lumpiest cam
Aren't the Whiplash cams and I would guess some of the others designed to maximize cylinder pressure on low compression engines but still sound radical? I know generally a lopey cam when its a true performance cam is because of overlap. Doesnt it have a lot to do with the intake and exhaust duration staggering on a lot of these?
yes/yes,and no/sortof,maybe sortof
lemmee fix it for ya;
>Aren't the Whiplash cams, and I would guess some of the others, designed to sound radical, yet attempt to maintain some half-decent cylinder pressure on low compression engines?
answer; yes
>I know, generally, a true performance cam is lopey, because of overlap.
answer; true, but, the overlap exists not by specific design, but as a result of, the long intake and exhaust periods.
>Doesn't it have a lot to do with the intake and exhaust duration, staggering on a lot of these?
answer; If by "it", you mean the idle-lope, sorta yes.
If by "it" you mean the overlap, absolutely yes.
Mostly, with these Whiplash-type cams, the exhaust duration is increased way beyond what would be considered normal, for the amount of the intake duration, which creates extra overlap,and,after re-timing the cam, results in additional lope. Since it is in fact overlap, the potential to make a lil powerbulge at higher rpm does exist..... but the intake duration is not there to support a significant amount.
I understand that this type of cam has an appeal to some, but because the exhaust duration is so large, it steals some of those degrees from the powerstroke, which leaves quite a bit of energy still in the exhaust when the valve opens.... energy that could have been used to drive the rear wheels,and that leads to less potential for good fuel economy.
As for my opinion, if I have to sacrifice fuel-economy, I'd rather actually have the power that should go with that, instead of just sounding like it.
IIRC the 318-Whiplash is around
[email protected], which should power peak at maybe 4600, so it's a nice street-sized cam. But the overlap on it is usually found on a cam of a couple to several sizes bigger. So idling in the next lane, I can't tell if it is or is not, a funky cam, until he steps on it; then it's easier to spot as the Rs wind up. This is fine if that's what you want.
As for me, I'd rather pump the compression up, and install a proper 213* cam. Because at low speed/low rpm, pressure is king. Without it you have to band-aid the engine with a hi-stall TC ,and usually, more rear gear. And yes, the whiplash-type cam does lose pressure.
Here's a 318LA example;
Stock, at nominal 8/1 and with the 240/248/111 cam, in at +4, the Ica comes to 48*.
and the 318 Whiplash; has .050-advertised at 213/226/109+5.. Hughes does not publish the .006 or .008 tappet-rise figures so you have to guess. I'll guess the ramps might be ~50 degrees, making that cam to be 262/276/109+5. and then, the Ica becomes 55*, and the pressure loss comes to about 12psi@1000ft elevation.. The 318LA cannot afford that. That 12psi represents a performance loss of 13% at sealevel. So even tho you have moved up from about 196* intake duration to 213*, which should have got you nearly two cam sizes more power, say 25hp, instead, you might get just 22; but that's not the big picture. Which is, that, the loss of pressure means the power is reduced everywhere in the rpm band, compared to what it could be, and specifically, below ~3000 it will get progressively weaker than the stock cam was. Which is a bad thing, especially with a manual trans.
The actual numbers predicted by the Wallace calculator are 139.76(stock), to 127.58(Whiplash), at 1000ft.
With a proper 213 cam and pumped up compression, the psi might be 160, and accompanied by an across the board performance increase below 3500 of about 20%. But with 115* now of power duration, a guy should be able to tune that for great fuel-economy. And sadly, the overlap would be down to 37* versus 51*with the Whiplash, so not much lope goin' on there.
Fun with math.
Well, I guess I should add;
A 318LA
with just 128psi is a sick,disappointing,wet-noodle kindof thing.
at 140psi, altho normal,performance is lackluster
by 160psi, she has really perked up, even with the factory cam. Coupled with a true 213* cam, she could be a lotta fun.
Jus spitballin'
