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Thread: Boost limiters

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    Boost limiters

    In case you haven't heard of a boost limiter valve, it's a simple adjustable pressure valve that bleeds pressure above whatever you adjust it to. It's not a blow-off valve, a waste-gate, or a boost controller, because it opens on pressure instead of vacuum, so it holds the pressure at a preset level (once it gets up that high). Here's one: http://www.928motorsports.com/parts/...mitervalve.php

    Combined with a smaller supercharger pulley, it allows you to increase boost at lower RPMs without overboosting your motor on the top end.

    As an example, take the stock Vortech kit on a stock 5.9. At engine redline of 5200 the impeller is only spinning 40,250 RPM - almost 10,000 RPM below the impeller's 50,000 redline, but still producing over 12 lbs of boost... but at 2300 RPM the impeller is only spinning 17,800 RPM, and only 1.7 lbs of boost - barely enough to feel.

    Now, install a 2.7" supercharger pulley: at 5200 the impeller is at 46,500, and about 16.5 lbs boost - too much for a stock motor compression, but at 2300 the impeller is up to 20,500 and 3.7 lbs of boost - more than twice as much as the stock pulley... but what would you do with the excessive 16.5 lbs of boost at redline? - you simply adjust the limiter valve to something more appropriate for a stock motor, 10 PSI for example. With this setup, you hit 10 PSI at about 4100 RPM, and hold 10 PSI to redline.

    Some of the benefit here is obvious - noticeable boost (more than double) at the stock torque converter's stall speed (can you say "launch"?), reach your desired peak boost about 600 RPM earlier, and not be afraid of excessive boost closer to redline... less obvious is better fuel economy (due to more torque at lower RPM, and the impeller at efficient RPM more), the ability to manually crank the boost down in case you're loaning your Jeep to a teenager, and you can crank it up to max boost on race day if your motor is set up to handle it.

    Obviously, there is a cost to this benefit, but it's a small one: once RPMs exceed your preset limited boost level, the charger continues to compress increasing volumes of air to the same pressure, but the excess air is vented - so you're using power to compress air that's wasted. But unlike a blowoff valve, the waste air increases gradually, so the amount of wasted air isn't much until higher RPM. There is extremely little temperature increase because almost all the energy put into compressing the wasted air is vented with that air when it's wasted. Also, it takes less power to compress a given volume of air to 10 psi than to a higher pressure, so the compressor isn't working as hard as it would without the limiter... a side benefit to this is pulley slip would be less likely since peak load is less.

    It's one extra tool to dial in your supercharger setup. If you think about what RPM range our 5.9 trucks spend most of their time it makes a lot of sense. I want one... what do you guys think?

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    Eddie MonaDeRio's Avatar
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    Does it replace the BOV ?
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    Quote Originally Posted by MonaDeRio View Post
    Does it replace the BOV ?
    No... the BOV activates with vacuum from throttle lift, so cuts off the surge before it happens. I think the boost limiter would open too late as a reaction to the surge and vent to little, so you still NEED the BOV or bypass- the limiter is optional. Each performs a different function for a different purpose.

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    Eddie MonaDeRio's Avatar
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    I got it. They recommend to install it near the BOV. Adjustment of 10 or 12 psi will be fine for me. I had 2.5"pulley before and car ran much better on low rpm than with 2.7" pulley now. Could be a good thing but the price is killing me.

    http://www.ebay.com/itm/Universal-Ad...f03f7d&vxp=mtr
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    Quote Originally Posted by MonaDeRio View Post
    I got it. They recommend to install it near the BOV. Adjustment of 10 or 12 psi will be fine for me. I had 2.5"pulley before and car ran much better on low rpm than with 2.7" pulley now. Could be a good thing but the price is killing me.

    http://www.ebay.com/itm/Universal-Ad...f03f7d&vxp=mtr
    Yeah, that price is ridiculous... but it's 'designed' for Porsches. It's a ball in a tube with a spring preloaded by an adjustable threaded bit. It couldn't be simpler to engineer or make, and has about $5 in materials. There has to be another one out there and I just haven't found it yet. If we can't find one, maybe I'll make my own- it would just take a couple hours on my manual machines, and calculating the spring specs and ball size is a piece of cake. Maybe we could do a small group production run if there was enough interest, like Sandy did for the brackets.

    I too saw the 2.5" 7 rib pulley- I'd love to go there, and I'm wondering if the limiter would make it practical. It would hit 12lbs boost at about 4100 RPM, 10lbs at 3600, 8 at 3400, 6 at 3100(!), and should be safe for the impeller (unless you have a high-revving motor) because it wouldn't exceed 50k RPM until the motor hit 5200 - the down-side is you would be dumping a lot of air out of that limiter valve on the top end. I don't know about you, but I rarely get over 4700- I've probably only hit 5000 once or twice... though it might happen more after the SC install and SCT tune adjusts shift point.

