Building a GD427 Cobra Replica » engine

Throttle cable assembly

mrb — Mon, 01 Mar 2010 09:37:25 +0000

The throttle setup, converted from the electronic standard one to a cable operated setup, touched slightly on the block.

A careful couple of minutes of filing made sure it ran freely. On the outrun to the back of the engine of the cable I mounted two rubber P-clips to guide the cable across.

I think I’ll put some shields on top of the valve covers later on, which can then neatly hide the cable from sight.

As said earlier, I would rather have the electronic throttle valve, but for safety reasons that’s not allowed.

Engine bits nearly complete

mrb — Fri, 26 Feb 2010 08:48:57 +0000

To complete the engine—gearbox mating I just need one part now, which is the pilot bearing for the front of the gearbox. I ordered the original GM-part earlier, not realising my Tremec gearbox is of the Ford variety, which has slightly different dimensions. So, I still can not complete the mating, but there’s lots of other (little) stuff I can complete, such as installing the fuel rail adapter. Click! Done.

In the batch of parts I collected last week, I got the correct length drive-belt. Installing this is also a job of two seconds. The coverage on the pulley isn’t that big, but the belt only has to drive the alternator, so it should be ok.

Startmotor can be bolted on now I have the correct length of the bolts. It’s pretty close to the exhaust, I could not even get it assembled without removing the header, so the starter will probably need some heat shielding.

Bits, pieces, parts

mrb — Sat, 19 Sep 2009 07:00:03 +0000

Fetched about half the ordered parts from speedon on friday. The other half still wasn’t there! Come on GD, I’ve been waiting forever now. Apart from unpacking and identifying what is what I went about on a trial fitting spree.

The gearbox was the bottleneck for delivery, (Tremec == GM so that may have something to do with it). It is here now but still without a flywheel and clutch assembly, so the only thing I can can do with it is temporarily mount it on the adapterplate and bell-housing and put it away for a while until the other bits arrive.

The throttle valve was converted to a cable operated one, but on assembly to the engine it touches some little pipe behind it. (what is that, anyway?) So, some adjusting to be done there.

The engine mounts go together with an adapter plate. As assembly they are mounted onto the engine in two steps, easy peasy. I noticed the mount does not mount flat onto the adapter plate, should there be a rubber between them or is is just forced onto it? On final assembly I’ll get back to that.

And finally, the modified thermostat outlet. I’m going to polish that a bit later on to smooth out the welds a bit. Also, there are basically 2 ways to mount the outlet. Shown here is the one where the outlet is most ‘outwards’. If the outlet is turned 180 degrees it moves a bit inwards. When the engine goes in the chassis I’ll have to revisit this too, judging what’s best at that time.

Little bit of progress

mrb — Fri, 28 Aug 2009 15:40:08 +0000

Having a rolling chassis is nice, but having it rolling of the hoist is another thing (not that this has happened yet). So, a working handbrake seemed like a logical thing to do next. The original handbrake end-bracket was to small for the supplied handbrake cable. Adjusting it (by cutting a slot in it) did not seem a good idea, as it would create a very small contact area for the bit at the end of the cable.

In one of the drawers at speedon Mischa found something that could fit, and with a bit of effort, it indeed did.

(apologies for the blurry picture) With a bit of sanding on both parts, i.e. the cable and and the bracket, made it fit.

The ECU has arrived too with a nice semi-assembled harness. Now I need a handful of connectors and I should then be able to construct a complete harnes and finish that part.

No parts yet…

mrb — Mon, 22 Jun 2009 17:33:29 +0000

So, no parts this week yet. Might as well tell a bit about what I’m waiting for.

Here’s a rundown of the list of stuff I’m waiting for:

engine mounts
Tremex TKO 600 gearbox
propshaft
complete ss exhaust + headers

The position of the exhaust will be a bit different at the back. Instead of the two exhaust pipes in the centre as is common for GD type cobra’s,

or an option seen lately, at the outside:

Mine will be somewhere in between those two types. I like the wider looks of the exhausts, but not too wide as in the picture above, so mine will be situated between the lights and the vertical chrome thingies.

omex 710 ECU + wiring

The omex needs a little adjusting (amplification I think it is called) to be able to drive the injectors of the LS2 directly.

alternator + bracket
starter motor
air intake box + filter
radiator + fan kit
straight thermostat outlet

The thermostat on the LS2 is normally at an angle, which does not fit in the GD chassis, so a straight version needs to be mounted. (if you look at this picture at flickr you’ll see the notes about the thermostat etc. I’m hoping to get those notes working on this blog directly someday.)

