New big cam, lots more turbo lag??

[Clifton]

Adding a thicker head gasket will advance the valve timing some and then you advanced it a little more on the gear. Typically advancing adds bottom end, while retarding gives top end. The cam I just got had some advance in it already. If yours did too you may just be to far advanced. I would get a degree wheel and check it.

[JMortensen]

The cam specs sound like NA cam stuff to me. Is it possible this is a case of too much overlap? That would be laggy I imagine...

[big-phil]

sounds like I might need a degree wheel? the .008 exh. setting sounds like that might be what I want? can anyone confirm? I'm going out there now to work on it. I'm going for the happy middle and put the cam gear in #2, see how that feels. Check the timing, adjust the valves, go for a drive.

 

thanks again guys.

[Doc Hawk]

For those who don't know, this is Chris and his car.

 

Saw the video... nice ride. Chris, do you have all that car running with just a lap belt? Or do you have a 3-point or a harness installed, and you just aren't wearing them? Wear yer damn belts! Car control + no death & dismemberment = no brainer.

 

'cause we love you,

David

[Doug71zt]

If you are running a stock L28ET with a 2MM HG, your compression ratio will be around 7:1. That may be why it is such a dog off-boost. Adding a performance cam may make that situation worse.

[TONY C]

I ran my new l28et p90 stock cam tho. 2mm hg and dished pistons for 1500 miles with a header and no turbo to break it in without breaking it.

ran it at the strip a couple times like that too. still ran faster and quicker than my stocker.

put the t3/t4, 1085cfm IC, and picked up 16mph in the 1/8 at 14lbs. full boost at 2200-2500rpm.

I really think cam timing is Phils prob. who knows. a regring could be 10-12deg off . an adjustable cam gear may be in order

[big-phil]

Ok I just got done checking timing, valve gap, put the cam gear in #2. The head gasket/compression ratio thing sounds on key also. The turbo hits at 4k rpm which right now is to high for me. I did a data log and ran it to about 6500 rpm, 18.64 lbs of boost, 74% duty cycle, 12.2 afr which is a bit lean but the meth is there, I will richen that spot up. and 24deg timing.

 

It pulls hard, and strong. But there is still too much lag. The stock cam hit at the most 3000 rpm. So I'm going to put the stock cam back in and port evrything at a later time with a rebuild to my other P90 head. Then try the cam again with it all ported. I would just leave this cam in untill then but I daily drive the car and its killing me to have so much lag.

 

p.s. I think thats the most boost I've run without blowing the motor:icon12:

[Bernardd]

Phil, have you changed your timing at all? You now have less cyl pressure than before and it lasts longer/higher up in the rpm range. Your engine will tolerate more advance during the spoolup and it can easily make a huge difference in response. I'm not going to say how much timing you can run, but I don't pull any timing until I reach 18psi when running methanol with a large cam. I also run a lot more advance off boost.

[big-phil]

Phil, have you changed your timing at all? You now have less cyl pressure than before and it lasts longer/higher up in the rpm range. Your engine will tolerate more advance during the spoolup and it can easily make a huge difference in response. I'm not going to say how much timing you can run, but I don't pull any timing until I reach 18psi when running methanol with a large cam. I also run a lot more advance off boost.

I can't think at the moment but I am running more timing 24 at 18 lbs boost, thats comming down from about 40? when boost starts. We have played with that a bit, and now that my CR is SO low I think I will try more timing.

 

How much are you running at 15-16-17-18 lbs??

 

I tryed to put the stock cam in without pulling the head but my Isky springs and retainers cause the stock lash pads to fall in too much making the rocker hit the retainer. So after all that I'm back to having the big cam in again. I really really really want this cam to work. I love the power when it hits. Maybe a head shave?

[Clifton]

I tryed to put the stock cam in without pulling the head but my Isky springs and retainers cause the stock lash pads to fall in too much making the rocker hit the retainer. So after all that I'm back to having the big cam in again. I really really really want this cam to work. I love the power when it hits. Maybe a head shave?

 

 

I have run a stock cam/lash pads with the deep aftermarket retainers. I had to grind a tiny amount (maybe .020-.040" tops) off the bottom of the rocker arm. I am still running the same arms and they have seen 7500 more than most cars and never had a problem. I wouldn't shave the head, just turn the boost up a few psi more and run a little more timing before peak boost.

[cygnusx1]

Phil, sometimes a hotter cam just doesn't work on the street. It's a common mistake to overcam for the street. Not saying that it's not something else in your case, but it's a possibility. You might be getting more horsepower at the top but less torque and power down low which makes it feel slower on the street.

 

My friend has a Cobb Stage Three Sti that he assembled himself. One day he had it tuned on a dyno and got more HP. However, he liked it better before it was tuned. He gained about 30HP up top after the tune but lost a bunch of torque and mid range.

