75mm TB on a 3.4 DOHC-too big?

[HayesPerformance]

I CNC'd my TB to 72mm, And YES, it can be done but ONLY if your calculations are correct or your screwed.

On my set up I love it. When I get a day to breath I'll put on the 96'+ intake I have. Most go with a 75mm MAX on 4 cyc's , I6's and V6's...

[no_doz]

im just gonna wait to do any modification to the tb for now, since its going in a lighter vehicle i dont have to push as much power to take my buddy's 370z here in a few months, im going to hold off on the m112 & put a m90 on this engine with a custom intake made/modified by a machinist friend and myself, what tb should i go with on that if id eventually like to push 350 horse? (i was originally shooting for 400-420, but with the datsun weighing 500lbs less that the lumina i can push 300 with the LQ1/m90 & stomp him, maybe before he gets back i can get one of those IC kits for it with a bit of modification & have it pushing 350, altho thats not necessary for the time being.

what size tb should i go with if id like to push 350hp eventually but for now am shooting for 300, and does anyone know of any other companies that sell IC's that go between the roots blower & intake for a bit less than the $600 for the zzp kit?

[bszopi]

Get the engine in the car before you start worrying about any of this other crap. I have a feeling you are going to have a hard enough time getting just the stock engine installed, up and running. If you can't do that, no reason to spend the money for everything else.

[no_doz]

understandable, and thats what im doing first, once its in the car & i can drive it down the road, then im getting the m90-wideband-tgp chip-& etc...

what fuel pump should i get for this since i intend to go boosted later on?

[robertisaar]

warlboro 255...

[no_doz]

thats what i figured but i wasnt sure if those will accommodate 350hp

[OldSkoolGP]

I'm running a Northstar 75mm TB and it works fine. Very good low end and cruising power and all the top end you'll ever need. I think if you've P & Ped your heads, and you opened up your exhaust system with bigger piping or whatever, you need to increase incoming air. 70mm is a good start, 65mm is not enough. The factory TB is 64mm.

[jmgtp]

Mine is also a northstar 75mm. I have p&p heads, full exhaust, etc and it works great in conjunction with those things. You wouldn't want it on a stock motor, def need to have a motor that can use that air.

The mouth of the tb is 4" and up until last week I had a rubber reducer on it so I could use my old 3" intake. I just put a 4" filter right on the tb and the difference is incredible. I had no idea how much the 3" was choking the top end. I don't think it was the lack of flow but rather having a low pressure area right before the tb plate caused by the reducer. With all the mods, namely heads, exhaust and modded plenum it feels like it wants to rev higher than the ECM 7150 that the ECM allows. I shimmed the valve springs so I do think they float, I bet it could rev meaningfully to 7300-7400 if the ECM let me.

[OldSkoolGP]

I made an itake out of PCV pipe that matches the same 4" entry to the TB. I think the reduction in size down to 3" gives the air a bit more velocity on the way to tne engine so you can get that little extra bit of air.

[jmgtp]

I think my problem was having a 3" intake filter/tube that went to a 4" TB mouth and then back down to 3" at the TB plate. My theory is that going from small tube to then to a larger area right before the TB made for a low pressure area right in front of the TB plate. Either way, with the 4" intake on it, it runs SO much stronger up top - and that is with a filter right on the TB eating hot engine air... I'm waiting on the tubes to get delivered to make it a CAI - I ended up cutting out a good porting of the battery tray (its in the trunk) and I'm going to route the intake down there.

[robertisaar]

I think my problem was having a 3" intake filter/tube that went to a 4" TB mouth and then back down to 3" at the TB plate.

reading maximum boost, that is a very horrible thing to do, really screws with the airflow

[no_doz]

im not sure-but isnt choking it off like that defeating the purpose of putting on the bigger tb? its moving the location of the restriction a little bit & making the overall airflow not consistent throughout-probably creating low pressure spots & such (not sure-ask someone who actually knows a good deal about flow).

is my logic incorrect?

[jmgtp]

Yes we established this a few posts ago. I wouldn't describe it as choking the mot since the tb plate and intake size are both 3" so they should flow about same air. The proble
was the mouth of the tb is bell shaped to 4" and using the reducer probably created a low pressure area and turbulence right before the tb plate.

[SofaKingWeToddDid]

man, didnt you guys ever make a bong in highschool? this is just like that, if you have some little virgin lung kid you cant have a HUGE stem on the bowl, otherwise it gets too much flow and the kid chokes and coughs, but the seasoned smoker on too small of a bowl stem doesnt get a big enough hit. it all relates i swear.