Got a stock k20a2, will be going in a rwd car with 3.73’s and possibly 4.10’s with a 6 speed cd009, breather mods (intake manifold throttle body, piping etc)

looking at the gtx3076r and wondering which AR should I get for fastest spool till about 8800rpm MAX goal is 400whp and maybe more on 91 octane and in the future 450-470whp IF I can get there on 93 octane

I will be upgrading the oil pump once I go above stock factory rev limit for the k20a2

reason why I want a quick spool is I had an a4 1.8t before loved that it made pretty much full boost (butt dyno feel) from 2500 rpm, I realize it may not be that early with this turbo on a k20a2 but would like to know which AR would be best for that while also being able to breathe up top in the rpms

also would I be able to spool more quickly IF I get a turbo manifold made with say 1 7/8 primaries or is the usual 1 5/8 inch about as good as it gets on a turbo k20a2 when it comes to velocity?

Im a Honda newbie, school me please

 

You can't go any smaller than 0.63 with that turbo on that engine. The K20A2 really needs to breathe at high rpm so the 0.82 will give better efficiency at high rpm but sacrifice some spool. You won't be able to replicate the feeling of a K03 turbo on a 1.8T creating peak boost at 2500rpm. Quite honestly you wouldn't want to either, because as the 1.8T would have started dying off at 5000rpm, that's where the K20 will just start coming alive.

If you do go with the 0.63 make sure you give it a decent size wastegate so the wastegate can help reduce backpressure at higher rpm (plus K series engines need a lot of wastegate in general due to boost creep). If you focusing on spool and response, I would stick to 1 1/2" runners. Its pointless giving the engine "room to breathe" via large exhaust manifold runners and then creating a bottle neck with a small turbine housing - it needs to be balanced.

Sounds like an interesting project - what car/chassis ? Nice choice of trans.

 

Exactly the reply I was looking for, so keeping in mind that eventually I will be going for 9500rpm down the line the .82 ar with this turbo will be able to go there as well? When it comes to the project it will be a v8 car from the 90’s that’s all I’ll say for now, main reason is that it’s decently light by modern car standards (3200-3400lbs) and will be lightened further with fiberglass body panels in the front to bring it down to about 3000 with the k20 and 6 speed with 50/50 or near 50/50 weight distribution and it has tons of aftermarket support for the chassis when it comes to suspension, brakes, frame bracing etc, the trans adapter plate and flywheel is from a company online that’s allows you to use aftermarket clutch from a 350z

 

Please for the love of God, tell me you are not putting a Honda motor in a Mustang.

 

could be a mustang, could be a camaro, could be a transam...excellent platforms, great aftermarket, Miata is too tiny imo and prefer spaciousness, I have a fwd car as a daily driver and that’s the only thing I’ll use a fwd car for. I like oversteer, I like the fact that I could literally go on any of those forums and figure out the best suspension set up for drag racing, roll racing, track days etc with minimal trial and error. yes you can get a fwd to hook off the line but I prefer the stock stoutness of these chassis with some bracing...besides...if I did put it in a mustang, stock 302 blocks splits in the 450-600 crank hp range, lt1’s would require a coil pack conversion for optimal efficiency and bye bye rod bearings if you keep shifting above 6600 rpm in those lt1’s, t5’s are junk with stock power and torque, t56’s don’t like high rpm’s without a full gone through and building, Stock ls1’s are nice but I’ve been there done that and want a different project, this will be a daily driver, good power, better fuel economy, 4 spark plugs and coils instead of 6 or 8, k series are plentiful and most go towards replacing a numb nuts tsx engine because they didn’t change the oil on time, and I’m not the LS junkyard motor guy, 8000+ rpm without having to convert to solid roller cam and lifters and worry about bent cranks over time. Love it hate it, with these American cars I’ll have a good choice of parts and differential ratio’s and be able to take advantage of the wide rpm range without having to fiddle around with rim diameter and tire height, and I’ll be killing fwd honda’s From a dig, from a roll, at the half mile runs etc while cruising and getting good fuel economy in the city and the highway.... Keep in mind...I like fwd honda’s...as a fun daily driver grocery getter that I’ll need to have as a car with daily driving full coverage insurance so that I can whip my classic cars around on classic car insurance...plus these American v8 cars can be made to handle really well if you’re not an idiot. No Miata or civic project for me.

