GLoBaLReBeL420

Anyone switched over to the new 258's that Tomei is putting out? I recently jumped over to them and am noticing some pretty crazy vacuum drop at idle. With the stock cam-shafts I was pulling -20 to -21(at sea level in Cali) no problem. I just switched over to the 258's and I'm barely pulling -14 now at idle. I had to bump my idle up to 950 rpms just to keep her stable.

I haven't had a chance to dyno her yet, but I feel like she pulls WAY harder up top 5K+ but I lost a ton of torque down low (3500-5K). Just seeing if anyone else noticed the same issue?

SR20DET S13 Blacktop
Tomei 740cc injectors
GT2871R (.64AR)
SS headers
Z32 MAF
ACV-R Boost Controller @ 1.2 Bar
Walbro 255 FP
Fuel at 43 psi no vac

Any input is greatly appreciated..

Already tuned with NisTUNE

geiesrp

that doesen't sound what tomei promised about 'stable idle' bro


well, I bought them too, they ll arive in the next few days. ill send you an update as soon as they are under the hood. As for me, i'll put them in with new lifters, rockers, oil spray bars, some Kind of mini revision. I know two other guys (one from Germany, the other from Austria) bought them too.

GLoBaLReBeL420

Did you ever get those cams in? Trying to see if anyone else is noticing the vacuum drop at idle? Under deceleration I pull a good -19 to -22 ng and that's what I was pulling at idle (at sea level) before I had switched out the cams.

Also, is anyone else switching their valves and springs with these babies? I only run my 93 SR BlackTop to about 7200 rpms, but I can tell these cams would really shine with a much higher rev range. My turbo woulnd't be so happy, but the car would certainly enjoy it haha.

pacotaco345

I ran 256 poncams in my car for years, only recently when the motor ingested a throttle screw (which held an intake valve open, threw a rocker and trashed the intake cam) did I spring for new cams and valvesprings (JWT C2 cams and their recommended springs).

From my experience stock valvesprings with 256 poncams are good for at least 7600 rpm, thats what my rev limiter was at. Those cams were designed to work with stock valve springs so throwing stiffer springs and titanium retainers under them often does more harm than good. I've seen people with stock cams and BC springs/retainers throw rocker arms at like 7200 rpm while I've never had an issue.

__________________

240boosted

yes my vacuum did drop at idle also not too much but i did drop

Kingtal0n

The small tomei cam (256) with low lift is ideal for daily drivers

The vacuum at idle should be in the 18" range

If you are only getting 14" they may need to be degree'd
Or they are off a tooth

I believe the 264's with a healthy lope pull around 12-14"

If you upgrade springs, use the same manufacturer (tomei cam = tomei springs) as a general rule for sr20 engines.

GLoBaLReBeL420

Thank you for your help!!

I've checked the timing MULTIPLE times and rechecked the teeth count on the cam gears and everything looks good to me.

Are there any quick tests or ANY tests i can do to validate my timing is correct other than my timing gun and counting the number of links on the chain between the two points on the cam-shafts?

I have it tuned to run at around 17 PSI and it holds great and doesn't break up or lose spark. Also running at around 11.8 - 12.4 AFR under WOT runs.

240boosted

well now i switched to haltech with greddy intake manifold built up engine a bit more but I want to say king is right 18 ish was mine next week i tell you what mine is

Xaser

Ups, sorry i wrote in spanish, i think cali as colombian city, no california.

Yes is normal, becasue the cam is less efficient at low rpm, but better efficient at high rpm.
I have the 270's and i have to tune the After enrichment to let stable, a 1100/1050 rpm, with big turbo, ported, big throttle etc etc. At 850 can idle, but is rough and with Air conditioned ON, try to stop.

PS: i delete the iacv because he try to stabilize and make "less stable " the idle.

__________________
https://www.instagram.com/200sx_type_x/

LoSt180

Stock headgasket blew, these are on my list of "while you're in there" mods.

