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At mild boost could a 307 take additional compression? Like 2 points with premium pump (93) Could the internals of the air compressor for the AIR system be beefed up to push more air through the exhaust manifold?
Last edited by carpenternotmechanic; January 14th, 2021 at 10:03 AM.
At mild boost could a 307 take additional compression? Like 2 points with premium pump (93) Could the internals of the air compressor for the AIR system be beefed up to push more air through the exhaust manifold?
If you mean can it take boost, probably they were all low comp but windowed mains are not your friend for putting out power.
Not sure what you mean by 2 points. 2lbs? That'd basically be a big hair dryer. 2 pts of additional CR? Kinda the opposite way you'd wanna go for a turbo unless you're running E85.
Turbos force more air through the same manifold by compressing it, not speeding up the air flow (actually slower) , so I'm really at a loss at the last Q, it sounds like you're asking if you can swap turbo internals... which... just buy one sized for your application.
If you mean can it take boost, probably they were all low comp but windowed mains are not your friend for putting out power.
Not sure what you mean by 2 points. 2lbs? That'd basically be a big hair dryer. 2 pts of additional CR? Kinda the opposite way you'd wanna go for a turbo unless you're running E85.
Turbos force more air through the same manifold by compressing it, not speeding up the air flow (actually slower) , so I'm really at a loss at the last Q, it sounds like you're asking if you can swap turbo internals... which... just buy one sized for your application.
windowed mains are bad for high revs i thought. Im talking about keeping the range of the power band the same or similar. And its the turbo and additional pressure from the turbo that raises the cr. E 85 might be am option, or E 50. Methanol injection would work wonders im sure. Add e50 or 85 with injection amd you could probably get away with a significantly higher cr prior to detonation setting in.
to spin a turbo adding moderate boost, but remaining at or below 10.5 cr. Thw point would be additional power using systems already in place.
A turbo is driven by the high velocity exhaust gas flow through the turbine. As Joe P pointed out in your other thread, the A.I.R. pump is not capable of injecting high velocity, high volume air - it is a tiny compressor with small diameter piping to add a small amount of oxygen to the exhaust to enhance the catalytic converter efficiency. Its output is miniscule compared to the output of the engine's exhaust.
Originally Posted by carpenternotmechanic
windowed mains are bad for high revs i thought. Im talking about keeping the range of the power band the same or similar.
The RPM doesn't matter, it's how much downward force is added to the crank. Increase that force sufficiently at a lower RPM and stuff can still break.
Not sure what you mean by "systems already in place" as a turbo isn't already in place.
The AIR pump won't help at all as it's not the air flow that drives the turbo but the heat energy.
Putting a turbo on a 307 would be a waste of $$. If you added enough boost to make it fun you stand a good chance of grenading the block.
windowed mains are bad for high revs i thought. Im talking about keeping the range of the power band the same or similar. And its the turbo and additional pressure from the turbo that raises the cr. E 85 might be am option, or E 50. Methanol injection would work wonders im sure. Add e50 or 85 with injection amd you could probably get away with a significantly higher cr prior to detonation setting in.
Bad in general, actually! I mean, good for weight savings... but bad for structural integrity. Forces on the crank are based on forces on the pistons/rods, which track pretty well with HP. Low revs aren't going to prevent the bottom end from flexing like a wet noodle at high HP levels. Gonna be tempting to go to those levels if you drop the money on a turbo.
Valvetrain on the other hand, that's very rev dependent! Backpressure dependent to a much lesser extent, if at all, so you can likely get away with stock valve springs at low boost.
A turbo is driven by the high velocity exhaust gas flow through the turbine. As Joe P pointed out in your other thread, the A.I.R. pump is not capable of injecting high velocity, high volume air - it is a tiny compressor with small diameter piping to add a small amount of oxygen to the exhaust to enhance the catalytic converter efficiency. Its output is miniscule compared to the output of the engine's exhaust.
