blowthru turbo
12-16-12, 06:44 PM
#26
Excellent ideas. My car has a 3/8" send and 5/16" return using a walbro 255 and a GSL-SE gas tank. I've got a mallory boost referenced fpr ready to install. I'll also add a remote fuel pressure gauge so I can watch it shoot up from the driver's seat. That should be cool to look at.
I've got a question about adding pressurized air to the throttle shafts. My boost prepped Holley already has some holes and a channel connecting them to a tube but I'm not sure where to hook up a hose to feed the pressurized air. Do I add it from the carb hat or from ther charge pipe? Or how about under the carb like on the manifold or something. Remember I'm a total noob at this boost stuff. Things that may be obvious to most people aren't to me when it comes to this particular subject. Thanks.
I've got a question about adding pressurized air to the throttle shafts. My boost prepped Holley already has some holes and a channel connecting them to a tube but I'm not sure where to hook up a hose to feed the pressurized air. Do I add it from the carb hat or from ther charge pipe? Or how about under the carb like on the manifold or something. Remember I'm a total noob at this boost stuff. Things that may be obvious to most people aren't to me when it comes to this particular subject. Thanks.
12-16-12, 07:14 PM
#27
Yeah, I'll cut power to the coils. I'm also playing with the idea of having it cut power to the coils, and bleed boost at the same time... Not sure. I'm going to leave the dizzy unlocked and use 2 timing retard devices to cut timing under boost too. I'm not meaning to clutter the thread, but I really think these failsafe tricks can be the key to having a blowthrough (or drawthrough) carb turbo setup that doesn't blow up during carb tuning. Jets too small? Oops there goes the failsafe. Less terrifying than "oops there goes the motor"
Jeff, I still think a REPU would look cool with a hoodscoop
But I understand you wanting to keep it looking original.85Rotarypower - I think with all the mods needed to run a 2nd gen CAS, it would kinda defeat the purpose of sticking with the carb. Another option is a 12at distributor which has a timing curve designed for boost.
12-19-12, 06:20 PM
#28
Excellent ideas. My car has a 3/8" send and 5/16" return using a walbro 255 and a GSL-SE gas tank. I've got a mallory boost referenced fpr ready to install. I'll also add a remote fuel pressure gauge so I can watch it shoot up from the driver's seat. That should be cool to look at.
I've got a question about adding pressurized air to the throttle shafts. My boost prepped Holley already has some holes and a channel connecting them to a tube but I'm not sure where to hook up a hose to feed the pressurized air. Do I add it from the carb hat or from ther charge pipe? Or how about under the carb like on the manifold or something. Remember I'm a total noob at this boost stuff. Things that may be obvious to most people aren't to me when it comes to this particular subject. Thanks.
I've got a question about adding pressurized air to the throttle shafts. My boost prepped Holley already has some holes and a channel connecting them to a tube but I'm not sure where to hook up a hose to feed the pressurized air. Do I add it from the carb hat or from ther charge pipe? Or how about under the carb like on the manifold or something. Remember I'm a total noob at this boost stuff. Things that may be obvious to most people aren't to me when it comes to this particular subject. Thanks.
12-19-12, 06:59 PM
#29
F**K THE SYSTEM!!
My main concern with the blowthrough is detonation. A hiccup in the fuel supply could potentially blow seals. With no knock sensor and ECU to electronically retard the timing, you're at the mercy of your fuel system and boost spikes. During my last autocross, I ble a fuse and lost power to my fuel pump. The carb ran out of fuel while I was at WOT. I can't imagine that would have gone well under boost. Some sort of boost retard would make me feel a bit better.
Another idea I've had is a bleed valve on the intake to keep boost right where I want it. I'm using a stock S5 turbo with an internal wastegate, which even when ported can be prone to spike. I'm thinking with a one way valve on the charge pipe with a spring set just right, I could bleed off excess boost. You can't do that with EFI since the air is metered, but I figure it won't make a difference to a carburetor. Think it'll work?
Another idea I've had is a bleed valve on the intake to keep boost right where I want it. I'm using a stock S5 turbo with an internal wastegate, which even when ported can be prone to spike. I'm thinking with a one way valve on the charge pipe with a spring set just right, I could bleed off excess boost. You can't do that with EFI since the air is metered, but I figure it won't make a difference to a carburetor. Think it'll work?
