CH 4g69 Turbo conversion

[Radical_Ralliart]

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.

How do you work out the inlet pressure your engine makes to determine the pressure ratio?

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

 

[SDate42]

How do you work out the inlet pressure your engine makes to determine the pressure ratio?

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

Pressure ratio is inlet pressure over atmospheric. We usually discuss boost pressure relative to atmospheric. Atmosphere is 14.7PSI, if you want to make 10PSI of boost, your pressure ratio calc is (14.7+10) divided by 14.7. Gives us 1.68. I think I rounded up in my last post.

On an N/A car, you can only ever have a maximum of near 0PSI (relative) inlet pressure, so that is calculated as (14.7+0) div 14.7, giving us a pressure ratio of 1.

That's also just the peak number, so while the turbo spools its going to be a little different, but you get the idea and you can visualise where it might sit on the map.

 

[Radical_Ralliart]

Pressure ratio is inlet pressure over atmospheric. We usually discuss boost pressure relative to atmospheric. Atmosphere is 14.7PSI, if you want to make 10PSI of boost, your pressure ratio calc is (14.7+10) divided by 14.7. Gives us 1.68. I think I rounded up in my last post.

On an N/A car, you can only ever have a maximum of near 0PSI (relative) inlet pressure, so that is calculated as (14.7+0) div 14.7, giving us a pressure ratio of 1.

That's also just the peak number, so while the turbo spools its going to be a little different, but you get the idea and you can visualise where it might sit on the map.

Okay awesome thank you for that, I’ve had a look at that compressor map differently now.

Not sure how well i can control how many lbs/min the engine can output, but looking at the chart being at a maximum of 10psi, running about 25 lbs/min of airflow sits me right at the bottom of the efficiency island.

Looking at that figure now doesn’t look very ideal especially when i’m only using stock internals..

 

[Radical_Ralliart]

Just had a read through the compressor maps for GT2871R and GT2867R turbos, it seems with the 2867R i’m alot closer to the middle of the efficiency island with a pressure ratio of 1.7 and an airflow of around 25 lbs/min

 

[SDate42]

Okay awesome thank you for that, I’ve had a look at that compressor map differently now.

Not sure how well i can control how many lbs/min the engine can output, but looking at the chart being at a maximum of 10psi, running about 25 lbs/min of airflow sits me right at the bottom of the efficiency island.

Looking at that figure now doesn’t look very ideal especially when i’m only using stock internals..

Lb/per min is a figure that relates to HP and is a direct result of the engines efficiency.

You can actually calculate it at any point, but we’re talking generalisations anyway AND focusing on max HP conditions.

You’ll find your motor will use approx 10lbpermin for every 100hp made. So 300hp is around 30lbpermin.

Combine what you know about your motor already. It makes 160 at 0psi. That should double at 14.7psi.

So 300hp is found at 30lbper min and at around a pressure ratio of 2.

 

[SDate42]

Just had a read through the compressor maps for GT2871R and GT2867R turbos, it seems with the 2867R i’m alot closer to the middle of the efficiency island with a pressure ratio of 1.7 and an airflow of around 25 lbs/min

Dont have to be in the middle but that is somewhat ideal and gives you room to be wrong in calculating things. If you are in the middle at peak HP you’ll be on the map in good spots while spooling, which is the main difference if you go for the 3071.

 

[Radical_Ralliart]

Dont have to be in the middle but that is somewhat ideal and gives you room to be wrong in calculating things. If you are in the middle at peak HP you’ll be on the map in good spots while spooling, which is the main difference if you go for the 3071.

I did check out a post by @Fab360 with his topmount turbo 4g69 build using the smaller 2871R turbo, i believe he was using a 0.86 rear housing which would make the boost come on later. Just judging off his tuning numbers for a stock 4g69+T over 300 whp is pretty nuts

I could use that turbo with the bigger turbine housing, even on 7psi of boost would be a significant power increase

 

[SDate42]

Yeah his ported manifold and fab work will make that difference, along with water/meth injection.

That’s a good build to go off tbh. 2871 is still a fairly chonky turbo, it’ll do you well. Also probably be able to take it with you to your next car when you get over the CH, provided it doesnt explode

 

[Radical_Ralliart]

I’ve unfortunately made the decision to shelf the turbo ideas for my 4g69 CH, it’s not the right time for me now, but i’m happy to give out any info to anyone else and discuss about boosting 4g69’s. Still very interested in this topic.

I have heard that Alvin from off the clock motorsports is currently gathering information and experimenting with a certain red boosted CH in queensland though.