No problem at all doing it that way. Somebody always chimes in with "wastegates should not see vacuum", but then never gives a single example of any harm that has ever done. I suppose they use the same logic for the boost controller.

 

The wastegates are not just on/off switches. They crack a little bit at well under the pressure that fully opens them. With the right MAC valve configuration you can completely kill opening pressure to the bottom port while sending closing pressure to the top port. This almost pins the gate closed until the ebc switches the flow to let it open.

 

Ideally you want the most pressure for the best control and highest boost ranges. So that’d be at the compressor or pre IC. You can have a significant pressure drop post IC (at the manifold) vs what the compressor is spitting out.

I’d also think it kind of depends on the gate control plumbing you use. Unchecked vac to the upper chamber could open the gate during cruise.

 

Think overall pressure differential. If his bottom line and top line come from the same source, any vacuum to the top of the gate will be equal or less than vacuum to the bottom of the gate. As for going with the compressor cover or anywhere pre-IC, that will give higher potential boost pressure, but that would also make the boost curve less flat depending on the flow rate vs pressure drop across the IC. With an ebc this would not be an issue, but we are specifically talking manual controller.

 

Right, depending on plumbing. Some don’t incorporate the lower port at all.

I prefer to have as much pressure as possible for control to ensure the gate stays closed until I want it open. I don’t see that causing unstable boost targets. I run 100%DC to the top port only until desired boost pressure is reached. Then vent the top to the bottom port to control w a 3-port mac valve.

 

I fully agree with what you are saying as it applies to using an ebc. You have a much wider range of possible control with the setup you are talking about. However, he specifically asked about a manual control setup, which has much more limited capability.

 

Well since I don't have an IC or any pressure drop measuring from the manifold isn't an issue then right? Right now I'm teed off the back of the Dorman LS6 manifold as it as a nice small vac port for the BOV which I Teed to the WG as its half way between the gate and compressor anyways. So now I am confusion. How do I plumb the manual boost controller? I've seen 2-3 ways the one that I have is the voodoo 30psi one here https://www.ebay.com/itm/175425530712. Turbosmart diagram puts there MBC inline to the lower WG port and vents the top (currently my lower sees vac/boost from the manifold and the top is vented) so it would splice and connect and done. I then see ones where you tee into the current bottom line and then run that to the MBC and then the output of the MBC to the top of the WG (this is basically how I have my solenoid run on my firebird using truboost EBC). Which way should I run it?

Now onto what I just datalogged today. I only had one onramp to log on my way to work, 52*F out so I was being careful not to go WOT as the new ultimate summer tires are still breaking in. I went to about 70% TPS according to my log, car felt faster and feels real strong up to like 4k and then feels like its tapering off. I checked the logs at work a min ago and heres what I found. Remember I have about 10psi cracking pressure on the bench with both 4.6 and 6.2psi springs installed.

I had 2 boosts logged back to back in the same run as I let out as I was already doing 100+ and tires felt alittle loose.

First Blip
4800rpms
70% TPS
125kpa
87*F MAT
11.86:1 AFR

Second Blip
4500rpms
70% TPS
129kpa
90*F MAT
11.68:1 AFR

Logs show a max boost of 3.9psi initial on boost and tapers off down to 3.1-3.2psi. So Going from 4.6psi spring to 10psi total I'm only seeing 3psi boost WTH. You can feel the car kinda like nose over as the boost lessens about 1lb. With the #5GPH snow nozzle I'm seeing MAT temps at the start go from 95-85*F and then pick up again after I let out. While driving around MAT never got higher than 150*F and while cruising (40 min drive of city 40mph and lower) temps are 130's maybe 140*F.

At this point I think the MBC sounds like it would make the most sense. Now referencing the intake manifold vs compressor and how do I plumb it? I would think that I would need to double the spring pressure to net 6psi of actual boost.

 

Do u have a build page for this car, from what i see in the pictures it looks to be a c3 vette i could be wrong but those front fenders look very distinctive, if u dont have a build page/forum on it can u post a couple of pics of the car……a boosted LS swapped c3 is a build i wanna do next, if ca. gets that new Leno law in place i might just actually do it…….anyways good luck with your build it looks to be coming along nice from what i can see!!!

 

Yea I believe it's that 78 Vette in his sig

 

I have a turbo build thread on the vette forum. https://www.corvetteforum.com/forums...5-3-build.html

it’s a 78, I got about 2k in the whole turbo setup, from turbo to exhaust bends.

I’ve been struggling with boost at the moment. I had 15lbs of spring in it and only managed 4.6psi. The car is much quicker now tho. I really only want to build 6psi as I figure that will put me around the limits of the build 700r4 and the batwing rear. Yes the car is a 78 but 40 years ago was in an accident and the guy converted to a 80-82 front end, rear bumper and they put the 80-82 rear end in it. Traction is now a problem even with the new 18x9.5s and 275 ultra summer tires on all 4 corners.