I believe they are called pop off valves. My first was a 1986 300zx. I swapped a turbo motor , of the same year, into it. This motor in factory form come with a pop off.valve as they call it in the z31 forum. The.z31 is a maf efi system. First mod before raising boost was to swap "pov" for a pipe.plug on the intake.plenum/manifold or using n/a plug.
Thing is I had completely forgotten about.these. I will see if I can include this pov idea to my turbo build. It seems like a common sense mod for my Haltech e6x Efi build.
12-20-12, 01:14 AM
#30
LizardFC, I have 2 retard devices on my ignition. Under boost, it'll pull timing down to 10btdc and 0. That way I won't lose low end drivability and fuel mileage. I have periodically scoured ebay to find them cheap. To buy them new would be expensive enough that I'd might as well go with EFI.
I know many people say "forget the trailing ignition," but no matter how much I play with it, and where I set the timing on the leading ignition, I always seem to make more power with leading and trailing. So I came up with a way to retard both under boost. I'm just pulling all the timing at once with a boost activated switch. I've noticed on the stock tII map, the boost comes out very quickly under boost, not proportionally, like an MSD BTM. That's why I'm pulling the timing all at once with a switch.
I know many people say "forget the trailing ignition," but no matter how much I play with it, and where I set the timing on the leading ignition, I always seem to make more power with leading and trailing. So I came up with a way to retard both under boost. I'm just pulling all the timing at once with a boost activated switch. I've noticed on the stock tII map, the boost comes out very quickly under boost, not proportionally, like an MSD BTM. That's why I'm pulling the timing all at once with a switch.
12-20-12, 05:46 PM
#31
Blow-through is OK - but if i were to do it again I would go EFI hands down. To me, running wires is FAR easier than trying to learn how to tune a carburetor AND turbo setup at the same time. Carbs do not make one bit of sense to me at all.
Downside to EFI is you'll need a shop to tune it in for you, or a place to drive your car and butt-tune it. Oh and roads that arent covered with ice and snow
but honestly, I could (and would, and did, and DO) say the same for carb'ed setups.There are shops that build solid blow-through kits. PM me if you're interested. I would mention it here but I have lingering suspicion i would get b4nned for my blasphemy.
12-20-12, 08:32 PM
#33
I'll look into the pop-off valves as well as the boost retard devices. I need to do some studying as to just how the entire dizzy mechanism functions, especially concerning the vacuum advance. Basically, I need to find a spare one and take it apart.
Tuning a carburetor isn't too bad after you've taken it apart and put it back together a dozen times. It's just not as simple or automatic as fuel injection. Since there's no sensors to automatically adjust for air temp and humidity, you have to re-tune for the season. I'm going to do my tuning in the winter and let it run rich in the summer.
Tuning a carburetor isn't too bad after you've taken it apart and put it back together a dozen times. It's just not as simple or automatic as fuel injection. Since there's no sensors to automatically adjust for air temp and humidity, you have to re-tune for the season. I'm going to do my tuning in the winter and let it run rich in the summer.
12-20-12, 09:51 PM
#34
Blow-through is OK - but if i were to do it again I would go EFI hands down. To me, running wires is FAR easier than trying to learn how to tune a carburetor AND turbo setup at the same time. Carbs do not make one bit of sense to me at all.
Downside to EFI is you'll need a shop to tune it in for you, or a place to drive your car and butt-tune it. Oh and roads that arent covered with ice and snow
but honestly, I could (and would, and did, and DO) say the same for carb'ed setups.There are shops that build solid blow-through kits. PM me if you're interested. I would mention it here but I have lingering suspicion i would get b4nned for my blasphemy.
12-23-12, 10:59 AM
#35
Senior Member
iTrader: (1)
Join Date: Jun 2006
Location: west bend, wi
Posts: 412
Likes: 0
Received 0 Likes
on
0 Posts
Could you just get a boost prepped holley or edelbrock meant for a V8 and bolt it on? I know they sell specialized rotary prepped holleys but at the end of the day a carb is just that thing you throw on the sucking side of that big glorified air pump known as the engine to make fuel and air happen. Also what about a carburetor Enclosure? use a boost referenced fpr, and run an unmodified carb. All you would have to do is make sure the fuel floats wont crush under pressure.
