davidt's Scat 1915cc Megasquirt and Supercharged build

[panel]

I thought I'd start this thread for David here. He can answer all the questions as I just posted the pics only. After seeing these pics I think he might get a lot of questions re his build.

Quote from David:

You could fit an AMR500. It is a 500cc twin lobe rootes style blower from the Japanese Kia class of cars from the 1980/1990's.
I have fitted one to my 1915cc Scat engine in a 1972 Superbug. I run Megasquirt EFI and E85 fuel with 6 injectors, sidewinder style 1-5/8 stainless exhaust and a cold air filter box. Engine is making 7.6psi from a pulley ratio of 3:1 and that is the maximum the the blower will make with my size engine. Has awesome low down pull that turbos can only dream of (try 6.5psi at 1500rpm)

Just an update with my AMR500 fittment. She has been on the Dyno. Scat 1915cc, Megasquirt ECU & custom fuel injection, E85 fuel and AMR500 supercharger. Made 116hp (at the wheels) at 4900rpm but had a minimum of 110hp between 4000rpm and the rev limiter at 5700rpm. Maximum torque ran between 2500rpm and 4000rpm and peaked with around 525lbs of tractive effort. As a comparison a standard 1600DP makes 38-40hp and 250lbs of tractive effort on the same Dyno on the same day. After the Dyno session I found a loose L/H inlet manifold plus on the data logs the air-fuel ratio was in the 10's (quite rich) above 5000rpm so there may be more in the old girl yet. The boost varies depending on revs. During the Dyno run, the boost starts at 7psi at 2100rpm and then dips down to 5.3psi at 4100rpm and then climbs to 10.9psi at the 5700rpm limiter. Since the AMR500 is a positive displacement blower, the actual air getting pumped into the engine cannot vary, give or take pumping loses, etc. The boost pressure that is registered on a gauge is just a representation of the restriction of the actual air flow getting pumped through the intake system, cylinders and exhaust system. So I believe that the boost pressure is not actually dipping in the mid range. That is where the engine is at its most efficient and is flowing the best. On my Scat 1915cc engine the intake plumbing size, intake port size, valve size and cam profile are set-up for max torque in the 2000-3000rpm range and max power around 5000rpm. So in summery I think that if I ported the heads, fitted even larger valves and installed a more aggressive cam suited to Supercharged forced induction, then I would expect the boost to be more linear and the power would increase. An intercooler would really help as well but there is not enough space.

So if you are thinking of going the Blown route then I would recommend it. After all, "It is better to be blown than to suck".

[Vee Dub Nut]

Neat build... very unique and well done.

[itawolf]

WOW very nice setup---and different

[juki48]

very cool setup! what are the IAT's under boost?

[miniman82]

Has awesome low down pull that turbos can only dream of (try 6.5psi at 1500rpm)

OK fine, but an intercooled turbo will make more power at the same boost. Maybe not as low, but certainly more fun.

[davidt]

Thanks everyone for your kind words. I will try to shed some light on how my engine set-up performs and also some pro/cons between turbo and supercharging.
My set-up only uses a small 500cc supercharger as I wanted the stealth look and for the whole set-up to hide under the deck lid without having to use stand-offs. This is the same as fitting a small T2/T25 size turbo to your engine. If I went to a larger blower (Toyota style) then I would make more horsepower but at higher revs just like when you fit a large turbo. The larger the turbo, the higher up your rev range you will be before you make decent boost and power. The larger the turbo, the longer the boost lag will be. Supercharging does not have this issue. I had a 1.6L Holden Gemini that I could run with either a T25 or a T3 turbo. When running the same boost, the smaller turbo pulled hard from 2000rpm to 5000rpm but died in the arse after that. The larger turbo ran like the standard engine until 4000rpm and then went feral until 7000rpm. That is just an example of what can happen and turbo's now days have much better response. If you correctly size your turbo or supercharger than you should get a configuration that suits your driving style and the driving conditions (eg, drags, hill climbs, street traffic, circuit racing). I love both forms of forced induction. Each to their own. Of the many people who have now driven my car (one person owns a 2.4L naturally aspirated 67 Beetle with just over 200hp and his car pulls 12.7 second 1/4 miles, another built Beetle drag engines back in the 80's), non of them think that my car is not fun to drive. I think it is because of the instant response and shove from small throttle openings and low revs.
Inter-cooling reduces intake air temps and that makes extra power. However I am space limited plus I use fuel to help cool my intake charge. The temps are very high and I am still working on a cure. Currently I am trying to plumb a BOV to act as a by-pass valve. This would connect the blower outlet to the blower inlet during idling, cruise and deceleration. I think it will make a positive difference. My engine also uses water injection and runs E85 fuel which is also helping. The temps have peaked at 148C (melted an air temp sensor on the way to the dyno day) on deceleration down a long hill and run around 80-90C during cruise. Full boost acceleration gives around 120-130C. So as you can see I need to lower those temps.
Anyhow, that is enough rambling for now.
If you have any questions then please ask.

