Dyno'd my Cartech Drawthrough Turbo (12a)
08-09-10, 10:35 AM
#1
Dyno'd my Cartech Drawthrough Turbo (12a)
So we had a small dyno day this past weekend and I was always curious how much improvement there was running the Cartech Drawthrough turbo system. This is a very modest system running at 7psi and using a Holley 4bbl 375 cfm carb marketed in the early 1980s.
The first run produced a peak of about 127 bhp which seems reasonable since flywheel horsepower equates to about 160. The second run showed there might be some more gain by going to 6500 rpm but the engine bay temps had risen dramatically since the first run (15-20 C as shown on a digital meat thermometer!) and probably accounts for the power dropoff. The dyno was calibrated with a temperature sensor that reflected only the interior of the garage.
I believe the original Cartech literature stated 180 bhp (flywheel) as the target at 7psi. Load dynos like the Mustang are typically more conservative and an inertia dyno reading would likely reach this value.
Everyone was impressed how well the carb was maintaining a consistent and safe AFR during boost.
Here's a link to the video: http://dl.dropbox.com/u/4852049/Jims...-%20iPhone.m4v
Jim
The first run produced a peak of about 127 bhp which seems reasonable since flywheel horsepower equates to about 160. The second run showed there might be some more gain by going to 6500 rpm but the engine bay temps had risen dramatically since the first run (15-20 C as shown on a digital meat thermometer!) and probably accounts for the power dropoff. The dyno was calibrated with a temperature sensor that reflected only the interior of the garage.
I believe the original Cartech literature stated 180 bhp (flywheel) as the target at 7psi. Load dynos like the Mustang are typically more conservative and an inertia dyno reading would likely reach this value.
Everyone was impressed how well the carb was maintaining a consistent and safe AFR during boost.
Here's a link to the video: http://dl.dropbox.com/u/4852049/Jims...-%20iPhone.m4v
Jim
08-09-10, 10:45 AM
#2
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neat, that does seem to be working well.
if it was mine i'd be temped to pull a couple of degrees of timing, richen it up and up the boost a tad
if it was mine i'd be temped to pull a couple of degrees of timing, richen it up and up the boost a tad
08-09-10, 11:46 AM
#3
Waffles - hmmm good
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Maybe a mod will move this to the dyno sticky thread for you. You'll get more input
there.
I have to say I'm surprised it didn't do better. You saw 127 with a turbo on a
Mustang dyno. Even allowing that the Mustangs under reports by 10%, the corrected
figure would be 139, maybe. My stock port 12a does 134 hp to the rear wheels
and its a NA using a big Dellorto. Also you said 127 hp equals 160 bhp. I always
thought drive train losses should be about 12% for our cars, ok 20 if you want to
be conservative, so at 127 whp you would say its at 152 bhp. Thats a far cry from the
180 bhp the Car Tech is said to deliver.
Maybe theres an issue? Is your compression down? I'm not sure but I do know
you should be spanking me with a turbo on there.
there.
I have to say I'm surprised it didn't do better. You saw 127 with a turbo on a
Mustang dyno. Even allowing that the Mustangs under reports by 10%, the corrected
figure would be 139, maybe. My stock port 12a does 134 hp to the rear wheels
and its a NA using a big Dellorto. Also you said 127 hp equals 160 bhp. I always
thought drive train losses should be about 12% for our cars, ok 20 if you want to
be conservative, so at 127 whp you would say its at 152 bhp. Thats a far cry from the
180 bhp the Car Tech is said to deliver.
Maybe theres an issue? Is your compression down? I'm not sure but I do know
you should be spanking me with a turbo on there.
08-09-10, 12:03 PM
#4
That's interesting. Before the Cartech I had the Racing Beat modified Dell'orto system and the Cartech definitely pulls harder. Turbo lag does seem to be much more than other people report so I'm not getting the benefit of boost across a much wider rpm range that I think I should be. This was a system I picked up from eBay about 4 years ago after the first owner wrecked his car.
