Please explain boost in each gear!?!?!?

[computerGeek]

Hi again, I've been reading about Boost here, since i am about to up mine a tad, and was wondering why, to some of the answers i got from the blown moter post going around right now.

Some one please explain to us FI newbs, in lamen and detail, why in gears 1-3 12PSI is ok and in 4-5 less than 10PSI. Why is there more pressure in 4-5?

If i set 10PSI at 1-3 and 8 for 4-5 I should be OK??? I know there is no guarantee but i am just looking for ok-ish.

Some one help me understand so i don't blow out my bottom end too!!!

Thank you so much to who ever helps out!

 

[low_psi]

Its not based on pressure from the motor that kills rods in higher gears...

Boost is essentially higher compression, so when you get into a high gear that's loading the motor dramaticlly more than a lower gear, its asking for problems. Not only do you have gear based load, you've got the added load from the combustion process due to boost.

 

[BOOSTR]

I am not an automotive engineer, but our motors have a higher than normal compression ratio for turbo applications. Each psi of boost pressure added makes the overall effective compression ratio higher. It should be no mystery why motors are blowing when the effective compression ratio is exceeding 16.1:1 and higher. No stock FS block will withstand that abuse for long.

Don't up the boost unless you can afford to rebuild at some point. You have to pay to play.

 

[Swerny]

Don't up the boost unless you can afford to rebuild at some point. You have to pay to play.

Werd, and upping the boost on an otherwise stock car won't really do that much anyways, so don't bother.

 

[low_psi]

I am not an automotive engineer, but our motors have a higher than normal compression ratio for turbo applications. Each psi of boost pressure added makes the overall effective compression ratio higher.

8.5:1 compression ratios are overrated... i'm only half serious.

you just have to realize that we have a truck motor that wasn't designed for boost. Honda motors are much higher compression-wise and, like the fs-de, can only hold so much boost until you open it up and drop the CR down. our 9.1:1 isn't high compression by any means. whether or not you drop the CR down when you build a fsde depends on your peak power and power delivery goals.

 

[jeffmsp]

fyi- if u are using an mbc, chances are you will also boost higher in 4th and 5th gear than what the boost is set at in say 1-3. i guess this has something to do with the additional load from the higher gearing.

 

[jurgs01]

Get a wideband and you will see another great reason.

 

[computerGeek]

I am getting a EBC and a wide band but i am no car geek. you all talking about compression is like me talking about database optimization.

So basically at a higher lower gear (4-5) more power and load is put into the engine. Sucking in more air and fuel. Our block or bottom end cannot handle this pressure and thats why we get the holes. Correct.

still makes little sense to me. how will new pistons and rods help that? the block is still weak?

I realize for my immediate future i will not get a EBC and just upgrade SMIC and bolt-ons for now and maybe later i will get the EBC and Wideband.

The reason to get the wide band is to make sure i don't go to lean??? Is it true we are dangerously lean at around 3500 rpms

 

[KpaBap]

Think of 5th gear on your car as the highest gear on a bicycle, you can go very fast (top speed), but it is very hard to turn the pedals and you get tired quickly. Same thing in a car, 5th gear is an overdrive gear, which means that it takes something like 0.85 revolutions of the engine, to turn the tranny output shaft 1 revolution, therefore just like on your bicycle it is a lot harder for the engine to turn, and that's what load is. (not sure of exact gear ratio). In 4th gear the load is less but still more than lower gears, it is a direct gear, so 1 rev of the engine makes the output shaft turn once. Lower gears again are like lower gears on your bicycle, you can turn the pedals really easily and fast, but your top speed won't be that high.

Smack the top of the piston with nearly 1000psi of combustion pressure, while the bottom of the rod has to work extra hard to turn the crankshaft, and you can see how with repeated stress, the weakest link will eventually give up.
Even in an unboosted car, 5th gear makes the engine work extra hard, only it doesn't have to deal with an extra 150-200 degrees of intake air temperature. A turbo elevates intake air temperatures, which in turn increases peak cylinder firing pressure, pushing the engine even harder.

It is the rods that are weak, not the block. The block is only weak when a rod decides it wants to leave. But then again, even the strongest block won't help you there, since rods are made of a much stronger material than blocks, and they can just punch their way through.

