As some here may recall I am in the market for an IMCA Sport Compact car.
https://grassrootsmotorsports.com/forum/cars-sale/looking-for-a-sport-compact-dirt-car/155266/page1/
A post here the other day about a Ford Escort Zx2 reminded me that I had an interest in one but thought they may be ineligible because the IMCA rules state: No “variable cam-timing”. With my tech knowledge not being up to date I got to wondering about variable cam-timing vs. variable valve-timing.
Are they 2 slightly different terms for the same thing or . . . are they 2 specifically different things or . . . are they 2 slightly different things?
If there is a difference why might several sanctioning bodies (at least 3 that I know of) address variable cam-timing and not variable valve-timing?
The answer would likely affect the models of car(s) I have to choose from.
Thank you
I think I could be and likely am wrong but VTEC would be an example of variable valve timing without variable cam timing. VVT or something similiar would be variable cam timing that directly correlates to variable valve timing.
Variable cam timing would be any system that actually advances or retards the intake centerline of the cam or overlap. At least how I would interpret it.
For virually all OEM's, the are exactly the same thing. (some have more mechanisms, which more separates the cam timing to valve timing). Just something that changes the angle of the camshaft relative to some base position.
Noting variable cam timing makes the rule easy to see and enforce- do you have a mechanism that changes the angle of the cam. If you do, no matter the name, it's illegal. I would expect them to include VTEC into that rule, since it has the same goal.
In reply to Patientzero and alfadriver (Forum Supporter) :
Thank you guys
My take on it (not being a racer, myself):
I'll abbreviate because I'm lazy. VCT would be VVT, but VVT is not always VCT. Much like a square is a rectangle, but a rectangle isn't always a square.
Assuming you have something that varies the cam timing, it will in turn vary the valve timing. The only way I can think of varying the valves without changing the cam is with old-school Rhodes lifters. They were basically crappy hydraulic lifters used in old school V8s that bled down at idle and pumped up as oil pressure rose with RPM. It was basically a way of taming a wild cam to make it more useful in the lower RPMs and getting the full lift/duration at higher RPMs. What they actually did was suck.
In reply to L5wolvesf :
I know this is an old post but I'm in the same sort of predicament and was wondering what you ended up doing? The rules specifically state no variable cam timing but make no mention of variable valve timing. While the two essentially do the same thing, they do it in different way. VCT has phasers that advance or retard the cam, while VVT such as VTEC changes rocker arms to for a differnt cam profile. The rules as stated say no VCT. I'd say it's a gray area that until specifically stated VTEC cars can be ran.
Curtis73 (Forum Supporter) said:
My take on it (not being a racer, myself):
I'll abbreviate because I'm lazy. VCT would be VVT, but VVT is not always VCT. Much like a square is a rectangle, but a rectangle isn't always a square.
Assuming you have something that varies the cam timing, it will in turn vary the valve timing. The only way I can think of varying the valves without changing the cam is with old-school Rhodes lifters. They were basically crappy hydraulic lifters used in old school V8s that bled down at idle and pumped up as oil pressure rose with RPM. It was basically a way of taming a wild cam to make it more useful in the lower RPMs and getting the full lift/duration at higher RPMs. What they actually did was suck.
I never knew that about Rhodes lifters. I thought they were just another brand of lifter. They sure must have sold a bunch though - or at least sold a lot of decals. Every hot car I can remember as a kid had "Rhodes" lifters.
A 401 CJ said:
Curtis73 (Forum Supporter) said:
My take on it (not being a racer, myself):
I'll abbreviate because I'm lazy. VCT would be VVT, but VVT is not always VCT. Much like a square is a rectangle, but a rectangle isn't always a square.
Assuming you have something that varies the cam timing, it will in turn vary the valve timing. The only way I can think of varying the valves without changing the cam is with old-school Rhodes lifters. They were basically crappy hydraulic lifters used in old school V8s that bled down at idle and pumped up as oil pressure rose with RPM. It was basically a way of taming a wild cam to make it more useful in the lower RPMs and getting the full lift/duration at higher RPMs. What they actually did was suck.
I never knew that about Rhodes lifters. I thought they were just another brand of lifter. They sure must have sold a bunch though - or at least sold a lot of decals. Every hot car I can remember as a kid had "Rhodes" lifters.
Maybe they only work with 3/4 race cams?
The rules mean what the person who wrote them meant, not what they said.
I have seen rules that said "steel cylinder heads only". Well, I haven't seen an engine yet that had a steel cylinder head, so that means everybody is illegal. Or maybe the rule maker meant iron and didn't know the difference.
The rule writer probably meant no VTEC. VTEC is varable valve timing, but doesn't always have variable cam timing. Cam timing stays fixed in any VTEC engine with a timing belt. You could show up with an Integra GS-R engined car and rules-lawyer an argument that the camshaft timing is fixed, so it meets the rules. And then they'd say shut up, get out of here...
I didn't think VTEC changed the timing, only the lift?
In reply to MiniDave :
VTEC switched to a second cam lobe- so both timing and lift are altered (probably, I've never measured the cams, but I would presume they change everything). VCT/VVT just moves the cam to alter the valve opening and closing times.
In reply to alfadriver :
The valve timing was affected. The cam timing was not. Honda did not start doing that until the i-VTEC engines like the K20/K24. (Just to be confusing, Honda called it VTC.)
With non VTC, VTEC engines like the D/B four cylinder and the J six cylinder, valve lift and timing are switched, but the camshaft keeps its timed relationship with the crank.
mmandros51 said:
In reply to L5wolvesf :
I know this is an old post but I'm in the same sort of predicament and was wondering what you ended up doing? The rules specifically state no variable cam timing but make no mention of variable valve timing. While the two essentially do the same thing, they do it in different way. VCT has phasers that advance or retard the cam, while VVT such as VTEC changes rocker arms to for a differnt cam profile. The rules as stated say no VCT. I'd say it's a gray area that until specifically stated VTEC cars can be ran.
