New L31 low vacuum question

I need help guys.

Build
94 K1500
New L31 long block
Vortec heads
Ramjet cam
1.6 roller rockers
Carb eps intake
Bored ported tbi with 18lb spring (iirc 600-650cfm)
Shorty headers
Vortec fuel pump

Currently running, waiting on Chuck at finish line transmissions to finish my transmission up. 2 weeks out.

1st initial start, it started right up no issues. Rpms jumped up 1k or so then idled down perfectly. Now since iv been catching coolant leaks and fixed the power steering leak, I'm only getting 13-14 or so on vaccum.
I bumped the timing up about a degree or 2 and vacuum is at 15 now, idles a little better. As iv researched before, timing should stay around 0 so I don't want to advance it too much but did it to get a smoother idle to check for vacuum leaks. I currently have no tune except stage 2 jet bs chip. My tuner says to get some logs before he will tune it. Egr is disconnected so I assume that don't help till I get it tuned out. I have ran a propane torch all around the tbi, carb adapter, and intake with no leaks that I'm aware of. Idle is a bit choppy but still idles. Pcv is from breather to large port on front of tbi. I will include pictures so you guys can see how I plumbed the tbi.

I guess my question is, is this normal with where I'm at until I get the tune. I honestly wish I could go ahead and get a tune close to what iv got. Iv read that there should be no vacuum problems with the ramjet cam. I really don't want to spray carb cleaner unless I have too, and I triple checked with the propane torch with no difference in idle. I think it's weird it ran great the first start up then it started getting choppy. Unless that's the computer saying, "WTF did you do to me???" Code 32 35 42 when I checked it. Also it pulls hard when I give it throttle which is good, just concerned with idle. Almost all new sensors except map which was replaced about 2 years ago. Injectors spraying nicely.

Any input appreciated also if I forgot a important details, just ask.

The cam manufacturer should be able to give you both idle timing advace and engine vacuum, to a reasonable degree based on intake valve closing, engine size, and static compression. For now, just turn the distributor at idle until you find best vacuum; then you'll know what it wants for idle timing and you'll have some more data for your tuner to work with. The cam will probably like more timing all the way through, so don't be afraid to leave it +4* or so even if best vacuum is more like 10-18.

Start about 6-8* BTDC on the timing, maybe as much as 10-12*. The Vortec heads need substantially more timing than the swirl port heads did and thus the ECM was programmed to provide.

Thanks both of you! I appreciate the input. From what I just looked up, looks like base timing should be set to 10BTDC so I'll play with it and report back.

Connect a scan tool, look at fuel trims. 18 PSI seems high. Verify EVERY sensor, including O2 once they warm-up. Does the spark-advance work? IAC counts reasonable?

Lack of EGR is likely causing some amount of grief, at least until it's removed in the tune.

Are #5 and #7 plug wires appropriately separated? When it was me, I kept the OEM plug wire looms and stock wire routing ESPECIALLY for #5 and #7.

Do you have enough valve spring, and enough clearance for the RamJet cam and 1.6 rocker arms?

How did you resolve the coolant bypass with the Vortec engine? Doesn't look like you've got Vortec bypass hoses on that water pump.

Did you degree that RamJet cam, or just stuff it in "dot-to-dot"? What is the cranking compression pressure?

Schurkey said:

Connect a scan tool, look at fuel trims. 18 PSI seems high. Verify EVERY sensor, including O2 once they warm-up. Does the spark-advance work? IAC counts reasonable?

Lack of EGR is likely causing some amount of grief, at least until it's removed in the tune.

Are #5 and #7 plug wires appropriately separated? When it was me, I kept the OEM plug wire looms and stock wire routing ESPECIALLY for #5 and #7.

Do you have enough valve spring, and enough clearance for the RamJet cam and 1.6 rocker arms?

How did you resolve the coolant bypass with the Vortec engine? Doesn't look like you've got Vortec bypass hoses on that water pump.

Did you degree that RamJet cam, or just stuff it in "dot-to-dot"? What is the cranking compression pressure?

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Great questions and food for thought. Haven't ran a scanner yet, just a paperclip.

Clearances all checked out when I installed the rockers.

Few holes drilled in the stat.

I did not degree the cam, that's where I'm at today.

Compression is 9.6:1

Spark advance works and plug wires are in aftermarket wireloom spacers but they are kinda messy going to the dizzy.

Hoosierlong90 said:

Great questions and food for thought. Haven't ran a scanner yet, just a paperclip.

Click to expand...

Paper clip is two steps ahead of useless.

Hoosierlong90 said:

I did not degree the cam, that's where I'm at today.

Compression is 9.6:1

Click to expand...

I don't care about compression ratio. I want to know the cranking compression PRESSURE as an educated guess as to camshaft position--advanced or retarded from where it should be.

Hoosierlong90 said:

plug wires are in aftermarket wireloom spacers but they are kinda messy going to the dizzy.

Click to expand...

Are #5 and #7 AT LEAST half-an-inch apart EVERYWHERE they run next to each other?

Food for thought too. I have done numerous L31 vortec head setups. The water pump bypass or lack of it has never been an issue on any of them provided they have continous flow through the heater core or a GM 4 port water bypass valve. Not to mention I drill a hole in my thermostats anyway. Drilled thermostat is more effective than an internal bypass and does not slow down the engines warmup noticeably, however it helps control temperature fluctuations by always allowing a small amount of coolant to flow to the radiator.

18 is where I suspect the fuel pressure will need to be with stock injectors to get enough WOT fuel. The 395 cammed Marine L31s with TBI used a 30 psi regulator and the later 454 46# high pressure injectors for 74# each of fuel on a 2" bore TBI. Tuning is fairly easy, get enough fuel for WOT and AE, then dial back the VE tables to deliver less fuel at part-throttle and idle.

My 9.6:1 395 cammed 350 made right at 200 PSI. Charged battery, stock PMGR vortec starter, all 8 plugs out of it and the throttle WFO.

I just crunched the fuel pressure needed. In reality they may even need a bit more pressure to get the flow needed. Straight math shows 19.25 psi to get 74.2 lb/hr each from the 61# injectors rated at 13 psi. In reality the injectors flow less linearly as the pressure increases which gives somewhat of a diminished return as pressure increases. Probably need to be around 22-24 psi to ensure the engine has enough fuel once you start actually getting it tuned.

On a side note I want to know where you found that sweet air cleaner spacer. I need a shorter than stock spacer for the proflow system on the G20 van and do not want to settle for a crappy plastic spacer.