Bullet Cobra Jet Cam

I've been reading reading reading. Enough reading about cam selection already. I'm nostalgic. That's the whole reason for the Mustang in the first place. So I want a street car that has much improved performance over what I had previously, 1970 H code 351C 2V Mach 1. I really like the blueprint laid out for a 4V CC build in Sticky#3.
I have the carb, dual plane intake, distributor/coil/module, ped mount rocker arms and the D1ZX balancer I stumbled upon. Assuming manual trans, tallish gears and headers/exhaust to suit.
I have talked to Bullet and they have very strongly recommended modifying Georges Cobra Jet Cam recommendation to a 113 LSA (Yes, I've read this before)and then installing it a further 2 degrees advanced.
My question is what will this screw up?
Duration @ .050 223/235
Valve lift : .567/.568
LSA : 113 degrees
ICL : 110 degrees
Intake opens @ 27.5 BTDC 1.5 @ .050 lift
Intake closes @ 67.5 ABDC 41.5 @ .050
Exhaust opens@ 79.5 BBDC 53.5 @ .050
Exhaust closes @27.5 ATDC 1.5 @ .050
Overlap of 55 degrees is centered around TDC
Overlap of 3 degrees at .050
67.5 + 360 + 79.5 + 507 degrees of crank rotation
I plugged the info into a couple of dynamic compression calculators and have come up with values still under 8:1 assuming a static CR of +- 10:1
If the cam is advanced a further 2 degrees to open the intake valve sooner then it will no longer be centered at TDC. What effect will be noticed?
I have read other street cam recommendations elsewhere that have tighter LSA's (110), open the intake earlier 105 ICL and run less duration or more overlap or both.
Oh, and yes I already have a Wife telling me about "Cart before the Horse" scenario she has to live with.

Original Post
Installing a cam slightly advanced is only significant if you also install a brand-new cam chain. Normal wear on a 351-C chain soon retards the cam while running, which is the main reason why some cam grinders specify installing their product a bit advanced. Cleveland chains wear faster than normal due to the large heavy valves, so on an older chain, you may not need the fiddling required for an extra 2 degrees advance. If the chain has over 5000 miles on it, your engine likely could use a new one.

As for more LSA, as you know from your reading it maximizes power, raises where maximum power & torque occur by a couple of hundred rpms (up), reduces overlap of intake & exhaust valves and increases vacuum for your power brakes. A hot engine may idle smoother with less chance of knock (more significant with iron heads than aluminum) and crank over a little easier (if you don't have a hi-power mini-starter).

Mike at Bullet Cams knows his products which are well respected and do not exactly compare to other brands, and in any case the difference in LSA from 110 normally only varies max horsepower by 3 or 4 in a 500 bhp engine. Is this cam a hydraulic roller? They behave a little differently than a hydraulic flat tappet.
I sent Bullet the G.P. recommendation (see below) copied from a previous thread. I read in the same thread that Bullet was recommending a 112 LSA then a 113 LSA. The reader finally got his way (customer is always right). My question was/is: Will the 113 LSA, based on my earlier spec's, make that big of a difference seeing as how the closing/opening events are still centered at TDC with minimal overlap @.050 lift. Assume a new timing set. Bullet must think it will make a big enough difference as the Gentleman I spoke to said he had run plenty of Clevelands over the years. As I have only run 1 I must assume that plenty means at least 2! Ha ha.

Camshaft Spec:
Grinder: Bullet Racing Cams of Olive Branch, Mississippi
Telephone (662) 893-5670
Engine: Ford 351 Cleveland, 4V cylinder heads
Hydraulic flat tappet camshaft
Intake Lobe: #HF275/328 (CRA, designed for Ford 0.875 tappets)
Intake lobe mathematic centerline = 112° ATDC
Exhaust Lobe: #H287/3283 (CRA)
Exhaust lobe mathematic centerline = 116° BTDC
114° lobe separation angle (camshaft degrees)
Exhaust valve opening = 79.5° BBDC
Intake valve opening = 25.5° BTDC
53° overlap
Exhaust valve closing = 27.5° ATDC
Intake valve closing = 69.5° ABDC
275° advertised intake lobe duration
223° intake lobe duration at 0.050"
Intake lobe hydraulic intensity = 52
0.567" theoretical intake valve lift (1.73 rocker ratio)
287° advertised exhaust lobe duration
235° exhaust lobe duration at 0.050"
Exhaust lobe hydraulic intensity = 52
0.568" theoretical exhaust valve lift (1.73 rocker ratio)
Monty, what are YOUR priorities?

