Quote:
Originally Posted by Toni94ZR1
Wooow Pete, you have a very big intake cam, this will do a rough idle and high speed idling?
Your relative little exhaust cam I think is because you don't loose too much low end torque and car driveability, large exhaust duration will probably cause a decrease in power on a stock 350.
Yes, same (Prim, Sec) intake lobe profile shape is the best design and give more power, diferent profile cause a different (Prim, Sec) air speed flow filling the cylinders so can cause turbulent air flow in the inlet runner when Plenum and IH are Siamese .
As I will assemble stock cams regrinds or not, I only do siamesed runner on the plenum, the IH and Head are no siamesed only porting to 36'5 mm to keep independent air volume storage and air speed. Siamesed inlet plenum it's a must because total inlet length measures about 14 in. from plenum to valve seat, too long and the plenum inlet runner have a bad 90 degree curve, I smooth the short corner ( make the radius bigger ) as much as possible of the 90 deg. curve of the plenum port to minimize the air flow loose.
To get a higher lift the lobe base circle had to be regrind (decrease in base diameter) keeping the same lobe nose. The primary lobe has a big lobe acceleration rate and at the secondary the acceleration rate is less. If regrinds both base circles to get .425 lift (prim, Sec) the acceleration rate on primary will be too high so will need bigger valve spring to control floating valve problem. The solution to decrease the acceleration rate is increase duration @ .050 but the primary lobe does not allow do this, needs to be reground and then regrind. .415 lift may be are the maximum lift primary lobe admit to keep the floating problem under control. If regrind the base circle to get a .415 lift i think the maximum resulting duration will be about .222. on a primary lobe. Doing a cycle graph will tell me the max duration allowed when regrind to .415 lift.
As I can see your inlet cams are not the stock regrinds, may be are a SGC stage III ?
And your exhaust cams I doubt if are stock regrinds or SGC stage I ?
As the inlet and exhaust cams are different, not a single cam engine, you can modify the Lobe Centerline Angles (LCA) so the amount of overlap. The more overlap (tight LCA) an engine has, the greater tendency it has to run badly at low rpm, low vacuum and bad idling but good cylinder filling so more power.
Which are the timing numbers of your cams, LCA or Overlap and Intake Open Degree from TDC. ?
Pete I know my English is not very good, if you don’t understand what I said please let me know and I will explain on a different way.
Thanks very much
Toni
|
My intakes are SGC stage III my exhaust is my own regrind master.
My Z does have a nice cammy idle like an old big block but drives like a stocker in traffic and pulls away nice from a stop,i always offer people to drive it.
Reason for small exhaust cam is, i have tested big exhaust cams before and after on big & small cube LT5's same results more low end power no sacrifice on peak power they tune drive drive much better.
All of our fastest 10 sec Z's have .224 exhaust cams in them.
Timing you're safe with 114-108.
Pete
Your english is just fine.