SS header tank
several hoses and wiring

Hoses in black, wiring semi-assembled, courtesy of the omex guys.

fuel pump and filter

I would like to assemble the fuel pump like so:

The above is a euro chassis, not the jag based one I have, so we’ll have to see if there is enough room (esp. with the brake discs inboard).

mechanical throttle

Apparently the electronic throttle is not allowed, so it needs to be replaced by a mechanical one. Not sure what the precise reason for this is. but my guess would be that it has something to do with paranoia about (aftermarket) ECU’s going berzerk and giving an uncontrollable full open throttle signal, with the imaginable consequences of that (esp. when an automatic gearbox is fitted).

So, lots to do when the stuff gets here.

Undressing engine

mrb — Thu, 14 May 2009 15:45:24 +0000

Having ordered a boat-load of engine-related parts, I started to prepare the engine for it. This consists mostly of removing parts from it and cleaning it up.

The exhaust headers, thermostat outlet and the flexplate all need to be replaced by specific parts, either specifically made to fit the GD (like the exhaust headers) or modified to fit into the engine bay.

Gearbox thoughts

mrb — Tue, 12 May 2009 16:02:03 +0000

It’s about time I made up my mind about a gearbox to put behind the LS2. When I started to focus on a gearbox I had not a very good idea what criteria to use to evaluate gearboxes. I sort of tried to deliberately ignore (but not completely) the obvious choices in the different forums; not because they are bad or anything, but I wanted to reason my way into a gearbox choice based on technical criteria and personal preferences.

So, the first thing I did was read up on how the thing actually works.

The way I look at it, the drivetrain from engine to the wheel on the road is a divider, where you can control the division factor by selecting gears. Other than the gearbox there are is only one other factor which determines how 1 turn of the engine-output-shaft translates into a movement of the rear wheels.

This is the differential ratio, 3.54 in my case. Once the gear is known, you can calculate how many rotations of the engine it takes to let the wheels rotate once.

How that translates into road-speed and handling, which is what I am ultimately interested in, is a bit more complicated. The size of the (rear) wheels is one thing, their grip on the road and the influence of all sorts of drag are others.

It is pretty easy to create a set of graphs with the above information and the gear ratios of the gearbox. These graphs show you rpm vs (ideal) road-speed and a ‘shift behaviour’ graph, which shows the drops in rpm given a shiftpoint. Here’s what that looks like, given a Tremec TKO600 gearbox and 275/40-18 rear wheels.

Obviously this is all theoretical. The speeds will be lower in practice as drag increases with speed and how the ‘dry numbers’ will translate into actual experience is the big surprise I guess. What can be determined from the numbers however, is if the setup of engine,gearbox and differential makes sense overall and helps giving a quick visual overview of the length of the gears, an indication of the effect of the overdrive etc. The second graph above clearly shows the length of the overdrive vs the first 4 gears.

I’ve done this graphing for a couple of gearboxes and stared at the numbers and graphs for a day. Combined with my personal preferences these are the conclusions I came to:

manual gearbox;
in the ‘grand touring’ theme I’d like an overdrive in top gear(s) which gives me a cruising speed of around 100 km/h at 2000 rpm;
‘open box’, that is, the gearbox needs to be documented and serviceable (by me);

After all that, the choice boiled down for me to a Tremec TKO600 5-speed or the Tremec T56 6-speed (big surprise… not!). Having no hands on experience with either of those two boxes, I spoke to a couple of people having some experience with one or both. Apart from the obvious differences like 5 vs 6 speed and the TKO being a bit stronger on torque allowance, the main thing I distilled from the comments was that the TKO is the more ‘raw’ box, more aggressive perhaps and better suited to track (ab)use, and the T56 being a bit softer and perhaps more suited for cruising.

Making my mind up, I think I’ll opt for the TKO 600. The bigger torque number gives some playing room with the engine, and I think the LS2 has enough torque to already let me skip 2 gears, so why bother with a 6-speed?