In regards to street cams, my specs fall into two categories:

(1) Lowest overlap ... the priority is drivability and vacuum. Nowadays the cams I spec with this priority are all 114° LSA. A little bit of power is given-up to achieve these goals. The guy interested in this type of cam will never miss the nuance in power that is lost, but he WILL miss the drivability if he chose a cam with more overlap.

(2) 60° overlap +/- 2°. The priority is a bit lopier idle and a bit better power, but still usable vacuum and drivability. Boss 351 kinda power characteristic.

I stopped specifying 115° LSA because of the resistance such cam specs received, now 114° LSA is getting resistance? The spec of mine you quote is 114° LSA and +2° indexing. This is a cam for the guy who wants the drivability and vacuum. 115° LSA would be better, but I already explained why I no longer spec cams with that much LSA.

The Bullet spec is 113° LSA and +3° indexing. That amounts to 2° more overlap, and the intake valve closing 2° earlier. Small changes in cam timing don't amount to a hill of beans. I'm surprised Bullet would make a big deal about it. I get the feeling when guys sweat small changes that the changes are based upon a computer program ... not experience. Some guys at Bullet seem to do this, others do not. Having written that, I'll make these comments.

As long as the intake valve opens and the exhaust valve closes within the dwell period at TDC, all is well. That's 30° BTDC and 30° ATDC. Both cams fit that criteria. I consider any cam that has 55° or less overlap to be a "drivability" cam. My cam is 2° better in that regard, but both are within that criteria as well. Finally, the Bullet cam closes the intake valve 2° earlier, which will increase dynamic compression a small amount.

The Bullet cam opens the intake valve 2° earlier, which "should" make more power, but we're not talking about a big difference. Blocking the manifold heat passage would make a bigger difference ... as would lower back pressure mufflers.

If "power" is the priority, we could pen the same lobes with 111° LSA, +4° cam indexing, an intake centerline of 107° and 59° overlap. This cam would perform a bit better than the cam suggested by Bullet. So, getting back to my first comment, what are YOUR priorities?
Drivability and vacuum are a priority that's why I like your cam. I'm curious as to why the "Cam Guy" felt the need to modify your spec. Maybe he felt he wasn't doing his job if he didn't have an opinion. I've read about a big concern about leaving power on the table on the bottom end but honestly if you can't keep your street tires from spinning, who cares!
I still want it all even though I know I can't have it and don't need it!
Thanks the help.
Want it all?

How about a single pattern hydraulic flat tappet cam which uses a cam lobe that is the "mother of all" hydraulic flat tappet cam lobes, not too far from the intake lobe I spec'd for the previous cam. This new lobe's number is HF277/335. Here's the spec:

277°/277° advertised duration
228°/228° duration at 0.050
0.580/0.580 advertised lift

114° LSA
+6° cam indexing (108° intake centerline)
Only 49° overlap
Hydraulic intensity is 49° as well, which means the overlap at 0.050 is zero.

Seated valve events based upon duration at 0.006
EVO = 78.5° BBDC
IVO = 30.5° BTDC
EVC = 18.5° ATDC
IVC = 66.5° ABDC

The overlap period, the period occurring between the intake valve opening and the exhaust valve closing, when both intake and exhaust valves are opened simultaneously, occurs within the dwell period at TDC (i.e. between 30° BTDC and 30° ATDC) when piston motion is minimal. This minimizes the impact of the overlap period upon low rpm performance.

In terms of a hydraulic flat tappet street cam, I believe this cam IS is as close as you'll come to having it all. The engine responds very well to this cam.

Originally posted by 4V & Proud:

the Simple Ripper ?

I haven't come-up with a catchy name yet. I've over-used the Cobra Jet name. Perhaps something with the name "Rhino" in it, like the Rhino Cam. Or perhaps we should call it the "street Boss" cam, following the example of Tim Meyer and his track Boss products.
FYI, here's feedback from a Canadian fellow who installed this camshaft in their 351C many years ago.


