Still having nuisance start up.

[StupidJeep]

Technically starts fine every time then gets a surge. However only if there is a bit of heat in the motor. Dead cold no problem, warm no problem. somewhere in the middle, surge but only for about 20 seconds after it fires up.

Any suggestions would be great!

feb4 luke warm surge.hpl
Jan 29 surge tune.hpt

[LilSick]

try this

[StupidJeep]

Tried it today, still does it all thought the amplitude of the surge is different.... Also at the end of the log I get I big stumble with a bit of throttle input. It doesn't do that all the time but often enough. typically only does it after start up in the first minute maybe. If it wait long enough it doesn't do it and doesn't do it when its warm....

surge fix attemp.hpl

[LilSick]

why is the pressure ratio so high at idle?

is your cam timing is off or is there a significant intake leak?


your timing being retarded past TDC until 40 degrees C prolly is not helping the idle issue either

[Spray-Cam Hell-Ram]

Your pressure ratio at idle looks just fine to me. However, I do agree with Lil Sick about your startup timing. But I think your issue might be due to the lack of a range of idle timing. Part way through your log, the range in which your timing can swing improves and the surging starts to fade it seems. Not totally sure if this is issue you are referring to. But if so, you can give this a go and see if anything improves. Im just going off of what I was seeing in the log anyway.

[StupidJeep]

why is the pressure ratio so high at idle?

is your cam timing is off or is there a significant intake leak?


your timing being retarded past TDC until 40 degrees C prolly is not helping the idle issue either

No leaks as far as I can tell, the cam was degreed when installed 2 years ago.... Ive always seemed to fight it between winter and summer with the substantially colder air vs our summer...

[StupidJeep]

Your pressure ratio at idle looks just fine to me. However, I do agree with Lil Sick about your startup timing. But I think your issue might be due to the lack of a range of idle timing. Part way through your log, the range in which your timing can swing improves and the surging starts to fade it seems. Not totally sure if this is issue you are referring to. But if so, you can give this a go and see if anything improves. Im just going off of what I was seeing in the log anyway.

Thanks appreciate it, Ill give this a shot after I dig out of the snow we got last night.

[LilSick]

the cam was degreed when installed 2 years ago....

where is the ex centerline?

has it always idled around .65 pr?

how much overlap?

[StupidJeep]

where is the ex centerline?

has it always idled around .65 pr?

how much overlap?

Once it's warm it typically idles around .6 in gear and .5 in neutral.
As far as the rest of the info I'd have to go digging for the sheet we had everything written down on. Which is buried in a box with the old cam and lifters a couple hours a away....

[StupidJeep]

Your pressure ratio at idle looks just fine to me. However, I do agree with Lil Sick about your startup timing. But I think your issue might be due to the lack of a range of idle timing. Part way through your log, the range in which your timing can swing improves and the surging starts to fade it seems. Not totally sure if this is issue you are referring to. But if so, you can give this a go and see if anything improves. Im just going off of what I was seeing in the log anyway.

Tried your changes....still does it...

[Spray-Cam Hell-Ram]

Yea. I misunderstood what your actual problem was initially. I think I may see a couple tune inputs that might cause this issue. But first question I have for you is what fuel injectors are those that you are running?

[PurpleRam]

where is the ex centerline?

has it always idled around .65 pr?

how much overlap?

Cam is Comp HRT stage 2 .596/.582 220/230 @ .050 113 LSA , Should be installed at 109/110 ICL for best results.

.50 to .70 P-ratio is the Norm for this cam at idle the Larger Bore/Stroke builds can idle around .45 depending on Compression ratio.

with 3k+ convertor we don't have this issue at all.

[LilSick]

a cam with only 220 deg at 050 on the intake lobe...

that still has a relatively wide lobe separation angle...

and is installed 4 deg adv...

(113-109=+4)

if everything is right (and sealed up) should make more vacuum than that.


the 5.7 has a pretty nice bore to stroke ratio

3.917/3.578=1.095

four stroke engines seem happiest at 1.1 (or better)

the 5.7 is very close

the 392 is slightly better at 1.099


actual overlap depends on how weak the rate is but that is not a lot of camshaft

[StupidJeep]

Yea. I misunderstood what your actual problem was initially. I think I may see a couple tune inputs that might cause this issue. But first question I have for you is what fuel injectors are those that you are running?

Still just stock injectors. I have more recent log I'll post it up when I get back the laptop.

[StupidJeep]

I'm just baffled at why it only does this surging at what seems like a certain engine coolant temp. As when it sits long enough it doesn't do it or if if it's a real short period of time it doesn't do it.... And general only for about the first 20 seconds of run time.

[StupidJeep]

Current tune and a log of the surge again.


surge feb 14.hpl
current tune Feb 16 surge.hpt

[PurpleRam]

a cam with only 220 deg at 050 on the intake lobe...

that still has a relatively wide lobe separation angle...

and is installed 4 deg adv...

(113-109=+4)

if everything is right (and sealed up) should make more vacuum than that.

Hate to break it to you but that is the Norm for this camshaft in a 5.7

[PurpleRam]

This cam is -1* overlap IN valve and Ex valve are closed during Overlap 1* , at 109 ICL the Intake opens while the piston is in TDC dwell ,Exhaust valve is already closed it closed 1* before INVO , NO scavenging to add vacuum. the INV opens while there is still minute residual pressure in the Chamber, at ICL of 117 , this cam will make OEM type vacuum.

[LilSick]

IN valve and Ex valve are closed during Overlap

maybe in your engine, but not in any engine i have ever worked on...

[LilSick]

Hate to break it to you but that is the Norm for this camshaft in a 5.7

at ICL of 117 , this cam will make OEM type vacuum.

which is it

it cannot be both : )