Whats cams should i go with? on a 97 cobra, d1sc blower, 18-20psi, 11:1 compression, ethanol fuel.I want custom grinds and i want a rough idle
Custom grind cams????
- Thread starter 97crystalwhite
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You going to be running e85? Call up crower, comp, l&m anyone to make you a custom cam
Yes sir. I have called comp and lunati. I should call and talk to crower also
i. Just seeing if anyone has a similar setup with cams and what they went with.
i. Just seeing if anyone has a similar setup with cams and what they went with.
NA SVT on this forum does custom regrinds and he's very knowledgable in the camshaft/modular subject.
Yes pm na svt he is the man when it comes to cams, he is very helpful and will point u in the right direction!!!:rockon:
A rough idle and boost combine to reduce power.
just curious but is that due to the overlap that makes that rough idle? :rockon:
no
-Duration is the length of time the valves are open
-Lobe seperation Angle (LSA) is the degrees between the intake and exhaust lobe centerline ((intake LC + Exhaust LC) divided by 2 = LSA)
-Overlap is the period where both the intake and exhaust valves are open (at the end of the exhaust stroke and beginning of the intake stroke)
-The duration of the overlap period is determined by the LSA and duration length, lower LSA and longer durations = more overlap
-The longer the overlap period the more rough the idle
-Forced induction engines require less overlap than n/a engines as the pressurized a/f mixture will be blown out the exhaust during the overlap period
With that, engines lacking intake valve area require a longer overlap period to draw the a/f charge into the cylinders. The greater the cylinder volume/intake valve diameter ratio, the more overlap the engine will require. Conversely, small engines with large intake valves require less overlap. Therefore, a 281ci engine with a large intake valve area (like a mod motor) requires no overlap to make power and adding overlap to the equation will take away power throughout the entire range. To make things worse, adding overlap to this same combo will reduce efficiency even more.
Any aftermarket 4v cam set can be made to idle rough, all you have to do is lower the intake and exhaust LCs. This reduces the LSA and increases overlap.
In conclusion, stick with a 2v if you want a rough idle.
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:lol:
Wow that makes a lot of sense!
I may have missed something but most cammed mod motors still have the cool sound but pick up power which I assume everyone is referring to as a rough idle.. What is changed between the cams, (stock vs. aftermarket) just trying to figure out how it works since I am trying to figure out if cams are worth it as well for a turbo application with a shortrunner. I love the sound of cammed cars but also want the most power possible.
Any street turbo combo staying under 7000rpm should use the stock cams.
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There's a vendor on SVTP that claims to do custom cams and are recommending cams with way too much duration. This same vendor has called me and asked for cam specs which tells me he doesn't know shlt about what cams work in mod motors. With that, before buying cams ensure the person spec'ing them knows what the hell he's doing.
here are 2 cams, both are advertised as 270 degree cams. both are dual profile but thats another story all together. just focus on the intake side for each. the first cam is for a 2v, the second for a 4v.
102600 - Xtreme Energy
106400 - Xtreme XE-R Series
notice the 2v has slightly less LSA but an earlier intake centerline degree. youll also note that the 2v cam has more lift. the 2v needs an earlier IC and more lift because its not as efficient as a 4v head. btw, youll notice the 4v head has a slightly higher useable range because the wider LSA allows for better high rpm breathing.
the differences are a smaller on paper than they appear in the real world. the difference in the real world between the cams in real world application is MUCH larger but results can be skewed due to parts (mis)matching.
102600 - Xtreme Energy
106400 - Xtreme XE-R Series
notice the 2v has slightly less LSA but an earlier intake centerline degree. youll also note that the 2v cam has more lift. the 2v needs an earlier IC and more lift because its not as efficient as a 4v head. btw, youll notice the 4v head has a slightly higher useable range because the wider LSA allows for better high rpm breathing.
the differences are a smaller on paper than they appear in the real world. the difference in the real world between the cams in real world application is MUCH larger but results can be skewed due to parts (mis)matching.
This is by no means a good comparison because Comp's 2v LSA is too wide and doesn't result in the best performance. They (Comp) do this to promote high vacuum and a smooth idle. Also, Comp's RPM range for their 4V cams is off by a great amount so they mean nothing.
The lower intake centerline (and tighter LSA) for the 2v cams is not due to the heads inefficiency, it's because of the low intake valve diameter to cylinder volume ratio and this is something common to all 2v engines, not just the mod motors.
The optimum lift for any valve is about 1/3 of it's diameter. For example, the 37mm intake valve of the 4v has an optimum lift of .480" while the larger 2v intake valve is around .575".
A properly spec'd set of n/a 2v cams will have an LSA no higher than 110, with most being around 108 with a 4Vs LSA being no lower than 112, but preferrably around 115.
Cams with more duration will increase power even if they produce a rough idle. However, if the LSA is widended to reduce overlap and to smooth the idle the engine will make even more power. You can't get something for nothing:
-long durations = higher hp with lower tq
-short duration = less peak power but more midrange hp and tq
-long overlap period = rough idle with less hp/tq
-tight LSA with short duration = good tq and mid range, power falls off quickly after peak
-long duration cams with a turbo will slow spooling, especially with a manual transmission
-a short runner intake will slow turbo spooling but add power above 6000rpm
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I'd go with a 220/222 installed on 112/118 LCs. For the dreaded rough idle I'd recommend 226/228 installed on 112/116 LCs, any tighter and the fresh a/f charge will be blown out the exhaust during the overlap period.
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Todd is the man, he really knows what he is talking about if you didn't see that already. :beer::rockon: He set me up with where I wanted to install my cams at, I went for a rougher idle, sacrificed some power, but I don't drag or race my car, it is mostly for cruising and car shows. Oh and Todd, do you want those four spare cam retainers I have? I'll never use them, I don't plan on taking my engine apart for a long time, they are just taking up space.
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