Isuzu G-series Twin Cam

ok im planning on rebuilding my g180w for my panno when i return home from working away. The motor is currently sitting on my shed floor but is setup with twin 40idfs, unknown dizzy and a nice big set of 4-2-1 extractors. Ran very nice once i tuned it properly (cam was out a tooth when i got hold of it) but is on the lower side comp wise and felt generally tired.

Now my plan atm is upping the bore to take std g200w pistons, decking the block or head for highest comp i can get away with, carbs will be replaced with 48idfs, new inlet to suit and ports cleaned up to match larger carbs, and thats probably it. Also i amtrying to source a g200w ratchet timing case as well.

Does any one have any suggestions/recommendations with this setup? it will be for my stripped out td panno, I also have an apparent close ratio twincam box to suit but need to count the gear teeth to confirm.

cheers for any recommendations
danny

Why deck the block? (Never deck heads!!!) Isn't 230HP enough?

Or you can have 400Nm with the standard engine and twin DCOEs as per my 150HP with 300Nm@2k & 383Nm@3k - I didn't do the 220-230HP mod because I didn't want to spend on forged pistons.


PS - I preferred early Gem boxes with their 0.782 5th gear - IMO much better for a hi-torque GW engine than the usual 0.855 5th.
The only other difference to the ZZR ratios is the lower first gear - namely 3.467 instead of 3.207 (ZZR, GT Bellett, etc).
2nd, 3rd (and obviously 4th) gears are often the same ratios throughout the Isuzu range.
BTW - I do 10 rotations of the input shaft and count the rotations and final angle of the output shaft to calculate box ratios. I use a common round plastic engine timing disc bolted to a an "Omega" or Ω or horseshoe hose or pipe clip to clip onto the output shaft.

i was only going to deck the block or head to get the comp up as high as i could really, if standard g200w pistons with the g180w head will suffice then i have no need as i wont be getting custom pistons made.
That 230hp though is with cams and since there isnt anyone about to make up those cams/shims anymore its kind of a stab in the dark... I will be getting cams/shims done later, but the problem im havng is no one knows what this l1 profile is that i havw spoken to. Especially if the valve pockets need deepening etc Just seems all the knowlege is now lost or retired

I have been trying to research the L1 as I like the sound of the 230hp package.
The BDA cosworth twin cam has an L1 listed and it's spec is around what I would expect to need for that horsepower.
Will dig up the spec and post it.

Yep, it's the L1 profile for the GW engines.
An L2 causes the valves to hit the pistons.

The ~400Nm is all in the exhaust tuning.

And of course if your Webers don't have F2 emulsion tubes, forget everything.


BTW - the pistons are only because the OEM G200W pistons are only spec'd to 180HP tho a few have claimed (reliable?) operation at 220-230 HP, but maybe they aren't really pushing their engines as my Guru and others did.

That's the beauty of the torque tuning - no major power gain but it doubles vehicle acceleration...
The only snag is you need a clutch that is twice as strong.
But the engine remains as reliable as ever. And that's logical since there are no engine mods involved, and the big-end & main bearings are the same as used for the 2.6L 4ZE1 and some of them have pulled 500HP.
[ As to those that think G180Ws & G200W are unreliable, I'd really like to know what crap they base it on. Of course all I know based it on modified engines, and they've generally been done by people that kink oil lines else and think the oil-pump determines oil pressure, grind off chamber divots (not that they exist in GWs), fit Celica cams, prefer to put out boot fires to engine bay fires, etc etc. ]

Ok then i think ill just get the head/block faced as required.
with the carbs a 48idf and 45 dcoe are similar in throat/venturi fitout so will deffinately suffice, and they have f2 emulsions which i pinched for the 40s when it was in the car.
The exhaust i have is a nice set of 4-2-1 pipes which finish about the first third under the passengers feet so should be suitable for a torque setup.

Also i thought twincam crank/rod bearings where the same as g200z bearings not 4ze1?

The 3kRPM peak torque tuning is a 26" to 29" two-into-one section from the standard exhaust manifold.

I know Geminis could not use the OEM exhaust manifold - unless perhaps(?) they used the diesel cross member (and maybe Bellett/Florian/Wasp front-type engine mounting?). As to extractors that match or exceed the OEM manifold - Guru said that that are very few and far between...


