Propane cam selection questions/advice

[liteon]

Hi all,

I'm currently in the middle of a rebuild regarding my Pontiac 389 engine.
Currently thinking what cam i'll drop in.

The engine is a Pontiac 389cui, bored to .030 (=395cui). Going to run flat top pistons (Keith Black Hypereutectic) in combination with the stock cast iron closed chamber heads (~70cc, 1.88/1.60 valves with hardened seats).
I'll be running a Impco 425 + Impco E(B), and I have a Innovate MTX-L AFR meter to keep an eye on the mixture.
I want to turn this engine into a low-mid torque monster. Although I won't race this car, i'll floor it from time to time, just for fun. I don't really care about top end performance as 90% of the time i'll be just cruising around in the 900-2500rpm range. On the highway my engine will run around 2500rpm. On top of that, this engine will never see 5000+rpm.
I've been reading a lot on camshaft selections, and found out that a single pattern cam would be a good choice for LPG as this would compensate the 30% bigger LPG mixture.

I have 2 camshafts in mind, but the dynamic compression is what keeps my away from making a decision.
I think that in my situation, I should go for the option with a short duration cam, which of course will cause increase in cylinder pressure.
I'd expect that more dynamic compression would result in a more efficient LPG engine, as long this stays within safe limits.
So far I know the LPG in my region has a octane rate of approx 108-110 (say 108).
Both cams shafts I have in mind have roughly equal duration and LSA, but have quite a difference in DCR:

Comp Cams High Energy 260H:
- RPM range: 1200 to 5200
- LSA: 110
- Duration: 260/260
- Duration @ 0.50": 212/212
- Valve lift @ 1.5: .440/.440
- Intake Opens: 24 BTDC
- Intake Closes: 56 ABDC
- Exhaust Closes: 16 ATDC
- Exhaust Opens: 64 BBDC
============================
Lunati High Efficiency 260/260:
- RPM range: 1200 to 4800
- LSA: 110
- Duration: 260/260
- Duration @ 0.50": 210/210
- Valve lift @ 1.5: .441/.441
- Intake Opens: -1 BTDC
- Intake Closes: 31 ABDC
- Exhaust Closes: -8 ATDC
- Exhaust Close: 39 BBDC


I've already done some online compression ratio calculations with these results which are based on the intake closing value:
Static compression with my combination would be approx 10.3:1
When I would run the Comp Camps 260H cam, I calculate a Dynamic Compression Ratio 8.71:1
When I would run the Lunati 260/260 cam, I calculate a Dynamic Compression Ratio of 9.81:1

RPM wise it looks like Lunati is more interesting for me. But looking to that the DCR of that Lunati cam... I think that's going to be a very tricky one isn't?

Does someone on this forum has an recommendation about this?

[storm]

Pontiac heads, especially those before the 67-79 400-455 engines, are notorious for exhaust flow not being able to keep up with intake flow. That is why Pontiac themselves used the types of cams they did. If your not worried about performance I'd be sticking with a small to medium Pontiac style cam with more exhaust duration. The engine must get rid of the exhaust and even with LPG a single duration cam will not work as well as a well though out split duration cam.

[liteon]

Hmm, so split plattern is the way to go. Then i'll have to look again to the Xtreme Energy line of cams which have fast ramps.

Comp Cams Xtreme Energy XE256H:
- RPM range: 1000 to 5200
- LSA: 110
- Duration: 256/268
- Duration @ 0.50": 212/218
- Valve lift @ 1.5: .447/.455
- Intake Opens: 22 BTDC
- Intake Closes: 54 ABDC
- Exhaust Closes: 20 ATDC
- Exhaust Opens: 68 BBDC


Or XE262H version of the cam above;
- RPM range: 1300 to 5500
- LSA: 110
- Duration: 262/270
- Duration @ 0.50": 218/224
- Valve lift @ 1.5: .462/.470
- Intake Opens: 25 BTDC
- Intake Closes: 57 ABDC
- Exhaust Closes: 21 ATDC
- Exhaust Opens: 69 BBDC

My engine runs low RPM (900-1300 rpm) when cruizing <45MPH. So I think the XE262H is bit to much. Tranny will also upshift before 5000rpm.

[storm]

Hmm, so split plattern is the way to go.

On a traditional Pontiac engine it is. What cam did your engine come with?

[GasE150]

Hi liteon

What are you planning to use the vehicle for?

This will determine better what advice you may receive.

[storm]

What are you planning to use the vehicle for?

Read the OP it says

I want to turn this engine into a low-mid torque monster. Although I won't race this car, i'll floor it from time to time, just for fun. I don't really care about top end performance as 90% of the time i'll be just cruising around in the 900-2500rpm range. On the highway my engine will run around 2500rpm. On top of that, this engine will never see 5000+rpm.

[Maddcarson]

Following. I have a 350 small block that I just purchased the XE268H cam for in a 82 Chevy dually. Not to far off from your cam so I will post an update if I feel I’ve gained a lot better bottom end vs. stock 290hp engine cam

[Maddcarson]

UPDATE••••
I installed the XE268h cam and right off the bat needed to adjust the idle mixture screw. Installed new R44T ac delco plugs and new wires. Is there any way to adjust cruising mixture and WOT mixture on the x450 mixer? Idle had a nice lope to it but not crazy enough to where I need a stall converter . I noticed it didn’t have a lope mmmmmmm

[C3H8]

Yes and no.
It depends on when the mixer was made. Early versions had an adjustable power valve right at the mixer vapour inlet. For some reason that was removed on newer versions. Adjusting the cruise is a possibility but can be difficult ad the adjustment has to be in very small amounts. The mixtures are controlled by the 3 rods in the mixer and these are set at a precise height by the distance the connector is pressed into the mixer ring. Prior to any adjustment the depth of the splined position should be measured so you can return the rod connector to it's original position. Once that is done it is possible to press the spline further in or out to change the rod depth. Out will result in a leaner mixture. Pressing it further in will richen the mixtures. Keep in mind that changing this position will change the complete fuel curve. The movement is very tiny. Basically thousands of an inch at a time until you get a value you are searching for. Too many adjustments can even loosen the spline so don't go pressing it in and out too often. In the event you richen the cruise and find the WOT too rich you could install an inline power valve in the vapour line to control full load mixtures.

[Maddcarson]

Thank you for the info! all try that