[als427]

Hi all , having debated changing cam or not I will first change intake from single ( very low rise) plane to dual plane for better street use / manners.
wasn't sure if cams too big but after car was sitting 3 years pulled the plugs , squirt of oil , hand turned engine then used starter to push some oil around.
That being done though Id do some compression testing. Hit 155-170 psi which I think tells me its a pretty good street cam?
ie not too big and losing too much compression through overlap bleed off!
Local engine guys ( Im in the uk ) said anything over 140psi good for a street car.
sound about right?
runing 93+ octane
thanks

 

[jjjaffo]

What would be helpful here is engine size, static comp ratio, aluminum or iron heads and what it is in. I could say that you are in a good range, but could be leaving power on the table too. What are the cam specs?

 

[als427]

hi , roughly 9.5-10:1 iron heads 427 bbc . 230/236@50 on a 114lsa flat tappet
Had seen a few references that its a reasonable indicator of suitability.
In that a bigger cam with more overlap would givee a lower cranking compression.better for high rpms but less so street use lower rpms
ie a

 

[Steve69SS396]

Did you conduct the compression test with the throttle wide open? It needs to be wide open.

 

[als427]

hi , yes throttle wide open.

 

[65cayne]

hi , roughly 9.5-10:1 iron heads 427 bbc . 230/236@50 on a 114lsa flat tappet
Had seen a few references that its a reasonable indicator of suitability.
In that a bigger cam with more overlap would givee a lower cranking compression.better for high rpms but less so street use lower rpms
ie a

Well sort of, but overlap does not affect cranking compression. Your intake valve closing point (IVC) does. Typically larger cams will have a later IVC meaning the piston is traveling farther up the bore before the valve closes and you actually start to compress air/fuel in the cylinder. This is what guys are referring to when they say larger cams "bleed off compression".

Larger cams can have more overlap, and maybe typically they do, but that is not always the case. The LSA and the lobe size together will dictate overlap.

It's also worth noting that where your cam is degreed in at (advanced or retarded) will affect the IVC and thus your cranking compression. As a rough comparison, my ~10:1 460 with a 229/241@.050 cam has 195-200 psi cranking compression.

 

[als427]

Well sort of, but overlap does not affect cranking compression. Your intake valve closing point (IVC) does. Typically larger cams will have a later IVC meaning the piston is traveling farther up the bore before the valve closes and you actually start to compress air/fuel in the cylinder. This is what guys are referring to when they say larger cams "bleed off compression".

Larger cams can have more overlap, and maybe typically they do, but that is not always the case. The LSA and the lobe size together will dictate overlap.

It's also worth noting that where your cam is degreed in at (advanced or retarded) will affect the IVC and thus your cranking compression. As a rough comparison, my ~10:1 460 with a 229/241@.050 cam has 195-200 psi cranking compression.

thanks - thats useful.My 114 lsa puts my 230/236 intake closing 4 degrees later ( all @50) - that cant help - feels like the car needs more street friendly power.
Will i seat of the pants feel a difference on a cam with 38degrees IVC vs 145 degrees IVC?

 

[mr 4 speed]

thanks - thats useful.My 114 lsa puts my 230/236 intake closing 4 degrees later ( all @50) - that cant help - feels like the car needs more street friendly power.
Will i seat of the pants feel a difference on a cam with 38degrees IVC vs 145 degrees IVC?

Not sure what you mean by more street friendly power..sometimes people over think this stuff.
My 70 has a 248/254@.050 110 LSA solid and the 69 has a 238/248@.050 114 LSA hyd. (both big blocks) and both are very streetable and perform at the drag strip (but not really race cars)
And both cars will shred the tires at 40-55 MPH

 

[BillK]

Do you know the camshaft part number ?

 

[magicrat56]

I vote to leave it alone,swap the intake and see where you're at.

 

[als427]

hi , will swap intake first and retune.
Think part of it is I was used to a much smaller cam - so the shift in "feel" Im still getting used to.To be fair if you guys are running 238/2448's on 110-114's on there street I probably am overthinking it! Maybe I should just get a bicycle.
Its a cb4e herbert

 

[GTO44]

I’ve got a hydraulic roller 236/242 on a 110lsa in my small block 355. Been street driving it for 22 years. The cam in your big block is not that big. As others said, its probably the single plane killing power down low. I’ve got a dual plane rpm airgap and even with a pretty big cam for street driven small block it still roasts the tires anytime i want.

 

[als427]

thanks - thats what I want to hear. cant wait to get this thing smoking some tyres.
Thought 114 las might be an issue but to be fair it dynode a flatter curve but all good power - 350-420ftlbs - not amazing but should bemore than enough for my needs.

 

[68Chevele]

Was this low intake an Eddy Torker II? if so you're going to like the power gain and torque of a dual plane intake.

 

[bracketchev1221]

My 355 was a 250/260 with a 106 lsa and it drove fine with a 4 speed and 3.42 gears. The higher the LSA the milder the cam is at idle.

 

[als427]

intake was like a torker II , a low rise singel plane holley street dominator.
single open plenum , short runners , low rise....v similar