Need some professional advice on cams

[NeedForSpeed]

The major cost is modded cams is welding. I believe the exhaust lobe can be successful without welding, only reducing the base circle. Potentially, a low-budget option, perhaps the best bang for the buck of any mod?

Now, let's Zee those "interesting" specs.

[oab_au]

Originally Posted by NeedForSpeed

The major cost is modded cams is welding. I believe the exhaust lobe can be successful without welding, only reducing the base circle. Potentially, a low-budget option, perhaps the best bang for the buck of any mod?

Now, let's Zee those "interesting" specs.

Yes Ron, we can get the same specs as the welded ones, by grinding the lobe profile smaller, so that the base circle is 1mm smaller, and just rely on the lifters to take up the extra gap. But we still need a profile for the cam grinder to use. We either need an existing cam with that profile, or we need to make a profile that they can use.

Harvey.

[longassname]

Well good luck with your cams for otherwise stock svx's. They don't pertain to my area of interest so don't take my ignoring any discussion about that line of cams the wrong way. I'm just only interested in the higher performance svx'ing and will be continuing along the lines of the specs I mentioned earlier. I'll throw in a little advice though before signing off of the mild cam discussion. The intake valves are shorter than the exhaust valves but the springs are the same for both. If you make the exhaust lift in the neighborhood of .7 or .8mm more than the intake your spring tensions will be more equal and you will get a smoother running valvetrain. Also on the discussion of lift I would be very suprised if you didn't continue to get enough benefit from increasing lift on up to 30% of valve diameter to make it worth while.

A few of you now have gotten the svx cams measured by camshops; could someone please verify the actual base circle measurements please?

[NeedForSpeed]

Mike, I have more than one project, so I'm interested in mild low-budget cams for otherwise stock svx's, as well as the higher performance options you are profiling. I'm not ignoring either discussion, I'm interested in your persuit of performance. I believe someone posted the base circle in one of the threads, did you search it?

The profiles you mentioned, for high perf NA, or for the next Stage 3?

Harvey, the major cam grinders do have the exhaust lobes copied or cams to copy, so no worries there. Reduced base-circle exhaust lobe intakes should cost less than $100 per cam. Could be one of the best 'bang for the buck' available. That, plus program changes, should be huge for otherwise stock svx.

Originally Posted by longassname

Well good luck with your cams for otherwise stock svx's. They don't pertain to my area of interest so don't take my ignoring any discussion about that line of cams the wrong way. I'm just only interested in the higher performance svx'ing and will be continuing along the lines of the specs I mentioned earlier. I'll throw in a little advice though before signing off of the mild cam discussion. The intake valves are shorter than the exhaust valves but the springs are the same for both. If you make the exhaust lift in the neighborhood of .7 or .8mm more than the intake your spring tensions will be more equal and you will get a smoother running valvetrain. Also on the discussion of lift I would be very suprised if you didn't continue to get enough benefit from increasing lift on up to 30% of valve diameter to make it worth while.

A few of you now have gotten the svx cams measured by camshops; could someone please verify the actual base circle measurements please?

[oab_au]

Mike this 240* 8mm lift inlet cam, is not just for stock engines. It is for engines that are going to operate in the < 7000 rpm range. This includes the blown engines, Positive Displacement, Centrifugal, or Turbo. They operate in this rev range, and will benefit from the extra lift, to allow the cylinder filling to continue higher up the rev range, instead of dropping off as the 7mm lift engines do.

Engines that are to operate in the >7000 range, need the inlet tract length reduced to raise the torque peak to 6000 rpm. Regardless of the cam timing/duration used, the torque peak will still follow the resonate peak. The inlet tract reduction, is it the order of 3"/75mm.

This is a basic simulation of the engine using a seat to seat duration of 257* 8.75mm lift fast opening cam, on both inlet and exhaust. The first has the standard length inlet and exhaust tract lengths.

RPM KW NM
3000 93.84 298.68
4000 142.32 339.78
5000 193.92 370.38
6000 213.72 340.14
7000 212.46 289.8
8000 203.76 243.18

When the inlet and exhaust tracts are shortened to suit the higher torque rpms, it looks like this.

RPM KW NM
3000 90.36 287.7
4000 132.18 315.48
5000 186.54 356.22
6000 221.22 352.08
7000 239.46 326.7
8000 224.34 265.8

Having the tract changed to move the torque up the rev range, moves the power up another 34 HP, at 7000. with the same cam shafts.

Harvey.

[longassname]

The camshafts you speced are not big enough for the blown engines, sure they are better than completely stock but they aren't the best. Like I said before I would be suprised if increases in lift on up to 30% of valve diameter decreased the speed of low/mid rpm airflow enough to have a big enough impact to make it not worth the extension of torque past peak on a stock car; on a blown engine there is no question that further increases in lift would be worth it. We need a longer duration as well. We need to start the exhaust flow out of the cyllinder earlier.

I Know you have grabbed onto resonate frequencies with both hands but you have to remember that you can only take advantage of the resonate effects after you have dealt with the gas effects. The 256 cams are well proven on wrx's, z's and both na(jdm) and turbo supras. They allow the aiflows we are looking for with lots of streetable power accross the entire power band.

[Trevor]

Originally Posted by longassname

The camshafts you speced are not big enough for the blown engines, sure they are better than completely stock but they aren't the best. Like I said before I would be suprised if increases in lift on up to 30% of valve diameter decreased the speed of low/mid rpm airflow enough to have a big enough impact to make it not worth the extension of torque past peak on a stock car; on a blown engine there is no question that further increases in lift would be worth it. We need a longer duration as well. We need to start the exhaust flow out of the cyllinder earlier.