The RPM doesn't matter, it's how much downward force is added to the crank. Increase that force sufficiently at a lower RPM and stuff can still break.
i am aware of how a turbo works. I asked if the air compressor could be improved upon that it might add to thw exhaust pressure. In the other thread i was inquiring about simply using the AIR system itself for boost; not using a turbo. And im talking mild applications for a relatively mild increase in torque/ power. The exhaust turns the turbine which in turn turns the impeller attached with a shaft that sucks in cool air amd introduces it into the intake. It doesn't take crazy velocity to turn a turbo. It takes proper turbo sizing and plumbing. You are comparing two things but i am asking about adding the two; not running a turbo off of the AIR system alone. I am aware that that wouldn't work very well.
Not sure what you mean by "systems already in place" as a turbo isn't already in place.
The AIR pump won't help at all as it's not the air flow that drives the turbo but the heat energy.
Putting a turbo on a 307 would be a waste of $$. If you added enough boost to make it fun you stand a good chance of grenading the block.
The AIR pump adds air to the exhaust gasses. If the pump was upgraded and the made to push more air then that would equate to more exhaust gas pressure pushing the turbo. And i already have all the parts x2. And im talking about low boost with a cr not above 10.5. If that blows the engine then screw that piece of crap.
Bad in general, actually! I mean, good for weight savings... but bad for structural integrity. Forces on the crank are based on forces on the pistons/rods, which track pretty well with HP. Low revs aren't going to prevent the bottom end from flexing like a wet noodle at high HP levels. Gonna be tempting to go to those levels if you drop the money on a turbo.
Valvetrain on the other hand, that's very rev dependent! Backpressure dependent to a much lesser extent, if at all, so you can likely get away with stock valve springs at low boost.
thank you. If boost was kept to 5-7 pounds above atmosphere, and cr kept below 10.6, would that still cause failure due to the windowed crank in your opinion?
You would want compression to stay where it is with boost, factory is around 8 to 1 compression, just under on the 85 and up version. One guy turboed a windowed 260, supposedly went like hell in comparison but blew up in a very short time. Build a 76 and earlier 350 with a 330 crank, aftermarket rods, forged pistons and a 5 main Halo, it will take a good amount. Remember your carb is super lean, the factory computer advance puts out a ton of timing, neither will work. You have weak cast pistons, soft forged rods and a weak lightweight crank in a windowed main block, not an ideal boost combo.
At anything above approx 8 to I cr and any usable amount of boost you would need some way to control detonation. At 10 to 1 you'd need some electronic nannies and an intercooler as well as a much stronger short block.
The OP already asked this question in a prior thread, didn't like the answer he got there, and apparently wants to keep asking it until he gets an answer he likes...
thank you. If boost was kept to 5-7 pounds above atmosphere, and cr kept below 10.6, would that still cause failure due to the windowed crank in your opinion?
When building a turbo motor most will take the tradeoff of running lower compression *so that* they can run more boost, because you'll get more power out of running an additional pound of boost versus an additional point of compression. Also, to run that extra compression, you're looking at swapping internals, at which point you're investing in a full motor rebuild. If you're doing that, you're spending a bunch on components/labor, and you may as well tailor for your build. Do a high compression high revving NA build! Do a low-comp low-revving turbo build! Combining the two is a bad idea. Yeah that turbo will spool easier with the higher CR, but your effective compression ratio at 10.5:1 with 6 lbs of boost is 14.8:1. That'll grenade it on pump gas. Should be OK on ethanol but that'd basically be your boost limit. Meanwhile at 8:1 your effective CR doesn't hit that same 14.8:1 until 12 lbs of boost.
Handy chart for SC applications above -- as others have said you can get above that 12.0:1 number with blowing it up -- methanol injection, intercooling, aluminum heads -- but it adds to the cost.
If swapping internals, As 307 & 403 said, better to start with a 350 block without the windowed mains at that point! Short blocks are cheap compared to all the other costs of building a windowed 307 block up over 350 HP.
Last edited by InfinityOlds; January 14th, 2021 at 07:33 AM.
The OP already asked this question in a prior thread, didn't like the answer he got there, and apparently wants to keep asking it until he gets an answer he likes...
afternoon sunshine. The other thread with mentioned something similar as an aside, in reality, did not pose the same question. Thanks for nothing.