AFAIK, all G-series engines and 4Z series share the same dimension big end & main bearings. That's from G150 thru G160 & G161 to G200 in all variants - including "non-Isuzu" (engine-wise) Holden-Isuzu Gemini's. (I think even the G130 had the same.)
The centre thrust bearings may have their variances.

There is variation as to the number of oil holes. I think G200Z engines have a 2-hole shell. Not sure about 4Z (though I have a new set for my 4ZE1 somewhere).
There was recent discussion re that on HoldenGemini. It seems G200Z big ends are prone to failure...


BTW - good to see you use the GW's torque. I never understood why people tried for (high RPM) power from these torquey 8-valvers when IMO they should have been using more modern 16V engines.
However I know the G200Ws etc were pulling at least 8500RPM providing the original reluctor dizzies were not used (their magnet plate would crack up at 7500RPM; hence another reason for the RG dizzies), but they were in racers that required OEM engines.

On a side note, I contacted the fella from sleeka spares and he can still get the g200w gasket kits apparently. $370 each or 2 for $350 each. Does anyone remember what was in the kits exactly? I seem to remember hearing they where a complete gasket kit including sump and the little timing case gasket. I this correct?

Hopefully it's the MDS kits (Moorabin, Melbourne). They include the front cam chain "valley" (usually orange) rubber gasket that sits between the front covers and head. The Permaseal VRS kits omit this (which they shouldn't) and I'm not sure if they are included in the Permaseal full gasket kits (I think not - but I could check mine).

I'm interested in an MDS set but I'm probably not fiscal enough.
Poida was going to see about a bulk buy for us twincammers.

Here is the L1 profile from the cosworth that I think matches the performance description.

I/E Advertised Duration Nett Lift Lobe centres


308/295 Duration, .402"/.334" Lift. L1 / BD3 profiles 308 295 0.402 0.334 104 108

ISU069
Let us know if you think this is on the right track from what you know.

I have no idea...
All I know is "L1", and that it's a "mild" racing profile - and apparently too cammy for street use in most engines, but GWs are not most engines.
Also that is is a well known or common profile. (I think Cortinas were mentioned.)

I also recall someone (I think) on OzFem wanting better than L1 "because it was mild" and inquiring about L2 etc. (I was amused because - as usual - the L1 had not been tried yet they were already off to an "on paper" enhancement. Reminds me of a mate with a "hot" 14psi boosted Piazza who was told by Guru to use <whatever> cam and DROP boost to 10psi. As usual, Guru's spec blew the other into the weeds.)
This was one of the things I asked Guru when I last saw him Easter 2012 - the L2 profile causes piston-valve overlap, hence it's discounted. (But more power - yes, not that it may have been the best solution.

http://www.newman-cams.com/pdf/lotus.pdf
this link has an L1 profile that is similar, but given it says "original L1 profile" for a lotus twincam this could be close as they are a similar era motor and similar architecture.
Could be way off but without getting a standard cam measured its hard to say if this profile would suit standard pistons....

The L1 will suit a G200W with standard pistons.

Now I am really curious. That L1 spec is significantly " bigger" than the one I found and it is noted as a race cam. This would be a spec I would not expect to see in a street engine but ISU069's comments got me thinking.

I measured the cams I have on hand from a G200W out of an injected 117 coupe and I got around 385 thou for the inlet and 375 thou for the exhaust. They also check out with the engine manual numbers.

That lift figure puts the standard cam straight into the "fast road cam" bracket on that data sheet.

Now it is only part of the puzzle as I don't have the duration yet,that will be a weekend job with a dial gauge but I think we are getting closer.

Checking the lift to head flow and the using coarse rules of thumb the extra lift on the cam only gives a 5% power increase on a standard head but once again this supports the theory of chasing torque as the power figures are good for the type of engine if you add the exhaust and the intake improvements.

Sorry a bit of a tangent but I thought I should share.

I should say that I don't know how they adapt a profile grind (like L1) to a different engine, but from what I gather, just specify L1 and the grinders will know what to do. (Of course if that is yet another skill that has been lost...)

The L1 info came from my Guru, and she or he has yet to be wrong (well, excluding (refugee) boat people being "illegal immigrants", & an argument I might have had regarding the G200W's EFI ports & motorbikes...).
And from what I gather, L1 was also the profile used by HDT for their Gemini twincams.


Of course, don''t deck the block - and NEVER deck heads!