08-09-10, 03:04 PM
#6
I was afraid that this thread would evolve into a numbers issue. There is a notorious variance in horsepower numbers measured between load and inertial dynos and even between same machines depending on the care at which it is calibrated. We know that Mazda says flywheel hp of the stock 12a is 100 bhp so on the best day rear wheel power is 80-85 bhp. I'm happy I got 50 bhp more than that. Maybe the turbo itself is a little tired and needs a rebuild and maybe power is slightly off expectations but without standardized dynos, your numbers can't really be compared to mine with any real meaning. 8)
08-10-10, 04:48 AM
#7
UGH I wish I had 12 hours with that car. I could almost guarantee I could get you near 150whp. I think the carb is seriously choking her. According to MY calculations a stock 12A will flow more than 355 CFM at 7000 RPM. 364 to be exact. A bigger Holley will do you wonders.
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08-10-10, 05:09 AM
#8
I know this is getting slightly OT but Cartech reccomended this size carb for their system. Your calculations may indeed be correct but for some reason the carb is not the limiting factor. Most of the 12a mods run carbs that are really too big and that of course impacts on fuel efficiency and driveability. Would be great if some of the carb gurus would chime in and give us a short definitive explanation.
08-10-10, 11:39 AM
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I know this is getting slightly OT but Cartech reccomended this size carb for their system. Your calculations may indeed be correct but for some reason the carb is not the limiting factor. Most of the 12a mods run carbs that are really too big and that of course impacts on fuel efficiency and driveability. Would be great if some of the carb gurus would chime in and give us a short definitive explanation.
if you're happy with the car though, that's the important part
08-10-10, 12:04 PM
#12
I did some research and to be different but sized properly... I've got a Holley 2bbl 500cfm carb. The 2bbl vs 4bbl ratings are different, so this one flows something like an equivilent 364cfm 4bbl. For a small turb. Blowthru. If you're sustaining the 7psi I don't think the carb is a problem. What's your timing at? About 23?
08-10-10, 12:40 PM
#14
NO disrespect to Hyper but I did a quick archive search and gleaned this posting from Sterling:
It's very simple math. No need to overthink it.
The 12a has two 35 cubic inch chambers that are compressed, or fired, or exhausted during each revolution.
That's simply intaking 70 cubic inches per revolution.
I use an unusually high Revolution Per Minute of 10,000, both for ease of multiplication as well as to nip any arguements right at the bud regarding the .05% of rotary owners who actually have an engine built to handle those RPMs.
This equals 700,000 cubic inches @ 10K RPM.
Multiply 12 cubic inches by 12 cubic inches by 12 cubic inches, and you get 1728 cubic inches in one cubic foot.
Divide the 700,000 cubic inches @ 10K RPM by 1728, and you get 405 cubic feet per minute.
Now, for arguement's sake, I like to go ahead and give kudos to the bestest porters in the world by multiplying that 405 CFM @ 10K RPM time a Volumetric Efficiency of 110%.
The result is...
445 cfm!
Yes, a 12a at an incredible VE of 110%, running at an incredible 10,000 RPM, needs a flow of FOUR HUNDRED, FORTY-FIVE CFM.
(BTW Sterling is trying to be sarcastic in that posting)
So if we redo more reasonable numbers, 100% VE and 7000 rpm the maximum air flow is only 283 cfm. So not sure where 364 cfm came from.
It's very simple math. No need to overthink it.
The 12a has two 35 cubic inch chambers that are compressed, or fired, or exhausted during each revolution.
That's simply intaking 70 cubic inches per revolution.
I use an unusually high Revolution Per Minute of 10,000, both for ease of multiplication as well as to nip any arguements right at the bud regarding the .05% of rotary owners who actually have an engine built to handle those RPMs.
This equals 700,000 cubic inches @ 10K RPM.
Multiply 12 cubic inches by 12 cubic inches by 12 cubic inches, and you get 1728 cubic inches in one cubic foot.
Divide the 700,000 cubic inches @ 10K RPM by 1728, and you get 405 cubic feet per minute.
