Hello--

I just got my turbo setup running a bit better with the help of timing control and methanol injection. Rough setup is:
1.5L toyota 3ac, reverse flow gasket matched head, 272 cam
Synchronous weber 32/36
Garrett tb2531 from a '91(?) saab running .5bar (7.75psi)
Draw thru setup

This issue has been present since I got the setup going. My friend noticed it, as well as I and all I can think is it may be a restriction issue.

I am still running the stock manifolds--they are rather dinky, but are sufficient for a factory 62hp setup. When you start laying into the throttle, once you get past ~1/2-3/4 throttle, it doesnt seem to make any more power. Power just seems to taper off. The fueling used to be around 8.5-9.5:1, but I have downjetted to get it closer to 12.5-13.5:1. Even if you open the throttle more with the roll off, the afr doesnt seem to fluctuate all that much.

Timing control is basic. Mechanical advance has been locked out, and vacuum timing pulls ~5* when accelerating. I've got the timing ball parked to around 25* at idle with the vacuum advance connected so I can watch it move when I blip the throttle.

I am still very new to this, and am unsure what to look at. I was thinking of giving it a smidge more timing, but with how the power roll off is, I am thinking the intake just cannot flow enough air to take advantage of the full throttle power.

Thoughts?

 

12.5-13.5 afr is lean under boost. You would wanna richer it up to 11.5 to 12 .

 

Gotcha. Do you think that may be the issue? And, do you think being rich would have the same symptoms?

 

The 12.5-13.5 isnt causing your power loss. Its enough that it will drive right through it and kill things if its unhappy.
But is does need to be richer as stated.

 

gotcha. i honestly made a blind down jet -- went from 150/160 to 120/130. will prolly go 130/140 and see where its at.

 

That turbo is not designed for carb draw through, have you put in carbon seals?

Don't add timing without doing plug chops. Do you have a boost gauge?

 

yes, its been converted to carbon seals.

i do have a gauge, but i currently have it disconnected as the only spare port i have is being used for the methanol pressure switch.

Is there something i should be looking for with a boost gauge?

 

Yes, you are looking to see if boost is coming in with throttle, if it is stable, falling off, etc. You are essentially blind to what the turbo is actually doing right now. Can you just tee that port and run the meth and boost gauge?

 

I can take a look at getting it hooked back in.

I do want to run through the two theoretical situation.

If the boost is stable, and fuel isnt all over the place, what would that indicate?

If the boost is falling off, would that point towards a wastegate issue, or some sort of restriction?

 

If fuel is stable at a safe number, and boost is stable, but power is falling off it indicates something else. Plugs will tell you about timing.

If boost is falling off it could be turbo size or a restriction in the intake or exhaust. Boost gauge will tell you a lot.

 

I think it may just be the crappy head design. Fuel is stable (albeit a bit lean) and boost isnt dropping..much. Gauge is showing 9psi till ~6k rpm when it starts to peter down to 7psi. Redline with my cam is 7-7500rpm.

Heres a video of me making a couple passes with it.


I will need to do a plug chop next I think.

 

Mmm, you shouldn't be dropping boost at all; when it spools it should be full boost. Are you using the stock size carb?

 

what do you mean by stock size carb?

 

I mean are you using the stock carburetor? If your running 7 psi draw through it seems like you would need 50% more available airflow

 

ha no. the original carb was a 2-barrel feedback carb. Whats on it is a weber 32/36. I'm not entirely sure what the cfm of the two carbs are, but based on a loose formula I found a while back, the 32/36 cfm-wise is a bit big for the 1.5L.

How did you get the 50%?

 

Youratmospheric pressure is about 14.7psi at sea level, so if your adding 7 psi that's about half, makes the engine act half again as big. If you were blow through you can just run stock size

 

hm. so, at 7psi, its making the 1.5l act like a 2.2L?

I thought about blow thru, but i didnt want to deal with either building a pressure box, converting the carb for pressure, and dealing with boost regulated fuel pressure + pumps...

Whats your suggestion? Get a higher cfm carb?

What would happen if I increased the boost levels with my current setup?

 

What does it have for valve springs?

 

Double valve springs.

 

Are they stock, oem springs, or are they something stiffer?