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Thread: How much boost is too much boost

  1. #1
    Supporting Member Turbo Mopar Contributor A.J.'s Avatar
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    How much boost is too much boost

    I would like to start a conversation about what is a safe level of boost to run, with a proper tune of coarse. I'd like to know what people have run (25 psi+) and what you did to get there. I would like to run 30 psi in my van on my basically stock 2.4 (pistons, combustion chambers, valves, & exhaust runners are ceramic coated and I'm using ARP head studs) but is that safe? Again with the proper tune. I'm going to start tuning this week with E85 which will help me run that much (or so I think). I'd like to know what people have run, what problems you've experienced along the way, and what you did to resolve those problems and reach your goal.

  2. #2
    turbo addict
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    Re: How much boost is too much boost

    Keep going till it blows, then back it off a hair.

    I'm not sure anyone with a proper tune has found the limits of the factory pistons. Most swap to forged because they keep melting them down. I'm pretty sure the head would lift from cylinder pressure before the piston would crack.

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    Re: How much boost is too much boost

    Speaking only from what Ive seen/read on high hp builds, the three things that limit a build are mechanical parts limits (hp rating), fuel, and money. With the proper tune, and no detonation whatsoever, Im sure you *could* get 300+ easy out of stock 2.4 parts. But the cast pistons and stock rods are less resistant to detonation, and once you lose fuel, its all over.From what Ive seen, most seem to run an alky/meth injection past 25 psi, as the fuel needs at WOT would make idle rich as well as "lopey"Not saying I am the authority on high hp builds, but from all I have seen, those appear to be big reasons why people use x parts and run meth at x boost levels.

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    Supporting Member Turbo Mopar Contributor glhs727's Avatar
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    Re: How much boost is too much boost

    Quote Originally Posted by turismolover22 View Post
    Speaking only from what Ive seen/read on high hp builds, the three things that limit a build are mechanical parts limits (hp rating), fuel, and money. With the proper tune, and no detonation whatsoever, Im sure you *could* get 300+ easy out of stock 2.4 parts. But the cast pistons and stock rods are less resistant to detonation, and once you lose fuel, its all over.From what Ive seen, most seem to run an alky/meth injection past 25 psi, as the fuel needs at WOT would make idle rich as well as "lopey"Not saying I am the authority on high hp builds, but from all I have seen, those appear to be big reasons why people use x parts and run meth at x boost levels.
    From firsthand experience wth our shop having done LOTS of srt-4 motor builds. 22-24 is OK, 30 psi is a piston breaker... The rods are weak. I have seen several motors with a rod through the block..... I personally would not run a big turbo 2.4 without hbeam rods and forged pistons.
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    Supporting Member Turbo Mopar Contributor A.J.'s Avatar
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    Re: How much boost is too much boost

    Quote Originally Posted by glhs727 View Post
    From firsthand experience wth our shop having done LOTS of srt-4 motor builds. 22-24 is OK, 30 psi is a piston breaker... The rods are weak. I have seen several motors with a rod through the block..... I personally would not run a big turbo 2.4 without hbeam rods and forged pistons.
    That's the kind of information I'm looking for. Thanks.

  6. #6
    Super Moderator Turbo Mopar Staff contraption22's Avatar
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    Re: How much boost is too much boost

    I feel however that too many people use boost as a measure for power limits. It's kind of misleading. Boost is a measure of pressure. Basically a product of restriction and heat generated when trying to force air through an engine.

    The stress on rods and pistons can vary greatly if you are pushing a small turbocharger way out of it's efficiency range to register "30psi" on your boost gauge vs a larger turbo that's much more efficient and pumping much more air at the same boost gauge reading. Other factors come into play as well. Intercooler efficiency. Engine airflow capability.
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    Re: How much boost is too much boost

    I had a friend in VA that put 400 whp down on 25 pounds in a 2.4 swapped 79 omni. It was a complete stock long block with a ebay header and a 50 trim. It was ran on megasquirt. Never took it to the track to get numbers but it was fast and pretty consistent on dyno pulls on different days. It is all in the tune.
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    Re: How much boost is too much boost

    Quote Originally Posted by contraption22 View Post
    I feel however that too many people use boost as a measure for power limits. It's kind of misleading. Boost is a measure of pressure. Basically a product of restriction and heat generated when trying to force air through an engine.