I Know you have grabbed onto resonate frequencies with both hands but you have to remember that you can only take advantage of the resonate effects after you have dealt with the gas effects. The 256 cams are well proven on wrx's, z's and both na(jdm) and turbo supras. They allow the aiflows we are looking for with lots of streetable power accross the entire power band.

Michael, I agree whole heartedly.

As I have said before and now say again, the figures suggested throughout, have not been aggressive enough and will not provide bangs for bucks. In this respect the safe option IS the safe option for anyone recommending when they are not spending on the project.

[oab_au]

Originally Posted by longassname

The camshafts you speced are not big enough for the blown engines, sure they are better than completely stock but they aren't the best. Like I said before I would be suprised if increases in lift on up to 30% of valve diameter decreased the speed of low/mid rpm airflow enough to have a big enough impact to make it not worth the extension of torque past peak on a stock car; on a blown engine there is no question that further increases in lift would be worth it. We need a longer duration as well. We need to start the exhaust flow out of the cyllinder earlier.

I Know you have grabbed onto resonate frequencies with both hands but you have to remember that you can only take advantage of the resonate effects after you have dealt with the gas effects. The 256 cams are well proven on wrx's, z's and both na(jdm) and turbo supras. They allow the aiflows we are looking for with lots of streetable power accross the entire power band.

Mike the objective of any modifications is to improve the performance of the car, not just the engine. What ever engine type you build, it has to go in a car and do the normal duties. A PD blower on a road car may spend probably no more than 10% of its running time on boost. The rest of the time it has to drive smoothly, and economical.

Now I don't know what type of engine your objectives are, but you need to define them. What speed do you want the engine to operate at. Less than 7000 rpm, or above, up to 8500/9000? Is it a 100% race engine, or a road engine?

There is no point in using a long duration cam, if it is not going to rev above 7000. A short duration cam, that has very large lift (30% of valve dia.), will need very strong valve springs to handle the very fast acceleration rates, that the lift will produce.

The main point in fitting a Positive Displacement blower is that it increases the air pressure that the engine operates under, across the entire rev range. This means that you don't have to increase the revs that the torque is made at, to increase the HP. The engine can be relative standard, and still produce the HP, from 2000 up.

To increase the rev range that the engine will operate at, you still have to do the same breathing mods as an N/A engine. Longer duration, more lift and larger valves. It will still have the same low speed problems as the N/A engines have. Fitting a PD blower won't negate these effects.

So what do you want, it to be?

Harvey.

[Trevor]

Originally Posted by oab_au

Mike the objective of any modifications is to improve the performance of the car, not just the engine. What ever engine type you build, it has to go in a car and do the normal duties. A PD blower on a road car may spend probably no more than 10% of its running time on boost. The rest of the time it has to drive smoothly, and economical.

Now I don't know what type of engine your objectives are, but you need to define them. What speed do you want the engine to operate at. Less than 7000 rpm, or above, up to 8500/9000? Is it a 100% race engine, or a road engine?

There is no point in using a long duration cam, if it is not going to rev above 7000. A short duration cam, that has very large lift (30% of valve dia.), will need very strong valve springs to handle the very fast acceleration rates, that the lift will produce.

The main point in fitting a Positive Displacement blower is that it increases the air pressure that the engine operates under, across the entire rev range. This means that you don't have to increase the revs that the torque is made at, to increase the HP. The engine can be relative standard, and still produce the HP, from 2000 up.

To increase the rev range that the engine will operate at, you still have to do the same breathing mods as an N/A engine. Longer duration, more lift and larger valves. It will still have the same low speed problems as the N/A engines have. Fitting a PD blower won't negate these effects.

So what do you want, it to be?

Harvey.

Mike has posted information which absolutely confirms his knowledge of the subject. He has a right to feel insulted as a result of a prolonged, arrogant lecture, from a proclaimed know all, instructing him how to suck eggs.

It is stated. ---- "To increase the rev range that the engine will operate at, you still HAVE to do the same breathing mods as an N/A engine."

Forced induction will increase breathing throughout the rev range regardless, and most certainly improves cylinder filling at the top of the rev range. In respect of an engine driven blower, the key in this respect is gearing.

[longassname]

Harvey,

The 256 total duration cam is an excellent cam for below 7000 rpms. The powerband of the lobes I offered up the specs on is a nice, wide, streetable powerband.

Comparatively the cams you are specifying do not have the lift or duration necessary for efficient evacuation of the ehaust on the blown cars even at moderate rpms. In fact I will probably go with a 264 duration exhaust cam.

[longassname]

Harvey,

You are right that the duration constraints you are placing on the cams you are spec'ing limit the increases you can make in lift without replacing the valve springs. If you want to increase the lift on the mild cams you are spec'ing for the stock guys they can use the same springs I'll be using with my cams. I can supply them for $300 a set.

[mikecg]

Originally Posted by longassname

Harvey,

You are right that the duration constraints you are placing on the cams you are spec'ing limit the increases you can make in lift without replacing the valve springs. If you want to increase the lift on the mild cams you are spec'ing for the stock guys they can use the same springs I'll be using with my cams. I can supply them for $300 a set.

What....... Your going to sell cams for the Stage III people....... $300!!!!......I'm in. You want my car for testing??? I've got a vaction to Orlando coming up end of January.

[NeedForSpeed]

That's not how I read it!

Originally Posted by mikecg

What....... Your going to sell cams for the Stage III people....... $300!!!!......I'm in. You want my car for testing??? I've got a vaction to Orlando coming up end of January.

[mikecg]

Originally Posted by NeedForSpeed

That's not how I read it!

Ooops, I just reread that. He's offering springs....... My bad.

[sicksubie]

300.- per cam?