Another idea would be to possibly ditch the turbo Idea and run a cheap and common Eaton M90 supercharger (found on gm and ford supercharged V6's) Paired with a side draft carb bolted directly to the back or normal carb with a 90 degree elbow, then get an intake flange and scrap metal to make an intake plenum for the supercharger. It could handle tons of power, you wouldn't have to tune a carb to handle both vacuum and pressure (suck through), the car would run better with static timing (no intake vacuum), it would be cheaper and easier, and it would have that coolness that such a trick setup would have, just a thought.
Another idea would be to possibly ditch the turbo Idea and run a cheap and common Eaton M90 supercharger (found on gm and ford supercharged V6's) Paired with a side draft carb bolted directly to the back or normal carb with a 90 degree elbow, then get an intake flange and scrap metal to make an intake plenum for the supercharger. It could handle tons of power, you wouldn't have to tune a carb to handle both vacuum and pressure (suck through), the car would run better with static timing (no intake vacuum), it would be cheaper and easier, and it would have that coolness that such a trick setup would have, just a thought.
12-23-12, 03:23 PM
#36
V8's and rotaries have far different requirements for air and fuel. So a carb "made for a V8" isn't going to give you ideal performance on a rotary. That being said, sure you can throw it on there, swap out jets, make a manifold adapter, and it will work. I've heard of people running a holley 650 DP with a blowthrough because they are common and easy to boost prep.
Carb enclosures also work. It's an arguably simpler way to boost prep a carb. Some people even make their own.
I'm not even going to get into supercharging. That's a topic for another thread.
Carb enclosures also work. It's an arguably simpler way to boost prep a carb. Some people even make their own.
I'm not even going to get into supercharging. That's a topic for another thread.
12-23-12, 08:54 PM
#37
Then I will (briefly) talk about sueprchargers and carbs.
You can throw any V8 carb off the shelf onto a supercharger like a Camden because of the open plenum leading to the peanut shaped spinny bits. They mix and air and fuel so well you can actually get away with a somewhat less than ideal tune and it will still work fine.
I've had success using Edelbrock 600 performer series carbs right out of the box. However I've improved them a little by swapping in stronger springs for the metering rods so they lift a little sooner at a lower RPM. It kicks the carb out of a mid RPM lean condition caused by the metering rods staying down longer than needed for this application.
You can throw any V8 carb off the shelf onto a supercharger like a Camden because of the open plenum leading to the peanut shaped spinny bits. They mix and air and fuel so well you can actually get away with a somewhat less than ideal tune and it will still work fine.
I've had success using Edelbrock 600 performer series carbs right out of the box. However I've improved them a little by swapping in stronger springs for the metering rods so they lift a little sooner at a lower RPM. It kicks the carb out of a mid RPM lean condition caused by the metering rods staying down longer than needed for this application.
01-13-13, 10:46 AM
#38
updates? pics of the setups you guys have been working on? I for one would love to see an archived thread on prepping a carb for it instead of being told I should search 5+ year old threads that do nothing but ask me to send money to a shady company in california I won't even mention.
01-13-13, 10:58 AM
#39
Sorry, I closed the carb so quickly I took no photos. Just got it all buttoned up this weekend. I will take pictures while tuning.
On startup, locked dizzy at 5' BTDC, 15' split, idles at 14.3 AFR 2k rpm. Pulls 9 Hg not bad for the porting. Just free reving the engine it shows 5psi at 5k rpm. Just gotta deal with an oil leak and muffler then it is tune time.
On startup, locked dizzy at 5' BTDC, 15' split, idles at 14.3 AFR 2k rpm. Pulls 9 Hg not bad for the porting. Just free reving the engine it shows 5psi at 5k rpm. Just gotta deal with an oil leak and muffler then it is tune time.
Last edited by ArmyOfOne; 01-13-13 at 10:59 AM. Reason: Add picture.