The short answer is no. And no one around here was running anything that had a “Variable” engine. I decided, based on that and the replies here, that it would be simpler to avoid any of the “Variable” engines for that project.
Then came - finding a decent built car out here in the west. The closest I could find anything was Colorado, but most were in the Midwest or further.
Then “progress” bit us in the arce. The track I was going to run, only an hour away, was shut down. Effectively due to residential expansion for a very large (“ thousands of jobs”) computer chip plant being built.
I am now looking at doing a rallyX program.
Pete. (l33t FS) said:
You could show up with an Integra GS-R engined car and rules-lawyer an argument that the camshaft timing is fixed, so it meets the rules. And then they'd say shut up, get out of here...
Yeah, this was a factor in me not looking for "variable" anything cars.
A 401 CJ said:
Curtis73 (Forum Supporter) said:
My take on it (not being a racer, myself):
I'll abbreviate because I'm lazy. VCT would be VVT, but VVT is not always VCT. Much like a square is a rectangle, but a rectangle isn't always a square.
Assuming you have something that varies the cam timing, it will in turn vary the valve timing. The only way I can think of varying the valves without changing the cam is with old-school Rhodes lifters. They were basically crappy hydraulic lifters used in old school V8s that bled down at idle and pumped up as oil pressure rose with RPM. It was basically a way of taming a wild cam to make it more useful in the lower RPMs and getting the full lift/duration at higher RPMs. What they actually did was suck.
I never knew that about Rhodes lifters. I thought they were just another brand of lifter. They sure must have sold a bunch though - or at least sold a lot of decals. Every hot car I can remember as a kid had "Rhodes" lifters.
Rhodes also sells (or sold... I think they're dead now) regular lifters as well, but I think they were the only game in town for variable lift pieces.
matthewmcl said:
A 401 CJ said:
Curtis73 (Forum Supporter) said:
My take on it (not being a racer, myself):
I'll abbreviate because I'm lazy. VCT would be VVT, but VVT is not always VCT. Much like a square is a rectangle, but a rectangle isn't always a square.
Assuming you have something that varies the cam timing, it will in turn vary the valve timing. The only way I can think of varying the valves without changing the cam is with old-school Rhodes lifters. They were basically crappy hydraulic lifters used in old school V8s that bled down at idle and pumped up as oil pressure rose with RPM. It was basically a way of taming a wild cam to make it more useful in the lower RPMs and getting the full lift/duration at higher RPMs. What they actually did was suck.
I never knew that about Rhodes lifters. I thought they were just another brand of lifter. They sure must have sold a bunch though - or at least sold a lot of decals. Every hot car I can remember as a kid had "Rhodes" lifters.
Maybe they only work with 3/4 race cams?
I'm old but not THAT old. My dad used to talk about those when he talked about hot rods in the '50s.
In reply to MiniDave :
You're right, unless it's i-vtec which does both.
"VTEC" is just a marketing name, there are a ton of different technologies with that label. All it really means "This is a Honda and we did something involving the valves". Could be timing/phasing, could be a more aggressive cam profile that gets switched in, could be cylinder deactivation, etc.
I guess if you wanted to play rules lawyer you could argue that a lock-in-different-cam-profile system that only changed lift but not duration or the relative angle of the cam and crank would not be "variable valve timing", but I doubt that's what the rules writers intended and it seems likely to be one of those things that would only work until the next opportunity to change the rules and make it illegal.
In reply to codrus (Forum Supporter) :
VTEC means something very specific: the use of multiple cam lobes and the ability to connect the rockers to effect two different valve lifts. It is not always for performance, but the original versions were. Some of them open one valve a lot less at low load, for chamber motion reasons, and at high load the VTEC pin locks the rockers together so both have the same lift.
When Honda moves the camshaft position relative to the crank, that is VTC. When both are combined, it is i-VTEC.
Pete. (l33t FS) said:
In reply to codrus (Forum Supporter) :
VTEC means something very specific: the use of multiple cam lobes and the ability to connect the rockers to effect two different valve lifts. It is not always for performance, but the original versions were. Some of them open one valve a lot less at low load, for chamber motion reasons, and at high load the VTEC pin locks the rockers together so both have the same lift.
As well as longer duration on the higher lift lobe. The duration on some of those VTEC lobes I saw as much as 235 at .050", which is a lot of duration on a small 16V 4cyl.
The later, lesser performance ones, as well as the i-VTEC motors run as a 3V (1 intake, 2 exhaust) under normal conditions, and 4 when the VTEC engaged. It was for economy and not performance.
Our 06 Odyssey which says i-VTEC on the engine cover, it has the "feature" of shutting 3 cylinders completely off. The "i" is supposed to stand for "intelligent" but you could argue if it is, or isn't on our van, as I deleted it 
I think it means something quite different on a k24a2.
In reply to L5wolvesf :
Where did you used to race? I race in Utah/Wyoming
mmandros51 said:
In reply to L5wolvesf :
Where did you used to race? I race in Utah/Wyoming
In the mid 80s I raced ITB in southern California mostly, with some races at LVIS and Sears Point.
In the early 90s I raced H-Production nationally out of AZ, with some races in Cali, CO, OK and Road Atlanta.
Roundy wise once at Ascot and a season at Tucson Raceway Park.
I never got up to Utah or Wyoming. What do you race?
In reply to L5wolvesf :
Sorry for the late reply, I've been swamped with work. Right now im racing imca sport compacts and stock cars. Used to race an asphalt super late model