When building a turbo motor most will take the tradeoff of running lower compression *so that* they can run more boost, because you'll get more power out of running an additional pound of boost versus an additional point of compression. Also, to run that extra compression, you're looking at swapping internals, at which point you're investing in a full motor rebuild. If you're doing that, you're spending a bunch on components/labor, and you may as well tailor for your build. Do a high compression high revving NA build! Do a low-comp low-revving turbo build! Combining the two is a bad idea. Yeah that turbo will spool easier with the higher CR, but your effective compression ratio at 10.5:1 with 6 lbs of boost is 14.8:1. That'll grenade it on pump gas. Should be OK on ethanol but that'd basically be your boost limit. Meanwhile at 8:1 your effective CR doesn't hit that same 14.8:1 until 12 lbs of boost.
Handy chart for SC applications above -- as others have said you can get above that 12.0:1 number with blowing it up -- methanol injection, intercooling, aluminum heads -- but it adds to the cost.
If swapping internals, As 307 & 403 said, better to start with a 350 block without the windowed mains at that point! Short blocks are cheap compared to all the other costs of building a windowed 307 block up over 350 HP.
i must be saying something wrong. I never meant to insinuate that i would want to increase the compression ratio; but that boosting anything raises the compression. And in knowing such; would 10.5 be doable on premium perhaps with meth injection. No intercooler should be needed if carburated.
So again; would thw 307 live at 10.5 cr with meth injection and premium? Assuming the blown through carb and nominal boost? Can you calculate the cr if all things as are but with 6lbs boost? Isnt 10-10.5 doable. Not talking about ******* it constantly. Just curious.
No disrespect intended, but I don't think you really do, or else you would not be looking to do this or even asking these questions.
Assuming your A.I.R. pump had sufficient output, it would be pushing cold air into the exhaust, which would immediately reduce the exhaust gas temperature, which would then reduce the exhaust gas velocity, and diminish the turbocharger effectiveness. It's all about thermodynamic gas flow.
If you are really set on something along these lines, look at a belt driven centrifugal supercharger instead of a traditional exhaust gas driven turbocharger.
Last edited by Fun71; January 14th, 2021 at 10:56 AM.
You're trying to do silly things on a shoestring budget that won't work. I presume you have a mid-80s Cutlass with a 307.
The first, cheapest, easiest, most value performance upgrade you do to that 307 is remove it and put in a 350 or better. A 403 would be stellar, and it would probably cost less than your turbo work, and it would look stock. While you're in there, if you don't live in an emissions inspection state, take the AIR stuff off. If you do, then you have you have to think about things.
At that point, you can build the engine solid, and put in a turbo.
But, to answer your question, no, you should not use the AIR pump to give more exhaust gas pressure to a turbo and expect to get higher power out of it, because the parasitic loss it takes to spin the AIR pump is more than the energy in the pressure it puts in. This is sometimes called the First Law of Thermodynamics.
...No intercooler should be needed if carburated...
The intercooler wouldn't be able to tell if either a carburetor is mounted or an injection system. The reason it's used is for the same reason airline pilots prefer to take off from a runway in winter rather than in summer
WE are discussing a act of futility here. This post is is solidly wedged between fictional ideas and wild dreams without any finical backup. Doubtful anyone learned anything but I did get a giggle here and there....Tedd
No disrespect intended, but I don't think you really do, or else you would not be looking to do this or even asking these questions.
Assuming your A.I.R. pump had sufficient output, it would be pushing cold air into the exhaust, which would immediately reduce the exhaust gas temperature, which would then reduce the exhaust gas velocity, and diminish the turbocharger effectiveness. It's all about thermodynamic gas flow.
If you are really set on something along these lines, look at a belt driven centrifugal supercharger instead of a traditional exhaust gas driven turbocharger.
was just curious and was talking about mild boost. Having the exhaust temps a little cooler would minimize oil coking and burning and though it may make the exhaust nominally more dense; this isn't a discussion about an full effort build. More of a what if amd could it work/ be done. But yes; im aware that the cooler the exhaust stream the less efficiently it will spin the turbo. Reliability over max effort.