S15 SR20DET btw

GLoBaLReBeL420

Has no-obne else switched to these yet? I called Tomei and they told me that I shouldn't have that large of a drop in vacuum and my midrange should stay what it was, but it sure doesn't feel that way!

LoSt180

I got mine installed, and honestly the vacuum at idle doesn't appear to have changed at all. I just have the stock S14 DIN gauge though, so the exact numbers are hard to translate (it's range is -/+ 700 mmHg). At idle, the vacuum is down to almost -700, lets call it -675mmHg. Which is unchanged from my stock cams. This is in an S14/15 SR if that makes a difference.

As far as validating mechanical timing, the best option is using the colored links on the chain during install. That way you don't really have to count links, line up the marked links with the timing dots on the cams and that's it. You can see the yellow chain on the crank sprocket by removing the lower oil pan and looking up with a flashlight. That's how I set mine recently since I was replacing the head gasket with the engine still in the car.

I think setting TDC and counting links on the chain is the only "quick" option you have.

I'm having other issues now, so haven't had a good chance a driving impressions. Only thing I can suggest otherwise for your issue is to double check all your vacuum lines, including brake booster, and verify you didn't damage or get anything caught in the manifold gaskets that might cause a vacuum leak.

GLoBaLReBeL420

I checked my timing by doing the exact thing you mentioned (except I did it from above since I'm keeping my head on the engine and just looking from the top of the cam gears). I still beleive there's something else wrong. The car moves, and moves FAST but that vacuum issue is a real problem over the long run.

I'll just tear the valve cover off and see what I can check out again. UUGGHH!!

Note: I just did the conversions and -675 mmhg is like -26 in. Hg so that a crazy strong vacuum if that's what you're getting. A stock well built SR20DET should see almost exactly -20 in. Hg at idle.

geiesrp

I never saw such a strong vaccum on any SR. Is your stock ventilation hose (the hose beween valve cover MAF) still installed?


-700 = -0.93 bar










I live in Switzerland, around 500m above sea level. With the stock cams and the tomei 256 aswell, I always had around -0.6 vacuum @ 850rpm.


With the 258 poncam it is way down to -5.2 at idle. However idle is fine. Timing is set to -15, no leaks.


@2000 rpm I'd -7.0bar with 256poncam. with 258poncam it is now -6.8bar @2000rpm.


I do not believe in a timing issue or leak. As for now I think going back to the 256poncam, since with the 258 change I have also changed the turbo from hks gtss to GTX2860gen II, which means i'll be unable to judge the cause of the loss in low or midrange.

LoSt180

All stock vacuum hoses are still in place, even that little charcoal canister next to the radiator.

GLoBaLReBeL420

I'm having as hell of a time converting values to get a feel for what everyone else is seeing vacuum wise for their cars.

-5.2 BAR is -153 Inches Mercury (which is CRAZY VACUUM compared to my -20 inches mercury)

I'm happy that I'm not the only one seeing the vacuum drop after the cam-shaft install. I'm just amazed that Tomei didn't say anything about where the car would idle at and the change in vacuum!!

geiesrp

Sorry, of coz i meant -0.52 bar, thats how much mercury?

as for units, me too. As far as I know you have normally -19 - -21 what? PSI? I found a pressure converter somewhere and the only value that fits was foot of something. Please let us tell the correct units, there are several people around the globe in this thread involved.


Just for clarification:
I'd -0.62 bar with stock cams AND WITH Tomei 256 cams.


Now with the 258 cams I have barely -0.54bar at idle. I might have an explanation for that behaviour. Maybe Tomei improved the cams for VVT, i.e when the engine runs VVT in 'sharp' mode. That would explain the massive power drop below 5000.


And if this is the case, I'll kick out the 258 right now. I actually bought them to improve lower and midrange, i don't drive the car in every gear to redline.

GLoBaLReBeL420

So, -0.52 bar literally falls right where I am at with mine . .