 

I dont have a corvette forum account (yet) hopefully in another 4yrs when the kids are done with school or if that leno law happens i will get me one……either way that car is badass….hard to believe your only $2k into the turbo setup, your fab work is very clean….nice work man!!!

 

Very cool build, I'm not a huge fan of that year Corvette but you did it justice with the cool custom turbo kit and modern wheels.
Outta make a great cruiser for sure.

 

Thanks man, same here with the kids too... What is the leno law?

Yea, I used all cheap stuff, Turbo manifold was like $90, Ebay SS block hugger headers, Amazon Stainless pipe and bends, $170 summit WG, Turbo I got used off FB... I already had the 60lb Deka injectors. You can still do some things cheap lol. Its def cheaper than building a 383 to put in it.

 

I appreciate that. I personally like the earlier vettes (brother has a 68) and the C2s when they get built out. The c3 is the last ok looking vette to me honestly. C1-c3. Wheels were fun, with wider and shorter sidewall tires The steering feels a bit different than the 15x8s with 255/60r15s on there alot more sensitive at 100+ MPH. It does pretty good on the road, if I knew I was gona go turbo I prob wouldn't have done 3.73s in the rear... maybe 3.23 and 3.55 being the max. Car had 2.80s or something in it which made highway very nice.

 

Leno law is a new bill their (car guys) trying to pass along with trump maybe going 1 step above and getting rid of CARB and EPA and some other ones too i cant remember off hand , but if leno law pass’es we will not have to smog cars built before 1990 and the later one i mentioned im not gonna hold my breath but would love to see happen mainly because i have a duramax diesel …is trump shutting down the EPA and CARB….meaning there will be no smog checks at all….(yea fat chance on that one with ca. being a blue state) but if it does happen im deleting everything on my LMM duramax……i already have all the parts new in the box sitting out in the garage for the past 10 yrs now!!!

 

Dang that sux. In NJ and CT no emissions stuff on anything considered a classic which is 25+ years so a 2000 would qualify, plus you get classic plates. In NJ its lifetime registration (1 time... forever) in CT its not but its reduced car tax and you need to get vin verifies every couple of years which is a 5 min inspection of the cars mileage and other basic things. I believe NJ and CT are both blue states as well.

 

Took the car out today with 21lbs of spring in the WG, I was at 15lbs and got 4.6psi, so I'm hoping for 5.5-6.5psi with 21lbs. I did a log and then something happened when I was pressing the buttons (stupid handheld screen sucks). I couldn't really get on it that hard after that log due to how many cars were on the road at 7:20am. While cruising on the highway in 4th with the converter locked I did a 75-100mph medium throttle pull (no downshift) and I saw on the handheld 160kpa which is higher than I have ever seen (140s). I got to work to check the log and nothing was recorded... FML. Car felt really good on 50-75% throttle tho. I will go out and plug into the ECM and see what the fuel learn tables tell me. That generally will tell me what the motor has seen for Boost as its tuning any MAPvsRPM table point that I hit. So I will at least have some point of reference. I will try to get a log after work on my way home too and confirm.

 

Car ran fine on 87 and meth. I'm tired of seeing 150-160*F IATs and The summer heat isn't even here yet. I'm in the process of swapped in a FMIC to see what that does. I might keep the Meth but idk if its necessary or if it is at a much lower 2GPH rate and at a higher 5psi boost activation to assist the 87 pump gas.

 

Drove the car today for the first time with the FMIC... worked out real good. IATs are 95-110 cruising on a 88*F day. Didn't go crazy with boost but temps drop as I give it gas, at idle temps creep up. I have a feeling the RIFE IAT is so sensitive I can see when the TB blade is closed and airflow doesn't pass over the sensor in real time. This was without METH as I pulled the fuse. I might get 1 log on my way home with some boost to see what the IATs are doing in boost. I would say 40*F drop easily with this FMIC. Engine temps are in the 185-188*F range even with the FMIC but I'm running mostly straight water and super coolant in the system at the moment.

 

FMIC is installed and I ran it to get some logs. My IATs have dropped by over 40*F without Meth injection. My boost has also dropped by about 1lb which could be from the cooler charge and the IC restriction. Whats interesting is that my fuel usage is up. I was at about 6-6.3lbs of boost but my fuel usage was at 290-295 which is about 10lb/hr increase at the same boost as below. I did have some boost leaks around all the injectors again in the dorman intake manfiold and last night swapped out the orings for bigger LS2/LS3 conversion orings from alper motorsports. They fit snug and no boost leaks during leak checks. Planning to add the water meth back but reduce to 2GPH as this is really just for detonation control with the 87 octane, I would like to sneak up on the timing a bit more but worried about the quality of 87 depending where I drive so the wiper fluid would offer some protection.

53% TPS
150 MAT now 100-114*F
283lb/hr now 290-295lb/hr
6.4psi
22.3* timing
5221 rpms

Before intercooler
Basic calcs put me at 470hp at .6 BSFC and 283lb/hr

After intercooler
490hp at .6 BSFC and 293lb/hr so thats a 20hp gain with just dropping IATs by the 40 degrees.