Hi all,

I am looking for cam suggestions, but my criteria are a little different than usual.

I'm building a 505 stroker (4.25" stroke) that will be going into a 4000lb car, 2.88 rear diff, and probably about 2000rpm stall. 10:1 CR.
One thing I need is to have decent vacuum and only a very mild lope (would prefer something very subtle.)
I'm looking for something in a hydraulic roller cam.

The motor is going into a luxury GT car (a Jensen Interceptor) and I want to keep it that way...so no radical cams. Needs decent vacuum to operate the HVAC system and power brakes. I guess that 15" vacuum would be about the minimum I would want. I've had a few cars with hotter than stock cams that had about 15" of vacuum and they always sound just right (you can hear that it is not stock, but it's still very subtle) and had plenty of vacuum to operate accessories.
So this will definitely be more of a low rpm torque motor with peak HP somewhere between 5000-5500.

This might never make it to a track, so I am not looking for the fastest possible 1/4 mile time, but I do not want to leave too much on the table, either. I still want to make as much power as possible, given the restraints (don't we all...)

I'm no expert. There are wiser people than me to give guidance, but I will give it a try.

I suspect you will need a custom grind. The focus should be on the lobe separation angle, overlap, and intake closing. LSA no less than 113 degrees. Overlap no greater than 45 degrees at .05". Intake closing should be dependent on static compression and stroke.

Lift will have no effect on torque curve or idle so get as much as is reasonable. Duration should stay within the boundaries of a wide lsa and early intake closing for idle quality.

I would look at the LSA, overlap and intake closing of a stock magnum or gen III for a starting point.

Good luck.

Do you think you'll run into detonation issues with that high of compression, combined with you tall gears, low stall and relatively high weight? A lot of guys run compression that high for sure but it's usually in a lighter car with a loose convertor and deep years, just food for thought.
I'd GUESS you'd want a narrow LSA to bleed off some cylinder pressure? A 505 will eat a lot of duration so that'll help as well in picking a more aggressive cam to bleed off low speed cylinder pressure. Again I'm guessing that the suggestion will be cam it for torque, and get as much lift as possible to carry the HP into the rpm range as far as possible.

What heads?

Sorry, forgot to specify:

Stealth heads. So being aluminum, I think there won't be any detonation concerns @ 10:1 CR.

If I owned a Jensen I would want a wicked sounding and wickely fast motor

HELL YA CAB............. Me too man......

I run 243@.050 and 108 LSA in a 496. Vacuum is 12-13" with tuning which does OK with power brakes and vacuum operated HVAC. It starts to wake up around 2000 RPM. I run a 5 speed and 3.23 rear.

For your situation this would be a bit too much I think. It would work... but the idle is a bit lumpy and smelly. Not subtle.

As a guess, around 220-230 degrees and 112 LSA would fit the need... especially considering the rest of the Jensen powertrain including rear ratio was designed for a stockish big block.

I am a believer in the same LSA for all rpm ranges, because the heads flow the same at overlap. As duration goes up or down to suit rpm range, so does overlap duration. David Vizzard has done extensive testing to confirm this. Sooooooooooooooo, just WAG on my part, but an lsa of roughly 106 with about 232 @.050 on both sides might work well. If the recommendation is for more exhaust duration, then the LSA is just wide enough to get back to the same overlap duration for best results.
A call to a pro is the real answer, since you have a very special need and a few more $$ is very well spent. Dwayne Porter of Porter Racing Heads frequents this board, and is really sharp on cams. He can have one ground to fit your exact requirements.

being a Jensen you probably don't have a ton of hood clearance so you may want to look at the Indy 440-2D dual plane (sits lower than a performer RPM or a Holley Street Dominator. You're probably going to have to run exhaust manifolds that fit the chassis (or possibly small tube block huggers) as well as a relatively small-ish 2 1/2" max dual exhaust. That said I wouldn't over-think it and find a nice single pattern Hydraulic Roller in the ~236 @.050 duration and around .540-.565 lift and I would run about a 110-111 spread and put the intake centerline in around 106-107. You will have absolutely wall-to-wall torque and a very strong powerband along with excellent vacuum for power brakes. The combination will definitely feel like 505" when you tap the gas and should pull at least into 5600 rpm range. That mid 230 range for a hydraulic roller is a great all-around balance for awesome street power and torque with heavy cars and street gearing. If you wanted to you could go with a similar intake duration and a much longer but also slower exhaust ramp for that "cruise-in" "Thumper" idle....but to me that would seem out of character for a Jensen, I would go with a single pattern 236-ish @ .050. It's also very similar to what I run in my 427" Stroker small block in my Cobra Replica and the 442" AMC in my Buddy Nat's 12 second Jeep CJ-7, Great idle with just a hint of chop, instantaneous throttle response and tire melting torque all over the powerband and in any gear.


