boost and vtec

I plan on installing a turbo on my 93 prelude vtec. I have a simple tuning question-If you are boosting is it standard to disconnect the vtec solenoid, because the valves are just trick timed to draw in more air and if you are boosting you dont really need the valves to stay open longer. Also how much can you boost safely considering you already have the necessary fuel upgrades ie. fuel pump, rail, and injectors. Considering the compression ratio is so high I know most people do not want to boost over 8lbs. What do I need to do to boost 16-18lbs? Can I lower the compression ratio? Don't know I'm kinda new with turbos

actually, you'd want the valves open longer when you're boosting. on top of the upgrades you've mentioned, i would strengthen up your internals. the h22 is reknowned for having very weak ringlands and are prone to break under any additional pressure outside of stock. that's pretty much the only downside of the h22, albeit a pretty significant downside. it is harder to lower the compression on the larger H22 compared to the b series coz the cylinder walls are much thinner. the h22 is capable of handling up to 700hp, while there are b series engines puttin out 900hp.

Thanks for the heads up, but while I'm in vtec and I'm boosting lets say 12lbs I won't be running to lean? Because I should be fully boosting at 4000 rpm's well before vtec kicks in, and as soon as it does the engine wants more air, how well does the ecu pick it up. I'm not too sure how the ecu is mapped. I already have a fully rebuilt head, new valves, springs, retainers, the head is even ported and polished. I'm going to stregthen the bottom end with forged rods and pistons. I don't plan on pushing more than a little over 300hp want to keep it streetable. How much stronger is the h23 block, is it worth all that trouble? One more question How strong is my tranny, I already have a six puck clutch (not that I need it yet) but it already puts a lot of stress on it. I lied, I got one more question- How well does a front mount intercooler fit, I don't want to cut the cross member, and it looks like it will block the radiator, or is it more feasable to use a top mount and install a hood scoop, plan on using a t3/t4 turbo. Gots lots of trouble in a little space, thanks for all inputs and suggestions

You will have to cut the centre out for a front mount job or you could install it like drift has, inplace of where the airbox should be.
I prefer the front mount for looks and airflow. Its does impead the flow to the radiator slightly but nothing to major. I actually installed some ports in the front bar to direct more air to the radiator and my blower.
The factory ecu will not cope at all with boost so u will either need a piggyback job or a replacement unit depending on your needs. I still run stock injectors but have added a big bitch to come on under boost. you will also need to vary the vtec point for an improved power curve, mine is set at around 4750 rpm. I also run a stock bottom end and on 7.5 pounds it makes some 300hp (on 12 to 14 pounds a h22a should make some 400hp). The benefit with my blower is it boosts from the start.

All the best:flash:
P.S. Gen fours with 300hp run into the 13s.

It looks like all I need is 12-14lbs then, instead of a t3/t4 should I go with a t25 for faster spool up time? I plan on going with the greddy e-manage for the piggy back fuel management system, although I do not know if it connects to the vtec solenoid, if not I'll probably buy the apexi vafc. Which boost controller is the easiest to tune? Because if I use the t25 it will spool up too quick in first gear and I'll get too much wheel spin, I want to get something that is easy to program that I don't have to spend all day at the dyno trying to figure out. So if you are boosting, then vtec kicks in, does it feel like you are boosting twice? thanks for the inputs, I'm kind of a rookie

VTEC lobe design is based on NA tuning. to create more power when NA, you want more overlap at higher RPM so the intake charge helps push out the exhaust charge.

because of this overlap, boost escapes thru the motor as both sets of valves are open for a longer period of time while in VTEC, causing a pressure drop, and resulting in less fuel/air in the cylinder before the intake valves close up for compression.

with stock cams, advance the intake cam and retard the exhaust cam with adjustable cam gears to help reduce the amount of overlap in VTEC.

if you want to buy cams, Crower makes a turbo version of their stage 2 cam, with less over lap and a wilder non-VTEC lobe.

Vtec is NOT valve overlap. :smoka: Overlap is when the piston is at TDC and is begining the intake stroke. Vtec is, yes, an extra lobe, but its to keep the second valve open longer. This is to protect torque at high rpms. At such speeds, air has trouble completely filling the cylinder, but with the valve open longer, it fills the cylinder more "hearty" and gives you torque again, and we all now that torque @ rpm / 5252 is horsepower.

Now with vtec and turbo. Vtec wasnt designed for just specifically NA. It was designed for like i said to protect high end torque to make 100 hp per litre, that great thing honda does. Now even with turbo apps, vtec still helps, and it helps EVEN more because of the higher pressure inside the motor. Theres more air per cc, obviously, so the same stands, high engine speeds, valve lift duration lengthened, and more combustion.

If you guys really think that honda isnt thinking about you little boy racers turbocharging their engines, think agian. And just for example, the top performance honda motor right now is the motor that honda's R&D develops and manufactures for CART racing. The HR-1: 2.65L turbo V8. 800hp @ 15,000 rpms. Yes, they know how turbo works.

