Project "Ultimate 1983 Rabbit GTI"
Engine & Transmission ...
Index of Project web pages
Project Overview, Goals & Initial design specs
Project car initial condition
Bodywork & Paint
Suspension, Wheels, Tires & Braking System
Engine & Transmission
Electrical & Fuel System
VW Vortex Thread on this project
My original 1983 Rabbit GTI (owned 1983-1987)
I was always interested in Callaway turbo kits for my original GTI and came close to acquiring an 84 GTI with one of these kits installed on it. But turbo kits add weight and they change the engine's free revving characteristics which were perfectly matched to the 5 speed trans. Like many other people I feel that the ultimate mk1 GTI has either heavily worked over 8V heads or carefully massaged 16V heads (keeping an eye on mid-range torque), a 2L block, and a close ratio 020 transmission. So I contacted Josh Arnold at Techtonics Tuning in Portland, Oregon, (who did the engine development work at his own business with his dad, Mark (Mark's VW Service, Amity, Oregon) and asked him if he would do the ultimate 16V buildup. He started sourcing the components and building up the motor in late November 2012 and completed it in March 2014 (for more info on Josh, TT, and a similar project, see this VWVortex thread).
We choose a VW/Audi ABA-ABF hybrid short block (used in the mk3 VW/Audi 93-97 16V 2L cars producing 150hp) and Josh built a 2092cc 16V motor around an ABA block with ABF internals: a new VW OEM 95.5mm stroker forged crank, custom forged rods, 83.5mm 12:1cr custom pistons and a lightened/balanced intermediate shaft. The heads are high velocity/turbulence 9A 16V (used in the mk2 VWs) with +2.0/0.5mm over sized 34.0/28.5mm valves/seats, 5.5mm super small intake stems, tapered guides, etc. - with a full 'stage 3' head treatment. And the cams are TT 288 degree solid lifter (DLC coated) race profiles to deliver moderate midrange torque and a targeted 240hp peak at or slightly above 8000rpm. And to top it off we are using an individual DTH (direct to head) ITB intake system from AT Power, the Holly HP EFI system (with 8 injectors - 1 set for low RPM/part throttle, and the 2nd set for high RPM/full throttle), and a dry flow nitrous system to add mid range torque and 60hp at 8000rpm for a total of 300hp).
To fit in the ATPower TBs and their long curved 280mm individual intakes, I am designing a custom radiator that tucks in behind the grill. German Transaxle of America has built and delivered to Techtonics an 020 AGB 2Y (mk3) close ratio transmission (same exact 3.45/2.12/1.44/1.12/0.91 1st thru 5th gearing as the original 020 2H trans but with a 3.67 final drive ratio rather than the earlier 3.94 ratio) with a Quaife differential and many other performance goodies. It will be shifted via a Techtonics shift kit. HD rubber engine/trans mounts have been selected to provide a performance oriented mounting system without undue harshness or vibration. A high performance 210mm clutch with lightened flywheel will be used. The car will cruize at 70mph at 3465rpm and will be at 150mph at 7500rpm in 5th gear.
High quality race prepped 100mm OEM CV joints and axles have been fabricated/assembled as well.
Initial Engine Assembly photos - taken at Mark's VW Service and Techtonics Tuning - Feb 15, 2013
Josh Arnold - engine builder extraordinaire
The VW (mk3) ABF block, (mk2) 9A cylinder head and 83.5mm forged piston
95.5mm stroker VW forged crank and rods prior to lightening and finishing
11.5:1cr forged 12% silicon (low expansion) forged piston
VW 9A 16V cylinder head
Combustion chambers with 34.0/28.5mm oversized valve seats, prior to blending, valve unshrouding and bore matching
Intake ports (left unpolished to foster mild turbulance)
Tapered 5.5mm intake valve guides and blended 34.0mm (+2mm) valve seats
Polished exhaust ports, tapered exhaust valve guides, 28.5mm (+0.5mm) valve seats, port matched to 1.75" primary exhaust header tubes
Comparison of 5.5mm stem x 34.0mm diameter intake valve with stock 7.0mm stem x 32.0mm diameter intake valve and retainers
Comparison of 28.5mm diameter light weight/undercut exhaust valve with stock 28.0mm diameter exhaust valve
Techtonics HD valve train components
Techtonics factory/warehouse tour ...
