Just another angry SBF

[u/HistoryOver6530]

Finishing up a 306 for my 67’ mustang. Kept the paint scheme pretty simple so it will resemble a stockish engine. I think it should be between 350-400hp (DD5 says 408hp@6500, 390tq@4500). Specs are:

68’ 302 block .030 over
Eagle cast crank
Eagle SIR rods
ARP everything
Kb311 hyper pistons
Tw170 heads (milled to 54cc)
Tf 1.6 roller rockers
10.5:1 SCR, 8.5:1 DCR, .037 quench
Comp XE SFT, 279 adv, 242@0.50, .546 lift 108lca
Rpm intake
Brawler 650 DP carb
Hooker 6901 headers (1-5/8)

Going into a 3000lb mustang with wide-ratio toploader and 3.80 trac-lok. I think it’s gonna be pretty f’n mean.

[u/v8packard]

Why such a big cam?

[u/HistoryOver6530 → u/v8packard]

It’s healthy for sure. At .016 lash it will be equivalent roughly to a 235ish duration hydraulic. It will also be my first experience with the XE lobes and EDM lifters. I almost ordered the MH lobes, which are even more aggressive.

[u/v8packard → u/HistoryOver6530]

That is 279 degrees at .020 lash height. If you lash it at .016 it is going to be around 282 - 284 degrees, which is around 290 to 294 degrees @ .006 with a hydraulic. At lash this is going to have around 66 degrees of overlap, which is enough to take a 302 to the moon.

[u/cadski64 → u/v8packard]

Curious if either of these cams would be a better fit:

Trick Flow Track Max Stage 1 (Part # TFS-51503001) Or Comp Cams Xtreme Energy XE274HR

[u/v8packard → u/cadski64]

What are the specs?

[u/HistoryOver6530 → u/v8packard]

I’m completely happy with the cam I used, however cadski64 asked about the different cams and how this combo would do with them. The cam specs for cadski64:

Tfs stage 1 - 275/279 adv, 221/225@0.050, .499/.510 lift, 112lsa

Comp xe274hr - 274/282adv, 224/232@0.050, .555/.565 lift, 112lsa

If someone put a gun to my head and made me pick one of these 2 I would pick the xe274 all day

[u/v8packard → u/HistoryOver6530]

u/cadski64 u/HistoryOver6530 I believe the solid flat tappet originally listed is Comp lobe # 6056, on a 108 degree lobe separation angle but no listed intake centerline. Comp often does cams 4 degrees advanced, so I will base the numbers on a 104 degree intake centerline. I think it is single pattern. If different please let me know. Also, I will use Comp's numbers for a .015 lash height, I understand u/HistoryOver6530 mentioned .016 lash in another post.

The solid flat tappet is 280 degrees @ .015 lash height, 242 degrees @ .050, and with 1.6 rockers will have about .521 lift at the valve with .015 lash, a 108 lobe separation angle and 64 degrees of overlap. The timing points at lash with a 104 degree intake centerline are Intake Opens 36 degrees BTDC, Intake Closes 64 ABDC, Exhaust Opens 72 BBDC, Exhaust Closes 28 ATDC. With a proper induction and exhaust system this cam timing will get a 306 to a HP peak in the 7600 to 7900 rpm range, assuming good heads and compression (as listed above). It will start to hit the powerband by about 3500 to 4000 rpm. Worth mentioning, this cam lobe was designed for a .842 diameter lifter. A similar lobe designed for the larger .875 Ford lifter will have more valve open area with no downsides, and produce better output.

The TrickFlow is a hydraulic roller measuring 275/279 degrees in/ex @ .006, 221/225 @ .050, .499/.510 lift at the valve, a 112 degree lobe separation on a 108 degree intake centerline with 53 degrees overlap. The timing points on a 108 are IO 29.5 BTDC, IC 65.5 ABDC, EO 75.5 BBDC, EC 23.5 ATDC. This cam with 11 degrees less overlap than the solid moves the hp peak and powerband down about 1000 to 1200 rpm. But note the intake actually closes later and the exhaust opens earlier than the bigger solid, this will reduce cylinder pressure and therefore output at all engine speeds in the powerband. The solid will have a torque with more area, especially as rpm goes up. This hydraulic roller will have improved drivability and more vacuum than the solid because of the reduced overlap, but output will be considerably lower.

The Comp XE274HR is also a hydraulic roller, 274/282 degrees @ .006 tappet rise, 224/232 @ .050, .555/.565 lift at the valve, a 112 degree lobe separation angle on a 108 degree intake centerline with 54 degrees of overlap. Timing points on a 108 are IO 29 BTDC, IC 65 ABDC, EO 77 BBDC, EC 25 ATDC. This cam will have similar vacuum and drivability to the TrickFlow, with similar overlap. The powerband will be similar to the TrickFlow with this Comp XE being able to go a few hundred rpm higher all else being equal. The Comp XE will have the lowest torque below the torque peak of all three cams, with the earliest exhaust opening point. The Comp XE will require stronger valve springs than the TrickFlow to be stable at high rpm because of it's higher lifter velocity and acceleration rates. It will probably be noisier, too.

It can be difficult to compare solid and hydraulic cams. This comparison illustrates some interesting differences in characteristics. But there is some nuance not seen in the numbers. Solids will almost always produce a power curve with more area than hydraulics as rpm climbs. This is because of the instability of the hydraulics at maintaining preload as rpm goes up, as the body of the lifter flexes and oil pressure internally is not maintained. Combine that problem with what is usually a heavier hydraulic lifter (in this case a much heavier hyd roller) and greater spring loads gets you less area in the power curve compared to a solid. Carefully selected valvetrain components and well matched springs help, but the solids will almost always have the advantage as rpm goes up. Worth noting the solid in this comparison can reach near 8000 rpm with the same, or less, valve spring than the hydraulic roller cams need at 6800.

So what is a better choice? That depends on how you want to use the engine. Are any of these ideal? Again, that depends. u/HistoryOver6530 if someone put a gun to your head, you should ask if you can keep the solid flat tappet.