And by the way, that motor is only boosted at 7psi. hehe, pretty light if yah ask me. And thats just one more engineering feat by the great ppl at honda. :ylsuper

Originally posted by C32Bperformance
Vtec is NOT valve overlap. :smoka: Overlap is when the piston is at TDC and is begining the intake stroke. Vtec is, yes, an extra lobe, but its to keep the second valve open longer. This is to protect torque at high rpms. At such speeds, air has trouble completely filling the cylinder, but with the valve open longer, it fills the cylinder more "hearty" and gives you torque again, and we all now that torque @ rpm / 5252 is horsepower.


valve overlap is the amount of time the intake AND the exhaust valves are open at the same time. and no one said VTEC is overlap. VTEC is the use of a secondary cam lobe to increase valve lift and valve overlap at higher rpms to increase power output while maintaining lowend throttle response and fuel economy.

http://www.howstuffworks.com/camshaft.htm

read and be enligtened on camshaft operation and how valve overlap can help YOU.

Someone said it somewhere, i remember... should have quoted them.

I know what vtec is man, thanks anyways...

Oh and, that spot where the intake AND exhaust valves are open is when the piston is at TDC...

Have you ever heard the expression "Don't fix something if it ain't broke"? Excersise that will yah?

Originally posted by C32Bperformance


Now with vtec and turbo. Vtec wasnt designed for just specifically NA. It was designed for like i said to protect high end torque to make 100 hp per litre, that great thing honda does. Now even with turbo apps, vtec still helps, and it helps EVEN more because of the higher pressure inside the motor. Theres more air per cc, obviously, so the same stands, high engine speeds, valve lift duration lengthened, and more combustion.

If you guys really think that honda isnt thinking about you little boy racers turbocharging their engines, think agian. And just for example, the top performance honda motor right now is the motor that honda's R&D develops and manufactures for CART racing. The HR-1: 2.65L turbo V8. 800hp @ 15,000 rpms. Yes, they know how turbo works.



NA and Forced Induction motors are designed differently from a valve timing aspect. VTEC on the street is designed to increase performance as you said by increased valve depth and increased overlap for NA applications. the low camlobes are designed for increased streetability and fuel economy.

there are 3 lobes per cylinder on a VTEC cam... the two outside lobes are for independent valve operation... one valve opens more than the other, the other only opening enough to keep fuel from pooling on the backside of the valve. once VTEC is engaged and locks the rockers, both valves follow the middle lobe, which features increased lift (where the "left control" term comes from) and duration (where the term "variable timing" comes from) with duration in an NA application increasing overlap.

try http://www.crower.com/cat/import/honda/camshafts.shtml and look at the specs for their Stage 2 and Stage 2T cams... the turbo cams are designed for less duration on the VTEC lobe to improve Forced Induction performance.

increasing overlap in a forced induction application results in poorer performance due to less time the exhaust valve is closed, resulting in more of the intake charge being blown out the exhaust ports and less time for it to pressurise in the cylinder.

as for their CART motors, if you had a chance to see their cam specs, you'd notice the overlap is reduced for better FI performance... but no one but the Honda engineers have access to this pertinent info.

if Honda was thinking about people turbocharging their retail cars, they wouldnt use aluminum blocks, fibre reinforced metal matrix liners, unsupported cylinder sleeves, cast aluminum pistons, cast cranks, or wimpy rods. just a few more reasons to reveal to you that your statements are incorrect.

Hondas can have "wimpy rods". Since it doesnt take much boost to make good horsepower with them. (though it does take SOME kind of integrity to rev to 8000rpms and beyond in some motors) Oh and a side note: the s2000 has forged pistons. And maybe Im wrong here too, but most hondas dont have aluminum blocks. the ones that do have it, have it interweaved with another material i cant remember, which doesnt help my arguement, but the composite is just as strong as the cast iron blocks. I am curious though, why you described Vtec in its almost complete entirety, and then started talking about valve overlap hurting turbo performance.

I also want to know why the vtec lobe has to be made smaller for turbo.
In NA, none of the air is naturally flowing into the cylinder (not in comparo to turbo anyways.) So the valve being open longer only allows air more time to evenly fill the space in the cylinder. With turbo, the air is being forced into it anyways, so why not leave it open longer for that?
Also high rpms is murder on airflow, turbo or not, vtec is going to help with any kind of airflow.

And on your web site, either Im totally blind or you misread, it says clearly, low valveoverlap, high lift. Man, it said right on their, turbo apps, high lift. It said special high lift, which (I would assume, but could be wrong) means even higher than regular vtec lift.

While the valve overlap may hurt turbo performance in certain situations, it is not vtec, and vtec still helps, just the same, turbo or not. I wish someone would ackowledge that vtec has nothing to do with valve overlap.