The AT Power Individual Throttle Body intake system for the 2092cc stroker VW 16V ABF/9A motor
Photos taken March 12/13 2014 when the engine was completed:
NOS Wizards Quadranoid, a dry flow nozzle, and small ID plastic tubing - May 9, 2014
EAA Engineering's Serpentine Belt System, Fluidamper, and Denso Racing Alternator (all put together with clear anodized billet aluminum CNC mounts) - a must use system to clear the ITBs - May 9, 2014
Now that I have ordered the Davies Craig electric water pump and digital controller it is time to prepare the OEM water pump by cutting off the impeller, aux water return ports (which will be tapped and plugged), and smoothing the interior for its new function as a passive entry way into the block from the outlet of the EWP - August 17, 2014
Rough positioning of the Techtonics stainless custom 1-3/4" headers and 2-1/4" exhaust system plumbing (note, we are keeping the pipe size at 2-1/4" because this is the size that TT says has proven to produce the most power in normally aspirated cars: 2-1/2" is only suitable for turbo engines) - September 8, 2014
After a lot of machining and fiddling around I managed to complete the front cylinder head coolant outlet flange that is required to clear the ITBs and associated linkage, nitrous and vacuum lines, etc. - September 14, 2014
After speaking with Techtonics about the exhaust system clearance issues I cut off all of the tunnel flanges and bolts, filled, sanded, primed and painted it all so now there will be nothing hitting the pipes. I also sourced a really nice and small Vibrant stainless resonator that will be welded onto the back of the flex coupling: this way I will havee 2 resonators plus a muffler so that I can make 'quiet power' which is my goal - September 14, 2014
The shifter housing after cleaning it up and epoxy painting it - September 14, 2014
I have been busy using my Caswell Zinc/Copy Cad plating system to rescue all kinds of brackets and bolts since I have not been able to complete my brake lines until the MasterCool flaring tool arrives (ETA tomorrow). I plated the metal objects that were OEM plated and stopped there but for those parts that were originally painted black I first stripped them down, acid etched, plated and chromated them to provide an extra measure of protection before painting - September 23, 2014
This has been a big week with lots of progress. Below are photos of the plating/painting of the headlight housings, the various motor mounts and inserts/shift linkage, etc going into the car, and the heat shielding. Not shown is the braking system which is now complete and the Quaife steering rack which is also now complete (see other web page) - September 28, 2014
The rear end is complete and torqued to spec, the steering rack and shifter linkage is now mounted in the front and now I am getting ready to flip the chassis upright for the last time - October 6, 2014
... and the 020 2Y German Transaxle of America transmission with Quaife LSD is sitting here, waiting for the custom clutch/pressure plate which Josh says will ship to me later this week ...
Quaife transmission differential ...
There is an excellent VW transmission specifications reference site at http://www.rabbitgtipage.com/transmission.html
The engine is now getting very close to mating with the transmission, and installed into the chassis- hopefully this weekend. Below are some before and after photos of the cam position sensor, turning the OEM unit from a 4 position sensor to a simple TDC #! sensor - October 21, 2014
Major Project Milestone: Today was the big day - getting the clutch setup done, and then assembling the engine and transaxle, rolling it under the chassis and then hoisting it into place. Everything went well except for the fact that I had to remove the rear engine/trans mount to get the side mounts to line up first which is a lesson learned, and I also discovered to my dread that I will have to mandrel bend the intake runners another 20 degrees or so to clear the hood - October 25, 2014
I am building a structural support brace for the race header that connects the lower end of the header back to the base of engine block to keep the stress levels on the flanges to a minimum - November 2, 2014
Here is the completed structural support brace for the race header, also a photo of it after electrocleaning, and the header itself after porting/polishing but before internal ceramic thermal barrier coating - November 11, 2014
I completed the exhaust system this week. Below are photos of the V-band clamping system I have used to allow me to quickly swap the cat converter in/out in favour of a high performance resonator that will keep noise levels down to where I want them (a total of 3 'straight-thru' resonators make up the entire system), the welded up and polished components, and finally the 2.5" tip that says 'we mean business' - November 23, 2014
The 'optional' cat converter in place ... (I had to swap the flex pipe to the back end to clear the shifter boot)
The completed system with the 2.5" tailpipe ...
