supercharger

[kcbugeye1275]

I'm having a motor built for the supercharger (yehaw) & I was wondering about the heat sheild available from moss. Is it something that should be installed? KS gets hot in the summer. /ubbthreads/images/graemlins/cheers.gif

 

[Trevor Jessie]

The heat shield couldn't hurt since a cool charge is denser and can allow for more fuel/air and hence the bigger bang. It also helps reduce detonation. I'm going to fab one up myself (when I get a "round tuit").

I'm currently running a SC on a mostly stock engine, with plans to build a engine after I get my EDIS and oxygen sensor in place.

What are the specs on the motor you are having built?
Have you run the SC on the stock motor yet?

 

[jlaird]

The guy makeing the stainless steel heatshelds for moss has a prototype on his desk for H1 carbs and is proceeding. More to follow, I can give you his email if you wish. PM me.

 

[RobSelina]

loosely related question:

How do a super charger or turbo system compare to just a naturally aspirated high-compression engine?

In other words, if you took an engine with 7.5:1 compression, and reworked the internals to 9.5:1 compression, how would that compare to the 7.5:1 engine with a supercharger putting out 4psi of boost? (both would have about 140 psi at TDC in the cylinder). Does forced induction produce power in other ways than just increasing compression?

Sorry for going OT, just got me thinking /ubbthreads/images/graemlins/wink.gif

 

[kcbugeye1275]

A buddy(who also has a bugeye) & I are having Kent Prather build our motors, and we haven't got our blocks back from the machine shop yet. Kent found two sets of hepolite pistons, one .020 over and the other .040 over. so I guess one will be a 1293 & the other will be a 1312cc. As I get more info I will share it with you. A TR 6 friend found a sc kit and installed it on his stock motor, it really is a kick in the pants. He has experienced some blowby into his oil, so he changes it more often. Have you noticed this problem?

 

[Trevor Jessie]

I have not had any noticeable blow by, but I'm on a fresh rebuild of a low mileage engine.
What compression are you looking to have?
Any concern about blowing head gaskets with the .040 over?
What about head/valves/cam specs?

I'm glad I've found someone working on a build before I start mine! /ubbthreads/images/graemlins/wink.gif

Before I installed the SC, I had big plans for building my engine this summer. However, I've been so impressed by the power the engine is producing I decided to move the project to next winter.

 

[Trevor Jessie]

Not quite that simple. First of all... the boost is not linear. It comes in as RPM's increase. In a turbo the boost builds slower, but there is no parasitic drag on the engine as with a SC...but you knew that. And... just because you have 4PSI in the manifold doesn't mean it is efficiently reaching the cylinder in properly atomized form. Hopefully a person with some expertise will chime in. It's late I need to sleep. /ubbthreads/images/graemlins/tongue.gif

 

[RobSelina]

[ QUOTE ]
Not quite that simple. First of all... the boost is not linear. It comes in as RPM's increase. In a turbo the boost builds slower, but there is no parasitic drag on the engine as with a SC...but you knew that. And... just because you have 4PSI in the manifold doesn't mean it is efficiently reaching the cylinder in properly atomized form. Hopefully a person with some expertise will chime in. It's late I need to sleep. /ubbthreads/images/graemlins/tongue.gif

[/ QUOTE ]

Yea, I realize low RPM performance is different and turbo systems experience lag depending on exhaust routing and blow-off valve configurations, etc - but within the power band, assuming compression in the cylinder is the same, would there be a performance/output difference?

 

[Trevor Jessie]

Well, there is a physical limitation to the CR you can create and still have effective intake and exhaust strokes. Therefore, compressing the intake charge is a means of getting more charge in place.

 

[Matthew E. Herd]

Yes, I believe the thing with a supercharger isn't JUST the higher effective compression, but also the increased mass of charge, versus the standard (NA) version. Therefore, it's akin to having a larger cylinder (almost). However, the CR is also effectively higher which then limits the amount of charge you can pack in there. This is a good way to look at it, as a matter of fact.

Think of it this way: It's as if your cylinder displacement increased in a variable fashion, but the compression chamber remained the same. Thus, as engine speed increased, the cylinder size increases (because boost increases), but the combustion chamber is still the same (relatively small) size.

 

[RobSelina]

got it! thx!

 

[GTsRFine]

According to Carl Heidman (Eclectic Motorworks), the best thing about the SC on a street engine is that the torque comes on sooner in the RPM band. That puts it right where most street cars live (2500-4000 rpm). He's got some dyno curves on his website which are on the B engine but the response in the mostly stock A engine should be the same.

