limit boost for town driving and lock out at Highway speeds

[theKbStockpiler]

Hi, I'm interested in knowing how to keep a ACVW from boosting at under 2500 for around town driving and for keeping it not boosting at all for highway speeds where the engine RPM's are at around 3600 at 70 MPH.
Thanks for your expertise!

[buguy]

Boost only works when it's under a load. Unless you have a mega small turbo it shouldn't be a problem.

[theKbStockpiler]

Thank you for the responce, I would also like an in depth understanding of this. Transition points would have to be the answer. For the turbo to boost the cfm of the turbo has to be higher then the demand of the engine. The 'no load' reasoning also implies that the turbo is too small or is choked.So a wastegate does not apply at higher RPM's?

[Clonebug]

How much hp are you looking for and what size engine are you working with??

If your hp target is low and you use a small turbo that will just supply that hp...you will be at insta-boost at 3600 rpm.

My turbo supports 270 plus hp and at 3500 rpm it is right there. If I climb a 6% grade I can make boost just by moving my throttle a little bit. It is only annoying when you have water injection set up for max boost and it starts making the engine blubber at the lower boost settings. The solution is to limit boost to the point you don't need water.......simple when you have EFI and a well designed Intake cooling setup.

The best thing to do is run an Electronic Boost Controller like I do and if you have a carb then you need a solenoid to bypass a Manual Boost Controller so that you can run off the stock wastegate or else have a wastegate that can have different settings.

I have an Electronic Boost controller and I just flip a switch on my dash that limits boost to 6.0 lbs. Next to that is a switch that shuts off my Water Injection. I can drive anywhere and have driven a 3500 mile round trip to California and back with that setting.
No water is needed at 6.0 lbs or less and even if it starts boosting it won't hurt it.

The end result is that you need to set your turbo system up for your car and your driving style.
That involves picking the turbo, air temp management, boost level and a whole host of other variables.

The first thing you want to do is pick your hp goal.
Then you pick a turbo.
You next design an intake system to support that along with either WI and/or intercooler.............or..........keep the boost low enough that you don't need it. That brings you back to your hp target or goal.

I very rarely cruise at that high of an rpm......I can do 70 mph at 3100 rpm due to my 28 inch tall tires.

[theKbStockpiler]

I have a beetle project car on the back burner and want to turbo it for more 'practical power'. I don't want high octane requirements but want to get more power out of a 1.9 without having a short lifespan either. I want the engine to be able to use it's natural torque in high gear for town driving and the same for highway speeds at about 70-75. I think building a 1.9 without compromises to longevity with a lower boost is the way to go.I have put the numbers in a 'turbo computer' and 12-15 lb of boost is where I want to be or about 195 hp. I'm planning on using 195 65 15 tires on it and adapting a 914 system on it with a different computer. I only want a bare bones system, no semiconductors unless it is actually better and not just to bring the price of semiconductors down.Lol.

I was thinking of the 'no load' angle and 'throttle position'or 'volume of exhaust gases' is more intuitive in my opinion. I don't have any hands on turbo experience though.

I think from driving a stock 1.6 at 85MPH that it is possible for a turbo to boost because the throttle is all the way open at that point. I did this once for about 1/2 an hour.Lol. So at 70-75 I feel the math would have to be done to make sure it did not boost.

[Clonebug]

I have a buggy so I don't know how a bug would drive at 80 mph.

My buggy is like a brick going through the air at anything over 65-70 mph. It starts taking some hp to move it through the air and therefore it will get into boost to help it along.
I have been up to 109 mph with it and when I let off it is like a brake has been put on.....the windshield has a lot of resistance to it.
A 1915 will have more hp without boost but I can't say how it would react at that rpm and load.

My experience is with Subaru turbos and I know how they perform. The turbo I use on my 1679 would probably work great on your engine too but at 3600 rpm it will want to be in the boost at any extra load.

You will need to decide what you want out of the car......sometimes a turbo is a compromise. You can't have everything all the time.......

Start a build page and write down your goals and expectations......someone will comment on it I'm sure.

[theKbStockpiler]

I did the 85MPH with a decent tail wind and a fresh engine. The car was a curved windshield super. Wind does not have a direct target with the curved body but it is awfully light. It did seem to defy physical laws at times. Maybe it was the 009 distributor.Lol.The 65-70MPH goal is just because of the speed limit on the thruway. With a decent cross wind the goal should really be 55MPH and under. My whole 72 super project is based around it being a daily driver in almost any modern conditions. I'm going to put frame rails in it and a lot of other steel to make it safer. I'm planning on building my own sub frame and getting rid of the super's flimsy brackets on the inside of the wheel housings that the steering box and idler arm attach to.