Look what Santa brought me…

mrb — Thu, 18 Dec 2008 10:52:13 +0000

No words needed. At the moment I can’t do much to the engine yet, other than drool over it. (Well, I could go mad on polishing I guess)

Waiting on an engine

mrb — Sun, 14 Dec 2008 09:51:24 +0000

With the engine on the way, I went to Buitelaar machinehandel to pick up an engine stand and crane and some other things which had been on my shopping list for a while. Combined it was worth a trip. If you’re a “tool nerd” that shop is definitely worth a visit. Don’t forget the drool bib.

I went for the el cheapo option on the stand and crane; this showed during assembly. I had to augment the bolt pack inside with quite a few to get the things assembled, but alas it’s there now.

While I was there I noticed a little gadget which seemed perfect to set the camber and castor for the suspension.

It’s capable of doing both absolute and relative angle measurements and has a magnetic base. Sounds perfect in theory. I’ll report back on how the thing works out in practice.

Engine ordered!

mrb — Thu, 11 Dec 2008 16:10:50 +0000

After some more phoning and mailing back and forth, I parted with the money for a new LS2 crate engine. Now the waiting game begins. Hopefully sometime soon I should be able to collect it.

In the end I went for the complete engine package instead of building from bare or short-block. The deals you can get on crate engines these days are so good that building one from scratch is, at least money-wise, absolutely not interesting. I would have liked building one though. Oh well, it’s not as if there are no other jobs to complete.

There is no way this engine goes into the cold and damp garage for now, so the view from behind my desk should considerably improve when the engine arrives.

Engine thoughts

mrb — Wed, 03 Dec 2008 10:10:41 +0000

I want to take a number of preliminary decisions on the engine, so I can move forward in that area.

Spent more or less the weekend reading up on the differences between all the different models of LS engines and their architecture in general. A while ago I bought a book on LS engines because frankly, I dont know much about the LS engines.

Since I bought that book there have been some new LS engines, notably the LS2 and LS3. At this moment the LS2 is the most interesting, price-wise, when compared to a new LS1 or new LS3. I was also considering buying second hand, but the price difference is not that big and the uncertainty factor of what such an engine has been through on one hand and the limitation of choice (at least in the netherlands almost all second hand LS engines are LS1′s) on the other, made me focus on new engines.

So, my focus will be on new LS2 engines for now.

Second, how much self building do i want to do? In theory, if I look at my initial goals for this project, the answer would be ‘all of it’. However, that may not be the smartest thing to do. Building up the engine from a bare block will take quite a bit of time (not a problem, i’m not in a hurry). It will most likely be more expensive, not only because all the parts separately are more expensive than a prebuilt crate engine, but there’s also a need to purchase some special tools and other materials needed to build the engine. The difference in price can be considerable. The first part of an engine build; putting in the crankshaft and pistons seems to require some special tools and expertise, after that it seems to get easier.

Focussing on buildup from short-block for now.

Now, where to get one? This turns out to be actually the first thing to look into. There is no ‘easy’ way, as in walking to a supplier in the netherlands, sit down for an afternoon to get things right and place an order. Importing from either US or UK is an option, where the UK route seems a bit easier, especially because GD itself is a supplier of the LS engines. This part of the puzzle is ongoing.

So, to sum up, here’s what I am looking for:

LS2 engine, preferably short block, but open to crate engine deals
if short block a supplier which can supply all the parts too;
No ECU or loom needed (will use GD and OMEX stuff for that);
a detailed technical manual on how to build up such a beast.

Chassis ordered

mrb — Mon, 02 Jul 2007 15:34:00 +0000

The chassis has been ordered, that is, Mischa is visiting Gardner Douglas on wednessday an will order on my behalf. We spoke on what type of engine I wanted for the car. (I managed to decide on the cubic inches, but not on carburated or injection yet, although i’m beginning to like the LS1 more and more) Apart from the fact that most decisions on differential, engine, gearbox etc. are all related and you can’t really decide on one at a time, I’m also seeing the whole car as a concept which should be balanced. If I should choose for a classic 350 cui carburated engine, for me that has an effect on how the interior should look too. Likewise, if the choice is for the more modern LS1 or LS6 engine, that should influence the rest of the looks too. So, the two decisions were really just:

a GM 5.7 liter v8

a limited slip differential of ratio 3.54 or 3.31

Those two are enough to get me working on the donor parts and the rolling chassis. Oh, the outer wall is a bit higher today too…