    Did you have slippage problems with the 2.5" pulley? At what RPM did you get slippage?

    I'm also thinking about getting a larger idler pulley, and making a mounting bracket to move the idler up to increase wrap on the power pulley. You can also get any pulley coated with a high grip coating for $85 at that same 928 site http://www.928motorsports.com/parts/...ey_coating.php I think it's possible to run the 2.5" reliably, even if it's not a good idea. I still haven't calculated how much power the compressor would rob on wasted air at the top end, so that's a question... but for normal driving the 2.5" would be great.

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    Eddie MonaDeRio's Avatar
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    The last time I had the cylinder head gaskets blown with the 2.5" pulley and WOT. The boost was around 15 psi I guess. I had a slippage of the belt sometimes with 2.5" pulley when I hit the gas pedal fast but it didn't harm the performance. If I'll go with that valve I put the 2.5" pulley back and add the extra tensioner pulley between the blower and the alternator. I'm working on the custom bracket for the tensioner pulley now.

    Something like that

    https://www.gtmotorsports.com/product.php?productid=16475

    http://g35driver.com/forums/forced-i...parison-3.html

    http://rennlist.com/forums/928-forum/450916-new-product-boost-limiter-valve.html

    just $9 each lol
    http://www.grainger.com/product/CDI-...ES-Valve-6D915

    another one http://www.mcmaster.com/#48935k45/=vdstv5
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    I'm looking forward to seeing where and how you mount that extra pulley (I think you meant idler, not tensioner). My plan was to just move the existing idler that normally mounts straight onto the compressor. I was originally thinking of getting a bigger pulley too, but now that I think about it a smaller pulley moved farther up could give more wrap. I could mount a small one up above the oil inlet, using the top mounting plate bolt hole (the one that doesn't get used), and reinforce it with another bracket mounted to the face of the compressor. I think you could just about maximize wrap this way.

    When you blew your head gasket, did you replace it with a different type? I'm thinking about new heads when I do my install, so need to start thinking about gaskets too. Any thoughts?

    I'm pretty excited about this pulley/valve direction - I think it's the ticket for me... I'm just not going to give those guys $190 for a $25 valve! (might give 'em $85 for the pulley treatment though).

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    Eddie MonaDeRio's Avatar
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    Yes I meant an adjustable idler pulley. I don't know what kind of gaskets were blown but I put Fel-Pro 519 SD then. The best choice is Cometic gaskets but you have to shave block and cylinder heads before installing them.
    You can also use Fel-Pro 1008 LA gaskets. I saw much good reviews about them. I don't trust that pulley treatment because under a big pressure it could grind the belt. IMHO.
    Last edited by MonaDeRio; 01-08-2015 at 05:56 PM.
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    Quote Originally Posted by MonaDeRio View Post
    Yes I meant an adjustable idler pulley. I don't know what kind of gaskets were blown but I put Fel-Pro 519 SD then. The best choice is Cometic gaskets but you have to shave block and cylinder heads before installing them.
    You can also use Fel-Pro 1008 LA gaskets. I saw much good reviews about them. I don't trust that pulley treatment because under a big pressure it could grind the belt. IMHO.
    Yeah, that makes sense. I guess the best thing to do is to wrap the pulley as much as possible and see if that's enough first. That coating might be best for race use... depends on if it's rough like sandpaper, or just textured.
    I hadn't thought of making the idler adjustable, but that might come in handy for maximizing tension, or even using different pulleys with the same belt. Please post up photos when you do yours - it's going to be a couple months at least before I get that far.
    Thanks for the gasket feedback- I'll research.

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    RallyJeep GO
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    This boost limiter valve sounds exactly like a wastegate mounted to the charge pipe (instead of the exhaust as it would be in a turbo application).
    1998 ZJ 5.9 Limited - Deep Slate
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    Quote Originally Posted by comptiger5000 View Post
    This boost limiter valve sounds exactly like a wastegate mounted to the charge pipe (instead of the exhaust as it would be in a turbo application).
    I don't know much about turbos, but isn't a wastegate controlled externally by attaching the control side to to some pressure source? I think it's more like a blow-off valve in reverse (reacts to pressure instead of vaccum)...
    The boost limiter is much simpler (it's the simplest valve type), activated by the same pressure it's relieving, so no external control is used- only spring pressure. It also doesn't need to vent as much gasses since it's installed before combustion, so it's smaller.

