Blow through turbo charging

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JT68
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Re: Blow through turbo charging

Post by JT68 » Fri May 10, 2019 1:18 pm

There were many blow through turbo setups done in the 80's. Most went the way of the dinosaurs because many, many resulted in blown up/melted engines. The U is also a particularly poor choice for turbos since it is prone to head gasket issues as-is.
Yes, it can be done, but should be exceptionally well thought out - like the datsunrides car appears to be.

Also, unless you build the bottom end for a turbo, meaning lower compression forged pistons, the likely outcome is a melted piston or broken ring land. Cast roadster/H20 pistons are a terrible choice for turbo use-they were never intended or designed for that. If you don't lower the CR, you are begging for problems.

It only takes a few seconds of lean condition under boost and its all over. I'd have to agree EFI would be a far better approach, but you really need to understand the details of engine management completely to do this. Otherwise you will be rebuilding the engine in no-time.


J
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Gregs672000
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Re: Blow through turbo charging

Post by Gregs672000 » Fri May 10, 2019 1:32 pm

Dellorto carbs come ready or can be easily modified to accept boost. I love Dellortos, best carb I've owned. As noted the steering shaft takes a lot of room, that why I would go supercharger... a lot less complicated I think, no exhaust manifold to make, easy mounting place on the side of the engine that came stock (early) with the alternator mounted there (so there are acceptable places for bolts etc), and no need to relocate and make a mount for the alternator, already done. I would be comfortable using the carbs with a SC more than a turbo. Make a different pulley to turn the SC, consider going megajolt for ignition control, or maybe the 123 dizzy makes more sense here due to simplicity.

You'll need an appropriate SC, make a mount, figure out how to drive it, tubing to the carbs with a blow off valve, a sealed air box, a bunch of Dellorto jets, a wide band air/fuel meter, maybe an intercooler just to help with any detonation issues, and better timing control from a megajolt or 123 dizzy (megajolt much more difficult and requires crank pulley modifications and a laptop computer). Go easy on boost, jet the carbs carefully and watch your timing and expect to use the best high octane fuel you can find. THIS WILL NOT BE CHEAP, but I think it's quite doable, and would be a fun mod to an R16 as well. Price things out accordingly and add another 10%.

As JT just noted, you have to have an engine that can handle the extra strain. Forged pistons seem likely. LOWER compression is advisable if you plan to run more than maybe 8lbs (?) Consider your engine condition now. Detonation is a very real issue. Most boosted engines run into problems when they go lean due to excessive boost without a fuel system that can adjust accordingly, so you would have to build it specifically for the Boost you plan and no more. Changing boost on a SC is harder than a turbo, so you won't likely be tempted to turn it up. Back in the day they didn't have wideband A/F meters available to monitor systems on the fly, so that MAY help protect you some from meltdown, but you can't be stupid or you'll be on the side of the road. I run 11.7 to 1 compression and would never consider that engine on the street without the wideband.
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Alvin
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Re: Blow through turbo charging

Post by Alvin » Fri May 10, 2019 3:54 pm

Let there be Boost!

Plasmaboy's Weber-carb'd blow-thru setup:
Image
Image
Image

http://www.311s.org/pmwiki-311/pmwiki.p ... ysU20Turbo
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Re: Blow through turbo charging

Post by fj20spl311 » Fri May 10, 2019 3:56 pm

Blow through carb:
You need to run all the vents and overflows to the pressured chamber.
You will need a rising rate fuel pressure regulator so the fuel pressure can be set at chamber pressure + normal Dellorto fuel pressure.
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Re: Blow through turbo charging

Post by fj20spl311 » Fri May 10, 2019 4:21 pm

ryderfmjones21 wrote:
Thu May 09, 2019 12:35 pm
I’m probably leaning towards the more “cool” factor as a reason why. I want to challenge and see if I can make something like this work.

I do work in a cnc shop so making custom components isn’t a far shot!
If you want something "cool" I would make my own Fuel injection manifold.
Take at look at "parts" available from Ross Machine Racing http://rossmachineracing.com/intakepartspage.html to get an idea.
You would need to machine some aluminum flanges for the head.....I bet you could sell some to finance your build.
You can buy a lot of the raw material from Ross that just needs to be cut and fit.
Make a jig to hold everything in place and have a pro weld her up.

Your current carb set is worth maybe 2K
Phil
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datsunrides
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Re: Blow through turbo charging

Post by datsunrides » Fri May 10, 2019 6:34 pm

JT68 wrote:
Fri May 10, 2019 1:18 pm
There were many blow through turbo setups done in the 80's. Most went the way of the dinosaurs because many, many resulted in blown up/melted engines. The U is also a particularly poor choice for turbos since it is prone to head gasket issues as-is.
Yes, it can be done, but should be exceptionally well thought out - like the datsunrides car appears to be.

Also, unless you build the bottom end for a turbo, meaning lower compression forged pistons, the likely outcome is a melted piston or broken ring land. Cast roadster/H20 pistons are a terrible choice for turbo use-they were never intended or designed for that. If you don't lower the CR, you are begging for problems.

It only takes a few seconds of lean condition under boost and its all over. I'd have to agree EFI would be a far better approach, but you really need to understand the details of engine management completely to do this. Otherwise you will be rebuilding the engine in no-time.