Hooroo

David

[ToRy 70]

What an excellent looking build! Nice job David!

[davidt]

Here are the links to my videos from the Dyno pulls.

https://www.youtube.com/watch?v=IDOdciYfAUg

https://www.youtube.com/watch?v=ZCiwCKyI9EE

Hooroo

David

[fastback]

very nice build.
i think with a proper sized VGT turbo , mild cam ,you can get small boost at low RPM
at least i have it my TDI westy

[davidt]

I am happy you like it Fastback. Thanks.
VGT turbo's are not very common in the petrol engine world. This is due to the higher exhaust temps that you get with petrol engines compared with diesel engines. Somewhere in the vicinity of 900C compared with 500C. The high temp causes issues with the metallurgy of the vanes. Porsche solved the issues with the 996 (I think) 911 Turbo but you don't see them as an aftermarket fitment. They also need a complicated (usually computer controlled) controller to manage when the vanes are closed and open. I think that is the main reason they are not readily available.
Yes you are correct in saying that your TDI makes boost down low but would it still make good boost at 5000-6000rpm?
Turbo's can make boost down low if sized correctly but most people want the top end rush instead so they size them to come on boost in the mid rev range. A friend of mine makes 200hp with his 1915cc but under 3000rpm there is no boost and then by 3500rpm he is on his way to 15psi that then holds out to 7000rpm. Goes great in a light weight Baja. But in an 1100kg Superbug around town it would be a different story.
If anyone has a dyno print out of their street 1915cc turbo showing showing how much low down torque/power they are making, then I would be very interested in seeing it and comparing the torque/power curves to mine.
Again, I am not saying that supercharging is superior to turbocharging. It is just a different way to boost your air cooled engine and to have some fun with your pride-and-joy. I would love to see someone build a twin charged aircooled VW. Now that would be awesome and different!

Hooroo everyone.

David

[mads b (dk)]

I have a stock 1600 cc with a garrett GTC 1244 vgt and VEMS ecu, ill let you know how it performs when i get it messured.

[panel]

Couple more pics from David from the Dyno Day...........

[fastback]

yes the TDI VGT turbos are not rated for such high tempereatures as gasoilne turbos.

quote from a thread on TDI club.
" Design limits for steady state "turbine inlet temperature" are 750 C / 1382 F for the GT15 and KO3 turbochargers, and 850 C / 1562 F for the VNT15"
so for street use and running E85 a VNT15 should work. but near the limit.
done a lot of logging on my E85 engines running on the rich side and measured in the inlet of the turbine i have seen temps around 750-870 C depening on driving from dragrace to circle track . so for a street car that does not see high load over long time like the track i think (and hope) it could work.
using longer headers without insulation would maybe help to keep the exhaust temp a tad lower.

[davidt]

Hi Fastback,

That is some great factual info on VGT turbo's. It is certainly a possibility that the VGT would work as you said. Worth trying I think. Thanks.
What ECU are you going to use to control the vanes?
What parameters are you going to be able to use to control when and how far the vanes open?

David

[fastback]

i run Megasquirt and it has a boost duty table based on RPM and Throttle in the current verison i have now
together with a "n75" VAG boost valve or similar and a electric vacum pump i think this can work.
have'nt checked if the there is possible to use other parameters for the duty table on later software versions.