Greg, the only issue I have with tight lobe spreads is he's probably going to run a very restrictive exhaust, increasing overlap when you have a restricted exhaust can kill (or severely limit the effectiveness of) that "fifth cycle" scavenging effect, especially with the mild street type compression he'll be running. As for "optimum" LSA's that really depends a lot of the head flow and valve configuration, but this one wouldn't be anything close to 106 IMHO

I use a Howards hydraulic roller that sounds perfect for what you are doing. It's around .544 lift and 243° duration. Go to their website. Use a Crane composite gear and a Howards fuel pump pushrod.

The best advice is to have your Source heads CNC ported by someone like Modern Cylinder Head. You'll have well over 600 hp with very minimal effort.

Thanks for all the suggestions.

I've read most of Vizard's books, and his BMC A-series book was the first engine-technical book I ever read...a real classic!
But Streetwize is right...I believe his cam formula (for LSA/overlap) assumes a decent exhaust and the Jensen is severely limited in that area. The BEST I will be able to do is some heavily modified block huggers (because even they don't fit without modifying to avoid frame rails and steering linkage...hell the stock cast iron pieces BARELY fit) and a 2.5" exhaust.

I was also already considering a single pattern cam. I just had no idea (being a stroker) what sort of duration I should be going for. It looks like Streetwize's recommendation of mid 230s is based on experience, so that is exactly what I was looking for.

Thanks, it's great to get real numbers that come from experience.
And your numbers seem to align with Streetwize's recommendation. It looks like you're right: Something just a little bit less that yours will probably be just right.

Right now, I'm thinking mid 230's w/ a 112LSA or lower 230s on a 110.

I've done a little hand porting on my Stealths. The seat and throat were a little mismatched and I cleaned that up. Also, the casting at the pinch-point was very wavy/lumpy. I smoothed that out which opened up the pinch point about 0.125" with plenty of material to go. Plus I smoothed everything else out without actually reshaping it too much.

Hopefully that will make a solid difference. Certainly not as good as cnc porting, but a good chunk in that direction.

Since you want stock sounding, good vac.. you should
look at cam for a tow truck.. something with a wide
LSA for the vac.. low duration.. mid 220s... you will
hear more noise from the roller lifters than anything else
and with the alum heads and the compression you should be
able to run pump junk easily... your gonna have to do a
bit of work on the advance curve with all the low rpm..
dont get carried away with the port work.. you want the
velocity... EFI would work great on that

How soon are you doing this project?
I'm building a 505 stroker for my '73 Jensen Interceptor, but it might be a bit hotter than your looking for.
It will be around 10:1 compression, Trick Flow heads TFS-6161T784-C00, and Lunati Voodoo solid roller cam 40230732LK, 243/249@0.050", .578"/.585" 110 lsa, 106 icl.
Using the Harlan Sharp 1.6:1 rockers S70016KE, so lift will be a tad more.
FiTech EFI FIF-30012 on a Holley street dominator intake.
I plan to dyno the engine just to see how it does, but that would be with dyno headers. I plan to make custom headers for the car.

I have quite a few parts, but I am still waiting on the cam and EFI, and I haven't get the stroker kit yet as the engine is still in the car and I want to be sure it cleans up with 0.030" overbore.

I already have the engine at the machine shop and the crank (just came in Friday), rods and pistons. Got a K1 crank, scat rods and Icon pistons (-26.5cc). I've got a new 750 quickfuel carb (original holley was in bad shape) and a CH4B intake (with the Chrysler part number on it )
I'm having the machine shop put the rotating assembly together and I'll do the rest. I have all the major components except the camshaft.
I'm also going to 'restore' the engine bay while the engine is out. So it will still be a couple months (I'm guessing) before I am back on the road.

Sounds nice. What are you doing for the exhaust system?
Left or Right hand drive?

I have some block huggers...the cheapy SS ones on eBay. I know they aren't great and they will need some work to fit, but they have to be better then the cast iron manifolds and they are very compact. And they have 3" collectors, which I will extend for as far as I can until I am forced down to 2.5" for the rest of the exhaust.
Mine is LHD...I'm here in America.

"Greg, the only issue I have with tight lobe spreads is he's probably going to run a very restrictive exhaust, increasing overlap when you have a restricted exhaust can kill (or severely limit the effectiveness of) that "fifth cycle" scavenging effect, especially with the mild street type compression he'll be running. As for "optimum" LSA's that really depends a lot of the head flow and valve configuration, but this one wouldn't be anything close to 106 IMHO twocents "
Running a tight lsa means the total duration would be set to give the proper duration at overlap, not the other way around. If your cam suggestion of 236 @ .050 is on a 110 lsa, that would have 16 degrees overlap at .050 lifter rise. Soooooo, my thinking would be to get 16 degrees overlap with a 106 lsa the cam would have 228 degrees duration on both sides. You would have an intake valve closing 4 degrees earlier (better torque? vacuum?) and an exhaust cycle lasting 4 more degrees to gain a touch more torque.