I'm going to have my 225/233 hyd-roller cam reground to better work with the Miniram. I want to stay with the Hyd-Roller and did not want a solid roller.
I have noticed that the Lingenfelter 219 cam, TPIS 701 cam (242/242 solid) is a single pattern cam and TPIS says that the single pattern works better on EFI engines in one of ther mag articles. They say it makes for better tuning.
I understand the longer duration on the exhaust side is to aid in exhausting the heads fully,,,
I will be using AFR 210 race ready heads.
The people at bullet cams ( http://www.bulletcam.com ) are going to re-grind me a 233/239 hyd-roller and I am wondering if they should be making this a single pattern cam.
The relative exhaust/inlet duration is primarily a function of head flow characteristics. If the exhaust/inlet relative flow is about 0.75, equal duration is a good bet. If the ratio is less than 0.75 a longer duration exhaust is usually beneficial and the extra duration should be at the front the the lobe - open the exhaust valve a little earlier.
Conversely if the exhaust/inlet flow ratio is greater than 0.75 a slightly shorter exhaust cam via a latter opening exhaust valve can be beneficial. OE SB heads typically have an exhaust inlet flow ratio of 0.65, so they can benefit from an early exhaust valve opening. I think most of the modern aftermarket heads are closer to 0.75, but you should get some good data for your heads, and go from there.
EFI versus carb doens't have much effect, but how effectively the inlet manifold harnesses wave dynamics is a factor, since it will increase total inlet flow efficiency, but only in certain rev bands and may actually reduce flow in other rev bands.
These are just rules of thumb, and there will always be some combination of components that are exceptions. For any given combination a later opening exhaust valve will enhance low end torque slightly by allowing gas pressure to work the piston a little longer, but this can restrict the exhaust process at high revs and reduce peak power. Conversely an earlier opening exhaust can increase top end power at a slight expense to low end torque.
Properly tuned exhaust headers can make up for a restrictive exhaust port by harnessing wave dynamics to assist exhaust scavenging.
Like most engine configuration issues there are multiple interrelated variables that must be juggled to get the torque curve you think is best for your application. The best way to analyse this is to use a simulation program with accurate modeling for you components and then start juggling the valve timing until to get what you think is the best torque bandwidth.
Larry:
what results are you getting with the MR? Did you changed the manifold or also the ECU? I'm starting to build a 400-427 SB and doing some research on FI systems, looking at FAST and Holley's Commander 950 for the ECU, but havent decided on the intake.. aiming at 500HP.
Edgardo
ld85 i thought you were switching to a super ram :cheers:
OlRJ is going to fine tune the MR one more time with the new AFR heads, if it dosent come around then I will switch.
My goal from the start was 400RWHP, if we get that after the new AFR's are installed then the MR will stay on, if we gdo et the 400RWHP and cant get the glitches out with tuning I will swap to the SR.
Larry:
what results are you getting with the MR? Did you changed the manifold or also the ECU? I'm starting to build a 400-427 SB and doing some research on FI systems, looking at FAST and Holley's Commander 950 for the ECU, but havent decided on the intake.. aiming at 500HP.
Edgardo
I got 350RWHP and 376 RWTQ with a mis-matched cam and poor low lift flowing heads.
I cant really advise you on the intake as I am still fiddling with my setup, but I am sure some others can help.
Corvette Store
Single pattern cam for EFI
