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MG MGB GT V8 Factory Originals Technical - Mildest BOP/Rover cam?

I'll have the engine out this winter for some maintenance and may want to explore mild-cam/high-boost combinations a bit more. At the very least I am considering advancing the cam, but I would also like to find out if there is a milder cam available than the one I am using. The idea is to restrict the upper RPM airflow just a bit more for durability but to improve driveability and economy at the same time. I'm using a stock Jetfire cam I think. Anyone have a clue as to what would be milder? I know this is contrary to normal practice, and the common thing is to swap in a larger top pulley, but I am finding this approach makes for a very broad power curve and want to explore that phenomenon further.

Jim
Jim Blackwood

I know comp cams will grind a cam to whatever spec you want. Mine is custom from them. Maybe some desktop software would be a good place to decide what specs you want, and then have a custom grind from there?

Justin
Justin

Jim,
You might try Kenne-Bell in CA, Buick specialists. They make a cam with .462 intake and exhaust lift, 260 degree duration, and a 110 degree lobe center. Power range is supposed to be 1-5500 rpm. They 'were' at 714 941 6646, but this was a while back, who knows with all the area code changes in that area of the country. Best, Joe
Joe Ullman

Ontaria CA is either 909 or 818 now- or google the following

Phone
(909) 941-6646 For Placing phone orders, ordering & shipping information, order status, and product information. NO TECHNICAL SUPPORT. Hours: 8:00-12:00 1:00-5:00

(909) 941-0985 For technical information or assistance before ordering (Kenne Bell products only)

(909) 944-4883 24 HOUR FAX LINE: We recognize that our phone lines are busy, especially the tech line. For your convenience you may FAX technical questions and orders. We try to answer Tech questions the same day

Email Us KenneBell@KenneBell.net

Greg Fast

I appreciate the efforts guys, but the stock Olds cam had .384" of lift. Buick was .383", possibly the Jetfire used the same cam. I don't imagine the overlap was more than 108 but I don't have the specs. Justin, a custom grind may be the only way to go milder than stock. What was the expense on that? I'll have to check the actual lift when I do the teardown. One other option would be using rockers with a lower ratio, but it's an open question what's out there. The most practical solution might be to advance the cam and shift the powerband downwards. Maybe as much as 8 degrees would work out well. I could use more bottom end torque anyway. (Always ;-)

Jim
Jim Blackwood

Concentrate on lobe separation and lift, on a blower is very critical. When in doubt use more lift, it will slow down the mixture on a force induction thus improving torque band. Larger ports work well with a blower and allows to run higher boost.
higher rocker ratio is also good with a blower.



Bill Guzman

I Found the standard Rover Vitesse cam , with offset timing for more torque, gives excellent low speed power on the 3.5 engine (3.08 axle with 15" wheels), it will pull away from 1000rpm in 5th with no problem, and fuel consumption is very acceptable for a V8.

I am experimenting this winter with a larger bore throttle and shortened, enlarged trumpets on the Fi system to see if I can improve torque even more, the twin plenium Vitesse extracted considerably more torque as a result of its increased inlet area, and I am hoping that I will be able to improve on this.

Mike
Michael barnfather

Jim,
I paid 180 bucks for the cam and it took about 2 weeks to get. Not bad....

Justin

p.s. Does anyone have an opinion on centrifugal blowers (i.e. vortech s-trim's)? I've got a 4.2L sitting in my garage, and I'm thinking about putting a blower on it. It should bolt onto the front drivers side without many modifications to the car (maybe the radiator support panels, but that's about it.)
Justin

My research indicates that advancing the cam will hurt economy by blowing fuel out the exhaust. Mike, do you have any specs on that cam? I sent an email to Isky and hope to get a response from them on this. Bill, I don't think better breathing through the head inlet ports and valves is what I want. Exhaust maybe, but with the exhaust system I've got on it I doubt that is much of a factor (long tube equal length headers ~35" into header mufflers). I'm using the existing restrictive design of the inlet ports of the Olds head to limit the flow at the top end to prevent detonation from the excessive boost. The advantage of running excessive boost is that the inlet tract pressurizes at a much lower engine speed and boost comes up much quicker. This gives a broader powerband than any amount of porting and cam changes could accomplish but makes it necessary to restrict the top end to keep from blowing the heads off the motor. Reducing the overlap would help on the economy and probably power output, since the scavenging effect of the exhaust is not needed to pull the intake mixture into the engine as much and blowing the intake charge right on out the exhaust is a factor, but this means even more restriction is needed in the intake. Duration of the intake should not need to be increased and may be advantgeously decreased. Lift should not need to be increased. Exhaust duration could be played with a bit, a slight increase might help as might an increase in lift, but probably not that much, and again would require more restriction in the intake. I have to limit the output of this engine to the current level, or slightly lower. In exchange for that compromise, I want to either improve mileage or bottom end power, or both.

That is my thinking at this point in the project. Are there any reasons why I'm missing the mark? Thanks.