Now, for arguement's sake, I like to go ahead and give kudos to the bestest porters in the world by multiplying that 405 CFM @ 10K RPM time a Volumetric Efficiency of 110%.
The result is...
445 cfm!
Yes, a 12a at an incredible VE of 110%, running at an incredible 10,000 RPM, needs a flow of FOUR HUNDRED, FORTY-FIVE CFM.
(BTW Sterling is trying to be sarcastic in that posting)
So if we redo more reasonable numbers, 100% VE and 7000 rpm the maximum air flow is only 283 cfm. So not sure where 364 cfm came from.
08-10-10, 01:35 PM
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its true the math is simple, and correct. however his equation is for a carburetor on a plenum, which with the exception maybe of your cartech kit not what the rotary has.
also carbs are rated at a pressure drop of like 1psi, which is more than we want.
sterling himself proves it, if the engine only flows 300ish cfm, why is there a power gain when going from the stock 330cfm carb to a 465cfm modified carb. if he was right, going to the bigger carb would either loose power or not gain anything. instead we get a very noticeable gain.
also carbs are rated at a pressure drop of like 1psi, which is more than we want.
sterling himself proves it, if the engine only flows 300ish cfm, why is there a power gain when going from the stock 330cfm carb to a 465cfm modified carb. if he was right, going to the bigger carb would either loose power or not gain anything. instead we get a very noticeable gain.
08-10-10, 02:19 PM
#17
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but.. that would be a blowthrough set up, he has a drowthrough set up witch is more like having a camden sc on it.
blowing it through vs sucking it through changes things a bit.
just for fun..... isnt 84stock using a 500 cfm carb with a camden pushing 7psi ??
maby a water/ meth injection would help keep it cool and up the hp#
08-10-10, 02:38 PM
#18
Didn't even dawn on me. Yes he needs a bigger carb. That carb would be perfect for a BLOW THROUGH setup. But since it sits ontop, the carb needs to reflect the entire cfm requirement for the boosted setup not just the Engine itself N/A at a specific VE and RPM. Definitely need a bigger carb.
08-10-10, 04:00 PM
#19
I am one of the tuners out there who disagree with Sterling. No one no one but him uses a 15% correction. Every other tuner on I've ever met uses a 25% correction. I have done back to back dyno runs with my"overcarbed" cars where the only thing I changed was the choke size and gained horse power.
Now I haven't played with Holley's since the 90's but switching from a holley 600 to a 750 netted over 25 additional whp @8500 RPM on a 13B bridge port. If you ask Sterling the 650 was way too big for the BP even at 110 VE and 8500RPM. 110VE[(79CI×8500RPM)/1728]1.15=491.5CFM There are things in the real world that math cant account for.
With a 45 dcoe on a stock ported gslse engine I went from 136.5 @6450 rwhp to 139.0 @6450 rwhp by changing from 38mm chokes to 40mm chokes. I have dyno sheets to prove it. Nothing else changed but the chokes. A 45DCOE with 38mm chokes should flow well over 450cfm? so why the gain in power? There are all sorts of things that could attribute to a gain in HP by going to a larger carb besides just the added CFM. A decrease in turbulent flow due to the greater flow potential of the carb is worth a few ponies right there.
Remember you're turbo you're artificially increasing the VE of the engine. Once you have maxed out the carb's CFM you are only flowing 355CFM. You can keep turning up the boost but you're still only moving 355CFM. now you can compress and compress that 355CFM into more and more boost but all you're really doing is super heating the air and causing it to expand and therefore increasing the boost pressure actually causing a decrease in power. Fit a proper carb and your intake temperatures will drastically drop at the same boost pressure along with the added CFM that the turbo WILL draw and you will see huge gains in power.
Now I haven't played with Holley's since the 90's but switching from a holley 600 to a 750 netted over 25 additional whp @8500 RPM on a 13B bridge port. If you ask Sterling the 650 was way too big for the BP even at 110 VE and 8500RPM. 110VE[(79CI×8500RPM)/1728]1.15=491.5CFM There are things in the real world that math cant account for.