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    Eddie MonaDeRio's Avatar
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    I bought a pressure relief valve here http://www.mcmaster.com/#48935k45/=ve7rf2 . I'll get it in a few days then I will make a small modification to it (I'll drill 6 holes just like the op's link) and it will just bolt onto my discharge tube with existing 3/4" npt hole.


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    sfn's lonely vajay jay
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    Quote Originally Posted by carlmon View Post
    I don't know much about turbos, but isn't a wastegate controlled externally by attaching the control side to to some pressure source? I think it's more like a blow-off valve in reverse (reacts to pressure instead of vaccum)...
    The boost limiter is much simpler (it's the simplest valve type), activated by the same pressure it's relieving, so no external control is used- only spring pressure. It also doesn't need to vent as much gasses since it's installed before combustion, so it's smaller.
    It can be controlled internally or externally depending on how the turbine housing is set up. With turbochargers (stock) they have a wastegate flapper on the hotside of the turbo, and yes, it relieves pressure once it reaches whatever the wastegate arm/spring is set for. Usually, tension is around 7-8psi and you can upgrade the arm/spring to as much as 14psi. Same method applies to external wastegates.
    - Sandy

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    Eddie MonaDeRio's Avatar
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    The wastegates do the same job as a valve limiter from McMaster but the price of the genuine wastegate is too high.

    Avarage price http://www.ebay.com/itm/TiAL-MVR-44M...5b11fd&vxp=mtr
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    sfn's lonely vajay jay
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    ^ That is far from "average" when it comes to this particular set up. You would not need a 44mm kit. Even the 38mm would be too much. You also have to look at quality, and design. TiAL is like the Ferrari of forced induction components as they can be water cooled, give you the option of working with v-band, and are billet. I would say "average" for a genuine EWG would be more along the lines of $100-250 (non v-band), and knockoffs even cheaper.
    Last edited by BoostinChick; 01-09-2015 at 04:49 PM.
    - Sandy

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    Eddie MonaDeRio's Avatar
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    I checked a lot of reviews about wastegates on the different forums and much people are complaining about failure of the wastegates that's why many of them using that pretty simple valve limiter. . But I'm not an expert in this field. Just my opinion.
    I'll set my valve to 10 PSI and put into the discharge tube along with the Vortech Max Flow BOV..and put 2.5" pulley. Maybe this small valve will save my engine someday.
    SCT X3. Custom cam. Crane gold race roller rockers. Fully ported 2.02 R/T heads.. Mike Leach Headers. Full 3" cat back exhaust. Custom full return fuel system. Aeromotive 340 in-tank fuel pump. Aeromotive dual port adjustable fuel regulator. Holley 2 x 52mm TB. High stall torque converter 2800 . 24# Bosch Ford Racing injectors. MSD ignition box and coil.

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    Seems like most agree the concept is a good idea for street... the only issue remaining is what to use to do the job. Regardless of cost, I would rather have the simplest version that doesn't depend on a diaphragm and connecting hose to push the valve open. It just doesn't get any simpler than a ball-and-spring valve - if it fails it will vent, rather than failing to vent. I also think it will do better at metering and maintaining consistent pressure.

    Eddie- please let us know what that McMaster part looks like when you tear it apart. I hope your idea for cross drilling it works with that valve... just the fact that it vents from the top makes me wonder if there's something other than a simple ball in there.

    I also hope it's big enough to vent enough. The bigger the ball, the more accurate the pressure control, and more venting capacity. A quick calculation came up with about 220 cubic feet per minute at 12 psi would have to be vented at 5000 RPM with the 2.5" pulley. I'm way too tired to figure out the area of opening you would need to vent that much, but it sounds like a lot. It would sure be tough to beat that price if it works out though!

    BTW- You'll want to swap that Buna-N seal for Viton or Teflon, due to the temperatures in the charge tube. Buna-N is only recommended to 250 degrees, and it won't last. I like the idea of the harder and lower friction teflon, but Viton should be just fine, and easier to get a good seal.

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    sfn's lonely vajay jay
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    Quote Originally Posted by MonaDeRio View Post
    I checked a lot of reviews about wastegates on the different forums and much people are complaining about failure of the wastegates that's why many of them using that pretty simple valve limiter. . But I'm not an expert in this field. Just my opinion.
    I'll set my valve to 10 PSI and put into the discharge tube along with the Vortech Max Flow BOV..and put 2.5" pulley. Maybe this small valve will save my engine someday.
    I have the MVS 38mm TiAL on my other project car. No issues or failures, but I guess that is why they make them serviceable with seals, diaphragm, etc. With turbocharged applications boost is controlled by a manual/electronic boost controller that hangs off the wastegate usually to keep consistent pressure.
    - Sandy

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    Eddie MonaDeRio's Avatar
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    Quote Originally Posted by carlmon View Post
    Seems like most agree the concept is a good idea for street... the only issue remaining is what to use to do the job. Regardless of cost, I would rather have the simplest version that doesn't depend on a diaphragm and connecting hose to push the valve open. It just doesn't get any simpler than a ball-and-spring valve - if it fails it will vent, rather than failing to vent. I also think it will do better at metering and maintaining consistent pressure.

