sr20det 270/270 pro cams vacuum brake booster?

[Jake1992]

Hey guys,

as im finishing up my build im wondering if anyone has problems braking
as the car is making less vacuum with cams ? I replaced my stock brake booster with a r33 skyline one , its bigger.

thanks,
Jake

[jr_ss]

It could happen, but I wouldn't expect you to see anything lower than 10-12in/hg. That's still sufficient for braking, but you won't have much on tap. If you have less or feel 10-12 isnt sufficient, you'll need to add a vacuum pump for the booster.

[Jake1992]

thank you !

[EsChassisLove]

My JWT S3s are pulling -5 to -7 vacuum at idle and to be honest my braking went to complete shit. Z32s and a z32 BMC and I can barely get them to lock up.

We still haven't figured out why it's pulling such low vacuum.

[Jake1992]

im wondering what my setup would be to @ idle with 12.5 270/270 cams... I swapped out my brake booster for one that is twice as big to maybe prevent this from happening but now looking maybe for a vacuum pump... anyone else running these cams on their sr20's ?

[EsChassisLove]

You should be fine. I'm told this isn't a normal occurrence. The tuner said he's tuned 280s with more vacuum haha

[Jake1992]

Cool thanks!
do you have an aftermarket intake ? (with your problem)?

[EsChassisLove]

Yes an Isis (Freddy) manifold.

[jr_ss]

My JWT S3s are pulling -5 to -7 vacuum at idle and to be honest my braking went to complete shit. Z32s and a z32 BMC and I can barely get them to lock up.

We still haven't figured out why it's pulling such low vacuum.

What chassis are you on? What booster are you running? Is your pedal rock hard?

[EsChassisLove]

Running an ABS booster. Switching to the non abs next week so my lines won't be so close to my turbo.

Basically rock hard. I feel like I'm slamming into a brick most of the time. A booster needs around 15-20 to work properly. Unless I downshift and let off the gas, causing higher vacuum, then they work good.

I can get them to stop like they would with a functioning booster, it just takes damn close to every ounce of strength I have and then I'm riding that line between locking them up and not. 10/10 times I lock them lol.

[OnTheChip]

Is the check valve still in the booster hose?

[jr_ss]

Running an ABS booster. Switching to the non abs next week so my lines won't be so close to my turbo.

Basically rock hard. I feel like I'm slamming into a brick most of the time. A booster needs around 15-20 to work properly. Unless I downshift and let off the gas, causing higher vacuum, then they work good.

I can get them to stop like they would with a functioning booster, it just takes damn close to every ounce of strength I have and then I'm riding that line between locking them up and not. 10/10 times I lock them lol.

Based on reading I have done over on NRR, you're most likely running the 17/16 MC? Everyone that uses that size says there is no brake feeling whatsoever. The pedal is extremely stiff and they have a hard time modulating. Most guys swap them out for the non-abs automatic 15/16 MC from the S14 or opt for the smaller 1" MC from the Z32. They also say that the brakes are over boosted from the factory. I'd try the smaller booster first, but you may need to swap out to the smaller MC as well.

With that said, you should be pulling higher in/hg as it is. Those cams aren't super aggressive, so I would expect higher numbers.

[EsChassisLove]

I'm running the 1" BMC. During this next tune we aren't stopping until we figure out why vacuum is so low. I would rather see if vacuum fixes it, than go straight for a new BMC.

[EsChassisLove]

I've had this set up for a few years. Back when I was on a T25 and pulling the normal -20 vac the brakes were amazing. It started being funky when the vac went down.

[jr_ss]

I agree completely, I'd work that issue out first. I was just saying Z32 BMC'S seem to be overly powerful and aren't generally needed on the S-chassis.

[EsChassisLove]

Talked to my guy and he said timing is at 0. Says 0 will give plenty of vacuum but the cam overlap is why I'm not getting much.

S3 is only 260 overlap. Both builder and tuner did say that these cams do sound really lopy for 260s.

Better call JWT in the AM. I WANT MY BRAKES BACK.

OP sorry for thread jacking. <3

[AJZax]

I have tomei 12.5mm 270 cams (lash) in my SR and I'm pulling around 13-15 vacuum. on idle
Shouldn't affect braking, as you generally aren't idling while braking, you should be in gear on decel so it'll pull more vacuum.
That's also with freddy manifold, however I did port match and blend the intake manifold so that there's smooth efficient flow, no rough castings. Would it even make that big of a difference at idle anyway?

Have you checked for any leaks?
Do you have adj. cam gears? Maybe one is twisted off zero and so your overlap is changed and your vacuum weaker due to this?