I have been noodling away on solving my problem of the ITB intake runners being too high (interference wit the hood). This problem was caused by not remembering that the ABA block is a lot taller than the earlier mk1 and mk2 blocks. In fact my second injector fuel rail is close to hitting the hood as well! Anyway, I sourced high strength molding epoxy and built cardboard molds in the shape of the runners, which are 45mm ID, 48mm OD. I then mounted the epoxy molds onto steel plates and used threaded rods to allow me to apply bending pressure to increase the bend another 10 degrees or so - but those steel tubes would not budge 1mm, even with 500lbs of force. Eventually the epoxy 'caps' that I had made up snapped.
The good news is that today I finally found 48mm OD, 1.5mm wall thickness T304 stainless tubing, mandrel bent at 30 degrees, from the UK, which puts the intakes in the right position to clear the hood. I am trying to get an order placed along with another order from AT Power for another set of inlet/outlet caps for their ITB assemblies so that I don't have the try and un-glue the current intake runners (I did one today and made a mess of it as the glue, even when heated to 500 degrees, holds very strongly).
It looks like I should have this challenge behind me in a few more weeks. In the mean time I got the shifter linkage installed and all dialed in using the Techtonics shifter kit plus the 4crawler adjustable steel end links which allowed me to get the 1-2 gate positioned exactly where I wanted it (just to the right of the reverse lockout). I will get the brake system/pedal assembly done this weekend - December 9, 2014
Techtonics shifter kit plus 4crawler adjustable steel end-links (all dialed in) ...
I received my shipment from Any-Exhaust-Part of the UK for the 48mm T304 intake tubes today and so I could not resist cutting them up immediately and test fitting them to the throttle bodies. Success! I now have the right angle and length to avoid hitting the hood, leaving enough room for the radiator/shroud/fans and the proper geometry for an efficient cold air intake box. I will still have to wait for AT Power to ship me the new collars as it is a real bitch to unglue the ones on the existing intake runners (and then I have to machine the collar IDs about 1mm to fit the new tubes once they arrive) - December 17, 2014
With the new ITB intake runner collars now in my hands I was able to get the intake system completed: I previously sourced new 48mm stainless tubing that was pre-bent at a 30 degree angle, cut them to the right length, ordered new collars, machined them to match the tubing exactly, made up the back plate for the air intake box, glued the collars onto the runners, assembled quickly, aligned, and will let sit overnight to cure. Now I can start to fabricate the rest of the air intake box. No more interference with the hood! - January 18, 2015
I made satisfying progress this week on the fabrication of the intake vacuum plenum, related sensor mounting, and all of the machining and tapping of the various connectors, including the nitrous solenoid. I was missing a 1/16 NPT tap in my tool chest and there was no supplier open today with the part I needed so I have ordered it from Amazon and will finish the tapping of the 4 ITB vacuum lines later this coming week. I also made an important decision to make the air box out of clear Lexan and put 2 of 2.75"x2.6"x12" K&N air filter elements (they provide 50 sq. inches of pleated filter element per unit) between the top of my custom radiator and the cross member, creating a Lexan funnel into the filters in front of the radiator, and then having a straight shot into the air box, rather than trying to create a long indirect 3 or 4" tube to pull in cold air from under the car (I am really excited about this new idea and think it will work out perfectly) - January 24, 2015