Realistically i get that it would be unconventional and likely not the best set up. I also understand that the stock internals on the bottom end can't take a lot of abuse; yet another reason to keep things mild and limited to discussion.
Im willing to bet that hooking the turbo to the exhaust with an omitted AIR pipe would put out very similar results to hooking it to one with the AIR system still intact really. The additional air would do little. Maybe the methanol injection ran off the compressor would work before the intake.
Who knows; maybe you could use the compressor to keep the turbo spinning a little to lower spool times. I'll just stop.
The intercooler wouldn't be able to tell if either a carburetor is mounted or an injection system. The reason it's used is for the same reason airline pilots prefer to take off from a runway in winter rather than in summer
Might ought to research a little.
you generally do not need an intercooler if using a blow through carb.
You're trying to do silly things on a shoestring budget that won't work. I presume you have a mid-80s Cutlass with a 307.
The first, cheapest, easiest, most value performance upgrade you do to that 307 is remove it and put in a 350 or better. A 403 would be stellar, and it would probably cost less than your turbo work, and it would look stock. While you're in there, if you don't live in an emissions inspection state, take the AIR stuff off. If you do, then you have you have to think about things.
At that point, you can build the engine solid, and put in a turbo.
But, to answer your question, no, you should not use the AIR pump to give more exhaust gas pressure to a turbo and expect to get higher power out of it, because the parasitic loss it takes to spin the AIR pump is more than the energy in the pressure it puts in. This is sometimes called the First Law of Thermodynamics.
thank you for that last part. Its a late 80s custom cruiser. There really is zero space for a turbo unless i remove the heater core or ac components or headlights. Was just thinking. Turbos are just cooler than super chargers to me.
So even with better internals amd a smaller pulley, the AIR compressor would take more power than it would assist in making?
WE are discussing a act of futility here. This post is is solidly wedged between fictional ideas and wild dreams without any finical backup. Doubtful anyone learned anything but I did get a giggle here and there....Tedd
Way to assume things. I've got a fully built 552ci bb with gt45 twins, boost referenced pressure regulator super sniper efi, and blowoff valves. Intercooler and a few other parts ready to go including fuel system, and transmission. Im not wealthy by any stretch of the word, but you conflating poor eyesight and lack of herd mentality with lack of money and capacity to learn is too rich for my taste.
Next someone will say that the compressor can't be used to help cool charge air or inject methanol.
Im not above learning, and can appreciate constructive criticism. But you arent trying to teach or be constructive now are you?
Last edited by carpenternotmechanic; January 14th, 2021 at 05:58 PM.
If you think it will work, build it! It's your car, but please report back when it fails.
Your obsession with the AIR pump is strange. That little compressor will produce a few psi at a very low CFM. Only a tiny unnoticeable fraction of the 600 plus CFM at whatever psi boost you want, something like pissing in the ocean.
i must be saying something wrong. I never meant to insinuate that i would want to increase the compression ratio; but that boosting anything raises the compression. And in knowing such; would 10.5 be doable on premium perhaps with meth injection. No intercooler should be needed if carburated.
So again; would thw 307 live at 10.5 cr with meth injection and premium? Assuming the blown through carb and nominal boost? Can you calculate the cr if all things as are but with 6lbs boost? Isnt 10-10.5 doable. Not talking about ******* it constantly. Just curious.
Ok I understand your question now. 10.5:1 effective CR is easily survivable but that would give you... like 4 lbs of boost. So it might take that tired 307 from 140HP to 200 or so. You could probably run 5-6 lbs with no I/C, or 7 with an intercooler and if internals are in good shape.
So that's:
Turbo: $400
Sniper: $900 or blow through carb $900
"Other": $700 (transmission / exhaust / machine shop labor/piping)
Now you can start really throwing boost at that block. And you're $4k in instead of $2k. Now you're coming up at the limit with factory heads, or in the case of the windowed mains engines, the block limit won't be far away. Maybe you can hit 350 at the wheels. Not a bad return right?