PS - be wary of drawing parallels between GWs & other engines.
When I baulked at Guru's comment that twin (DCOE) 45's should be used for a 2L, s/he simply said that the GWs "breath unlike any other". Guru went on to say the the G200W should have twin DCOE48s - or even larger(!) - but the cost benefit was not worth it (for me...; back then Webers were pricey - emulsion tubes were $120 EACH!!).
I found that statement on par with other "non-comparisons" that I already knew so I didn't bother questioning.
BTW - the Isuzu twincams are not Ford nor Cosworth nor Alfa. Though the original G161W tuning was helped by an Italian mob, that's where any overseas connection ends. (I've seen published documentation & other websites that seem to think otherwise. As if there wasn't already enough stupidity!)

I will chat to a couple of camshaft suppliers and see what I can find out.

Did the Guru ever talk about compression ratios? I spoke to a guy that was reported to have built GW engines for the Rally geminis and he had suggested they will easily run 11 to 1. I believe he got that though careful replacement of pistons????

That would match the no decking rule.

IMO why increase compression? Isn't 400Nm/230HP enough? Or 390HP with turbo? Keeping in mind that they are without major mods; merely cam profiles, forged pistons, some minor porting, and external add-ons.

If you want to increase compression, get a 16V engine, Why use a GW? Sell it to someone that wants to double the vehicle's acceleration by spending a mere few hundred dollars and NO dismantling of the engine, still use 92 octane and get 10L/100km or thereabouts and have original reliability.
Get a Mitsubishi 4g63 (or whatever it was), spend $1k on cams and have 500HP.

If someone said the GW can have 11:1, ask what power it put out (and what other mods if it was above ~7k RPM).
Sure it can be done, but why - what gain? As I recall, the original Bellett GTR G161Ws were 10.5:1.

back onto this torque g200w build as i have now sourced a g200w ready to go when i return from working away.
So L1 cam profile as stated (will be a later thing), motor has the jap twincarb manifolds, 45 dcoe carbs will be sourced and i have my nice set of big 4-2-1 pipes. Your gurus layout essentially

My question now is what venturi size where you running inside the 45s? as going off the standard sizing charts im getting around the 38mm venturi for 7k peak rpm and g200w inlet valve size is 45mm.....
Sooo if twincams breathe alot heavier its pretty much pushing me up to 48 or 50 dco carbs as 45s can only take up a 40mm venturi.

As I recall, 36 or 38mm "chokes"; mains 165.
I did write the specs somewhere - maybe here on twincam, else maybe OzFemini - probably circa 2005-2006.

I wonder what twincarb manifolds you have since they never came out for the G200W.
The best are the "Hughan" manifolds that were made about 10 ... oops, 20? years ago. There were ~45 pairs made. They have tapered ports, are extended maybe 10mm with a carby face of 10 degrees - the max for Weber DCOEs (Jap manifolds were 12 degrees or maybe more). The extension was so the DCOE cleared the upper head flange/cover.

The motor is elkies ex drag gem g200w, so those intakes. I haven't seen them apart yet but i believe they are the kind you can still buy new from yahoojapan.
No worries I will have to have a hunt around the various gem sites to see what i can dig up.

During this lull in reason to reply, I thought I'd attempt a torque.

BTW - if increasing torque don't forget to upgrade your clutch. Remember, "a clutch is torque". You can increase power all you want, but if torque does NOT increase, you can leave the clutch as is. (With thanks to OzFem's BMX Hero Danny for "clutch is torque".)


I converted to torque years ago after motorbike experiences. The first was after getting my $400 Ducati GT750 on the road. Later reinforcement came when overtaking, or after invisible speed (aka invisible brakes - the effect of not feeling acceleration and thus doing 160kph instead of 60kph just before the bend or brick wall) on GPz900s etc.
Since then I have mused over various stories by racers that have converted. (I think I read where the late F1 driver Senna was yet to convert...)

I used to describe torque as "low down grunt". These days it's far simpler - it's the amount of twist the driveshaft undergoes. (Thanks Danny!!)

It can get confusing because torque and power are linked - you cannot have one without the other, and given one you can calculate the other PROVIDED you know the RPM (ie, speed as in angular rotation).
The relationship is:
P = T x RPM / 9549 (ISO/metric: kW & Nm)
{ or P = T x RPM / 5252 (Oldskool: HP, ft-lb) }

IOW you cannot SPLIT or separate one from the other.
In some forum I once stated how I doubled my (max) engine torque but my (max) power was unchanged. Someone replied that that could not be right... It certainly does NOT seem correct!
But then I explained that the double-torque was at half-RPM and all was fine.