Over the past few days I managed to work on the cooling system after receiving some of the key parts - unfortunately, the Davies Craig electric water pump -20AN fittings weren't properly machined so I will not be able to finish this until new fittings are sourced. I also had another delay with the completion of the custom radiator - in fact we are starting over with a 1" narrower radiator core so that the side tanks are a full 2" wide to allow for the proper mounting of the -20 ORB fitting and other fittings. The new core will be in the hands of the fabricator Tuesday and with any luck I will have the completed rad in my hands in another week ... I also got the 1/16"NPT tap for the ITB vacuum lines so made more progress on the intake system, plus I got the K&N air filters, the speedo electronic speed sensor for the 020 trans, and a few other items. Finally, I ordered all of the components for the nitrous 'push' system which I will cover in a future video: it consists of a 4500psi air tank, a high pressure solenoid controlled by an adjustable pressure switch, and a normal nitrous tank: the pressure switch is set to 950psi and opens when-ever the nitrous pressure drops, allowing high pressure air to 'push' into the nitrous tank and keep a consistent pressure at all times, regardless of nitrous level or temperature. This is a much more involved system than a bottle warmer and obviously reacts instantly to keep the pressure constant as the nitrous is flowing ... stay tuned for more info - February 1, 2015
Fedex delivered my shiny new custom radiator from http://www.bsandbradiator.com/ today. A quick test fit confirmed a proper fit under the hood and so I was able to order all of the remaining hose end fittings and start to plan out the fabrication of some stainless brackets to support the water pump and coolant-to-oil intercooler. Tomorrow I will pick up a lot of goodies including the remaining air box components, nitrous system components, etc. - February 11, 2015
After a number weeks of business travel I managed to make some GTI project progress this weekend, first installing the re-built wiper motor assembly with new rubber grommets, and then test fitting some new coolant hose-ends in preparation for this week's task of putting together the remainder of the air intake system, fuel system and coolant system. I also got a chance to run some more air flow testing on the low profile SPAL radiator fans (yes, they flow a lot of air when mounted to the rad, more than enough) - March 8, 2015
This last week I got the custom radiator mounted properly, sorted out more of the coolant fittings, discovered a major interference issue with the -16 upper hose running into the vacuum plenum, built a number of Lexan air boxes (a few fails and then a successful one), and ended the weekend feeling pretty happy that things were coming together as (almost) planned. I also got my nitrous bottles filled and played around with the system a bit more: I will be doing PWM calibration testing on it this coming week - March 15, 2015
Rubber grommet mounts for the radiator ...
Ahhh, the carbon hood looks good ...
air box fail #2 (fail #1 was trying to heat and bend the Lexan sheets) ...
success on attempt #3 ...
and the airbox doesn't look like it will hit the hood ...
Over the weekend I setup the nitrous system properly on the bench with the custom high pressure air 'push system' and ran a series of linearity tests while pulse width modulating the trick new Quadranoid solenoid (from NOS Wizards in the UK). I consumed 20lbs of nitrous doing all of the tests and learned a lot about the optimum settings for that solenoid. I don't want to run a lot of nitrous in my car as it could hurt my beautiful engine with its ultra precise tolerances (nitrous rapidly increases the combustion temperatures and in turn causes the pistons to expand, etc.). I only want a range of 15-60hp under computer control, not 100hp+.