    Eddie- please let us know what that McMaster part looks like when you tear it apart. I hope your idea for cross drilling it works with that valve... just the fact that it vents from the top makes me wonder if there's something other than a simple ball in there.

    I also hope it's big enough to vent enough. The bigger the ball, the more accurate the pressure control, and more venting capacity. A quick calculation came up with about 220 cubic feet per minute at 12 psi would have to be vented at 5000 RPM with the 2.5" pulley. I'm way too tired to figure out the area of opening you would need to vent that much, but it sounds like a lot. It would sure be tough to beat that price if it works out though!

    BTW- You'll want to swap that Buna-N seal for Viton or Teflon, due to the temperatures in the charge tube. Buna-N is only recommended to 250 degrees, and it won't last. I like the idea of the harder and lower friction teflon, but Viton should be just fine, and easier to get a good seal.
    I thought about the high level heat that hit the valve because the valve will be located above the header but I have the option to relocate it to a cool place. Just I'll install the adapter 3/4" npt to 3/4" barb for the hose.
    Anyway I'll try to play with the limiter valve to improve it for the high heat. To use the Viton is a good idea. Tnx.

    The 6 holes around the limiter is a good for the faster air pressure relieve.
    I'll take the limiter apart and then place the picture on my project thread.
    SCT X3. Custom cam. Crane gold race roller rockers. Fully ported 2.02 R/T heads.. Mike Leach Headers. Full 3" cat back exhaust. Custom full return fuel system. Aeromotive 340 in-tank fuel pump. Aeromotive dual port adjustable fuel regulator. Holley 2 x 52mm TB. High stall torque converter 2800 . 24# Bosch Ford Racing injectors. MSD ignition box and coil.

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    Quote Originally Posted by BoostinChick View Post
    I have the MVS 38mm TiAL on my other project car. No issues or failures, but I guess that is why they make them serviceable with seals, diaphragm, etc. With turbocharged applications boost is controlled by a manual/electronic boost controller that hangs off the wastegate usually to keep consistent pressure.
    I understand turbos a little better now... they limit boost by diverting exhaust pressure from the drive impeller so there's less power wasted in overboost conditions, and it's an advantage superchargers can't have unless we had a variable clutch or variable drive ratio.
    We only have three options: (A) drive RPM limit (bigger pulley), (B) pressure limit valve, or (C) intake CFM limiter.
    A: as discussed above, unless the motor is capable of handling the designed maximum boost (20lbs), we have to underdrive the compressor significantly, making boost at lower RPM insignificant.
    B: balance a combination of boost waste with smaller pulley size to get a better low-mid boost and torque curve, at the cost of wasting some amount of power once the pressure valve starts to open.
    C: this is effectively a HP limiter, which works by restricting the intake before the compressor to cap CFM, and boost is limited without wasted power. The drawback is boost actually drops when the restrictor takes effect instead of maintaining pressure. It's normally only used when required by racing rules.

    Just did some more OCD calculations:
    The power lost from compressing and venting excess pressure with a 2.5" pulley limited to 12psi at 5000 RPM is about 4.3HP, for 10lbs it's 7.9HP. This calculation assumes 220 CFM wasted, and accounts for 35% compressor efficiency loss (the upper loss range for V-1S). Keep in mind that at 4100 RPM and 12psi the loss is ZERO, and it builds gradually to that 4.3HP max. Also keep in mind that if you don't have a 2.5" pulley and pressure limiter you're making LESS power to just under 5000 RPM, because your boost hasn't hit 12psi yet. Of course these numbers vary depending on power and other variables, but it's pretty obvious that this loss would be more than made up for in performance under the boost limit for street use, AND racing applications.

    Just think of the benefits of earlier boost off the line, and maintaining boost after shifting. The only time you will lose anything at all in a quarter mile run is if you make it to top gear at over 4950 RPM. 1st gear to 2nd gear RPM drops from 5000 to 3000, and the other shifts are about 3500... on every shift you're benefiting from higher boost and more power 97% of the time!

    B is the correct answer!

