custom intake manifold

[karl]

I'm making a custom (FFIM) front facing intake manifold and have a question for any experts. I'm concerned about the distance the throttle body is located from the runners. Will this cause anything like throttle lag?? It's going into my 240z powered toyota 7MGTE turbo. I mainly am doing this to try and cut down on turbo lag by shortening the IC piping to IMG]http://i490.photobucket.com/albums/rr262/Karltritr6/Datsun4131.jpg[/img]the intercooler and cosmetically as well.

Edited December 7, 2009 by karl
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[jc052685]

And how exacly it that going to cut down on lag?

[karl]

Too much internal flow volume can affect turbo lag. Also longer piping is more likely to gain unwanted thermal energy. The shortest piping should always be from the intercooler to the throttle body. (Street Turbocharging by Mark Warner). The current piping on the car runs over the top of the engine and turbo, the piping will pick up heat from these sources. I'm not saying my lag is terrible, I would just like it to be a little better for auto cross. I rebuilt my 57trim ct26, It had a clipped turbine wheel on it which I did not like so I put an unclipped wheel and it made a significant low end difference. My car is a light weight 70 240z with 400hp, it's very fast, I just like to keep on improving anything that I can. I have a garage full of fabrication tools, I've been doing this stuff all my life and i'm simi retired, it's like a dream come true.

[RTz]

Karl,

 

The closer the throttle plate is to the intake valve, the greater potential for throttle response. The opposite is also true. Probably few 'sensitive' people would notice the difference between stock and what you have, though.

[karl]

Ron,

 

 

Thank you just thought I'd ask. If it doesn't work well enough i'll just cut it and reweld. You know It's not easy owning a 7MGTE, it seems some people want to tell you what junk it is so you have to make sure their always eaten the peebles off your rear tires.

[Tony D]

My bet is any 'lag' you are experiencing from that turbo setup is a result of asking too much from the combination.

 

Lag is defined as the time from WOT to Full Boost Pessure.

 

In EVERY case I have investigated in the last 10 years, EVERY one of them had no discernable lag. Less than a fraction of a second. Many cases the time from WOT to Full Boost was less time than 0.2 of a second (datalogging).

 

EVERY case of people complaining it took 2-3 seconds for 'full boost to come on' were from driving the car in the wrong gear for the speed. If you are not driving the car correctly (that meaning you are keeping the rpms below boost threshold) the car WILL NOT make full boost until that rpm point where boost threshold is met.

 

Above that point, boost is instantaneous.

 

This is no different than driving a cammed car: you have to drive it right for it to perform right. Nobody floors a 3.2 at 700 rpms and expects it to rocket away from the stop sign. For some reason when they add a turbo, they expect it to!

 

I'm prone to agree the placement of the throttle plate will have far more effect on how a change in throttle position will 'feel' than ANY affect it will have on 'lag'.

 

If you take the compressor output under wastegate closed positions, and calculate that output in liters per second, then compare it with the actual volume of ALL your piping, including the intercooler you will see that it will not take seconds to fill up the piping. It won't even take fractions of seconds. Realistically, with higher flowing turbos, the LAST thing they need to worry about it 'lag' but insufficient piping volume as the pressure rises so fast from the high efficiency cut wheels today, that you can actually surge because the pressure rises so fast!

 

If you are talking about 'low end' differences, my bet is that you aren't driving the car properly for the turbo applied to it. Many people with larger turbos have found that improperly driving the car (WOT before boost threshold) gives them more modulation capability as they can feather the throttle as boost comes on...they refer to it as 'using the lag to their advantage' but that's not what they are doing. There is no lag. They are simply using the most inefficient part of the flow map to give them subpar power they can control. Most turbo cars are a case study in misapplications of wheels, gears, and in most cases turbos. I'm thinking where you have the T/B won't make any difference in practical terms of 'lag reduction'. It will, however have an impact on how the throttle movement is perceived by the occupants of the vehicle. The turbo will do what it will do, regardless of the placement of the component. And the difference in 'lag' you can find simply by comparing the plenum volume before and after the proposed modifications. If you aren't shortening the intercooler piping since you've already changed that configuration (and from the looks of it, you are just moving where the valve is in a relatively straight run of piping) he volume will remain the same regardless of where the valve is placed.

 

In any case, the volume difference, compared to L/S of turbo output will give you exactly the time change you can expect to experience with the change. Be ready to work to the right of the decimal point to some extent, most turbos make several (10's) of liters a second, and most piping is less than 10 liters meaning 1/3rd of a second under proper conditions is the 'worst case'.

 

Having a properly sized compressor bypass/blowoff valve will keep pressure in the actual piping somewhat higher than atmostpheric on drop throttle, so in effect you will only be partially pressurizing the piping, with the downstream side of the manifold being the only portion requiring true 'repressurization'. And this is what was being referred to as the perception of response. All you really will be doing is repressurizing the manifold.This will be mere fractions of a 1/10th of a second. Even at 4 Liters!