When I initially installed the 20hp jets, instead of seeing 20/40/60/80hp at 25/50/75/100% duty cycle, I got a range of 80-110hp using a frequency of 35Hz. It turned out that while the Quadranoid is rated to 50Hz, it needs to have the plunger adjusted (a unique NOS Wizards feature) to a minimum height so the range of motion is dramatically reduced, and then it can be accurately controlled at high frequencies. With the seat height at the stock full open setting the plunger just floats when modulated at anything more than 15-20Hz and that is too low of a frequency for my application (intake valves open and close 60 times a second at 8000rpm). While 35Hz, which is the limit for my Holley Dominator ECU, is below the rate of intake valve opening at max rpm, I am feeding the modulated nitrous into a small chamber in the base of the Quadranoid, and then thru the distribution block/jets and then thru tubing to the intake runners: by the time the PWM controlled nitrous comes out the end of the tubes it is almost flowing smoothy - it has a slight pulsing to it but not a ton.
I found that even with the seat height set fairly low the Quadranoid still flowed a ton of nitrous so I switched to the 15hp jets and set the seat height even lower - almost off. And then I got the #s I was looking for: 15/30/45/60hp at 25/50/75/100% duty cycle. One thing I am really interested in is seeing if the 15hp setting will actually produce more like 25hp due to the cooling effect that nitrous has on the intake charge. Nitrous provides additional O2 but it also cools as it vaporizes so even really small amounts of nitrous can add significant power. I am not interested just in peak hp, I want to use the nitrous at the mid-range to tame the 288 degree cams and add back in some of the mid-range torque that is lost due to excessive cam duration ... - March 24, 2015
NOS Wizards uses a lot of BSPT and BSPP spec fittings plus they are religious about plastic piping (to keep the nitrous volume in the tubes low and the opportunity for vaporization down) so it is a bit of a pain to connect it to race spec AN fittings and such. One area that is really interesting is how they incorporate metering jets into their system: the brass jets screw into the 4mm plastic compression pipe fittings (on the insides no less) ...
Filling up my 5lbs nitrous bottle after chilling it in the freezer from the room temperature 20lbs supply tank ...
After realizing that the new custom radiator had a nasty interference fit between the upper -16 hose and the intake system vacuum plenum log I got busy and ordered up another -16 ORB bung, cut a hole at the bottom of the tank (too bad, it would have been better to have the hot coolant enter at the top) and got my buddy Danny Beaudry of Pro Gas Engineering to weld it in (I am not up to par on tricky aluminum TIG welding like this when it involves a combination of thick and thin materials plus when it has to be leak proof). I then mounted the radiator coolant recovery tank on the side of the fender and started to make up the coolant hoses (a job I will finish in the next week) ... - March 24, 2015
Cutting and welding in the new -16 ORB bung to solve the upper (no longer) rad hose interference fit ...
And then making a d installing the -12 and -16 hoses, plus building a mount for the rad coolant expansion tank ...
I got all of the cooland hoses complete, plus the remaining fuel system hoses, and the bracket fabricated to mount the coolant-oil intercooler - it turns out that there is no need to make up another electric water pump supporting bracket as the -20AN coupler to the radiator plus the -20AN short hose connection to the coolant-oil intercooler supports the EWP extremely well. I had trouble making up the -4AN vacuum lines that run between the vacuum plenum and each throttle body but I ended up ordering a Kool Tools stainless braided line funnel tool and cutting shears that should make the task of threading the cut hose into the hose ends for these really small -4AN hoses less of a torture session, complete with blood all over everything - April 5, 2015
After Joey on YouTube suggested I try a banjo type hose end fitting for the oil line that connects to the bottom of the oil-to-coolant intercooler, I got to thinking that a banjo type fitting wouldn't likely flow as well as another similar idea: machining a block of aluminum to allow a right-angle mounting of the -8AN fitting off the side of the housing. I got to work today in my machine shop and now it is all together and the oil line is now slightly above the bottom lip of the chassis so I no longer risk hitting a critical oil line on a block of concrete or road hazard - April 13, 2015