 

[kcbugeye1275]

I love all the tech answers that I only understand a little of. But there is another hidden ? that I asked myself making the decision to go with a sc. First, I don't think that a turbo works on a spridget for a number of reasons a>exhaust size, b>Where does the turbo and intercooler go, c>engine compartment heat. Second, the disadvantages of a high compression motor, a>finding high oct gas, b>pinging, c>making hp at a higher rpm and not having a nice streetable motor. With a sc'ed motor it will idle and run on like any other street motor til you want to go and then ......................... The last point, availabilty, thank you Moss Motors.

 

[Matthew E. Herd]

Just a few comments on the subject. It really doesn't matter what type you use. If you use a supercharger, it has a more gradual pickup of boost, but it also has more parasitic drag. Exhaust size is what you make it. Likewise, you'd have to develop new manifolds (intake at the very least) for the supercharger. Positioning the intercooler and supercharger are really not a big deal. Where there's a will, there's a way! The engine compartment heat is really comparable to stock, so that's not a big deal either. Heat tape or ceramic coatings help to reduce underhood temps. Just like the 1500, the A series has some versions with lower compression. They're generally in the 8:1 CR range, which is fine for a turbo.

As to high octane gas, you really don't need jet fuel to make any type of boost work properly. You just lower your CR. I have a full blown normally aspirated 1500 engine, and I use Sunoco Ultra94 with no problems. While pinging is always a concern, it's really not a big deal if you're cautious about increasing boost. Likewise, with the fairly decent CR of 8:1 or so, you're making no less than stock HP down low, but with a kick at the top. It's definitely no less streetable than stock, regardless of turbo or supercharger. NA tuned motors are much less streetable.

Basically, it's not a big deal, its just a matter of taste (and pocketbook size).

 

[kcbugeye1275]

Went to Prathers last night, the blocks are back from the machine shop where they had been line bored.
John & I had our Cranks home & had polished them (?, that always sounds just a little odd). I guess there is a chance that the journals could be a different dia. Just checking. The plan is to drive the bugeye during the spring & install the sc motor in the heat of the summer. With the lightning turnaround time at the machinist, it is a schedule I can live with.

 

[Dave Russell]

[ QUOTE ]
loosely related question:

How do a super charger or turbo system compare to just a naturally aspirated high-compression engine?

In other words, if you took an engine with 7.5:1 compression, and reworked the internals to 9.5:1 compression, how would that compare to the 7.5:1 engine with a supercharger putting out 4psi of boost? (both would have about 140 psi at TDC in the cylinder). Does forced induction produce power in other ways than just increasing compression?
Sorry for going OT, just got me thinking /ubbthreads/images/graemlins/wink.gif

[/ QUOTE ]
Hi Rob,
A supercharger crams MORE mixture into the cylinder & into the same combustion chamber volume. This increases thermal effeciency PLUS there is more mixture to burn. Raising the compression ratio merely compresses the lesser amount of mixture more tightly which increases engine thermal effeciency.

A rough approximation is that raising the compression ratio from 7.5 to 9.5 would increase power by about 13%. Raising compression ratio does not give a power increase which is proportional to the cr increase. Eg. a cr increase from 6/1 to 8/1 would give an increase of about about 18%, a larger power increase than a cr increase from 8/1 to 10/1 which would give 10%.

A supercharger with 4 psig boost would give a power increase of around 18%. 8 psig of boost would give about 36% power increase. The previously mentioned compression ratio increase would still give only 13% power increase. This is one reason that supercharged engines often have lower compression ratios. The lower compression ratio allows more supercharger boost & burnable mixture in the cylinder without exceeding maximum allowable cylinder pressures.

Somewhat related:
A turbocharger with a properly setup turbine, with an A/R ratio of say 0.6, & a proper wastegate, can be made to give quite high boost at low to mid rpm. The direct drive supercharger cannot give this high boost at the lower rpm. There is no doubt that the turbo plumbing & related controls are much more complex though.
D

 

[Morris]

HA! I have been looking for this link since this thread started. It's about adapting an MG Metro Turbo to a 1275 Spridget. The MG Metro claimed 93hp max output. Much higher than the numbers given by the Moss kit.

https://www.turbomidget.connectfree.co.uk/index1.htm

 

[RobSelina]

Thanks Dave.

I don't think I would use forced induction on this car now that I"m getting interested in autocross and I need to be cautious of throwing myself in a class where I'm hopelessly uncompetitive, but it's great to learn regardless!

 

[Timboy57]

Hey Morris here is another site regarding turbocharging spridgets.
I read up on it a little and was not sure if it could be done easily on a left hand drive car.
https://turbocharged-midget.tripod.com/index.html