-0.52 BAR = -15.35 In. Hg

My car reads at around -14 In. Hg after the 258 swap

Your stock cam and 256's read at -0.62 BAR (-18.3 In. Hg)

-18 to -21 In Hg is the normal for SR20DETs with stock cam shafts at sea level.

So, your drop was about 3 In. Hg and mine was more like 6 In. Hg, so a little worse.

Still think something is wrong with my setup even though the car runs great and everything. Its just driving me mad! :-(

Kingtal0n

25x is very small and should be 16-18" Hg idle 800~rpm

To verify what cam is, and how it is installed,
buy a CAMSHAFT DEGREE WHEEL KIT

and degree the cams in

Kingtal0n

For S14 motors: Are you sure VVT is turning 'on' do you hear the solenoid click when you touch the throttle (move the throttle blade by hand from the engine bay). Also you can try disconnecting the VVT solenoid and see if the engine behaves better.

I Once had a set of 272HKS cams and the engine would run much better with VVT turned OFF all the time. I put a switch on it though because if you leave it off indefinitely it eventually drains of oil and sounds like a rod knock. So it was necessary to run the vvt once in a while.

GLoBaLReBeL420

My engine is a 1993 SR20DET Blacktop, no VVT.

GLoBaLReBeL420

I really want to get the car dynoed but I just haven't had a chance to take it to a dyno yet. I no longer have the stock cam-shafts so no matter what I'm sticking with the 258's, I would just like my car to be working as good as it can be.

geiesrp

guess what i’m doing right now. cover is already off, will double triple check timing, if right, 256 comes back in.

btw: car won’t start if a tooth is off

geiesrp

news.

double checked timing yesterday, pressured up the whole system, no leaks at all. only issue i found the vacuum is highly timing dependent, seems normal for these cams.

endgame: i have my old tomei 256 in and the vacuum ist now as before. reason for that i never felt happy with them, i wish tomei would provide a diagram to see what and where in rpm band are improvements done


@g revel: any news from your side? did u check the whole system for leaks?

GLoBaLReBeL420

I will be tearing off the cover and checking timing and everything to be sure but if the SR won't even start with a tooth off, then I know my timing is dead on. Did the timing gun 3 times after triple checking the number of links between the two markers on the intake and exhaust gears.

I really feel like these cams should have come with a warning about the loss of mid-range tq and the weird idle. I only got the 258's because they were drop in, with maintained mid-range and increased upper range. These don't seem to be as "all around good" as Tomei sold them as....

Def

You will lose some really low end torque, like 1-2.5k RPM with mild cams like that, but beyond that it should start to pull ahead of stock cams. Losing torque in the 3-5k RPM range sounds like you got a cam a tooth off.

Easiest way to do a cam swap is zip tie the chain to the gears, take the gears off, then bolt them to the new cams (assuming your timing was good from the start).

__________________
S13 Hatch - Goes around tracks quickly
DEFSPORT

GLoBaLReBeL420

Cam tooth is not off for sure. (Just re-checked all the teeth and pins)

I use the zip-tie method when I did the shaft swap out, and I counted in-between, and it hits 15Degrees on the dot with my timing gun. So, I know my timing is dead on I just don't know if there's something else causing me this loss of tq/power around 3-5K. Its driving me insane!!

Kingtal0n

you need to degree the cam. It might just be a different cam than it says on the box. or whatever

GLoBaLReBeL420

I thought that as well, but when I put them in I verified the model of the cam shafts on each cam itself before installing. (Always gotta be sure)

I'm looking into degreeing the cam but that's like another $150 on top just to test them out (might not even fix anything).

I'll probably end up doing it, I'm just hoping to find something else as the problem before going that far to find out.

Anyone in South Bend,IN want to help me out :-)

Kingtal0n

Make your own degree wheel.. print out a circle on the computer and glue it down to some wooden or plastic circle piece you cut to fit then bolt it to the engine. then use a coat hanger as a pointer. All you need now is dial indicator like $10~ from harbor freight?