I have a mildly ported 13bt with a huge front mount, divided manifold, open vented tial 38m gatge, mandrel bent 2.25 charge pipes, 3 in. exhaust and controlled by a microtech w/ 1600cc secondaries. The turbo is a T04b .60compressor housing and 1.15 divided exh. housing. Ive been running 10psi on it with good results. spool is between 3 and 4k depending on the gear. Well I used a MBC to turn the boost up and I got it up to 15psi. high 11s AFR's. The funny thing was that once it hit 15psi I heard no wastegate opening. Remember its open vented, so its loud as hell, and if its open, you know it is. So I turned the mbc up higher and it wont go any higher. There is no way Ive maxed this turbo out is there? I know the compressor might be a little small, should I upgrade to a larger one? What could be going on? I have no flow restrictions that I can think of except that the IC piping isnt huge, but 2.25 is quite large.

 

What compressor wheel is in there? What exhaust turbine? P?

 

Ive lost the compressor and turbine sizes and I cant remember, but I mean its not like there can me a huge difference in sizes and still fit in the housings is there? Sorry if this is an ignorant statement, that just what I understood. Also if I were to upgrade are there too different sized shafts for turbos (a large and a small) b/c I think I have a small shaft, so upgrading this turbo may not work if it is the largest size that uses the small shaft.

Edit: I think it is a V-trim. This might be the compressor map..not positive though.

 

You say 2.25 inches is large? What do you think would happen if you used a smaller diameter charge pipe? Remember that bigger isn't better, but I don't know much about your setup, other than what you stated. 15 psi is pretty low for a TO4B, IMO. What about your front-mount? You said it was huge. Do you have the dimensions? Perhaps the pressure drop between the intercooler might be a culprit.

Where do you think your compressor efficiency lies on that map? Also, do you have a turbine map for your TO4B?

 

OK I'm going to take a guess here... follow me through on this and tell me if I'm smoking crack or what...

OK assuming you have a 1.15 exhaust, a P trim wheel (most likely), and this "V1 V2" compressor....

OK to get a given boost, the turbine harnesses exhaust power to do this and spins the compressor. How much exhaust power you need depends on the compressor and boost. If you have a smaller compressor or lower boost, you need less exhaust energy. A big compressor or a lot of boost needs more exhaust energy. OK easy enough...

The trick in finding a nice turbo for any engine is matching the size of the exhaust parts like the A/R and the wheel size with the size of the compressor side parts.

If your wastegate opens at 10 PSI, this means that the exhaust side has harnessed enough energy to make that 10 PSI and there is extra, so it bleeds off through the wastegate.

If you now bump up the boost to 15 and it holds it to redline but doesn't open the wastegate, this is telling me that you barely have enough exhaust flowing to support making the boost.

Some guesses:

1) Your intake has restriction, so 15 PSI of air translates into relatively little air... this gives the exhaust turbine less to work with to make boost. Maybe at 10 PSI, things flow a little better???

By restriction, I mean crush bent pipes, throttle body not open all the way or poor flowing, intake porting very small... anything... Also remember that "15 PSI" on your boost gauge might really be 17 PSI at the turbo since the IC has a pressure drop... so your turbo is working pretty hard.

2) Your compressor works much better at 10 PSI than at 15 PSI. This would result in having more energy to spin the turbine at 10 PSI than you need (so the wastegate opens)... but maybe at 15 PSI, it's not an efficient 15 PSI, so it barely puts out more usable energy than at 10. Does the car really feel any faster at 15 vs 10?

3) Your exhaust porting or manifold is too small to get 15 PSI's worth of air out quickly... so you end up recycling a lot of it back into the intake cycle and also lose out on energy to spin the wheel faster.. so wastegate doesn't open.

I mean there could be a million things... Have you dynoed the car to see how much power it is putting down? That could give you some valuable information about how much air you're moving at 10 vs 15 PSI....

Brian

 

Your simply asking for more then your compressor is willing to give up. On a decient street ported 13b your looking at anything from 40 to 50 lbs per minute at 2 bar (14.7 psi of boost). if you look at the compressor map for your turbo and plot 17-18 psi (pressure ratio of 2.20 roughly because what your seeing on your boost guage will be a few less psi than what your turbo is actually putting out). You can see your WAY WAY off the compressors effiency islands at those flows and pressure ratio. (ideally you want to stay in the middle islands). If you want more then 15 psi of boost reliably and effiently, upgrade the compressor wheel and houisng. (You really wont need more the 15 psi of boost if you run a better compressor wheel. 400 hp at the wheels is PLEANTY for a street car. and as you go higher then 15 psi your risking detonation and the need for race gas becomes more manditory [really depends on set up and tunning]). You have a small shaft, this limits you to a 62-1 which is about as big as you can go with a small shaft turbo. The 60-1 is a step down but still is nothing to scoff at, it will make over 400 whp and its sweet spots on the compressor map are from 10 to 15 (guage pressure) psi for a stock or large street ported 13b.

btw, at 15 psi with your to4b your pumping HOT air into your motor (risking KABOOM! ). I'd stick with 10-12 psi and call it good (still on the borders of effiency there too) or upgrade.


~Mike..............

 

I will probalby try to upgrade then. The thing is that it doesnt seem like the turbo is out of its efficiency range, b/c I was seeing 33* intake temps @ 15psi as apposed to 34* @idle. The intake temps were about 32* @ 10psi.

Also, I was trying to hit over 15psi in 2nd gear. I tried on the interstate and it shot up past 20 easily in 3rd. I let off and turned the boost controller back down. Sorry about my nearly useless post, I just wasnt thinking.