"... My engine has 10:1 compression, iron 4V closed chamber heads, 2.19/1.71 valves, Edelbrock RPM AirGap intake, Demon 750 vac sec (annular boosters) carb, Pertronix ignition. The exhaust uses 1-7/8" headers, 2-1/2" intermediate pipes, and magnaflow mufflers.

I was running a Comp Cams custom hyd roller 224°/230° @ 050, 0.572"/0.584" lift, 110° LSA, 110° ICL. The motor switched on @ 2200 rpm and was all done by 5600. Only 10" vac idling @ 1000 rpm; The motor had difficulty passing the smog idle test.

I installed the hyd flat tappet cam with 114° LSA you specified, ... I am ECSTATIC about the results so far! The motor will even idle down at 650 rpm now (wouldn't idle below 950 before) Vacuum at idle has jumped from 10 to 17 inches! And it idles cleanly (couldn't stand beside the car before at idle, it stunk so bad due to emissions) It has a nice lope to it, but still idles very well. I'd recommend this cam to anyone.

... the motor "turns on" at 1700 rpm now (was 2200 with the other cam) and pulls hard past 6200, I'm not sure how high it revs yet. Just blipping the throttle, it revs so freely now to 4500 it makes me laugh; and it melts the tires at will and even breaks them loose shifting into second gear now (never did that before); its been all you said it would and more! I'm going to need more tires under it though (laugh) ..."

Hi Rich.

That gentleman installed the single pattern version.

That spec uses a really "hot" cam lobe. And it shows.

One reason that cam worked for that particular application was because the car was fitted with a very good exhaust system. When the exhaust system has not been so good, I've used that same lobe on the intake with a longer duration lobe on the exhaust. Making what I feel is one of the best overall hydraulic flat tappet street performance cams ever.

check it out:

• Hydraulic Flat Tappet
• Advertised duration (at 0.006 tappet lift) = 277°/287°
• Duration at 0.050 inch tappet lift = 228°/235°
• Gross valve lift at 1.73:1 rocker arm ratio = 0.580/0.585
• ICL = 111° ATDC .............| An earlier ICL synchronizes air flow capability more closely with air flow demand and makes more power.
• LSA = 114° .....................| A wider LSA reduces overlap, produces a wider and flatter torque curve, and improves controllability.
• Seated Overlap = 54° .......| Limiting overlap to 60° or less improves vacuum, idle, low rpm torque and drivability.
• Seated EVO = 80.5° BBDC | An earlier EVO compensates for a muffled exhaust, improves idle, extends high rpm power.
• Seated IVO = 27.5° BTDC | Limiting the IVO to 30° or less improves vacuum, idle, low rpm torque and drivability.
• Seated IVC = 69.5° ABDC | A later IVC lowers the DCR, requires a higher SCR; and can lead to reversion at idle.
This is about as close as I can get using lobes from Bullet Cam's catalog.

• Solid Flat Tappet
• Advertised duration (at 0.020 inch tappet lift) = 276°/284°
• Duration at 0.050 inch tappet lift = 243°/250°
• Gross valve lift at 1.73:1 rocker arm ratio = 0.597/0.601
• Net valve lift at 0.029/0.028 lash = 0.568/0.573
• ICL = 110° ATDC ..........| An earlier ICL synchronizes air flow capability more closely with air flow demand and makes more power.
• LSA = 114° ..................| A wider LSA reduces overlap, produces a wider and flatter torque curve, improves controllability.
• Seated Overlap = 52° ....| Limiting overlap to 60° or less improves vacuum, idle, low rpm torque and drivability.
• Seated EVO = 80° BBDC | An earlier EVO compensates for a muffled exhaust, improves idle, extends high rpm power.
• Seated IVO = 28° BTDC | Limiting the IVO to 30° or less improves vacuum, idle, low rpm torque and drivability.
• Seated IVC = 68° ABDC | A later IVC lowers the DCR, requires a higher SCR; and can lead to reversion at idle.

(int. lobe F276/345, CRA | exh. lobe F284/3476, CRA)

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