The oil-to-coolant intercooler mounted up nicely with its new painted bracket, plus the oil lines were done and routed cleanly without rubbing against any painted surfaces (I did cutoff an unused bracket extension from the side of the starter motor to provide more clearance). With this job complete I have finished making all of the Stainless AN lines so I removed all of them from the engine and washed and blow-dried the lines so I can now install them permanently later this week when I will also install the heater core and air box inside the passenger compartment - April 20, 2015
After fighting with the old heater valve cable for about 2 hours (trying to lubricate it so that it would slide smoothly and open/close the heater valve) I gave up and found a replacement Gemo p/n 161819837 on ebay that looks like it will work fine in my mk1 application. I then fitted up the remaining cables that were in perfect working condition and mounted the heater/HVAC box in the chassis with its new gaskets. I was then able to hook up and complete the coolant system lines in the engine bay and pressure test the complete system to 15psi - success! I was also able to install many of the engine sensors and started to design a mounting bracket for the Holley Dominator ECU and ignition coils that will be placed in the rain tray on the passenger side (it is all weather proof but won't really see any water where it will be placed) - April 25, 2015
I managed to get the intake system 'final assembled' and get all of the fluids into the engine/trans: the coolant, and I tested the system with electrical water pump; the transmission fluid; the engine break-in oil, and I made up an oil pump drive tool to prime and test the system (using a VW p/n 027115027 oil pump drive gear from a 16V ABA motor, machining off the gears, and then TIG welding on a 1/4" socket); and finally the fuel in the tank and testing of the fuel system. And yes, there were lots of false starts, dripping fluids, and some new injector o-rings are now on order - May 19, 2015
I had been fighting the computer and sensors for the past several days but finally have it running now. Boy, it starts with authority and has a serious exhaust note to it (not really loud at all at idle but when the throttle opens it gets serious in a hurry). With the 288 race cams it will idle roughly at 900rpm but prefers to be closer to 1050rpm for smooth idle. I was expected worse ... seems that the ITBs saved the day.
I had fabricated a hall effect sensor for the crank position 60-2 wheel from a late model mercedes but it turned out to not like the tooth width/depth and would give the computer erratic timing info at anything past 200-300 cranking rpm. I had to go back to the ABA inductive sensor (analog output) that the Holley dominator ECU accepted. Once that was out of the way I got correct timing for the ignition/firing of all plugs, and all other sensors were operational. But then it would fire and immediately die after transitioning from the cranking parameters to the running parameters. Turns out that Holley means zero fuel enrichment when programmed for 100% - I had it set to 'zero' and that means 'kill the fuel injectors'. Go figure. Anyway, I have lots of programming left to do as the AFR learning is limited to modifying the parameters a fixed % beyond the base tables, not learning all of the fuel tables from scratch. My tables aren't close enough yet to allow the engine to run beyond 2000 rpm without leaning out so I will be at it again tomorrow sorting out the tables. It starts nicely now, builds lots of oil pressure, the cooling system programming all seems to work nicely (the electric water pump speeds up and slows down as required, the cooling fans speed up and slow down as well, etc - all really trick/nice to see).
Boy a new engine smells a lot when it first heats up!
I used the brakes and put the trans into 2nd gear and got up to about 40-50% throttle on it up to a little under 5,000rpm to help quickly seat the piston rings and auto-learn the base fuel tables. All went well and now I am going to take a much needed break from the project for a few weeks and go on a family holiday and will then head into the fall with the idea of completing the car and getting it licensed and on the road ... - July 22, 2015
Tragedy has (almost) struck the ultimate GTI project. Cylinder #2 high mount 30lbs/hr injector failed (this never happens) in the ‘on’ position, filling the engine with fuel when I was doing ECU fuel table learning under load. Potentially serious issue as fuel is not compressible and could result in bent internals. Freak failure. Never seen or heard of this happening before. Not an electrical issue. Simply an injector that decided to die and let the fuel pour out of it. I took the intake system apart, cleaned up and got the fuel completely out, etc.