01-13-13, 03:56 PM
#41
I'm trying to figure out what to do with my larger return line. More specifically, how to mate it to the tank without blowing myself or the car up. One idea I had was drilling the sender cap and running it through there, but there's not a whole lot of room to work with. It's either that or drill the tank, not something I really want to do.
What's the best method for putting holes in a fuel tank without a large fire? I'm thinking drain it (it's S3, whew) and dump some chunks of dry ice down there to fill it with C02. I've read a lot of people fill it completely full of water, but that seems like a great way to rust a tank.
I'll try and get some pics up soon.
What's the best method for putting holes in a fuel tank without a large fire? I'm thinking drain it (it's S3, whew) and dump some chunks of dry ice down there to fill it with C02. I've read a lot of people fill it completely full of water, but that seems like a great way to rust a tank.
I'll try and get some pics up soon.
01-13-13, 05:36 PM
#44
Sorry, I closed the carb so quickly I took no photos. Just got it all buttoned up this weekend. I will take pictures while tuning.
On startup, locked dizzy at 5' BTDC, 15' split, idles at 14.3 AFR 2k rpm. Pulls 9 Hg not bad for the porting. Just free reving the engine it shows 5psi at 5k rpm. Just gotta deal with an oil leak and muffler then it is tune time.
On startup, locked dizzy at 5' BTDC, 15' split, idles at 14.3 AFR 2k rpm. Pulls 9 Hg not bad for the porting. Just free reving the engine it shows 5psi at 5k rpm. Just gotta deal with an oil leak and muffler then it is tune time.
01-20-13, 03:03 PM
#45
So far no issues with pressure build up in the tank. Remember the tank also has vent lines that go to the engine bay.
Here are some pics. Update, It makes 12 psi by 5500 rpm and I am seeing AFRs in the low 12 range. Time to add more primary jet, the boost referrenced power valve is working very well. I will take a picture of it in a few minutes.
Here are some pics. Update, It makes 12 psi by 5500 rpm and I am seeing AFRs in the low 12 range. Time to add more primary jet, the boost referrenced power valve is working very well. I will take a picture of it in a few minutes.
01-20-13, 03:53 PM
#46
So far no issues with pressure build up in the tank. Remember the tank also has vent lines that go to the engine bay.
Here are some pics. Update, It makes 12 psi by 5500 rpm and I am seeing AFRs in the low 12 range. Time to add more primary jet, the boost referrenced power valve is working very well. I will take a picture of it in a few minutes.
Here are some pics. Update, It makes 12 psi by 5500 rpm and I am seeing AFRs in the low 12 range. Time to add more primary jet, the boost referrenced power valve is working very well. I will take a picture of it in a few minutes.
12 psi is a heap of boost for a 12a, isn't it? Good luck.
01-21-13, 09:52 PM
#48
Senior Member
iTrader: (3)
Join Date: Dec 2006
Location: El Paso, TX
Posts: 273
Likes: 0
Received 0 Likes
on
0 Posts
So far no issues with pressure build up in the tank. Remember the tank also has vent lines that go to the engine bay.
Here are some pics. Update, It makes 12 psi by 5500 rpm and I am seeing AFRs in the low 12 range. Time to add more primary jet, the boost referrenced power valve is working very well. I will take a picture of it in a few minutes.
Here are some pics. Update, It makes 12 psi by 5500 rpm and I am seeing AFRs in the low 12 range. Time to add more primary jet, the boost referrenced power valve is working very well. I will take a picture of it in a few minutes.
01-22-13, 12:47 PM
#49
So far no issues with pressure build up in the tank. Remember the tank also has vent lines that go to the engine bay.
Here are some pics. Update, It makes 12 psi by 5500 rpm and I am seeing AFRs in the low 12 range. Time to add more primary jet, the boost referrenced power valve is working very well. I will take a picture of it in a few minutes.
Here are some pics. Update, It makes 12 psi by 5500 rpm and I am seeing AFRs in the low 12 range. Time to add more primary jet, the boost referrenced power valve is working very well. I will take a picture of it in a few minutes.
I like your turbo-to-intake design, super simple. The great thing about the shorter pipes is you dont have to compress nearly as much air before you're boosting!
