SB

okay , at .004" (Crane's info is at .004", most other aftmkt manufacturer gives you at .006" seat specs)



Mag BBC 454/502 Flat Tappet (rect heads)
.004” 296*, 296*
.006” 286*, 286*
.050” 224*, 224*
.200” 130*, 130*
Valve lift with 1.7 .510”, .510”
LSA 115.5
Merc Part#431-9830 / GM#14096209
ICL 114 ATDC
ECL 117 BTDC
===============
At .004"
IVO 34.0° BTDC
IVC 82.0° ABDC
EVO 85.0° BBDC
EVC 31.0° ATDC
Overlap 65°

TomZ

Thanks for that info!

So, did some playing around. Biggest hurdle was dealing with the exhaust. I'm trying to see if I can find another user out there that's made something similar.

With dyno headers, the stock 365 Mag makes right at 420 HP according to my simulation. With my attempt at simulating the exhaust, I get 381 HP. Both acheive peak at 5000 RPM.

Peak torque is achieved at 4000 RPM (485), and 3000 RPM (449) with the restrictive exhaust.

Exhaust really chokes this thing up, and my thinking is that the exhaust is a lot of help on the Mercury 420 (I'll load those specs later to see what I get there).

In case anyone is wondering... I'm using Engine Analyzer Pro to do all of this, and so long as I have very detailed information, this simulation is usually VERY close (stressing IF I have all the data).

Anyway, pretty interesting.

dereknkathy

I guess stock merc center dump exh with 4 inch risers is not pre-loaded into software? So the 365 is essentially a 420 with smaller exhaust rated at the prop instead of the flywheel...

TomZ

The software settings do not work that way. There are kinds of values to be entered, then saved, for a particular part. Diameter, wall thickness, runner coefficient (calculated), collector length, steps, etc. It gets complicated quick.

The base engine is the same across the two offerings (to my knowledge anyway). I believe (but cannot confirm) that the 420 short block was blueprinted and balanced by Mercury along with a better flat tappet cam, Holley carb, Gil exhaust. In addition to this Mercury rates their offerings at the prop shaft so a 420 could very be another 12-15% beyond that number (I'm not sure that this was the case on the older engines... hoping someone else might know more). The 365 is for sure measured at the flywheel.

apollard

Properly set up, EAP is close - but it does take time as you said. I've simulated two engines that went on the dyno, and they were within 5% on HP, and got the TQ peak within 100 rpm.

I mocked up the 7.4 on EAP and it came out at 335 or so (can't recall exact #, and the laptop at home). Given the loss through the drive, that puts it right at the 300 advertised. To verify the exhaust setup (the largest unknown), I mapped the actual exhaust back pressures at RPMs, then adjusted the exhaust in EAP to get the same pressure curve. Only way I could find to do it, EAP isn't set up to model something as bad for performance as the stock manifolds (no runners, just a open log, etc). Before I did that, I was getting much higher numbers - the exhaust back pressure on the stock manifold at 4600 rpm was in the 4 psi range (again, exact number not at the office).

FWIW, EAP says my build is 489 - near the limits of the 496 manifolds (according to Raylar). Based on the speed increase I saw alone, I'd have said 475.

bobl

Here are some HP numbers from various stock engines I have dyno'd (with full wet exhaust). 330 HP 7.4 made 325 at the prop. 502 mag made 440 at the flywheel. 525 efi made 570 at flywheel. HP500 made 502 at the flywheel. 6.2 made 340 flywheel. 496 mag 365 prop. 496 HO 397 at prop, 431 at flywheel. Mid 80's 350 made 240 at the flywheel. All these were in full dress including stock wet exhaust, using SAE standard correction factor.

Hope this helps,
Bob

airjunky

That 330 was a ringer if it brought you within 50 horse of a 502 mag

TomZ

Actually, the only LS6 option for '71 was the Corvette version. Less than 200 made, but definitely with aluminum heads. It is for the most part a detuned LS7. And the LS7, per GM's planned (but scrubbed) 1970 build was an aluminum head engine (the open chamber heads were a carry over from the '69 L88).

Anyway, just clearing that up.

TomZ

Good info!

Playing around with mine, I was able to "trick it" and got it to creat about the same exhaust pressure. Guess I got close! And the software knew something was up, too. Any time going into the exhaust parameters, it would complain saying that the exhaust was too restrictive for the engine's size and expected output. I thought that was pretty cool.

Have had similar results with a couple of my own builds. Small block stuff. Rather conventional drag race builds.

I built a 498 big block Mopar using the software to simulate parts changes (combined it with Drag Race Analyzer). This worked really well for me and kept me from spending where I didn't need it. *That car ('69 Dodge Coronet) ran 10.30's in the low 130 mph range.... back in the early '90's, tagged and insured.

bobl

It made 325, so about 350 at the flywheel. It was in an all original mid 80's cobalt. I was just curios what it would make, so I dyno'd it.