Hello all,
Car is a 94 with ~64k and basically all stock, with the exception of an aluminum ast and a RB dual tip. I've been getting about 11-12 psi max as a result of the RB exhaust. Today I installed an HKS downpipe for long term reliability. So far, the boost appears to be similar (11psi - 12psi max) with pattern of 11/12 - 9- 10. I do not have a modified intake, and use the stock mazda air filter.
Am i ok with this level of boost? I really don't really want to mod the car anymore, as i really enjoy it being stock and almost all "original".
any advice would be greatly appreciated.
regards
eric

 

It should be fine if it's holding at 11 psi, the stock ecu allows for minor spiking and elevated boost levels. I would be worried about colder weather though, and if you are regularly hitting 12 psi, you should consider some form of boost control. I prefer a simple EBC like the Profec Type-S.

 

I agree. After adding a downpipe, I got a transition spike in cold weather that caused overboost cut around 5.5 to 6K rpm - very nasty when that happens.

I was getting a pattern of 13-10-12, not counting the spike after transition. I fixed the spike by changing the restrictor pill in the wastegate actuator line to a larger diameter. It took a couple of tries but I got the spike under control and have a boost pattern of 13-8-10 now.

But I just installed a Racing Beat catback today, and if the extra heat under the floor doesn't blow up the gas tank first, I'll probably have to change the pill again to compensate for the reduced backpressure. Does the floor of your hatch get hotter after a while since you put in the catback?

 

thanks for the input...
i'll definitely look into the EBC.

would another option could be going back to the stock exhaust?
however, that would seem like a step backward after the beauty of the RB.

anything else that could be causing the higher boost? is this normal with the RB to see elevations of 1-2 psi?

thanks!!!

 

To give you a frame of reference:

A few weeks ago, I was all stock. Cat, stock muffler, pre-cat; it was all there. I hit 11psi primary, 8psi transition dip, 11psi secondary, then it tapered off to 7psi at redline.

I had a RB dual and DP installed recently [by someone else; the garage is a mess right now!]. I got consistent 13psi primary, 10psi very quick transition dip, 13psi spike, then holds a bit to 12psi until it tapers off to 10psi at redline.

That's too rich for my blood, so, the car's sitting in the back while I'm researching EBC's at the moment.


My stock exhaust finally turned to swiss cheese, so I had to change it out. My pre-cat was rattling a bit too. Frankly I liked the quietness of the stock setup. The RB Duals are louder, but it sounds great and is quite bearable dB-wise. So I wouldn't go back. Power-wise it isn't even a contest.

I didn't notice any increase in hatch-temperature. I was keeping my latop there, so I observed it at least twice a day after a 7-14mi drive. If anything, the car's cooler in the cockpit, but that's probably due to the DP.

Retserof, did you somehow remove any heat-shielding near the cat during the install?

 

I wish I had some extra parts laying around the garage after the install - it would explain things. But I don't. The only thing I can think of that might cause excess heat is that my downpipe is about an inch longer than the stock. This pushed everything to the rear and swung the catback on the rubber hangers up a little closer to the bottom of the car, but no more than 1/2 and inch.

I figured my only problem with adding the RB catback would be an increase in boost and another transition spike to contend with. Switching restrictor pills on a stock air intake is about a 1 hour job, including beers.

The cockpit became much cooler once I got rid of the precat. I had to run the AC all the time to cool off the cabin.

 

morning bump for additional ideas/input
thanks
in advance

 

looks like the profec type-s it is.....now my goal is to find a good deal on one and hope it is a piece of cake to install.

 

I have an Apexi intake, RB DP, RB Highflow cat, and HKS Carbon Ti catback, and my boost pattern is a solid 10-8-10, Ive never experienced any creep at all.. is this abnormal?

 

I was hitting over 12 psi with a downpipe and modded airbox. Enough to hit fuel-cut fairly often. After I added the RB catback I noticed a MUCH quicker throttle response and accompanying boost. I actually ended up blowing my engine within a month of adding the RB, after making a hell-run on a nice cold January night.

Needless to say, I am changing the restrictor pill when I rebuild the engine.

 

The answer to all of you are in this thread...there are a ton of ways you can do it.

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/cheap-way-turn-boost-down-454980/

 

thanks
yes, the home depot controller seems to get mixed reviews and usually just seems like it is being used for a short term fix until an electronic boost controller is purchased. Of course there are exceptions and people that have been using it for years.
I'm not ready to drill my pills yet...
so this profec type-s is looking better and better. Am I missing any glaring negatives?

 

Just so you know, you don't have to drill out the factory pill. Just get a few Holley carb jets from a good auto parts or racing supply house. They are not expensive and they come in a variety of jet sizes. They fit inside the wastegate actuator hose in place of the factory pill

 

Yeah, Pettit includes a Holley jet (part # 122-67) when you purchase one of their downpipes.

 

I tried the .067 jet that Pettit sent with my downpipe, but its opening wasn't large enought to correct the transition spike that led to fuel cut in cold weather, so I bought some larger jets and now have a .071 in place, IIRC.

 

hmm...that's interesting. so this is a simple pill swap? and pettit expects this when they sell a dp therefore includes them..cool!

now i must say....my underhood temps dont seem any cooler with the dp installed? it isn't wrapped, but i still expected some heat reduction, is this normal?

 

When I put on the downpipe, I didn't notice a reduction in underhood temps, but I did notice that it cooled more quickly without the mass of the precat. The cabin did stay cooler, however, without that precat to radiate heat through the firewall. The engine itself is a great thermal storage unit, so any thing you can do to improve it is good.

I wrapped my downpipe, so that may help move heat out better too. Also, my precat may have been clogging up, so it could have been getting hotter than normal.

 

Wow, my pre-cat must have been worse-off than I thought. Before the DP, the rush of air from opening the hood would practically singe my eyebrows off. Now, it's comparable to that of most other cars. My DP isn't wrapped or shielded.

 

I have the same situation right now, when I get my car back on the road I have some carb jets ready to go. My mods are downpipe, RB dual tip, and Efini Y-pipe, and I hit 12psi. The RB dual is the one that caused the jump.

In any case, fill with the 94 octane only until it's fixed. The extra margin is worth it.

Dave

 

hi dave...
tell me more about the 94 octane, is this to help the system accomodate for the higher boost?

i ordered the profec type s yesterday for 299 shipped from an online retailer....so i should get it today and can start the install tonight.

it sound slike the RB dual tip is the cause in most cases of "stock" rx7s experienceing higher than norm boost. some people are lucky, but that seems to be the minority.

 

Yeah, the higher octane is a little more insurance than 92 while the boost is running a little high. But if you install it tonight then it's no big deal.

I also prefer to fill with Sunoco 94 because they tank in only 2 grades - 87 and 94 - and the story I heard is they blend it at the pump to make the 89 and 93. So if this is true, I believe there is much less chance of them putting something other than 94 in the 94 - which I worry about when getting 'premium' from other pumps.

Dave

 

just a quick update...
the profec type-s arrived and is now installed!

fairly easy job and it is working like a dream. i'm now at 10psi and have no worries!

i mounted the controller in the glovebox....as i have the set it and forget it mindset.

thanks again for the advice
eric

 

How's the transition dip/spike, eric?

 

today i was able to open it up a bit...at least in 3rd.
the transition drop is a bit low, 10-6-10 in 3rd gear.
my transition was very tight prior to the install (11.5/9/10)

any tips or suggestions?
thanks!
eric

 

where can i get a larger diameter restrictor pill that some of you speak of?