I was actually describing my Grey Nurse's (Florian's) G200W with exhaust mods. (I did ignore its slightly higher HP - namely from 135HP to 150HP at 6kRPM - but that was due to the twin DCOE45s replacing the OEM EFI.)
That changed from OEM 186Nm @ 5kRPM to 383Nm @ 3kRPM - more than TWICE the torque at almost half the RPM.
The torque at 2kRPM was a massive 300Nm. That's pretty impressive... Not much above idle speed had 60% more torque than it once had at 5kRPM.

I described the change as doubling the torque at half the RPM - ie, doubling the (vehicle's) acceleration. Not bad for a $200 modification!
[ Iterating linearly between my 300 & 383Nm gives 341Nm @ 2.5kRPM - nearly double (372Nm) the st'd 186Nm @ 5kRPM. Since it's a curve and not linear, its probably above 372Nm @ 2500RPM. And since acceleration (at low speed before significant air resistance etc) is proportional to the square root of the power and since the power (torque) has doubled at half the RPM hence 2x2 = 4x the power, I thence say I've doubled acceleration.
Of course in the latter I'm mixing English power with mechanical power. Mechanical Power is actually "work done" whereas we talk of power as if it is a force. And torque is mechanical force. The twisting of the driveshaft is Force. Who cares about the total work done by that twisting times its speed? What has the most force - high torque down low or a lesser torque/twisting at 2x or 3x the RPM? ]

I recall some Holden fan on one of these forums (OzFem or HolGem?) with a TG Gemini with an old Holden 6 cylinder. Despite it being merely a fun project on a limited budget, IMO lots of work & expense was expended.
When I saw the dyno test I compared it to my G200W. I had a clear 20HP advantage across the whole rev range (2kRPM upwards; except perhaps at 5-6kRPM - I think I only had a 10-15HP advantage there).
So there was my OEM G200W with its $200 exhaust (and Webers) and its 2000cc killing a (what?) 3000cc(??) Holden engine with all its pistons and cam and EFI and ignition mods, and still getting great fuel economy.
Of course I also invested big researching my engine - a 30 minute phone call plus pencil & paper.

The irony is that at the time I underappreciated what I had. Despite having lots of fun during various interactions with other hot(??) cars - and overcoming my need to fix the rear suspension (that skipped around corrugated bends) - I was critical of its poor 27mpg; I was used to 35mpg or better.
Of course now I realise how good 27mpg (~10L/100km) was for such a beast. Having max torque (force) at 3kRPM meant half the fuel rate of former peaks at 5k & 6k RPM - though that ignores the greater fuel that the DCOEs could feed at those lower RPM.
I also recall another Bellettian that bragged about his Wolf-2D G180W (despite having all sorts of problems and cursing during the years it took to get going etc - his was the first non-rotary Wolf system). I finally asked him what fuel economy he was getting... I freaked when he said 17mpg - that's what mine got with its drilled main jets until I got it dyno tuned to its 27mpg figure.


Not that acceleration and performance (speed) is as simple as having torque - it's a combination of the 2 curves & other things (like racers probably want hi-RPM power; city racers probably want low range torque) - but I think anyone wanting variable speed performance would love high low-down torque, especially if they have always chased (hi-RPM) power.
I do recall F1 drivers that "converted" to torque, though F1s probably hit lower speeds (ie, sharper corners) with fewer straights than typical racetrackers.

Not to mention that G200W (& GW?) owners can double their torque at half the RPM with no engine works - merely exhaust & fuel tuning - and still have standard reliability. AND great fuel economy...
A car that eats V8s, rotaries, WRXs, etc off the line and way past speed limits that still gets ~10L/100km, or 12-14L/100km in suburban race modes...? C'mon - get serious!
Oh, did I mention its 91 octane fuel? (yTF are Bellettians running 95 octane? A need to launder money perhaps?)


As I posted, I ended up detuning my G200W. It was nice and predictable during take-off - no problems there. It was more the anti-hoon aspect; the splashing of (Weber!) fuel at idle; and if I did plant the foot a bit too hard around corners (in the wet...). Mind you, I didn't have my LSDs back then!

I'd love to compete in rallys now with a hi-torque G200W (and LSD).

And for high speeds (>130kmh), I'd consider a reduction drive to halve tailshaft RPM. (Remember - the World's Fastest Indian used torque - NOT power!)


