I've read a few threads, one of which was responded to by Grumpy and he had noted that the particular combination could yield such a high idle MPA but there were ways to deal with it. I wanted some feedback / insight to what we're seeing right now. I'm in the beginning stages of tuning this setup. Note, I'm using a 749 and $59 code but the mechanics of the issue / experience would be the same either 8D or 59 bins.

Setup:

383 sbc
Cam specs:
LIFT: INT / .520 / EXH .540
Duration @.006 LIFT INT 288 EXH 315
DURATION @.050 INT 236 EXH 248
LSA 113
HEADS: DART IRON EAGLE 215CC / 72CC
TPIS Bigmouth Intake
Siamesed SLP Runners
58mm BBK TB
60# Injectors

At 900-1100 RPM idle we're seeing around 81-100 Kpa ? Is this around the range for my setup? On the guage I'm also only seeing around 6hg of vacuum. IAC was around 60-70 steps @ 90deg F coolant temp VE between 48-51, SA between 10-11 relative to TDC, TPS Volts @ 1.04

 

Most engines idle at 40-60 kpa at idle but that with stock cams or mild cams. A moderate cam will be about 65-70 kpa.....the more radical you go...the more kpa it is b/c of less vacuum I believe.

 

When starting out tuning an engine it is not unusual to have high MAP at idle. The SA & fueling is usually off which contributes to this. As the tune gets better the MAP comes down, the TB idle setting needs tweaking, etc.

At idle with that cam try about 22 - 24 degress of SA (BTDC). That will help with the idle.

With the TPS so high it may end up throwing a code.

RBob.

 

Thanks for the comments thus far. I'll take another look at my SA tables and fueling. This is a 0 miles fresh engine so I'm just being over cautios not to destroy anything. I know this will be a STEEP learning curve so I'm trying to be patient.

 

I agree...I have a 383 with almost 11:1 comp and I'm running 23* of timing at idle. With those 60 lb/hr injectors are big for that engine unless you are going to run nitrous or forced induction. My VE in my idle cell is about 56 for comparison. The TPS needs to come down a little to about .6 volts and you can up the tip in acceleration in the chip. Also, make sure idle engine speed setting is about 850 or 900 for that engine from 64* C and above. Also, need to reset the IAC as well for the higher idle.

 

You are correct about the 60#'ers. I'm going to run the P1SC with 3.25" pulley I used on my 350, but I don't want to introduce this until I have the engine tuned on NA, broken in and dynoed. Only then will I introduce the blower and go back to tuning. My compression btw is only 8.7:1 (-16cc pistons). I've adjusted what I thought was about a 900RPM idle and reset my IAC but with the hunting idle I have (825-1100) I dont' trust what I've done and am going to hunt for vacuum leaks and the like that would effect MAP at idle.

FWIW, I'm running a 3bar MAP with my $59 code using the following for SA vs RPM vs MAP
1200 27.07 26.02 16.52 13.36 11.25 11.25 10.90
1000 26.02 24.96 14.06 13.36 11.25 11.25 10.90
800 24.96 22.50 14.06 11.95 9.49 9.14 9.14
600 24.96 21.80 13.01 11.25 9.49 9.14 9.14

 

Went through and checked things. What I did find is I had a vacuum port coming straight off my intake for my BOV. Well if my blower isn't hooked up and the blower piping going to my TB isn't connected and just open to atmosphere I'd have to think the vacuum port was pulling air through my 3" piping and intercooler, resulting in a high kpa reading. Well see when I restart the engine maybe tomorrow.

 

Vacuum leaks on a MAP system do NOT actually raise idle MAP, as long as they are "common" leaks that all cylinders can see equally (i.e. as long as it's not leaning out a cylinder, it's OK).

With that cam, the fuel and spark will take a lot of work for idle, so don't bother trying to "set" the IAC and throttle screw just yet (although it may help to open the throttle screw a lot, and basically disable IAC for finding the VE sweet spot). Just crank up the timing to 25 or more at idle, and start SMOOTHLY removing fuel. It will probably need to have a little bit of a steep ramp of VE from your idle MAP to 100 kPa.

I would have guessed a cam that size would idle in the <73 kPa area or better. Spark stabilizer might help the cause, as long as you give it some room to work (i.e. don't completely max out the idle timing).

 

For timing you all are talking total in the cell right? (I mean for 25degrees I'm actually putting 19 in the cell because my base is set at 6).
Anyway, plugging that port did drop the map kpa readings. Still very high so while I'm replacing my AFPR I'll check for other vacuum leaks. I've uploaded a csv file and the corresponding .adl file if anyone's curious (11th session is the most current).

 

Most, if not all, systems include base timing in the displayed timing. That means if you want 25, type 25 in that cell. Verify it with a timing light if you're curious.

With a big cam, and with 20-30 degrees idle timing, it's time to start making fueling changes (as long as all the hardware is working and all cylinders are firing). The VE will be almost NOTHING like stock at low RPMs.

 

I did notice your TPS volts at idle is 1.04 it needs to be set to between .5-.64 after you adjust your IAC steps. I would set your steps lower to at least around 30 to start with it even as low as 0 depending on how it runs and stalling, etc.

 

Thanks again guys. I've replaced my afpr with a new holley afpr. This unit is slick, no more 8mm screw. It's a knurled lid/**** now that you turn. I've also checked for vacuum leaks and will be replacing ALL my runner and plenum gaskets. I've also burned a new chip with 25-30 degrees from 400-1200 RPM and up to 88KPA. BTW, I'm using a 749 ecm and $59 code. I like it so far. I'll post my next engine log to see how the kpas reacted to all the above.

 

SO after taking my runners and upper plenum off, checking gaskets, replacing the afpr I now idle between 900-1000 RPMS with 68-71 kpa on the map3 readings. MUCH better. My autometer fp guage is fahked though....I'll be getting a replacement from them soon. I checked my fp with a screw on guage and I'm around 48 PSI at idle. SO, idle seems to be good. Off to put her in 1st gear for the 1st time in 4 years and since everything been replaced. I'll post more tuning updates soon.

FYI, I'm running a 749 ecm and $59 bin.

 

I noticed this too- my idle VE is around 30 %. After reducing timing to around 23 deg total at idle and getting VE in line idle is great at 40 Kpa solid, 15 counts IAC. (mine's the 350HO). I thought something was wrong when I kept dropping VE in those areas, but what the hell- it likes it. When I began tuning this engine my idle SA was like 27 or something...horrible idle, 50/55 MAP. reducing timing smoothed it right out

 

While your NA, you might want to bring the psi down to 43.....should help you at idle.

 

I filled my timing with 29.5 to 28.5 in the 400-1200 RPM range and all the way to the 88KPA range. My MAP3 readings are now steady from 60-68. I'm going by the "tune to what the engine wants" theory. I'm still rich (in the 11.8-12.7 range) so I'm pulling some VE% down in the idle area. I'm just trying to nail idle down so I can take her out down the street for a mild run / log and go from there. I'm VERY limited when I can actually start the engine because with LT's and glasspacks only you kind of get the neighbors attention quickly

 

You might want to try lower the psi down to 43 psi first for your engine while its N/A....lower your injector constant down a little bit too if your injectors are rated at 43 psi.