With a 45 dcoe on a stock ported gslse engine I went from 136.5 @6450 rwhp to 139.0 @6450 rwhp by changing from 38mm chokes to 40mm chokes. I have dyno sheets to prove it. Nothing else changed but the chokes. A 45DCOE with 38mm chokes should flow well over 450cfm? so why the gain in power? There are all sorts of things that could attribute to a gain in HP by going to a larger carb besides just the added CFM. A decrease in turbulent flow due to the greater flow potential of the carb is worth a few ponies right there.
Remember you're turbo you're artificially increasing the VE of the engine. Once you have maxed out the carb's CFM you are only flowing 355CFM. You can keep turning up the boost but you're still only moving 355CFM. now you can compress and compress that 355CFM into more and more boost but all you're really doing is super heating the air and causing it to expand and therefore increasing the boost pressure actually causing a decrease in power. Fit a proper carb and your intake temperatures will drastically drop at the same boost pressure along with the added CFM that the turbo WILL draw and you will see huge gains in power.
Last edited by Hyper4mance2k; 08-10-10 at 04:20 PM. Reason: spelzeng and grhammar correksonz
08-10-10, 04:24 PM
#20
Oh and a big free flowing exhaust will make drive-ability and HP potential skyrocket. 3"turbo back is my recommendation. Stick a good Magnaflow in the rear or use the RacingBeat turbo 3" universal mufflers, they're built very well. One up front and one in the rear and a Dynomax bullet presilencer and it'll be stupid quiet and flow ridiculously well.
08-10-10, 08:17 PM
#21
I thought I would chime in here.
Yes, the carb is too small!!
Now I am not some 18 year old with his first experimental rx7, at 47 years of age I have gone through the muscle car era and have driven rx7's for years. You could take apart a holley, BG, or edelbrock and throw all the pieces in a bag, then shake it up and I could build it.
Your cartech drawthrough is comparable in every respect to my camden including similar inefficiencies. Biggest differences, I use power to spin mine, you don't. I have instant boost and more torque, however yours doesn't rob power and should peak slightly higher in the top of the hp curve.
I have used edelbrock, barry grant and holleys on mine. All have their benefits however the barry grant is pure ****!
I have used a 500 cfm and 650 cfm edelbrock, (I have a 750 also which I have never tried) and a 650 BG speed demon blower carb. I also have used holleys in 600 cfm vac secondary, 670 cfm vac secondary (current), 800 cfm spreadbore dp, 850 cfm dp and will be testing a 700 dp next. Hmmm, guess how many I have in my garage all together??
On my setup, the bigger carb provides more power, but there is a limit. The 500 cfm was smooth and nice, great for a stock port with less boost, but power quickly fell off over 6000 rpm. The 850 dp had a limitless powerband but compromised drivability due to the large primaries. The spreadbore was awesome, best of both worlds, but it could not flow enough fuel through it's single inlet design. The holley 670 is almost perfect except dialing in the vac secondaries eludes perfection, hence the 700 being built now.
For a simple daily driver, the edelbrock 650 thunder series was among my favorite.
If you were here, I would bolt my 500 edelbrock and guarantee 10 hp. Next I would bolt my 650 on and guarantee 15+ hp or either is free, I am that certain!!
Edelbrocks are a cinch to tune, and the thunder series is a must have as you can easily dial in the secondaries to your choosing.
You also have a lot to gain with exhaust!!
I have tried magnaflow, aero, racing beat stockport and rb powerpulse mufflers. By far the powerpulse combined with the streetport duals has made a measurable improvement over all others. I would follow Hyper4mance2k advice and upgrade the exhaust, you will see immediate gains (search his history, he has plenty of personal experience in this area as well as me). Next the carb, I would go with the edelbrock 650, it has smaller primaries than a comparable holley and will give you the same economy and driveability as you have now with a noticeable improvement in top end.
Yes, the carb is too small!!
