NA DOHC Camshaft recommendation

[UCTURBO]

Im after a camshaft recommendation for a NA 6cyl aussie Barra 243ci DOHC. Setup has 11.5:1 compression, 50mm ITB's, 6>1 pipes, head has had bowl and short turn work ( around 270cfm ). Currently the engine has a pair of 250@1mm duration ( duration is at valve, engine has 2:1 rocker ratio ). The engine is done by 68-7000rpm.

Im wanting to get more hp out of it, the cams that are in it are virtually the largest off the shelf grind, I was thinking of going to something with around 250-260@50 at the cam and possibly revving it to 8000.

Current best is 12.1@112mph in 3200lbs car, 4.3 gears, 27" tyres, 4000 stall ( now has 4600 stall ).

Any recommendation would be greatly appreciated.

[gregsdart]

If you look at recommendations for the Ford Coyote 5.0 dohc motor, hopefully that will help you. The trick will be in keeping enough torque at stall speed to not go backwards there. Stall speed ideally should be raised with the change you want to make, since a bigger cam will shift the torque curve higher to get that power. Anything you can do to increase AVERAGE HP over the range from stall speed to shift point will help. Adding hp up top and losing hp at stall will not go well.

[mag2555]

How much vacuum do you have in the Intake Manifold at 6800 rpm?

If it's already very close to, or over 1 Hg now then running more Cam and or trying to get the rev's up higher will do nothing for you.

[Momus]

The compression ratio is relatively low.

Get it up to 15 or 16:1 before going to a long cam.

[Tom68]

At least add duration on the exhaust side, that's normally some free horsepower.

You can retard the intake cam and see if it moves the power up.

What intake runner length ?

[UCTURBO]

If you look at recommendations for the Ford Coyote 5.0 dohc motor, hopefully that will help you. The trick will be in keeping enough torque at stall speed to not go backwards there. Stall speed ideally should be raised with the change you want to make, since a bigger cam will shift the torque curve higher to get that power. Anything you can do to increase AVERAGE HP over the range from stall speed to shift point will help. Adding hp up top and losing hp at stall will not go well.

I look into it cheers

How much vacuum do you have in the Intake Manifold at 6800 rpm?

If it's already very close to, or over 1 Hg now then running more Cam and or trying to get the rev's up higher will do nothing for you.

essentially 0 going by the logs

At least add duration on the exhaust side, that's normally some free horsepower.

You can retard the intake cam and see if it moves the power up.

What intake runner length ?

have tried anywhere from 14" to 18" with small changes in rpm ranges

Have ordered a pair of cams with low 250@50 duration at the cam and around 0.080" more lift. Probably be a pig but we'll see.

[ptuomov]

Why 6-1 headers instead of 2x3-1 or 6-2-1? The reason for me asking is that i believe (but don’t know) that 6-2-1 system could be tuned pretty well to complement the intake across a wide power band which in turn would allow you to increase the camshaft overlap even more to protect the midrange torque. Just thinking out loud.

[BLSTIC]

What do the speedway guys run? They tend to be at minimum 280whp with the Barra and rev to 7500 a lot.

Based purely on how much work they haven't done at that power level (stock BA motor, plus cams, valve springs, oil pump, and headers) it wouldn't be surprising to hear of the top guys doing 8500 and 330-ish whp even with the limits of the fg plastic intake casting

[UCTURBO]

Why 6-1 headers instead of 2x3-1 or 6-2-1? The reason for me asking is that i believe (but don’t know) that 6-2-1 system could be tuned pretty well to complement the intake across a wide power band which in turn would allow you to increase the camshaft overlap even more to protect the midrange torque. Just thinking out loud.

Not sure why I did 6>1, all I know is when the engine was stock the pipes made absolutely zero difference in et and mph, admittedly the stock manifold isnt that bad.

What do the speedway guys run? They tend to be at minimum 280whp with the Barra and rev to 7500 a lot.

Based purely on how much work they haven't done at that power level (stock BA motor, plus cams, valve springs, oil pump, and headers) it wouldn't be surprising to hear of the top guys doing 8500 and 330-ish whp even with the limits of the fg plastic intake casting

Not sure what cams they run, but Id say this engine would be making around the 300rwhp mark. Theres no reason why these engines cant make 4-450hp flywheel NA, just the off the shelf cams are more turbo orientated. If thats the restriction that is.

[ptuomov]

Why 6-1 headers instead of 2x3-1 or 6-2-1? The reason for me asking is that i believe (but don’t know) that 6-2-1 system could be tuned pretty well to complement the intake across a wide power band which in turn would allow you to increase the camshaft overlap even more to protect the midrange torque. Just thinking out loud.

Not sure why I did 6>1, all I know is when the engine was stock the pipes made absolutely zero difference in et and mph, admittedly the stock manifold isnt that bad.

My impression (not actual first hand knowledge) is that to really make a lot of high rpm torque with this kind of normally aspirated engine, you need a lot of camshaft overlap and well-tuned header. If the camshaft doesn't have enough overlap, the header doesn't matter much. When the camshaft has a lot of overlap, the header is hugely important -- unlike my other speculations, this I have found out first hand in another four-valve normally aspirated engine. Small primary diameters and big camshaft overlap is in my opinion the ticket, but that's again just an opinion.

Can you independently adjust the intake and exhaust cam timing? If you can, how much camshaft overlap does the engine want in the power band using the current header?

[UCTURBO]

Unfortunately the cams are locked, intake is at 105, ex 108. Adjusting the cams does the usual of what to expect, eg advance retard.

[ptuomov]

Unfortunately the cams are locked, intake is at 105, ex 108. Adjusting the cams does the usual of what to expect, eg advance retard.

If you have to buy new cams for each lobe separation angle, then I’d seriously consider inputting the engine into Vannik’s engmod4t software. That would allow you to experiment with the LSA before ordering the cams.

[BLSTIC]

Locked as in you don't hand the adjustable gears available and have locked the factory continuously variable items to be fixed, or you do have adjustable ones and just can't vary the timing with the engine running?

[ptuomov]

Locked as in you don't hand the adjustable gears available and have locked the factory continuously variable items to be fixed, or you do have adjustable ones and just can't vary the timing with the engine running?

Great question.

[UCTURBO]

The cams are locked as in, adjustable just not vct.