didn't sound like a grocery getter and wasn't hurting for horsepower or torque, it was built for the street, will run vacuum accessories and runs on 91 octane fuel. Since you have a 540 and like dyno charts here is one for you. Did he leave power on the table running a 110 LSA? Probably! So what! It hits 600 HP @ 4800 RPM and 600 Ft LBS @ 4300 RPM and its streetable and set up for an additional 300 HP nitrous shot!

Link to thread:http://forums.corvetteforum.com/c3-p...777-hp-na.html

69427

That's certainly a reasonably important piece of information that seemed to be left out of the original post.

Thanks for looking that up.

Little Mouse

Can't see how anyone can complain about a 454 or bigger rat
on everything from off idle torque to 2500 rpm or higher up the scale,
with that many cubes on street tires there just a tire shredder its not going to matter much about which LSA squeeks out a few extra lbs torque, tires on 500/540 are not going to do much to hold it, so you might as well use whatever trips your trigger if you like lumpy idle go tight, smoother idle go wider its not going to matter for much anyway its like arguing my engine will blow the tires off for 400 ft but yours can only do it 380 ft.

engine that puts out 680 bls torque at low speeds whats the difference
if it ends up 657 or 680 torque if its murdering street tires.

63mako

If your only objective is to roast the tires off the car it doesn't matter. Either option will accomplish that fine. It is the other 95% of the time when your crusing on the highway in O/D, around town or in traffic that there is a huge difference. As I have said before, If it is a N/A strip only car the 106 LSA is the best choice. If it is mostly a street car with occasional trips to the strip (most of the members here) or has power adders a 110 or 112 LSA cam is a much better choice. This is concerning an on the edge build.
A milder build or relatively stock engine with lower compression and a short duration cam may also benefit from a tighter lsa to help build peak cylinder pressure and help contribute to the "muscle car" rumble. As you see nothing is carved in stone and best for all applications contrary to what the OP thinks. Intended use, gearing, compression, available fuel grades, head and intake flow, vacuum requirements, level of build and expectations from that build all have to be weighed and addressed for proper cam selection weather it is LSA, lift or duration. Will a 106 LSA probably make the highest power from 2500 and up? Probably. Is that the only thing you are considering on a street engine?

Solid LT1

Not to mention the ability to run with a set of mufflers on the motor. Dyno testing is one thing, real world can be quite different. I build my Vettes to drive on the street (including pasing by angry female police officers while on duty, and most are ANGRY in that profession) and I need appropriate exhaust systems to be able to live with my Vettes. I'll stick to 110 lobe seperations on motors with sufficient mufflers on them to pass the "angry person" test.

Little Mouse

The 302/327/350s I built all had 114 LSA high duration cams for there size no torque whatsoever SB engines thats the way it is, my 454 -265 .050 cam 87 degree overlap 108 LSA 3.36 gearing 2.20 low gear it had crap loads of torque off idle everywhere drove it all over little rock its hill billy hills at stop lights the car was one yr old so it had vacuum headlights that were up to snuff had no problems with slow operating headlights the power brakes worked no problems. all this you have to have a wide LSA to make your car more streetable could hold true with a small block where any amount of extra LSA to make it more docil helps when you have cubes nothing to worry about if your just taking off at idle or wanting to blow the tires off The LSA won't hurt those puppies I can only imagine 540 cubes what happens you put in a tight lash cam it becomes hard to drive Another thing I can't uderstand both my big block vettes had no problem overheating with the factory radiator ill bet that 454 12.5 compression with uncapped headers was making 550/600 hp never one time did it have problems overheating. same way with the 396.

63mako

I am suprised that a 454 with 12.5 to 1 compression and a 265 @ .050 cam with 108 LSA and high gearing will run well on pump gas. Must be a well engineered build.

Little Mouse

Were talking a lot of yrs ago but the compression is there in that engine for so much cam duration., but it does not matter much when your talking 454 + cube engines, even combo's like redicules 3.36 2.20 low gears big cam for the street the torque in a big block just soaks it up, sure that combo was not the right setup if you wanted to drag race the car but it was very easy to drive, you put anything like that in a small block the car would be miserable to drive, my point is I guess in big engines like that there is just no real worry what the LSA is just put in what you like hell people don't even like to build 454s when the parts cost the same to easly go bigger today.

howarsc

Then get a SMALLER cam... wierd concept huh?

Guru_4_hire

I believe that the grand national had a 107 LSA for one of the years.