Did a compression test: 180psi on all 4 cylinders on a cold engine. This is actually a great result given the 288 solid lifter cam with its large valve overlap specs. Will have a new injector tomorrow. Will change the oil and should be back in the game this weekend - August 6, 2015
After sourcing a new injector, cleaning up the mess from dumping so much fuel into the engine, lubricating the cylinders with Sea-foam cleaner/lube, cleaning and re-installing the O2 sensor and Denso spark plugs, and bolting everything back together there were no more fuel leaks or sticking injector issues.
I put more time into re-scaling the fuel and ignition tables, expanding the area from 70-102kPa MAP where the engine operates with the 288 race cams, tuning the idle IAC parameters, and also tuning the timing around idle and low-rpm part throttle, enabling idle stabilization via timing variation, programming in the acceleration enrichment tables, and otherwise leaning out the fuel table parameters to compensate for the low volumetric efficiency below 5000rpm, and after all of that the engine starts nicely, settles into idle smoothly, and has a very crisp throttle response, which is to be expected of an ITB setup.
Now that this is all done and a lot of the basic A/F ratio fuel table tuning has been done/learning completed, I won't fire the engine again until the wheels are on the ground and the rest of the interior and wiring is basically completed. It has 180psi cold compression on all 4 cylinders and is broken-in enough for me not to worry about idling it.
Now a few comments on the design decisions re. cam selection and other related engine components: We put these cams in at the last minute after previously deciding to build a set of race-ready heads and intake system with mild cams (a combination that pretty much achieves the best of both worlds) and then Josh (the engine builder) and I mused about first seeing what the potential of this engine was with the 288 cams, and then, if it was too much for the street we would swap in 276 or milder cams later on. I will likely also swap in softer sport H&R springs and have Bilstein re-valve the race struts for the same reason: first to demonstrate the full performance envelope of the project car and then bring it down to earth a bit with some de-tuning.
There is a birdie whispering in my ear saying that the 288 cams might actually be streetable simply because the ITBs allow for fairly smooth idle even with very low vacuum and the car is so light relative to the power output (likely 1800lbs and 250hp w/o nitrous) so the lack of low end torque may not be an issue - and it may help soften the throttle response at low rpms that otherwise might be over-the-top with the ITBs. I also have the option of having the nitrous come on below the torque peak at 2500-5000rpm to compensate and then shut off. We have used this trick with big turbo setups to spin up the turbos and cut lag by 70% or more and then shut off the nitrous. The ITBs are a related issue as the throttle response of this setup at low rpm is tremendous and I can only imagine how crisp and aggressive it will feel above 5500rpm when the cams are in their sweet spot. I like a crisp throttle but the problem I have with this engine is that the ITBs are huge (45mm but shaftless so equivalent to 48mm units) so essentially one throttle body can supply all of the engine air needs on its own and when those 4 blades all open together only a few % there is a dramatic increase in air flow. It reminds me of how my old 83 GTI felt when I swapped in a Weber 'Big Throat' TB - it got tiring after a while with the overly sensitive throttle - and that was with a 100hp/2100lbs car. I can only imagine how much more sensitive this project car's throttle response will be and how tiring it may be to have to be so careful with my right foot all of the time. We'll see soon enough ... fingers crossed.
Something else I was worried about was how the exhaust note would sound. I have used multiple race-type resonators stacked end-to-end in street/track cars in the past with great success (quiet yet no loss of top end power - actually building mid-range torque over less muffled exhaust systems) so I used 3 straight-thru resonators on this project car. I will have to get one of my studio big diaphragm mics out and record the sounds for everyone to hear properly. The exhaust is quite mellow with a deep bass but not a lot of high end - which is what I expected to hear. When the throttle is opened up it is quite aggressive sounding but not like the usual rice-rockets on the road these days. I think it will be perfect but I need to get the car out of the garage to hear it properly - August 9, 2015
Index of Project web pages
Project Overview, Goals & Initial design specs
Project car initial condition
Bodywork & Paint
Suspension, Wheels, Tires & Braking System
Engine & Transmission
Electrical & Fuel System
VW Vortex Thread on this project
My original 1983 Rabbit GTI (owned 1983-1987)