Sorry for the ramble. It's probably remembering all those that have wasted money on GW engines and worse still, ruined them in the process.

Hey nut,

Im doing something similar to you and from the sounds of things a bit further down the track than you are at the moment. Have had a fair bit of contact with people in the game so can answer or offer a few little tid-bits from the conversations ive had with an engine builder, a mate that built a 430rwkw S2000 Turbo and someone that used to rally these things back in the day.

I had my head ported by Kanaris Race engines [youtube his HQ - 9.6 @ 166mph] and his comments were the ports are already big enough, particularly the exhaust in his opinion flows too good and needs to be slowed down a bit. What he concentrated on were reshaping the short turn radius and blending it rather than resizing the ports - if you look at the port where the radius just before the valve seat [with the valve out] you'll see the spot that requires the attention.

Pre-porting



Post-porting





Note the port sizes arent larger, just all the transitions are much smoother.

In terms of cam sizing, the LARGEST you can physically regrind a standard cam to without welding AND still be able to shim it to spec is below:

Duration is 292 advertised / 242 @.050", timing is 34/78. Lift is .3830

This is the cam profile ive got from mine. In hindsight i shouldve gone bigger [more on that later] and its still not too late to change so who knows. I had the standard cam measured and i think the duration at .050 was around 218 from memory - have the sheet somewhere at home however as im renovating my place [hence why my car has ground to a halt] dont expect it any time soon. Its based off an ALFA twin cam grind by Ivan Tighe cams, in hindsight [and to help get around the exhaust flowing too well] i shouldve gone a larger inlet cam and, if i can get my hands on one [ie if anyone has one theyd care to offload cheap] i may still do it.

Valve springs will need to be changed if you are running anything with more lift than standard as they will bind. Cant remember the exact spec required but i sourced them through Victor Pace. Again, they are an Alfa part. Google him, hes pretty well known. $160 i think from memory they were.

Nick

Re port grinds, yeah, they are big enough and Guru told me they don't need much. I got the impression it wasn't much more than a polish. ("A slight grind was the quote. This is the Guru that explained the "standard" 230HP 400Nm G200W build; namely (then) twin DCOE45s with F2 emulsions; port grind/polish; L1 profile cam (L2 profiles hit the pistons).
Technically forged pistons are required above 180HP, otherwise omit the L1 cam and suffer 400Nm as per my 383Nm @ 3k (300Nm @ 2k) and ~27mpg (10.5 L/100km) with the 2:1 section from the standard manifold & a 2" system.

As usual I'd advise caution with anyone that bases a GW build on other twincams. I've been told the GWs are so different from others - ie, Lotus <-> Alfa may work, but not GWs.


I more than doubled st'd torque from~186Nm (at ~5k RPM) to 393Nm @ 3kRPM with the mere exhaust mod (& F2 DCOEs with manifolds) and HP should have increased from 135 to 150HP (100 to 112kW) but she measured only 135HP/100kW (a worn engine; or is that rwHP/kW whereas I was quoted engine HP?).
Someone likewise said rubbish about the mere HP increase until I clarified the lower RPM - ie, double torque at half RPM means the same HP/kW power.

An increase in torque may require a clutch upgrade; but not a mere increase in power.
REM- "clutch is torque". And torque is the amount of twisting of the driveshaft (hence clutch).


And IMO use 8 valve GWs for torque - don't bother about HP. IE - for high RPM power, IMO get a more modern 16V engine (eg, st'd Hyundai Mitsubishi 4G63 with yankee cams = 500HP without other mods (or so I was told).

As I've written, my 3k peak torque meant double the acceleration of whatever (Florian, Wasp, Bellett, Gemini, Piazza) to 3kPRM.
With my exhaust-only mod (& DCOEs), torque dropped to 270Nm@6k = 100kW. (As I said, that should have been 150HP/112kW but since my dyno tests were (presumably) rear wheel figures 0 oh well, yet again Guru understated the expected performance).


The only other decent build I know of is the 400HP (390HP) turbo as per the GT Bellett that sold in Adelaide some years back.
Though a different builder, I think he was from the same clan as my Guru and I suspect a similar HDT-based build. But I know that builder was good - one of the few I'd consider for a rebuild.
The 390HP turbo build engine is as reliable as per my 383Nm mod - or later L1 230HP build - which is as reliable as a st'd G200W. And I think you know how reliable G200Ws are - except for those that have others refurbished engines or have done any of the plethora of bad mods I have heard of.