Now I am not some 18 year old with his first experimental rx7, at 47 years of age I have gone through the muscle car era and have driven rx7's for years. You could take apart a holley, BG, or edelbrock and throw all the pieces in a bag, then shake it up and I could build it.
Your cartech drawthrough is comparable in every respect to my camden including similar inefficiencies. Biggest differences, I use power to spin mine, you don't. I have instant boost and more torque, however yours doesn't rob power and should peak slightly higher in the top of the hp curve.
I have used edelbrock, barry grant and holleys on mine. All have their benefits however the barry grant is pure ****!
I have used a 500 cfm and 650 cfm edelbrock, (I have a 750 also which I have never tried) and a 650 BG speed demon blower carb. I also have used holleys in 600 cfm vac secondary, 670 cfm vac secondary (current), 800 cfm spreadbore dp, 850 cfm dp and will be testing a 700 dp next. Hmmm, guess how many I have in my garage all together??
On my setup, the bigger carb provides more power, but there is a limit. The 500 cfm was smooth and nice, great for a stock port with less boost, but power quickly fell off over 6000 rpm. The 850 dp had a limitless powerband but compromised drivability due to the large primaries. The spreadbore was awesome, best of both worlds, but it could not flow enough fuel through it's single inlet design. The holley 670 is almost perfect except dialing in the vac secondaries eludes perfection, hence the 700 being built now.
For a simple daily driver, the edelbrock 650 thunder series was among my favorite.
If you were here, I would bolt my 500 edelbrock and guarantee 10 hp. Next I would bolt my 650 on and guarantee 15+ hp or either is free, I am that certain!!
Edelbrocks are a cinch to tune, and the thunder series is a must have as you can easily dial in the secondaries to your choosing.
You also have a lot to gain with exhaust!!
I have tried magnaflow, aero, racing beat stockport and rb powerpulse mufflers. By far the powerpulse combined with the streetport duals has made a measurable improvement over all others. I would follow Hyper4mance2k advice and upgrade the exhaust, you will see immediate gains (search his history, he has plenty of personal experience in this area as well as me). Next the carb, I would go with the edelbrock 650, it has smaller primaries than a comparable holley and will give you the same economy and driveability as you have now with a noticeable improvement in top end.
08-11-10, 05:37 AM
#23
Thanks to all for some great responses!
So I'm convinced, I could use a bigger carb.
I could probably use a bigger exhaust too! Currently running the Cartech downpipe into a RB presilencer then into stock connecting pipe and then stainless steel free flowing muffler of forgotten make that I had replaced a decade earlier because the RB muffler had rusted away where it has to go over the axle.
I try and post some engine bay images and see if I can find the muffler make. Definitely not 3" anywhere!
Jim
So I'm convinced, I could use a bigger carb.
I could probably use a bigger exhaust too! Currently running the Cartech downpipe into a RB presilencer then into stock connecting pipe and then stainless steel free flowing muffler of forgotten make that I had replaced a decade earlier because the RB muffler had rusted away where it has to go over the axle.
I try and post some engine bay images and see if I can find the muffler make. Definitely not 3" anywhere!
Jim
08-11-10, 06:17 AM
#24
Don't mean to hijack, but since you're on the topic of airflow, I'm interested in how well blow-through carbs flow under boost pressure. If you have your carb rated at say 465 CFM at atmospheric, will it flow twice as much at say 15psi? I would suspect that flow restrictions become more and more important under boost pressure because they would cause pressure drop through the carby...
From what I understand you guys are saying here, because it's draw through, you need a carby which can flow enough air for the TURBO instead of the engine.
From what I understand you guys are saying here, because it's draw through, you need a carby which can flow enough air for the TURBO instead of the engine.
08-11-10, 08:46 AM
#25
Don't mean to hijack, but since you're on the topic of airflow, I'm interested in how well blow-through carbs flow under boost pressure. If you have your carb rated at say 465 CFM at atmospheric, will it flow twice as much at say 15psi? I would suspect that flow restrictions become more and more important under boost pressure because they would cause pressure drop through the carby...