J
This was a concern of mine so although I have built a few motors, I never built a motor that was not factory designed for a turbo. I relied on the expertise of Rebello to build my motor and it has, so far, paid off. The main difference from a stock motor were the custom forged pistons with a reduced CR and having the block oringed for head gasket sealing. He also modified the jack shaft by drilling it deeper, but I think that was more general reliability. As far as I remember the rest of the bottom end is stock, just carefully rebuilt to Dave’s specifications. As these are not cheap motors to build, I did all my setup and initial tuning on a mule motor so I wouldn’t do damage to the fresh Rebello motor. There were some growing pains so I was glad to have done it this way. I know you want to use carbs in a blow thru configuration, but I’m just going to point out a few things my fuel injection system “automatically” does, based off a MAP sensor

-when the MAP senses boost, it increases the fueling
-retards the timing when boost is sensed
-increases fuel pressure (via a boost referenced FPR)
-accounts for air inlet temperature

These are things you will need to work out also, or your engine will probably not last long. While I like the cool factor of having possibly the only injected, turbo U20 Roadster, it was costly (even with doing most of the fab work myself). Not trying to discourage you, just want to make sure your eyes are wide open.
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Linda
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Re: Blow through turbo charging

Post by Linda » Fri May 10, 2019 7:59 pm

When the word "costly" is used what does that mean? We never seem to get a number. Is that because wives could be reading? :shock: I had heard 8K for a straight quality U20 rebuild, so all this would be a bit more I am thinking.
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JT68
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Re: Blow through turbo charging

Post by JT68 » Fri May 10, 2019 8:54 pm

If you use 8k as a basic number, you would be closer to 10k+ easy for a well built turbo engine-probably more.

The approach taken by datsunrides was smart which is why he didn’t end up with an oil pan full of piston shrapnel. $$$

I almost never recommend SR swaps - I am a U20 fan, but a plain vanilla sr20det will survive the turbo far better than a standard build U20. In this case an sr20det swap probably has a much, much better chance of survival.

If you have the cash for a high end U rebuild,that is a great start, then add really careful fuel and timing management-If you don’t address all these points, you will just destroy a perfectly good U20.

You were planning on a full rebuild before all this turbo effort right? If you turbo a semi-worn out stock U20, it won’t work well and will have a very short life indeed. Cheers
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Re: Blow through turbo charging

Post by fj20spl311 » Fri May 10, 2019 10:46 pm

Linda,
I use so many $$$$ per month a budget......LOL....Some things just take longer.

I paid 6K for a U20 motor with a complete rebuild, including new cam and rocker.
I am thinking of adding EFI, that's another 3K
Phil
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JT68
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Re: Blow through turbo charging

Post by JT68 » Fri May 10, 2019 11:51 pm

I think if I was going to turbo a roadster engine it would be a stroker R built around a u20 crank (not a h20) with forged pistons, turbo designed forged rods, lower CR and either an iron 66 head or a H20 head. Those heads really don’t have many HG issues and flow well.

With a blow through carb turbo on a "standard" U20, you would be seriously boost limited to the point that you would really have to ask "does this make any sense"?? Even a wideband isn't going to help much unless it is integrated into the engine management because by the time you have visually noticed its lean under boost, you have detonated and broken a ring land. It literally takes only seconds.

If you really want to turbo the U20, I'd strongly suggest datsunride's method of going "all in" with a purpose built engine, efi and proper engine management for boost, enrichment and integrated timing control.

A stockish engine with poor engine management will simply fail. boom,crunch,wap!

With an r21, correct CR, strong, lighter forged internals and an iron head (there would be no need to o-ring the head or block to keep a head gasket intact), very large radiator, very large intercooler, EFI and real engine management, you could bring the boost up to moderate levels and easily outpower any U20.

oh yes, don't forget valves. Stock exhaust valves will not be up to the turbo job for long-so custom exhaust valves, inconel is probably best... Anyway you slice it, this is a megabucks project if it is to work well.
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Re: Blow through turbo charging

Post by ryderfmjones21 » Wed May 15, 2019 5:24 pm

The u20 I have is already rebuilt. But I am not sure to what specifications. I assume the guy before me hadn’t even tried turning it over because the starter motor was trashed. I got a gear reduction one and wired up everything on a stand and got it running. I do know the pistons, bearings, and valves were all replaced but I’d have to call up the guy and ask him what he put in there. My car is in about a million pieces right now I have the frame complete with the motor on it moving on to putting some color on soon. Doing a frame off. I am getting a 123 ignition set up from a very nice gentleman named Brian or his Instagram @kadmodels. I’ll have to see how my motor is built to progress any farther is what it’s looking like.

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Re: Blow through turbo charging

Post by ryderfmjones21 » Thu May 16, 2019 1:44 pm

The pictures Allan posted of the supercharged roadster is very similar to what I have in mind. If I went that route that’s probably how I would set it up. I might get a smaller supercharger. Anybody know any types that would be good for the application. Keeping part availability and budget in mind?

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Re: Blow through turbo charging

Post by fj20spl311 » Thu May 16, 2019 3:11 pm

The MR2 is the smallest readily available used that I know about. If you want less pressure, use a smaller crank pully or larger Blower pully.

You will need to "Build" your motor for a blower.

Get your car together first, too easy to get distracted into "while I'm there"
Then IF you still want/need buy a second car as a mule to develop your blower motor. I think JT is correct in developing a R16-2L
Phil
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