The CART engines dont have variable timing. so the reason they have a less extreme valve lift is because it needs to make good power at a reasonably low rpm also. But wait, you didnt say anything about the lift, you said valve overlap again. My mistake! but what does it matter. Ill just talk about something slightly off topic too since I was talking about vtec and turbos, and everybody else decided to talk about valve overlap and turbos.

And final note. That howstuffworks page is the exact page I used to do a presentation on cams in my engineering class about a month ago. I guess I forgot that stuff in only a months time.

Originally posted by C32Bperformance
Hondas can have "wimpy rods". Since it doesnt take much boost to make good horsepower with them. (though it does take SOME kind of integrity to rev to 8000rpms and beyond in some motors) Oh and a side note: the s2000 has forged pistons. And maybe Im wrong here too, but most hondas dont have aluminum blocks. the ones that do have it, have it interweaved with another material i cant remember, which doesnt help my arguement, but the composite is just as strong as the cast iron blocks. I am curious though, why you described Vtec in its almost complete entirety, and then started talking about valve overlap hurting turbo performance.

I also want to know why the vtec lobe has to be made smaller for turbo.
In NA, none of the air is naturally flowing into the cylinder (not in comparo to turbo anyways.) So the valve being open longer only allows air more time to evenly fill the space in the cylinder. With turbo, the air is being forced into it anyways, so why not leave it open longer for that?
Also high rpms is murder on airflow, turbo or not, vtec is going to help with any kind of airflow.

And on your web site, either Im totally blind or you misread, it says clearly, low valveoverlap, high lift. Man, it said right on their, turbo apps, high lift. It said special high lift, which (I would assume, but could be wrong) means even higher than regular vtec lift.

While the valve overlap may hurt turbo performance in certain situations, it is not vtec, and vtec still helps, just the same, turbo or not. I wish someone would ackowledge that vtec has nothing to do with valve overlap.

The CART engines dont have variable timing. so the reason they have a less extreme valve lift is because it needs to make good power at a reasonably low rpm also. But wait, you didnt say anything about the lift, you said valve overlap again. My mistake! but what does it matter. Ill just talk about something slightly off topic too since I was talking about vtec and turbos, and everybody else decided to talk about valve overlap and turbos.

And final note. That howstuffworks page is the exact page I used to do a presentation on cams in my engineering class about a month ago. I guess I forgot that stuff in only a months time.


i never stated anything about reducing LIFT. i said reduce OVERLAP by decreasing DURATION.

the reason for such is that the intake and exhaust valves are usually open at the same time, the exh opens before the intake, on the exhaust stroke. this is so the intake charge helps to push the exhaust cahrge out completely. the exhaust valve then closes, and the intake valve is left open to fill the cylinder on the downstroke.

lengthening the overlap time allows the intake air to push more exhaust gases out and allow for a fuller charge.

on a turbo setup, this overlap will aloow the intake charge to be PUSHED out. by shortening the overlap duration, the exhaust gases will be pushed out as soon as overlap occurs, and the exhaust valves will close sooner, allowing the intake charge to be better compressed in the cylinder instead of some being pushed out the exhaust.

therefore, like i had been stating all along, on a turbo car, the cams need to be of high lift, low overlap/short duration. it results in better cylinder pressures for more efficiency.


as for VTEC being related to increased overlap, it is a TRUE statement. the VTEC lobe provides increased valve depth and duration. with increased duration comes increased overlap... increased overlap to the proper degree is one factor that allows an engine to breathe properly at higher rpm, allowing the intake charge to help push out the exhaust charge.

one more time... as you know, VTEC stands for Variable valve Timing and lift, Electronic Control.

you seem to have the "lift" part ingrained in your head with references to valve depth increase on the VTEC cam lobe... but you forget about "Variable Valve Timing", which refers to the duration change.

Ok, this is my final thought, and if you still think Im wrong, then it will have to end that way. Now, over 99% of the increase in duration happens at the END of the lift, not the beginning during overlap. The overall topic of this whole damn thing was that VTEC affects turbo performance. It does, and it does positively. Adjusting the overlap and saying you changed VTEC is like saying you rearranged your room after moving the lamp to a different table. The overlap on the cams is a universal thing, and the difference of the two in high and low stage timing and lift is so minute that its absolutely anal to say they are related. The turbo cams adjusted the overlap, your right... but I will not agree thats a change in VTEC. You must talk about these two things separately.

let me comment on this..

i'm boosting 7 psi on my b16 and when i'm accelerating, i don't hear or feel the vtec switch-over anymore. i guess it doesn't really matter anymore coz when the turbo is spooling it just keeps forcing air into the cylinder. i had the similar question before i boosted my car but after driving it into vtec while boosting, i don't feel anything anymore so i just didn't think about it anymore.

Me, either. When I stick my V-AFC on, I might just put it so high it just doesn't come on at all, or I might just leave it where it is. I'll test it with both. Also, he's going to need a something to control those bigger injectors.