stupid question...can i boost?
Racecar - Formula 2000
Joined: Sep 2002
Posts: 4,034
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From: Bath, OH
The electronic ones are a bit more complicated to install, but have more control options, and are easier to adjust.
Here is a link to some useful info on MBC's: https://www.rx7club.com/showpost.php...6&postcount=10
Last edited by DaveW; Feb 21, 2008 at 11:03 AM.
Reading between the lines here, it sounds like you got the car AFTER this rebuild was done. It IS a bit odd the RP is not being more forthcoming with information, but then again in this day and age of lawsuits, I can imagine them going into a non-committal mode when someone starts asking questions about a rebuild they did months or years ago.
10" of mercury at idle is pretty low, I have a pretty aggressive street port and I still pull 16 - 18 inches at idle.
I am also struck a bit by your assertion that your exhaust "does not seem to be extremely free flowing, pretty quiet". An exhaust does not HAVE to be irritatingly loud to be decent flowing. When you look at your overall mods, you basically have an intake and exhaust as performance enhancements as well as this undefined port job. A $8K engine SHOULD have some goodies in it, but not necessarily. One could assume that it is a $4K engine and the shop charged $4K for labor, you know?
Regardless, on a stock ECU you are playing with fire to go overboosting, period.
With no fuel upgrades such as injector work (even a good cleaning and flow-matching is important) or a higher volume fuel pump, you CAN have some problems.
Your saving grace is you still have a stock I/C, so you are not necessarily living on the edge with each drive, you just have to be careful.
Some sort of boost control is definitely recommended. You just shouldn't go bumping 12 - 13 psi.
10" of mercury at idle is pretty low, I have a pretty aggressive street port and I still pull 16 - 18 inches at idle.
I am also struck a bit by your assertion that your exhaust "does not seem to be extremely free flowing, pretty quiet". An exhaust does not HAVE to be irritatingly loud to be decent flowing. When you look at your overall mods, you basically have an intake and exhaust as performance enhancements as well as this undefined port job. A $8K engine SHOULD have some goodies in it, but not necessarily. One could assume that it is a $4K engine and the shop charged $4K for labor, you know?
Regardless, on a stock ECU you are playing with fire to go overboosting, period.
With no fuel upgrades such as injector work (even a good cleaning and flow-matching is important) or a higher volume fuel pump, you CAN have some problems.
Your saving grace is you still have a stock I/C, so you are not necessarily living on the edge with each drive, you just have to be careful.
Some sort of boost control is definitely recommended. You just shouldn't go bumping 12 - 13 psi.
thanks, i'll look into the ECU issue. i know that my boost spiking is a problem that i need to deal with asap. do you recommend any particular boost controller?
as far as the engine rebuild, it was $8,000 and performed by the previous-previous owner. rotary performance has given me general details about it, but when i asked for more information, they said they could not tell me about the rebuild due to "customer privacy issues". whatever that means...i know they are a reputable shop and do good work (my engine runs strong and returned excellent compression numbers). i just don't get why they're so hesitant to tell me exactly WHAT they did.
as far as the engine rebuild, it was $8,000 and performed by the previous-previous owner. rotary performance has given me general details about it, but when i asked for more information, they said they could not tell me about the rebuild due to "customer privacy issues". whatever that means...i know they are a reputable shop and do good work (my engine runs strong and returned excellent compression numbers). i just don't get why they're so hesitant to tell me exactly WHAT they did.
also running on stock fuel injectors, fuel rails, and fuel pump are also probably not in your best intrest...So becareful
7-8k is what the mazda dealer charges for a stock rebuild...A buddy of mine who used to work with an older guy got took on his stock rebuild...They replaced everything brandnew but still for that price...there still making a killing on labor...its stupid...
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From: usa
thanks for the input guys. i know that RP is a reputable shop, and in NO way am i trying to give them a bad rep. i just wish they would be more forthcoming and respond to my emails asking about the rebuild. they responded the first time by saying "due to customer privacy issues, we cannot release the receipts to you" which is funny, because i never asked for receipts. i only asked for them to tell me what parts they used and how it was done. after this, they send me another email saying "we'll see what we can put together for you" and have said nothing since.
DaveW, thanks for that link to MBC's. Couldn't help but notice the guy asking the question is running a similar setup to mine (stock turbos, ECU, ported waste gate) and was looking to bump his boost to 12. Is that wise?
DaveW, thanks for that link to MBC's. Couldn't help but notice the guy asking the question is running a similar setup to mine (stock turbos, ECU, ported waste gate) and was looking to bump his boost to 12. Is that wise?
be very careful with doing the mbc mod, and make sure you have a fully working boost gauge! you can end up with a **** load of unwanted boost if your not careful. the needle valves are pretty sensitive
not without supporting mods and a tune.
Couldn't help but notice the guy asking the question is running a similar setup to mine (stock turbos, ECU, ported waste gate) and was looking to bump his boost to 12. Is that wise?
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well I just talked with MazCare (the shop that performed the compression test less than a month ago saying it was in great shape) and they want me to bring it in again. They said that a 10" vacuum indicates engine damage and want to do a compression test again. This is ridiculous because I haven't really driven the car hard since I bought it and it has been in pretty much the same shape as the day they tested it. i'm really hoping at this point it's just a faulty boost gauge, because the car runs perfectly and hasn't given me any reason to suspect the engine has sustained damage.
well I just talked with MazCare (the shop that performed the compression test less than a month ago saying it was in great shape) and they want me to bring it in again. They said that a 10" vacuum indicates engine damage and want to do a compression test again. This is ridiculous because I haven't really driven the car hard since I bought it and it has been in pretty much the same shape as the day they tested it. i'm really hoping at this point it's just a faulty boost gauge, because the car runs perfectly and hasn't given me any reason to suspect the engine has sustained damage.
If your compression is good, your boost is good, and your idle is good; then don't worry about the "exact" reading of your vacuum.
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First off, 10 inHg doesn't necessarily mean damaged or blown. It could mean something isn't right *if* the engine held a higher vacuum given the same scenario. What I mean by that is vacuum readings will differ depending on idle rpm and/or altitude. As an FYI, a local friend has a Pettit motor running aroun 10-11 inHg which has no issues. Everyone on this forum kept telling him his engine was blown or damaged a few years ago...
If your compression is good, your boost is good, and your idle is good; then don't worry about the "exact" reading of your vacuum.
If your compression is good, your boost is good, and your idle is good; then don't worry about the "exact" reading of your vacuum.
Did your friend ever get the problem diagnosed?
Racecar - Formula 2000
Joined: Sep 2002
Posts: 4,034
Likes: 370
From: Bath, OH
1.
2. 1. 12 psi may cause fuel cut on the stock ECU - see the attached chart.
2. That's why I recommended the ball-spring type.
Dave
2. That's why I recommended the ball-spring type.
Dave
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well after looking around, it looks like the greddy profec B is a popular choice for the sequential setup. not sure if there is a huge diference between Profec B and profec B 2. also, driving home from work last night, at a stop light i noticed my vacuum read at 14". my car was angled down slightly on a hill, not sure if that affects it either (i doubt it). when i got home and parked, the idle was reading around 12 to 11. i think it's fairly safe to say that the vacuum gauge is sensitive and not too consistent.
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