 

It really depends upon the purpose of the platform will be,and the average rpm range that you'll be in for maximum efficiency, and not simply just max RPM used. The turbine wheel regardless of the A/R size will always have its limit in power, the question the A/R turbine housing answers is where in he rpm band will that powerband shift.

IMHO .63 A/R =street use. .82A/R = Drag strip. Which also deals with the primary runner diameter question you were asking, also.

 

drag strip and roll racinG, under normal driving around ill be shifting at 3000-4000, don’t mind if I get a little bit into boost under normal driving around town, starting goal is to be able to use this turbo to 8800rpm, and later on down the line 9500rpm, if I have to switch out for a bigger turbo or bigger AR than .82 for the 9500 rpm limit then I’ll do that, but for now max it’ll be seeing is 8800rpm for the next year or 2

Highway cruising rpm will be anywhere between 2700-3200rpm depending on my final drive ratio

 

Then I'd do a .63A/R in this case. after that, it would be about time for a larger turbocharger altogether.

 

Taking out a V8 in a V8 based car, to put a I4 in, with the purpose of drag racing and roll racing.

 

you ever see the video of the civic type r vs the Spoon type r that revs to 11,000? Higher redline gives you more room to play with, plus it’s getting to the point where modifying the particular car with its original engine in place is pointless based on cost compared to swapping with a k series which I can get for cheap goal is to keep the cost low and have more rpms to play with, less shifting is better for et’s...me and my cousin are building this car, he’s the Honda guy, I am the convincee after being beat by a k series making about 50hp less than my former v8 car, he won because he had more revs to play with and didn’t have to shift to 4th gear like I had to...this is with power shifting...hence the k series in the v8 chassis...now stop reading this thread like I’m an idiot and just help me out goddamnit lol

 

What was the weight difference between the k series car and the V8 car?

 

2009 si don’t remember the mods but it was 300 crank, at that time I was running a foxbody and we both weighed near the same (3000ish him slightly less but not by much)both with drivers and full tank of fuel and I was pushing 345 crank, he was revving to 9 grand and some change, me 6800...btw foxbody is not the car I am using for the k swap, beat me by 1 car maybe car and half if I remember correctly

also the car I am using can be lightened to 2800lbs but I prefer to have a full interior nowadays

 

If you still dont have the turbo get g30-770 with .63 a/r
If the G series is very expensive compared to the GTX, id get the gtx3071 gen1 or 2 with the .63 A/R housing.
If you want to invest on a great setup but with an expensive turbo manfold, t4 twin scroll internal twin wastegate exit EFR 7163 T4 .80 a/r is a GREAT turbo.
Size wise GTX3076 turbine 55//60 , compressor 58/76
EFR 7163 turbine 56/63 compressor 57/76.
3076 gen 2 can do probably 50hp more on the 0.82 a/r turbine housing but for daily driving nothing beats the 7163 with the twin scroll setup and the super lightweight turbine wheel.
Considering this turbo was run on Indycars and we can get it as simple comsumers its a big plus for me.
Well untill i guess g30-770 comes with the divided turbine housings and thats a maybe.

 

Don't forget the GTW line.. Inexpensive and VERY competitive.. The GTW3476 has a machined billet aluminum compressor wheel and inconel turbine wheel. Plus, it should have NO problems hitting the specified goal with room to grow. Spools nicely and would probably shine like a star on a K in a .63 exhaust..

 

Seems you have a lot to learn and your Honda buddy is telling you do this because you got beat by a K series car. Not sure why you are keeping what the car is secret but I can assure you, if it is a Mustang or Fbody from the 90's and you want to make it fast with a V8...The only thing keeping you from it is your imagination. Want to go faster than you are planning now with less money? Find a junkyard LS truck motor.

Or you can go with a Ford motor if it's a Mustang. Here's mine