    - - - Updated - - -

    Quote Originally Posted by MonaDeRio View Post
    I thought about the high level heat that hit the valve because the valve will be located above the header but I have the option to relocate it to a cool place. Just I'll install the adapter 3/4" npt to 3/4" barb for the hose.
    Anyway I'll try to play with the limiter valve to improve it for the high heat. To use the Viton is a good idea. Tnx.

    The 6 holes around the limiter is a good for the faster air pressure relieve.
    I'll take the limiter apart and then place the picture on my project thread.
    You probably already know, but the header isn't the only heat concern- discharge tube air can get up to 280 degrees, and Buna-N is only rated to 250. It would probably last a while in reality, but why bother doing it later if you're already tearing it apart to drill.

    Looking forward to your pics!

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    RallyJeep GO
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    I'm really glad this thread has come around, as I've been considering a wastegated centrifugal blower setup for my ZJ for a while now. Getting full boost earlier definitely makes up for the losses at high rpm from the wasted air. Makes it a lot more fun on the street too, as you don't have to wind it all the way out to get decent boost.
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    Quote Originally Posted by MonaDeRio View Post
    I bought a pressure relief valve here http://www.mcmaster.com/#48935k45/=ve7rf2 . I'll get it in a few days then I will make a small modification to it (I'll drill 6 holes just like the op's link) and it will just bolt onto my discharge tube with existing 3/4" npt hole.
    Eddie- when you try this valve keep an eye on your boost gauge. I finally got around to calculating flow through apertures, and at 12psi through an ideal 3/4" aperture, the most you could vent is about 200 CFM... but inside that valve is probably less than 3/4", and far less than ideal shape, so 125-150 CFM is more realistic. This would not be enough to hold it to 12psi at the top end - though it would obviously hold pressure down, I would guess it will max out about 14psi (better than 19psi though!).
    If you don't like what you see on the boost gauge, you could always add a second McMaster valve, and that should be enough.

    I calculated that a 1" aperture in a well designed valve should be adequate to hold it to 12psi in a 400 HP motor.

    The new larger valve from 928 Motorsports has a 1.5" NPT mount, and the ball in the valve also appears to be around 1.5" - and would vent more than 4 times the air of a 3/4" valve. The original smaller one appears to have been 1", which would be enough if they still made it. I think I'll call them to see if they have any of the smaller one left, or make my own 1" version.

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    Eddie MonaDeRio's Avatar
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    Probably 928 motosports had complaints about 1" NPT valves and made a bigger one with 1.5" inlet. In my particular case this small 3/4" NPT valve will be enough to prevent damage of the cylinder gaskets. . btw my Jeep is a daily driver and I do no more than 4000 rpm. I even don't need to put this valve but who knows.
    SCT X3. Custom cam. Crane gold race roller rockers. Fully ported 2.02 R/T heads.. Mike Leach Headers. Full 3" cat back exhaust. Custom full return fuel system. Aeromotive 340 in-tank fuel pump. Aeromotive dual port adjustable fuel regulator. Holley 2 x 52mm TB. High stall torque converter 2800 . 24# Bosch Ford Racing injectors. MSD ignition box and coil.

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  24. #24
    Member
    Join Date
    Nov 2014
    Location
    Seattle
    Posts
    710
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    Quote Originally Posted by MonaDeRio View Post
    Probably 928 motosports had complaints about 1" NPT valves and made a bigger one with 1.5" inlet. In my particular case this small 3/4" NPT valve will be enough to prevent damage of the cylinder gaskets. . btw my Jeep is a daily driver and I do no more than 4000 rpm. I even don't need to put this valve but who knows.
    Some protection is better than none- could still be the difference in something broke or not broke. I had to say something cuz if I didn't and your motor blew I'd feel real bad for several seconds.

  25. #25
    Eddie MonaDeRio's Avatar
    Join Date
    Oct 2010
    Location
    Brooklyn, NY
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    1,957
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    I got the valve today and here are some pix. I took it apart and I don't get how it work. Can anyone explain it to me? I thought the valve should be near inlet then spring. 928 motosports has inlet- ball valve - spring-6 holes outlet. I have inlet-spring-valve-outlet.
    Is something wrong?
    Attached Images Attached Images
    SCT X3. Custom cam. Crane gold race roller rockers. Fully ported 2.02 R/T heads.. Mike Leach Headers. Full 3" cat back exhaust. Custom full return fuel system. Aeromotive 340 in-tank fuel pump. Aeromotive dual port adjustable fuel regulator. Holley 2 x 52mm TB. High stall torque converter 2800 . 24# Bosch Ford Racing injectors. MSD ignition box and coil.

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