If a switch-able waste gate was used it could be set for a much lower setting for the expressway could it not? Maybe not even appreciably boost?




Thanks for the advice!

[Chip Birks]

Or just build it like mine, put a t3/t4 on it. It will only make boost when you want it to make boost. The trade off is that its not an insta boost type setup. Mine will make a ton of boost, and a ton of power on demand, but it does most of it above 4000 rpm. I have a race inspired turbo on the car right now, and will probably detune it slightly after this next race season, I'll probably get boost 500 rpm sooner than now.

I like the Subaru turbo idea for a super practical street car. There is nothing wrong with the combo making a little boost as you accelerate around town.

[Clonebug]

When accelerating you want the boost. It's just a matter of doing the math on what turbo you want for your target hp...

Do you want 100 or 300 hp.

A dinky little turbo will give you insta-boost on the street and in town for great acceleration off the stop lights and around corners. A big turbo will give you nothing until it's revved up.
It's all a matter of what you want.

Get a turbo that is capable of your max hp and a little more since you will want to turn it up.
Chip's turbo is great for max power and then some but takes a bit to spool it up. He has a big engine so he doesn't need the boost at lower rpms.
My turbo comes on as soon as 2400-2600 rpm and pulls all the way through my rpm range. It's not maxed out yet because it's sized correctly for my driving style and engine hp target.
I can limit it to the stock wastegate setting of 6.0 lbs and it can go anywhere without a worry and any speed.
At 6.0 lbs. it puts out 112 whp and 133 ft. lbs. of torque. It has plenty of pep around town at that setting. Flip the switch and it adds another 75 hp.

[buguy]

Sure you could have a switchable or adjustable gate that you could turn down or off at will. I'm not sure how that would affect the tune though? Trial and error I guess. The problem you might run into trying to drive it as a modern vehicle is that it isnt. It wasn't designed to do 75-85 mph on the freeway. You might be able to get away with it having a bigger engine to start with but I think you would need gears for it to work well. Then you might have to mess with pulleys to keep the fan running at the correct speed. Especially if your going to add weight to an already heavy super.
Also I think a 195 tire will be shorter than stock. Maybe you could try to get something taller that would be like going with a taller gear. I put 205/65/15's on the back of mine recently and they are slightly taller than stock. I wish I would have gone with a 215 to fill the wheel well up a little better.

[Dan Dryden]

I think you’re over-thinking this.
To make 195hp from 1915cc you will need a reasonable sized turbo (perhaps a T3 or a TD04).
These will not be giving inst-spool and on light load, partial throttle conditions, you are likely to still be seeing vacuum rather than boost.... even at 70mph.
If you haven’t experienced a turbocharged ACVW engine, I recommend that you try to find someone who owns one and is willing to take you for a ride. You will find that your theory does not match real world situations.

[madmike]

Hey Dan ,,Give him a 'Ride' sounds like he's in your neck-of-the-woods?
my 1915cc will cruise at 70-80 mph without boosting and town speeds also of 25-50mph,like said, it's all about the 'load'

[theKbStockpiler]

I had a 74 super and my current project is a 1302. Both registrations read 1649 for curb weight. I realize that most people will disagree with this but that is the number for both years.Maybe it's a screw up by NYS. 185-195 tires are as big as you can go, still have approximately the same tire height and be able to rotate them.

I thought that for cooling issues a ACVW engine could not be on boost for prolonged periods of time? I don't want to limit the ambient temps this car can be driven in.

What's a good turbo to try to source used for a air cooled 1.9,subaru or saab maybe? Which turbo be the easiest to adapt to? Should I aim for a factory 2.5 version to make it spool later?

Thanks for your expertise!

[madmike]

You herd correct that They can't be boosted very longtime ,for me 10-13 seconds is not very long
I don't think you understand most of the time our motors run in Vacuum mode (20"HG)Like a Normal Aspirated:N/A , until I step on the throttle only then it will start to make 'Boost'

[Chip Birks]

Curb weight for my 1960 is right around 1830. Add me to the combo and you are looking at 2000lbs. All the added equipment to make and handle the hp has added a few lbs. You have to remember, eventually load will eventually go away. You aren't always accelerating, boost will drop off.