    The stress on rods and pistons can vary greatly if you are pushing a small turbocharger way out of it's efficiency range to register "30psi" on your boost gauge vs a larger turbo that's much more efficient and pumping much more air at the same boost gauge reading. Other factors come into play as well. Intercooler efficiency. Engine airflow capability.
    Well said.
    Understanding that you intend to acquire the right tune for the build;
    be aware that the tune(or CAL) doesn't exist without changing several other engine components.

    To simply "get to" 30p.s.i. of boost isn't that difficult.
    However, getting there while also being reliable is the trick.
    You can get one great run(maybe) down the track with whatever your turbo will push but,
    to do this consistently, there are many-many NEEDS.
    (some of which are listed above)

    An alky kit IMHO is a NECESSITY at such boost levels.
    Not simply for the added performance but, the safer A/F mixture it'll create.
    (More dense and, "wetter"(lol)

    If I had to choose which is the greatest danger with higher boost levels,
    it would easily be the Leaning out of the A/F ratio(More air/Less fuel; which burns hotter and melts pistons, usually)
    To compensate for this, an AFPR, Proper injectors, Upgraded pump(possibly lines as well), etc.

    Hope this helps out.
    Although I intend for it to be more of a cautionary post to you my friend.
    BTW: All of the listed TM vendors are very knowledgeable on our cars and,
    have the information and connections to help tremendously with issues like this.

    Would love to see the progress.

  9. #9
    Garrett booster
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    Re: How much boost is too much boost

    to get over 25lbs.. i went the e85 route.. easier to tune etc.. but limited by availability

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    Super Moderator Turbo Mopar Staff contraption22's Avatar
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    Re: How much boost is too much boost

    Quote Originally Posted by fixit View Post
    to get over 25lbs.. i went the e85 route.. easier to tune etc.. but limited by availability
    I had considered E85 for my 2.4 build, but I am weary of the inconsistency with the E85 regularly available at pumps. It's my understanding they are pretty liberal with the claim that it is "up to 85%" ethanol". Could be 85%, might be 75%, might be 65%. What's not ethanol is 87 octane gasoline. The factory flex fuel vehicles have sensors to estimate the fuel makeup.
    Mike Marra
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  11. #11
    Supporting Member Turbo Mopar Contributor A.J.'s Avatar
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    Re: How much boost is too much boost

    Thanks for all the input. This is the conversation I was hoping for. I don't want to damage my engine so that's why I wanted input from others on what they've seen, heard, experienced, or read.

    I am not just going to turn up the boost and hope for the best. Just trying to get to 20 psi was a challenge because of a failing fuel pump. I replaced it with a larger pump (255 to 340 LPH), increased the size of the fuel lines (3/8") and wiring (10 gauge) to the pump. I have a duel ball bearing turbo (I'm still not sure the size of it/what to call it: http://www.agpturbo.com/agp-zeta-2-8-ball-bearing/) so I don't think I'm going to heat up the boost because I'm running too small a turbo. My A/W intercooler is suppose to handle 350 hp (I need 350 to crack 12's) and I think I should have followed the advice of the person in my build thread when he suggested the next larger one.

    I realize E85 is inconsistant. I'm going to be purchasing an E85 tester. I don't want to tune for E85, end up with a tank of E65, and melt something. If 25 psi on E85 can produce 400 hp on stock internals, I might just be happy with that and not have to go any higher until I upgrade the pistons and rods.

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    Garrett booster Turbo Mopar Contributor
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    Re: How much boost is too much boost

    Quote Originally Posted by contraption22 View Post
    I had considered E85 for my 2.4 build, but I am weary of the inconsistency with the E85 regularly available at pumps. It's my understanding they are pretty liberal with the claim that it is "up to 85%" ethanol". Could be 85%, might be 75%, might be 65%. What's not ethanol is 87 octane gasoline. The factory flex fuel vehicles have sensors to estimate the fuel makeup.

    My experience today with the inconsistency. I filled up at my usual station expecting the normal winter blend of E67,
    started the car and watched the Zeitronix gauge http://www.zeitronix.com/Products/Products.htm go from E67 all the way down to E24 !! With out the gauge I would have left the station and made my normal blast down the freeway ramp and probably had some serious engine damage. I did give it a quick punch and the check engine light lit up instantly. I drained the tank and refilled from another station, went back up to E65 (still had a gallon of the E24 left in the tank).

