Radical_Ralliart
Active Member
How do you work out the inlet pressure your engine makes to determine the pressure ratio?Just some quick numbers/info dump;
you need aprox 10lb per min of air for every 100hp you plan to make
pressure ratio is the inlet pressure divided by atmospheric
Left and right hand sides of the compressor map are big no-no areas. Left is surge, right is too hot.
Being under the map, I can't recall, I think its just inefficient due to shaft speed too low
So you want 7-9psi of boost? Gives you a pressure ration around 1.7ish.
4g69 makes 160hp, should double at 1bar boost, so we can say roughly that at 7-9 it wont make double but atleast 100hp extra. So for airflow we look to be around 25-30lb per min.
That sits you in the lower 1/4 of the maps for any of the turbo' we've talked about. Should give you a visual now when you look at maps. The closer to the center islands the better, too far right is hot, too left is surge. You won't hit the top of the map, don't stress!
You should be able to see the difference now, the 3071r will be in a good range at 9psi and making 250-300hp, but as you build up to those you may find it lackluster. 3071r is not as huge as I anticipated, still has a fairly good low response but I reckon you'd notice it. Small AR housing is a MUST or it'll be so slow to spool, there's such a big gap in the housing charts!
For a comparison, consider a 4g94 making 200hp at a pressure ratio of 2 for both a 3071 and a 2867 and that is a really obvious difference in turbo efficiency and makes your choice easier.
I’ve recently become more educated on turbo specs and the calculations on working out the most efficient turbo. Trying to figure out the math for a peak 300hp on a 4g69, but i don’t know how tf to work out pressure ratio