Jim
Jim Blackwood

> I'm using a stock Jetfire cam I think. Anyone have a clue as to what would
> be milder? I know this is contrary to normal practice, and the common thing
> is to swap in a larger top pulley, but I am finding this approach makes for
> a very broad power curve and want to explore that phenomenon further.

As luck would have it, I've been working up a list of cam specs for
off-the-shelf off-the-shelf cams. Most grinders will do custom cams.
The flat tappet ones are usually inexpensive. I don't know what
interchanges with the Olds rocker arms but if you can find a smaller
or larger ratio, you can use that to alter the timing.

In any case, here are the specs. Email me for a copy if the list software
screws up the spacing.

Dan Jones

Cams for:
215/300/340 Buick V8's
215 Olds
Rover 3.5L, 3.9L, 4.0L, 4.2L, 4.6L

Crower hydraulic flat tappet cams
50227 246HDP 246/253 184/190 .402/.421 112 idle to 3500/ redline 4500 300
50228 250HDP 250/258 192/196 .424/.430 112 idle to 3500/ redline 4500 340
50229 258HDP 258/260 196/202 .430/.446 112 1500 to 4000/ redline 5500 300
50230 260HDP 260/266 202/210 .446/.451 112 1500 to 4000/ redline 5500 340
50231 270HDP 270/276 210/218 .451/.477 112 1800 to 4500/ redline 6000 300
50232 276HDP 276/281 214/218 .488/.490 112 1800 to 4500/ redline 6000 340
50233 280HDP 280/286 220/226 .488/.501 112 2000 to 6000/ redline 7000 300
50234 284HDP 284/290 228/234 .512/.526 112 2000 to 6000/ redline 7000 340
84150 kit or springs

Crower solid flat tappet cams
P/N Grind adv dur 0.050 lift LSA RPM Range
50303 282FDP 282/287 238/242 .482/.488 108 2000 to 5500/ redline 7000 300
50304 292FDP 292/298 246/250 .502/.514 108 2500 to 6000/ redline 7500 340
50305 304FDP 304/310 256/262 .536/.549 108 2500 to 6000/ redline 7500 340
lash 0.022" intake/0.024" exhaust
84350 kit or springs

Isky hydraulic flat tappet
P/N Grind adv dur 0.050 lift LSA RPM Range Notes
256 256/256 202/202 .450/.450 112 1500-4800 Torque cam, good low spe
ed
262 262/262 208/208 .445/.445 110 2000-5500 (3000-6000 Ted) good mid
range
264 264/264 ---/--- .480/.480 108 (3500-6500 Ted) upper mi
d-range
270 270/270 216/216 .470/.470 109 2000-6000
282 282/282 224/224 .467/.467 109 2500-6500

Erson
P/N Grind adv dur 0.050 lift LSA Advance RPM Range
E640111 RV5H 274/280 202/208 .437/.448 110 4 deg 1000 to 4000
Excellent replacement camshaft for vehicles seeking improved low end
performance. No modifications necessary. Compatible with stock
compression and gearing. Good idle.

E640201 RV15H 288/288 214/214 .458/.458 111 4 deg 1500 to 4500
Rovers and TR8's with lightly modified cylinder heads, aftermarket
aluminum intake and free flowing dual exhaust system increases low
end torque and mid range horsepower.

E643121 TQ20H 292/292 214/214 .478/.478 112 5 deg 1500 to 4500
The Performer. Broader power and more mid-range performance from modified
engines. 4 or 5 speed manual transmission and low gears deliver best results.
Noticeable idle.

Kenne Bell
P/N Grind adv dur 0.050 lift LSA RPM Range Max
KB Mark 1XA 260/260 ---/--- .462/.462 110 1000 to 5500 7000
Street 215's. manual or auto, stock gears, stock idle, will work with
stock springs and retainers but stiffer recommended

KB Mark 2A 270/278 ---/--- .475/.488 110 1400 to 6000 7000
215-300-340 need stick or higher stall converter, max street cam for 215
slight lope at 800 RPM

KB Mark C114A 284/294 ---/--- .488/.494 114 2000 to 6000 7000
max sensible cam for 215/300/340 stick only pistons do not require notching
35 HP over stock

KB Mark 3A 305/310 ---/--- .518/.523 108 3000 to 6500 7200
50 HP rough idle at 1100-1200 needs stall converter clears pistons
if block and heads not milled, a handful on street in a 300

KB Mark 5RS 305/318 ---/--- .600/.592 106 4000 to 7500 8000
race only solid lifter ported heads, roller rockers,

Crane

P/N Grind adv dur 0.050 lift LSA RPM Range
H-194/250-2S-12 252/260 194/202 .400/.416 112 1000 to 4000 (10) 24
38 (16)
7.75 to 8.75 compression, smooth idle, fuel economy

H-202/260-2S-12 260/268 202/210 .416/.432 112 1500 to 4500 (06) 28
42 (12)
8.00 to 9.50 compression, smooth idle, 2200-2800 cruise

