I've put a ZC intake manifold on my D16A6, and it definitely pulls harder at 5000+ rpm!

BUT

Once I got out driving I noticed that at higher RPMs the brake pedal feels almost too firm and has little travel, but at idle its more soft like it used to be.

Is this something normal that I have been missing out on in the past, or is it something that needs to be looked at? The brake booster hose is plugged right in like it used to be... same valve I had on there before.

My guess is that the booster is not getting as much air at high load as it was before?

 

Do you have a vacuum gauge? If yes hook it up and check the vacuum at idle and when you are driving and having the hard brake trouble. There should be no difference in brake pressure with any different manifold as long as there are no leaks.

 

Maybe a leak at high rpms that would cause this.

 

unlikely there is a leak just at high rpm's, there is just less vacuum at part throttle than closed throttle at idle.

You can try using brake fluid and spraying around the gaskets of the mani with the motor running and see if it changes rpm to find a leak.

 

check to make sure the check valve in the booster is not backwards this will give a hard brake feel

 

think you mean carb cleaner! brake fluid would just make a mess

 

Its definitely not backwards. I'll try the carb spray trick. Thanks.

 

I didn't find any leaks. I drove it around some more to do more testing and it looks like the problem has gone away on its own. Thanks again.

 

Brake Clean