i searched, but most of the results seemed to be boosted stock blocks, which is a little scary since stock compression is 10.3:1. so, im making my own thread, plus its late, ive been working out in the garage and im tired and want to sleep. easier to post this. anyway, a #4 valve is pretty much screwed so im either goin NA or single turbo. looking for advice on what to do for a RELIABLE autocross/street car, if i go turbo, plans would be:

8.5:1 compression
15lbs of boost (about)
target of 400hp
engine built to handle 600hp
conservative tuning

seems like turbo kits added to stock blocks put 8-9lbs on 10.3:1 compression, so maybe 15lbs on 8.5:1 would be conservative to start with.

thoughts?

basically im trying to get info on whether or not that turbo setup will be reliable and last 100k miles, or if i need to stay NA with 270hp to achieve that reliability. thanks

 

any turbo kit can be considered reliable. depends on how well you maintaine the motor and how well the car is tuned. if your gonna go boost for a autocross setup i would go with a smaller twin setup then a big single setup for the simple fact you will boost faster at lower rpms.

 

I replied to your thread in the other forum. You won't need anywhere near 15 psi to bet to 400 whp. Maybe around 8 psi or so. A twin turbo kit with GT25 or GT28 turbos will spoolup faster than a single turbo. I would lean in that direction.

 

cant i have a quick spool up and quick power with the right single turbo? doing custom piping so a single is preferred for that reason

 

15psi is a little Much for you goals like Terry said about 8-9psi would be lots for your goal. If it is an autocross car that you are looking for 400whp I would go with higher compression either stock or 9:1 so you have power off boost as well. Tuning is what dictates reliability when FI so it is tough to speak to the reliability of each FI set up however NA is less stress on the engine so I would say it is going to be more reliable.

 

I posted in the other forum. A quick spool valve should help. Call Sound Performance Racing and see what the quick spool valve will do with a GT35R turbo.

 

built with stock compression and low boost @ 6-8 psi will be more than adequate. You could always turn the boost down.

i think 9.0:1 is probably a better setup than 8.5:1 given your typical planned usage

 

One other note, at 400 whp, you will be around 8.3 psi (.57 bar of boost), which is a 1.57 pressure ratio. You will be flowing about 45.8 lb/min on a single turbo, and 22.9 lb/min per turbo on a twin turbo setup. These are general numbers, and will vary depending on your build, how well the intercooler works, etc.

Assuming these numbers, with two GT2871R turbos you will be operating around 73% efficiency, and well away from the compressor choke line. With a single GT3582R turbo, you will be operating around 68% efficiency, and be closer to the choke line. Below are the respective compressor maps. With the higher efficiency of the GT2871R turbos, you will see lower AIT.

Also, the twin GT2871R turbos will give you more head room if you want to increase your power later on down the road.

 

ummm, english please? haha. but seriously, so are you just saying that twins would be more efficient and would keep ait down?

 

Yes. But remember that there are inherent benefits with keeping the AIT lower. The hotter the AIT, the quicker detonation will become an issue. In other words, with lower AIT, you should be able to run more aggressive timing for a given hp level. Also, you can push the upper hp limit of pump gas a little farther before you are on the ragged edge.

Not only that, twin GT28s provide higher total flow capability vs a single GT35 (should you want to increase hp later on down the road).

I provided the data to support these conclusions. Oftentimes in the forums people provide recommendations that are flat incorrect and/or are based on personal preferences, without any solid technical basis. When you have actual data to work from, it helps to make the decision process easier.

If you are still looking at going FI, compare the various single and twin turbo kits that are available. If you go with a single turbo kit that saves you enough money over a TT kit, it still may be the best choice for your goals. Now at least you have additional information to process to make an educated decision.

 

thanks! im leaning towards an na build, but somehting similar to boosted performance's single turbo kit is still an option. full boost at 3500 to redline, i think it was a 6165 t4 turbo.

 

I have not seen compressor maps for that turbo, but it should have higher flow capacity than a GT3582R, especially if it using a billit compressor wheel.

If you go single turbo, take a look at Sound Performance Racing's quick spool valve. From the data I saw on that about a year or so ago, it should really help with spoolup.

 

One more thing, as Sylvan Lake V35 stated in the other forum, trying to get 400 whp with a N/A setup will be tough and expensive. I think that your original intention of overbuilding the short block and using Fi makes a lot of sense. For 400 whp, I would go FI.

Choose your compression ratio and turbo kit based on whether you think there is any possibility you will want more hp later on. If no, stock compression ratio and a signle turobo kit should be fine.

Acceleration is addictive, however, and I found I quickly wanted more hp. If you think there is any possibility you might want more hp, go with a lower CR. I wish I saw more builds with the SPR quick spool valve. Absent the data, a TT kit is the safer bet for future HP increases without sacrificing spool up too much.

 

400hp na on a de is impossible without nitrous, either I do a sub 300hp na build and save $ and headache, or I go FI to get 400 and risk burning up my auto

 

my na build has a goal of atleast 310 to the wheels