If you're gonna spend $2k 200HP is a sad reward, if you're gonna spend $4k you may as well add another $500 for a 350 short block so you can go wild comparatively... up to 550+ whp potentially with aluminum heads or something to help prevent detonation.
Of course then you start eyeing girdles and stuff and end up with a $8k engine build after mission creep.
"Measure twice, cut once" is always good advice. I'd say study up on turbo efficiency, engine detonation, and if you wanna go wild with learning more about planning out a build work through cam profiles and their impact on dynamic compression ratio & powerband, because those are the things engine builders are thinking about, and their advice (which you'll get some of on here) is worth listening to, but you gotta cross that knowledge gap a little bit first to be able to have that discussion.
Cheers & good luck with the build.
Personally I'd say a nice 307 N/A build would end up cheaper to get you where you would get with a low boost setup. Go big or go home when it comes to boost IMO, gains are too easy NA with the Olds small blocks. First get pistons for 10:1 CR, prob get you to 160hp. Gm exhaust manifolds were garbage so headers give you 30hp, a cam can give you 40-60, intake another 10-20, that's 250hp NA. Aluminum heads or valve work on iron heads are pricey but that would give you another 50 if you were chasing it, so ~300hp that route, not too shabby. With the wagon I think a legit 250 crank hp would be a riot around town with the right gearing.
Ok I understand your question now. 10.5:1 effective CR is easily survivable but that would give you... like 4 lbs of boost. So it might take that tired 307 from 140HP to 200 or so. You could probably run 5-6 lbs with no I/C, or 7 with an intercooler and if internals are in good shape.
So that's:
Turbo: $400
Sniper: $900 or blow through carb $900
"Other": $700 (transmission / exhaust / machine shop labor/piping)
Now you can start really throwing boost at that block. And you're $4k in instead of $2k. Now you're coming up at the limit with factory heads, or in the case of the windowed mains engines, the block limit won't be far away. Maybe you can hit 350 at the wheels. Not a bad return right?
If you're gonna spend $2k 200HP is a sad reward, if you're gonna spend $4k you may as well add another $500 for a 350 short block so you can go wild comparatively... up to 550+ whp potentially with aluminum heads or something to help prevent detonation.
Of course then you start eyeing girdles and stuff and end up with a $8k engine build after mission creep.
"Measure twice, cut once" is always good advice. I'd say study up on turbo efficiency, engine detonation, and if you wanna go wild with learning more about planning out a build work through cam profiles and their impact on dynamic compression ratio & powerband, because those are the things engine builders are thinking about, and their advice (which you'll get some of on here) is worth listening to, but you gotta cross that knowledge gap a little bit first to be able to have that discussion.
Cheers & good luck with the build.
Personally I'd say a nice 307 N/A build would end up cheaper to get you where you would get with a low boost setup. Go big or go home when it comes to boost IMO, gains are too easy NA with the Olds small blocks. First get pistons for 10:1 CR, prob get you to 160hp. Gm exhaust manifolds were garbage so headers give you 30hp, a cam can give you 40-60, intake another 10-20, that's 250hp NA. Aluminum heads or valve work on iron heads are pricey but that would give you another 50 if you were chasing it, so ~300hp that route, not too shabby. With the wagon I think a legit 250 crank hp would be a riot around town with the right gearing.
thank you.
I already have the turbo amd sniper and fuel system amd transmission, but really would likely do a blowthrougb carb. Wonder what it would take to fit c6 in that wagon. Thanks again for entertaining my questions.
I really am starting to consider butting the 552 in there. It should be at least 500hp amd 600 fp of torque as it sets without boost. Would ha e to see what would need ro be done to fit a 385 series ford and a c6 into the ole cruiser. Thank you for being the only person to not wholly tru to shoot me down. I was thinking it would be around 200 hp . the carb would be pricy im sure. Seeing as how i already have moat everything but wastegates, the bb does make more sense. Thanks again.
January 13th, 2021, 05:42 PM
