1HD-T Intake Manifold Modifications

[ledgend80]

ok so i have started on my intake manifold modification and i am after some ideas on how i should supply the air into the manifold.

1.should i just go directly into the centre as per standard arangement
2. should i put 2 inlets into the manifold say above no2 and no5 cylinders

what your thoughts

here are some pics

or something like this

 

[TheBigBoy]

What size pipe?

 

[ledgend80]

What size pipe?

Ontop of the manifold is 100mm and from the Intercooler will be 63mm or 2.5".

 

[TheBigBoy]

I would drop it to 75mm.

 

[wrongway around]

I went front mount for the ease of pipeing. Probably would be better side middle entrance. The old guy who guided me said stay well away from any tapperred entrances due to surgeing controlled.might be a bit high you still want to maintain your original throttle linkage setup with just an extension .I was told it was better to extend it past the original manifold a bit . I also ported everything flush under the new piece to stop any weird turbulence, which could become an is;sue with dual entrances. But I'm no expert so take it with a grain of salt .I will say I'm sure glad I took the gamble and did mine.

 

[gerg]

Other than being cheaper, physically smaller and less lag, what are the bennifits to going smaller? I dont think lag would be a problem with these fast spooling turbos. Everything I have ever read about equal cylinder filling is increased by larger plenum, unless you go int othe intricate details of port mods and directing flow. The plenum is the easiest thing to mod and get good results, bigger that is.

 

[TheBigBoy]

He will be running a large front mount. There will be some lag. No fault of the turbo as it will still be spooling extremely early (Gturbo).

A large 1 can be run if going WTA.

 

[Adam B]

I plan to work on this in a couple of weeks. The idea is to use 3" pipe and roughly double the plenum volume (excluding the runners).

I will be sticking with a central entry, probably a single 3" to match the output of my WTA cooler. What are people's thoughts on removing the center divider between cyl # 3 + 4 versus leaving whatever remains of it or even extending it up to the single 3" entry?

I also think there was a suggestion to go a little bit longer at each end, compared to the original plenum. Again, thoughts? Weird turbulence?

 

[ForealBoreal]

I plan to work on this in a couple of weeks. The idea is to use 3" pipe and roughly double the plenum volume (excluding the runners).

I will be sticking with a central entry, probably a single 3" to match the output of my WTA cooler. What are people's thoughts on removing the center divider between cyl # 3 + 4 versus leaving whatever remains of it or even extending it up to the single 3" entry?

I also think there was a suggestion to go a little bit longer at each end, compared to the original plenum. Again, thoughts? Weird turbulence?

I was thinking exactly like you were. Really pumped to see your results on this and how your performance improves.

Sent you a p.m.

 

[gerg]

The idea behind extrnding the plenum slightly past the last runner and before the first runner is due to the fact that as moving air gets closer to a surface it slows dows considerably as it eventuallt sops at there. This is also true of runners, or trumpets, that are raised abover the planum floow to intercept the fast moving air stream and avoind the stagnant air in the planum. Those neato flow simulators show this well and help put the entrances in best location to catch the most amount of air. It would work in other places, but just not as well. Considering at the stage your at it is not much work, it would be worth doing. Now i know alot of people dont take much stock on computer simulators, but short of trial and error and actually building alot and compare them, its is a valuable too. Some plenums I have seen feature offset intake runners in the plenum to further aid in putting the openings in the high flow stream. here is a sim, I lost the actual construction pic. Although hard to achieve, the taperd plenum is used to keep the incomming air speed up as each runner sucks some out so that the flow is still fast for the last runner. You can see this with heatins ducts as the vents bleed off air, the pipe gets smaller to keep the speed up. If your wondering about my spelling, i had a discectomy today and am wacked out on meds so plaease fogive me. I really think your plenum will have good results. Keep up the good work and thanks for sharing. Oh...and uhh... i really love you man.