    I've noticed if I tune for 11.9-12.1 a/f with E77 ( the best I've found locally) the switch to E67 just richens it up to the mid 11's a/f.
    Sorry can't help on the cast piston stock rod question. I'm running J&E pistons and Eagle rods.

  13. #13
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: How much boost is too much boost

    Quote Originally Posted by contraption22 View Post
    I feel however that too many people use boost as a measure for power limits. It's kind of misleading. Boost is a measure of pressure. Basically a product of restriction and heat generated when trying to force air through an engine.

    The stress on rods and pistons can vary greatly if you are pushing a small turbocharger way out of it's efficiency range to register "30psi" on your boost gauge vs a larger turbo that's much more efficient and pumping much more air at the same boost gauge reading. Other factors come into play as well. Intercooler efficiency. Engine airflow capability.
    You beat me to it. I'm a fan of actually knowing when you're octane limited. I think I'm one of the few who still thinks that an EGT gauge is really helpful in finding where that point is. If you know the point at which you don't want to go beyond temp wise it's pretty easy to see when you can't pull any more timing. Pulling ign. timing will raise EGTs and you can only get so hot even at really numerically low AFRs before things get melty. IIRC I saw a 300* difference in EGTs at cruise in my old Omni by only changing from a stock 87 TII cal to an 89 MP TII timing map on the same cal. Once you get a feel for how your motor responds to the boost it's not bad at all to know approximately where you need to take the timing.

    On the mechanical front You've got to stick with people in the know just the same as the target EGT. It's great that Cindy was able to chime in with a good answer there.

  14. #14
    Supporting Member Turbo Mopar Contributor glhs727's Avatar
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    Re: How much boost is too much boost

    Quote Originally Posted by contraption22 View Post
    I had considered E85 for my 2.4 build, but I am weary of the inconsistency with the E85 regularly available at pumps. It's my understanding they are pretty liberal with the claim that it is "up to 85%" ethanol". Could be 85%, might be 75%, might be 65%. What's not ethanol is 87 octane gasoline. The factory flex fuel vehicles have sensors to estimate the fuel makeup.
    yea, I thought all e85 was the same. Then I saw a news article about gas testing and that not everything listed at the pump is really what they say! e85 can be 85%, 70% 40% and it can change weekly and from gas station to gas station.

    Larry mentioned using the e85 analyzer and if I ever go e85, I'm going to get one too
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    Supporting Member Turbo Mopar Contributor A.J.'s Avatar
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    Re: How much boost is too much boost

    Quote Originally Posted by larryB View Post
    My experience today with the inconsistency. I filled up at my usual station expecting the normal winter blend of E67,
    started the car and watched the Zeitronix gauge http://www.zeitronix.com/Products/Products.htm go from E67 all the way down to E24 !! With out the gauge I would have left the station and made my normal blast down the freeway ramp and probably had some serious engine damage. I did give it a quick punch and the check engine light lit up instantly. I drained the tank and refilled from another station, went back up to E65 (still had a gallon of the E24 left in the tank).

    I've noticed if I tune for 11.9-12.1 a/f with E77 ( the best I've found locally) the switch to E67 just richens it up to the mid 11's a/f.
    Sorry can't help on the cast piston stock rod question. I'm running J&E pistons and Eagle rods.
    I had no idea there was a gauge that measures E85. That's awesome. That little nugget of information made this thread worth it. Thanks.

  16. #16
    turbo addict Turbo Mopar Contributor
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    Re: How much boost is too much boost

    We built a 50 trim stage 3 SRT-4 about 8-9 years ago that still runs 20psi on pump premium and ran as high as 30psi on 110 octane race fuel at the track. (just to be safe)

    Full bodied, no CF and bone stock motor With BS still in there, still running original H/G to this very day. Just bolt on 50 trim kit with 750cc inj's, return line with AFPR, big FMIC and he's running an SC tune now, but it went the fastest with the Dtec.

    Fastest run was 11.3 @ 128mph

    Ran 27psi the previous year and 11.6 @ 126mph. Owner thought the was no reason to ever turn the boost any higher because he read on the internet that a 50 trim is only good to 27psi, then it just makes heat! lol (big problem with info on the net)

    So, SRT-4 2.4's are tough and it all comes down to how well you maintain your vehicle and how carefull you are tuning/ making power. We figured he was approaching 500WHP @ 30 psi with how heavy the car was.