H-218/280-2S-12 276/284 218/226 .448/.464 112 2000 to 5000 02 36
50 (04)
8.75 to 10.5 compression, good idle, 2600-3000 cruise

H-226/290-2S-10 284/292 226/234 .464/.480 110 2200 to 5500 08 38
52 (02)
9.50 to 11.0 compression, fair idle, 3200-3600 cruise,

F-238/3200-8 304/304 238/238 .512/.512 110 3000 to 6500 16 42
52 06
solid lifters, 10.0 to 11.5 compression, fair idle, 3400-3800 cruise,
0.022" lash
Dan Jones

Actually (this is me thnking at the keyboard) that if you restrict flow on the inlet side, that the tendency to detonate may be increased due to the increase in temperature (and decrease in density) of the fuel-air mix in front of the intake valve. So the result is that the engine may do better off-idle and part throttle, but will suffer later in the (full-throttle) rpms.

I have a feeling that to do what you want to do, it will take a bit more than just a cam change/adjustment. Based on what I've read for many years, the best overall performance comes from low-compression/ high-boost component selection.

Wayne
Wayne Pearson

Good info Dan. Looks like all of them are hotter than the stock cam though, and why wouldn't they be? Who's going to buy one that's milder? Looks like a stock cam of some sort or a custom grind I guess.

Wayne, a couple of other things enter into the equation. One is the intercooler in the intake plenum immediately below the blower outlet, and the other is the cooling effect of expanding the somewhat cooled air through an orifice and spraying fuel into it at the same time. I expect this offsets the heating from compressing the air to some degree. Anyway, it seems to work.

Jim
Jim Blackwood

Jim,
I haven't looked up the numbers, but everything I've read says that the US spec SD1 cam was the least aggressive stocker used.
David
David

Jim, the reason to enlarge the port I&E is to slow down the flow. The mixture will travel at greater velocities with a small port, so enlarging the intake and keeping the E the same size or q bit larger will help reduce detonation and increase efficiency on the force induction system. That's what we do with the blown big blocks and small block chevies. Combine with a stock camshaft and increase lift with rockers will give a very smooth running engine if run at 6-9 lb of boost. No blown head gaskets or crack heads.
This can be done with larger ports.
This is also what I am doing with the V6 blower.
Imagine the high speed induce by the blower into a small port, you are reaching mach speeds
Bill Guzman

David, sounds encouraging, where would I be able to find the specs?

Bill, I don't disagree with you, but I don't think you understand what I'm trying to do. While it is true that with a positive displacement blower at least theoretically everything that is pumped through must go into the engine, this does not take into account leakage, compression of the charge in the intake tract, and the restriction past the valve, to say nothing about mach airflow resistance. Admittedly however the intake pressure will continue to climb, at least slowly, as will the pressure in the cylinder, during the duration of WOT operation. You wouldn't normally set up an engine to run this way, but happily the small size of the car limits how long this can go on, there's a drop between shifts, and the leakage helps to mitigate the pressure buildup. As it stands right now, I appear to be at the point where it will work just fine as long as I don't work it too hard for a long period of time, but if I do it can blow a gasket. (Running the Dragon very hard posed no problems at all, but those were short bursts of maximum accelleration with curves in between.) In conjunction with getting a better seal to prevent that, what I'm trying to do is give myself just a bit more cushion than I have now without losing any of the bottom end, which is exactly what will happen if I decrease the boost. Bill, this thing is just phenomenal in terms of how wide the powerband is. Boost starts to build right off idle and at low engine speeds most of that boost is getting right to the cylinders and making a lot of power. About the only other way to effectively do what I want would be to rig the bypass valve to also act as a boost limiter and I haven't ruled that out by any means. I'm currently seeing the pressure in the intake manifold exceed 15 psi at redline, so that should give you some idea of what it is doing on the other end of the rpm range, and the only thing keeping it from going boom at speed is the restriction in the heads. Like I said before, I don't think less restriction in the intake tract is the answer because then I'd have no choice but to reduce boost and lose the bottom end. I'm not looking for any more horsepower, and I've not worked on developing a means of using the bypass as a dual function valve thus far. The heads will be off early next year which would make a cam change fairly painless if I decide to go that route, and that's the only reason I'm considering changing anything at all.

Jim
Jim Blackwood

Jim,
I can't find the specs in my files but I will look further today. In the mean time, are you familiar with Pro Racing Sim? With your level of interest it may be attractive.
David


http://www.proracingsim.com/index.html

http://www.proracingsim.com/camdiskmainpage.htm
David

Jim,
I can't find, or don't have, the cam specs. Ted Schumacher at TSI Automotive does, though. I'm sure you have his number. Kepp us posted.
David
David

Jim,
Just a thought here but since the Rover engine was originally intended for marine use does anyone have the specs on that cam?

Before Rover took it over to England it was with Mercury if my memory serves me right and as marine engines operate often at and just off idle this may be worth a look.

Cheers, Pete.

Peter Thomas

This thread was discussed between 17/12/2003 and 22/12/2003

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