GT74 High Compression Six Speed

I took off the IACV from under the Jun clone plenum last night and found the problem. A bent pin in the connector plug socket. This had resulted in the IACV plunger being wound fully open and locked in that position. No wonder why Martin was having so much difficulty in obtaining a reasonable idle. Rather than inducing stress in the pin by straightening it and possible make the pin more likely to fracture, I decide to change the unit for my spare as is it in much better internal condition and works perfectly.

Good news Phil

awesome work pal, any more parts ure looking at getting rid of lol?

I have quite a few parts left over, including a stock TT engine with auto flex plate, and parts to build a high rpm 900bhp block.

Since fitting my spare IACV mapping of idle progressed quite quickly yesterday. Martin will probably take a look at the cold start map when we get over to the workshop today. There are a few jobs left to do to get the car road worthy. We need to mount the bumper, lights and front indicators and fit the new brake discs and pads all round. The end of the build is in sight and I can't wait to get the car out and onto the road to see what it can do. I have a feeling I will not be disappointed.

The car sounds amazing, shaking the walls of the building yesterday, when we were holding 5000 rpm, according to Tom in the paint booth:d. The GT74DBB has simply amazing bearings, taking for ever to stop spinning even from idle.

I planned to get the car completed in time for TOB, judging by current progress that is still possible. Deadlines are not important though, get the car right it was matters.

I will try to get a few pics a clips of the car today. I take my camera most days but just forget to use it one I get stuck in to build mode.

Dropping my video camera on the workshop floor did not do it much good. So no clips for a while.

This clip was taken just after the car had fired up for the first time.

The oil was cold so the turbo as still cold, despite that the quality of the bearings is hinted at by the slow down of the turbo.

The oil was cold so the turbo as still cold, despite that the quality of the bearings is hinted at by the slow down of the turbo.

Oooooo pretty spinny thing

Looks like there is very little friction there What's the full spec of the turbo Phil, I seem to remember you saying it'd been custom built?

It is the the turbo in the PHR Stage 4 kit, I had Ben carry out porting on the housings to decrease spool time, he did some other work on the GT74 which is not for publication. When put together with higher than stock compression the power deliver should be interesting and hopefully very different from a standard GT74 DBB on a stock compression motor.

The last clip I took before the camera broke.

Sounds sweet:cool:

Sounds really nice. Seems to sound like an RB. How does it sound on WOT, or do I need to ask!

awesome

The camera mic could not cope really, as it was right in line with the exhaust flow. I agree it does sound a little like an RB, but when side by side with our RB25, you can't hear the RB. The 280 cams, high compression engine, over size valves and 4" exhaust system have totally changed the MKIV sound. It really sounds amazing on the road and so far it has only been off boost to about 4500/4800 rpm. WOT will be around 8250rpm, so it will sound pretty mean. When I get a new camera, I will get some fly by shots.

With extra gauges, I had several options, us a LHD pillar pod,loose the top glove box or use some form of dash pods. I think this pod does the job very well, the three gauges are angled to be in view when looking straight ahead.

I really like this option, the top glove box opens and closes easily and the passenger centre vent is still in full use.

nice work:)

Just a quick update. Still no camera so I could not record the moment. The car has come out of the workshop and been out on the road, for off boost shake down tests. It drove beautifully, thanks to Martins mapping. The triple plate OS Giken clutch is just so easy to use, the gear box is smooth and light to engage. The car pulls really well off boost, thanks to the high compression engine. The motor is very eager to rev, so it took a lot of self control not to push it. I followed my car, while one of sons drove it, the sound is fantastic similar to a GT race car. I can't wait to hear and feel the car when it starts making serious boost. Overall am I exceedingly pleased with progress so far.

Nice one Phil

Look forward to seeing this in action.

Excellent news Phil, looking forward to hearing more about this!

Good stuff! Look forward to seeing that on full chat.

Just a quick update. Still no camera so I could not record the moment. The car has come out of the workshop and been out on the road, for off boost shake down tests. It drove beautifully, thanks to Martins mapping. The triple plate OS Giken clutch is just so easy to use, the gear box is smooth and light to engage. The car pulls really well off boost, thanks to the high compression engine. The motor is very eager to rev, so it took a lot of self control not to push it. I followed my car, while one of sons drove it, the sound is fantastic similar to a GT race car. I can't wait to hear and feel the car when it starts making serious boost. Overall am I exceedingly pleased with progress so far.

bit confused here Termy your talking about high compression and serious boost, the two as i'm sure your aware dont sit together very well

quite obvoiusly with 9.5:1 we'll be limited on optimax. but we'll tune to the point where wot timing is starting to cause high egts then pull back. no point trying to be a hero on road fuel for the sake of 40rwhp.

ive got a feeling its going to be time for brown trousers on 98ron anyways.

as phil was saying the motor feels very strong and torquey off boost and brings on positive boost remarkably quickly for a big turbo.

all is well apart from a fuel pump failing. (they were second hand, think they were run out of fuel from the state of the brushes and comm inside.. appauling!!)

just another thought.. Vp import would support 30lb boost with 9.5:1 cr piece of piss. depends what you are calling serious boost!!!:D:D:D

bit confused here Termy your talking about high compression and serious boost, the two as i'm sure your aware don't sit together very well

I am aware of the old school argument, the bigger the turbo the lower the compression. I was very aware of it when I purchased the engine. The high compression, engine was a deliberate choice for my project. It was not a whim to purchase the engine, it was carefully thought through and discussed with very experienced and successful engine builders and tuners.

Martin has already alluded to the spool characteristics. A very well respected ex member predicted that my engine will rewrite the bottom half of all GT74 DBB graphs. If the off boost performance is anything to go by it will be quite quick;) Another tuner has suggested we could achieve high 8's, when coupled with my TH400 gear box, which I sold to Andy Hannaha. I am sure through a V160 and OS Giken triple plate, it will be all I had hoped for.

the classic "old school"..

yeah my dads got a cossie its on 90lb of boost and 6.3:1 comp.. we give it a big spray of eazi-start to fire it up.. hahahahah:)

Just a quick update. (My camera still dead, so no new clips or pictures.) my new fuel pumps arrived from the USA and are now fitted and running well. An aluminum breather tank, made by Martin now sits in front of the brake servo and behind the OS turret. I decided to go with rubber hoses for breathers rather than more stainless steel under the bonnet. I took off heat coated down pipe to wrap it and sprayed with high temperature paint. I started fitting and shaping panels round the FMIC and under the car to try to get as much air as possible passing through the IC, rather than round it.

I took the car out for some more off boost tests this afternoon. I had a lovely drive in the sunshine, with the car sounding awesome. I am really loving the clutch and gear box a great combination. So far I have put 50 open road miles on the car and enjoyed every one. It might be time to put an OS Giken in the RB gear box.

Not much more work to do now; prop loop to fit, under tray and ducting to complete and finally my splitter to fit, so the end is clearly in sight, barring any of the numerous little things that pop up in projects like this, then it is only mapping to complete.

Good luck mate, great thread so far!