 

[low_psi]

yea, when a rod snaps its like a weedwacker to grass... the crankshaft is moving very quickly and the rod just gets slung around taking out pieces of the block.

 

[yashooa]

Hi again, I've been reading about Boost here, since i am about to up mine a tad, and was wondering why, to some of the answers i got from the blown moter post going around right now.

Some one please explain to us FI newbs, in lamen and detail, why in gears 1-3 12PSI is ok and in 4-5 less than 10PSI. Why is there more pressure in 4-5?

If i set 10PSI at 1-3 and 8 for 4-5 I should be OK??? I know there is no guarantee but i am just looking for ok-ish.

Some one help me understand so i don't blow out my bottom end too!!!

Thank you so much to who ever helps out!

Well I know of three motors that went in 5th at 13PSI but they were flooring the car in 5th from a lower RPM and it was followed by several seconds of rattling detonation then of course the horrific sound of snapping rods followed by the equally horrfic sound of a grown man crying.
Basically do not boost hard in 5th. I do roll on the throttle in 5th but only with the revs up. It pulls hard and smooth but to jam that b**** I drop to third and hit 12PSI. I know in my car 12PSI has been a way better driving experience than my stock 5PSI. Not just in terms of speed but in terms of smoothness. It spools faster, and harder with my MBC in and has a nice instantaneous punch to it. I can only imagine what a PNP with a GLH exhaust would feel like

 

[Gbourdon]

The load on the engine is much greater in higher gears.

 

[wrigmatt]

Well I know of three motors that went in 5th at 13PSI but they were flooring the car in 5th from a lower RPM and it was followed by several seconds of rattling detonation then of course the horrific sound of snapping rods followed by the equally horrfic sound of a grown man crying.
Basically do not boost hard in 5th. I do roll on the throttle in 5th but only with the revs up. It pulls hard and smooth but to jam that b**** I drop to third and hit 12PSI. I know in my car 12PSI has been a way better driving experience than my stock 5PSI. Not just in terms of speed but in terms of smoothness. It spools faster, and harder with my MBC in and has a nice instantaneous punch to it. I can only imagine what a PNP with a GLH exhaust would feel like

So you guys are saying if you want to boost hard, boost hard in the first three gears only because the load on the engine is not as great. If wanting to boost hard in 4th or 5th you must keep revs up, 4000+? Either that or get an EBC and have it significantly reduce the amount of boost in the top gears. ( Lets say from 12 to 7 or 8 PSI )

 

[NRRfrogmanP5]

boost = fast go fast

 

[Yay-Boost]

Werd, and upping the boost on an otherwise stock car won't really do that much anyways, so don't bother.

I just took my boost controllers off for the winter. Even with the colder weather this car sucks stock. It just isn't as smooth without the added boost. I'm not going to dump thousands of dollars into modding this car. But the difference between a boost contoller and a FCD and stock IS night and day. Blown motors happen from people with lots of mods pushing over 250 HP and bad drivers. A few minor mods will never reach 250 HP.

 

[tracknfield423]

if i'm boosting 8-10psi in 1st-3rd should i turn the boost down more to be safe in 4th and 5th gear or just keep it at 1/2 throttle or so in those gears?

 

[Stormtrooper77]

I don't understand why people have to boost so high in 4th and 5th? How frickin' fast do you want to go?! Just don't be a dumbass and the car will last.

 

[Puckpimp71]

I don't understand why people have to boost so high in 4th and 5th? How frickin' fast do you want to go?! Just don't be a dumbass and the car will last.

(omg) (mswerd) That's the most smilies I've ever used in one post. Play it safe. Boosting in 4th and 5th, though I've done it, isn't smart to do regularly. You might win the race and prove a point to some Hyundai (like I did), but it takes its toll on your engine.

 

[Yay-Boost]

Exactly if you need to accelerate just downshift. If you are in 5th and need to accelerate fast and you can't downshift because of RPM's. WOW. I hope you've got deep pockets for those kind of speeding tickets!

 

[Yay-Boost]

Just watch your boost gauge. Going up a hill at half throttle can make your boost kick in. Watch how often an automatic downshifts. Some people drive a stick get up to 5th and just leave it there until they need to stop. Great way to break stuff.

if i'm boosting 8-10psi in 1st-3rd should i turn the boost down more to be safe in 4th and 5th gear or just keep it at 1/2 throttle or so in those gears?