  17. #17
    Garrett booster Turbo Mopar Contributor
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    Re: How much boost is too much boost

    Quote Originally Posted by A.J. View Post
    I had no idea there was a gauge that measures E85. That's awesome. That little nugget of information made this thread worth it. Thanks.
    A.J., I bought my gauge from the link I posted but the flex fuel sensor can be found for around $65 on ebay. Or around $80 from one of the GM parts outlets. I used the one for a Cadillac part number 13577379

  18. #18
    Supporting Member Turbo Mopar Contributor Ondonti's Avatar
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    Re: How much boost is too much boost

    I got my E85 always mixed by the same company that did all the supply in the state (to only 2 stations plus their oil company fuel station).

    If you are being responsible and have a wideband then you are not going to be surprised by bad mixes because they will make significant changes in your AFR, even at cold start when you are in open loop. You might be short on ethanol but that does not mean you will suffer disaster. The richer mixture will make up for some of the change and if your mix is really bad, it could get rich enough to completely misfire.

    Then with boost, 30psi is just 30psi restriction I agree. What I don't agree with is whether or not 30psi of hot air will kill a motor vs 30psi from a giant turbo.
    Both with proper tunes, 30psi boost from a 72mm turbo would nuke and engine much faster then a Super 60 t3 turbo at 30psi. You will be making 2.5x more power with a proper setup (stock longblock but everything else bling) on the larger turbo and that will find the mechanical limit of parts even if you don't detonate. If you detonate on either setup....sorry, the big turbo setup will also nuke the engine with much more devastation. The more HP you make, the more serious even tiny amounts of detonation are. That is because you have parts moving at or near their limit so going beyond the limit only requires a small bit of detonation (adding a shockload to parts). When you are cruising at the middle of an engines limits, detonation will be less damaging on the same shortblock.


    Also remember, the easiest/cheapest test is a graduated cylinder and some water when you are at the pump.
    Last edited by Ondonti; 03-12-2014 at 01:14 PM.
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  19. #19
    Super Moderator Turbo Mopar Staff contraption22's Avatar
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    Re: How much boost is too much boost

    Quote Originally Posted by Ondonti View Post
    I got my E85 always mixed by the same company that did all the supply in the state (to only 2 stations plus their oil company fuel station).

    If you are being responsible and have a wideband then you are not going to be surprised by bad mixes because they will make significant changes in your AFR, even at cold start when you are in open loop. You might be short on ethanol but that does not mean you will suffer disaster. The richer mixture will make up for some of the change and if your mix is really bad, it could get rich enough to completely misfire.

    Then with boost, 30psi is just 30psi restriction I agree. What I don't agree with is whether or not 30psi of hot air will kill a motor vs 30psi from a giant turbo.
    Both with proper tunes, 30psi boost from a 72mm turbo would nuke and engine much faster then a Super 60 t3 turbo at 30psi. You will be making 2.5x more power with a proper setup (stock longblock but everything else bling) on the larger turbo and that will find the mechanical limit of parts even if you don't detonate. If you detonate on either setup....sorry, the big turbo setup will also nuke the engine with much more devastation. The more HP you make, the more serious even tiny amounts of detonation are. That is because you have parts moving at or near their limit so going beyond the limit only requires a small bit of detonation (adding a shockload to parts). When you are cruising at the middle of an engines limits, detonation will be less damaging on the same shortblock.


    Also remember, the easiest/cheapest test is a graduated cylinder and some water when you are at the pump.
    Agreed on all points.

    It's cool that you can monitor your Alky content. I was not aware that such technology was available in the aftermarket, but I had pretty much stopped paying attention to E85 stuff for a while.

    Stiill sucks that you might have to retune with every fuel up, and that your car will not run consistently day to day without finding a controlled fuel source.
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  20. #20
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    Re: How much boost is too much boost

    DodgeZ's SRT-4 makes 380 whp on 93 oct, with the original AGP 50 trim kit and a BST tune, stock long block, 24 psi spike. Has been running on it for a few years now.

    On his 2.5 beater GLHS, we pushed up to 30 psi on the stock cast pistons, 150k+ junkyard long block and his own tune. Big turbo of some sort, 54 trim? 57?
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