 

Very nice Z Chris, and nice video work Phil!

[Tony D]

I'll chime in and say my turbo runs 15 btdc idle timing (Megasquirt) with high vacuum bins at 40, and full boost bins around 17-19. I don't see any reason to run 24 at idle. May make for snappy reponse off idle, but it's pretty snappy at 15 for me. I think the reason the 'stock' ECCS runs 24 BTDC is due to their system for trigger return retard.

I have asked a couple of times if anyone has ever charted the advance curve on the stock ECCS system. My old pneumatically controlled Corvair was set at 24 degrees, and that was that. When it went on boost it retarded timing through the cannister, and was basically a centrifugal advance distributor with pressure retard. N/A Vairs were set around 7-10 degrees, but had hellacious centrifugal advance, with another 7-10 added under high vacuum condtions---up to 47 degrees total in some cases. And guys wondered why they pinged on hot days in Palm Springs!!!

 

I think the ECCS has a really limited degree of timing adjustment, and as a result you have to fudge the idle timing just like the old 63-66 Vairs. When you tweak the base timing on the ECCS it just moves the whole map up or down. Really primitive timing control, considering.

 

Anybody know the 280ZXT ECCS Timing Curve?

[Bernardd]

 

How much are you running at 15-16-17-18 lbs??

 

I run about 10deg's more than you at 18psi.

[ktm]

One last statement regarding timing. Read the following link, especially the posts by Ron:

 

Give the engine what it likes

[datman]

I run about 16 deg at idle, I have a 2mm gasket also but my l28 was NA making CR of 8.35:1. Using the satndard NA cam works very well with a Holset. At 10psi of boost it will leave pretty much any car standing, at 10psi I think I have around 20 deg timing. No lag that I can notice.

[dapiper]

Too much cam. I tried schneiders 270° and got 3-4" idle vac and nothing below 3500. Overlap was like 55°. then tried 10° less cam and got 9" idle vac and nothing below 3K RPM. Felt like days with my old '64 vet with mech linked secondaries; a deceiving steep accell with a big hole down low. This is not the fast way. You want a broad torque curve.

 

I went on the dyno with both cams and the power was down 13-17 with much narrower torque curve.

 

My old Racer Brown cam has 20° overlap and power peaks at 6200 RPM has 14" vac at 750 RPM

 

I think my vac is so low because I have unshrouded the valves too much for street use; took out 3.5cc. CR is 8:1

[big-phil]

In the process I got the cam gear off by 2 teeth. I thought my coil was to blame for almost no boost but it was my fault.

 

All back together now with stock cam. I think it seems to be a combination off super low compression ratio, to much cam, to big of a turbo?? With the stock cam back in it boosts just before 3k rpm.

 

I've pulled the head about 4 times now in the past week so I'm in no hurry to try another combination of things with the big cam. CLIFTON I did try more timing just before boost but still boost hit about 4k and until that point it was a real dog. I don't think I could spin the tires with out getting into the turbo!! It was really that bad. On the hughway at 80mph I was at 2" of vac with the turbo whinning the whole time. With the stock cam I'm above 14" vac at 80 mph and don't need to even use the turbo unless I want to.

 

Thanks for all your help guys, when my back stops hurting and I'm ready to pull the head again I'm sure I'll be back with more questions.

[Thumper]

Damn sorry I didn't catch this thread earlier. Same thing happened to me. The cam was off a tooth. Let us know how the new cam goes once you get it installed again.

[Chris240zTurbo]

Told ya so!!!

 

:biggrin::biggrin::biggrin::biggrin::biggrin:

[jeffp]

Having the cam one tooth off changes the timing about 9 degrees if what I was told was correct. The thing is that one tooth is WAY to much either way and the engine will iether not run at high rpm's or it will not run at lower rpm's if the cam is off one tooth.

 

Your cam, I don't know all of the specifications, and if the ones you listed was lobe lift or valve lift. The duration is not to much, provided you are flowing well through the head and have no back pressure on the exhaust.

 

The vacuum should have told you all you needed to know. With a cam like that you should have 11-15 inches at idle. Lower is either a leak, or incorrect cam timing.

 

Cam timing is critical on this cam configuration. One degree of timing will make a significant change in the low end performance. So what is the opening and closing points of the intake and exhaust lobes? Also what is the lift of the lobe (the actual lift of the lobe from the cam card)

 

Valve lash, again this is critical, a change of .001 will change the opening and closing points of the valve by about 5 degrees of crank rotation. So you can see that a few thousands will have significant affects of how the engine runs.

 

I recommend a cam adjuster sprocket. You can get a nice unit and then go at it again. There is the write up on degreeing your cam, all of the information is there to explain what each adjustment will do to the cam card.