well i hear that its bad to boost heavly in 5th gear, is this true?

also its really lame im making 518whp on 14.7 psi.
but i am only able to rev to 7500. now is that cause the stock b16 valve train?

 

I revved my stock b16 head to 8200 for 2 years with no problems but to answer your question, holding boost in 5th gear raises exhaust gas temperatures which in turn causes knock. In short, it is harmful to your engine to some extent and is also dangerous due to the ridiculously high speeds on the road.

 

ok i gotcha its just because i cant rev that high, i am not doing as well as id like when i do some pulls with friends.

 

This is true especially if you hold that boost level accelerating at WOT for an average of 15-30 seconds. Anymore than that and EGTs will more than likely cause detonation to the point of failure.

 

ok i belive u as i still rep the STC decal on my car from back in the day.

 

interesting.

so how would one tune a car that the customer wants to do 5th (and 6th) gear pulls on the highway all the time?

 

Bigger turbo.. have more higher end power.. get a turbo that hits peak boost at 5700 rps... and have vtack kick in at 5300....

 

get an egt gauge. i have one and lay into it in 5th on occasion.

normally i run at 700 celcius in boost, and i just watch it closely if it starts creeping back up toward 800 i shut it down. also ive got the speedo pinned by then, so its too much going on and not recommended on anything but straight, open and empty highways. at your own risk

 

Geez... 500+ whp and on a stock B16 valvetrain?
I would do something about that to prevent valve float, than to worry about 5th gear pulls...

 

yes sir,, its all tuner. haha jk.

ill post vid for ya.

 

Why would you ever need to boost in 5th gear?

 

Passing without the desire to downshift... top speed contest... who knows...

My problem with this statement is I can't see how, if the engine is tuned correctly, that boosting in 5th gear would lead to failure. EGT's will go up, as they do with any WOT pull in any gear. Holding it in 5th under boost shouldn't cause any trouble though considering the amount of air moving across the radiator and intercooler at those speeds. Keep A/F ratio good and you have additional cooling from fuel as well.

 

Give it shot.. After about 30-35 seconds, let me know how the car is the next day. ;-)

 

You might have a point, I ran 5 back to back runs vs superbikes, all 5 where 280+kph, with one at 295 on gps....

I have a ls box on fully built B20TEC with T61 turbonetics turbo, walbro 255 in-atnk and bosch 044 before rail, ran with a/f's around mid to low 11's - octane total was around 115, with relatively conservative ign timing for the oct... (so there was "abit" of a safety margin in terms of - knock thresold)

Care was taken when building the motor with new pistons - ptw... etc, as the car was setup to do 1000m sprints, tuned on a roller load dyno, with many pulls - till we were satisfied.

WOT for over 35sec, the car is fine.. and still running.

BUT, prior to that with just the walbro, at 290+ I leaned out and all pistons went egg shaped and scuffed the bores.... a/fs where close to 12...

Its still more of a risk (engine, driver and other drivers), than running 400m at a time on a strip...
The turbo loads sooner and maybe even "over loads" in the longer gears - very very hard on the motor, and would think heat build up would be drastic with more time at WOT...

 

I was simply stating my opinion in hopes of sparking an intelligent discussion on the subject. I was more or less looking for someone to point out some facts on the issue that might support the idea of "your car is going to explode if you boost in 5th gear"... I certainly hope I wouldn't need 30 seconds to hit top speed after going from 4th to 5th either.

 

Oh, I'm not doubting the power you're making. I was just warning you of valve float, because even ITR valvetrain fail at those power levels.

 

i think the amount of heat/load would overcome the air cooling comign at those highspeeds
it makes sense but facts are facts the exhaust temp us going to rise and probably wont go down but keep rising

 

I need to get an EGT gauge. Then I guess I can monitor these things..

 

mostly cuz ihave valve flote and can only rev to 7500rpm and my speds arnt that great when using a ys1. so when im chasing a 650awhp evo im gonna go. but its not all the time its just been once and thought to my self that was not good if i recall.

 

you are correct, but damn 30 seconds wide open is one hell of a long time. with the 500hp the op has he would be going about 200mph.

if you are talking about rolling into it in 5th on the highway or continuing out a 4th gear pull, i dont see a problem with it.

side note i do have a friend that toasted a piston in a built vw motor from boosting in 5th for too long, even though the car had a solid standalone tune on it

 

Hmmm... It would be very nice if someone with an EGT guage would do a few tests to really prove the theory and complete a nice write-up. If I had one I would love to do it for the sake of learning . I love seeing hard factual evidence proving a theory

 

the last time someone did that was about 4 years ago, and his test showed (as he was being towed home with melted piston 4 in an 84.5mm sleeved block) that going from 4-5th gear in WOT was just too much load and too high an EGT (over 950c) for the motor to withstand further. Wasn't too much to write up.. "I was going after a 'Busa, and going from 4th-5th on a 61mm 500whp turbocharger, and about 28 seconds later, I let off. The car started to slow down, but as I tried to control acceleration, then engine simply seized". "after further inspection, I saw that #4 piston had melted". "I now have to get a new block to with my AEM".

He has since left hondas and gone to bikes.

 

Do you know of, the group c turbo cars that ran WOT 380+kph on the chicane-less straight at lemans...? back in the 80's
Those cars ran WOT for over a good few minutes....

Yes they had huge radiator surfaces, but today we have advanced motec systems....
Would it not be possible to do even 60s at WOT?

Question is what would it take to do it?
I gotta admire people like "Bob Norwood"...

 

Sounds like his tune wasnt on par to me then lol. I have done numerous pulls from 4-5th with a stock ls vtec making 350whp with no problems at all. Just never held boost in 5th for more than a few seconds as thats all it takes to max out the tranny rpms

 

All I know is that I've only ever did one 5th gear pull. I simply ran out 4th gear @ 120mph and continued my pull in 5th gear to 140mph. I looked down and temp was rising past 3/4 so it resulted in head lift and I had to get a new head gasket and arp studs. Never again!