 

[TheBigBoy]

Although that's all fantastic info. Don't forget what you are bolting it to. The mod can only really be done to the DT model. 12 valve per cylinder. 3500 rpm at average 20psi of boost. Your VE will only allow it to flow so much. If you did build an intake like that pic, maximised all piping flow, intake box/filter, snorkle, exhaust manifold, dump pipe and 3" mandrel flow through system. You would 100% know that the only remaining restriction would be the engines VE.

Personally. Instead of building the absolute best of all of these. I'd just build it as best you can and concentrate more on the intercooling. Not as much flow, but the colder air has more mass.

 

[gerg]

I would agree with you biggie. There could very well be better gains to be had for less effort than alot of these plenum tweaks. Alot of these plenums are truly the absolute best case scenario where the builder is trying to squeeze every last bit of performance out of a system. I was actually jsut trying to answer his question about plenum length and felt that the work involved would be minimal. And after 10mg pf oxycodone... i love you too man.

 

[Dougal]

The whole point of these is to improve VE.
You aren't limited by the engines VE. You are actively modifying it.

I don't see any lag problem with either a large front mount or a large plenum. This isn't a petrol suck-through setup. The system is always full of air. Pressure waves travel at around 330 metres per second.

That's pretty quick.

 

[TheBigBoy]

I would agree with you biggie. There could very well be better gains to be had for less effort than alot of these plenum tweaks. Alot of these plenums are truly the absolute best case scenario where the builder is trying to squeeze every last bit of performance out of a system. I was actually jsut trying to answer his question about plenum length and felt that the work involved would be minimal. And after 10mg pf oxycodone... i love you too man.

I've been on the oxy's before aswell. Hope all goes well for you.

 

[TheBigBoy]

The whole point of these is to improve VE.
You aren't limited by the engines VE. You are actively modifying it.

I don't see any lag problem with either a large front mount or a large plenum. This isn't a petrol suck-through setup. The system is always full of air. Pressure waves travel at around 330 metres per second.

That's pretty quick.

I like your wording. Either a large front mount or either a large plenum. Add both together. I have played with the size of my intake manifold. Up high I would agree with you. Down low - too large = noticeable lag. No matter how large your plenum is, your still governed by the int/ex runners and valve design and duration. It will go much much better with the plenum mod. But at a certain point. Increasing it further makes no difference.

 

[Dougal]

I like your wording. Either a large front mount or either a large plenum. Add both together..

No problem x No problem = No problem.
No problem + No problem = 2x No problem.

 

[TheBigBoy]

So your saying bigger is better with NO problems. At what point does this statement become void? 10,20,30 litres?

 

[Dougal]

So your saying bigger is better with NO problems. At what point does this statement become void? 10,20,30 litres?

When you can no longer fit a plenum under the bonnet.

You did see the Isuzu marine diesel with open runners? That one uses the whole inside of the boat as a plenum. Which shows there is no downside in steady state to plenum size.
So we're down to transients (lag) which IMO is influenced pretty much zilch by the volume to pressurise.
Turbos don't have any problem pushing volume. It's volume x pressure which makes them work. Another 100 litres is not measurable provided you haven't ruined something else in the process.

 

[gerg]

I havent done the math, but the overall plenum volume must only a 1/5 or 1/4 when compared to all of the piping and intercooler volume. I honestly dont think you would see much lag at all. What dougal said about a throttled engine will cause lag as it only responds to a drop in post throttle pressure and larger volume will take longer to drop. This is something I have considered for my 3B as it too is throttled, as well as 2hs. some of these fast spooling turbos making over 15lbs at 1500 rpm will surely make up for the extra volume. I could see with a stock turbo this being a problem but the bennifits must surely outweigh the drawbacks I would gladly trade a bit of throttle response for more torque any day.

 

[TheBigBoy]

Have to disagree. The lag is noticeable! When I drop my plenum size back to stock - 200rpm(ish) drop in spool up.