i am sick of this s*&t, Ben Wight, help pls!

[Mooch]

Ok, after getting 5000 kays out of my 4500 G200 rebuild it let go from a dodgy oil pump. Had the clutch replaced after i had only been driving the new engine for 1500 kays - it had plenty of meat on it but it was all twisted up! Now, my 1200 head has decided it wants to cracked in the exhaust port. Making it a throw away!!

My funds are starting to get low, and so far in the last 12 months the drive train owes me about 7 grand.

Heres my plan: stocko 1600 big valve head, get it cleaned up and freshened, and go for a blow thru turbo set up with a BOV ( i think this is right??)

My question is will the ACL duralites suffice with only 6-7 psi? I dont want massive hp just nice torque, i'd be happy if it makes 150 horses at the fly. The bottom end is 1500 kays old. Its just been run in basically. I gave it one good hammering, did the clutch, the next day, the head!

I dont want to spend more than maybe 1500-2000 bucks. I know forgies would be the correct way to go just incase it leans out. However, what is your experience with a G200 with ACL durlaites, ACL rings and bearings, balance, etc etc all done properly and a low boost turbo set up? Is this a grenade waiting to go off?

Am i better off finding another head and getting it ported again and just keeping what i had? How would i go with emissions on a 78 TD with a turbo? I remember you saying something about a turbo "package" you did? Unfortunately i have done a search etc etc but i am still left unsure. Just researching b4 i outlay more $$$ only to be disappointed again.

I know i have a few questions but i appreciate any advice you have to offer. One thing, being a g200, a 1600 head is gonna give me a about 10:1 so i would need a decomp plate i guess too. Unless some one has a g200 head lying around! I am not really up to speed with the turbo thing!

Cheers
Mooch

[Ben Wight]

Hey Mooch,

unfortunately with the 1600 big valve head, they have a small combustion chamber. I have 2 heads with big valves, both from TD's, One has been shaved a little, it has 42.5cc chambers, the other has been shaved to the valve seats, it has 40cc chambers. Assumming a stock head has about 44cc chambers, this still gives you a static compression ratio of about 10.8:1 with a standard head gasket. This is not very turbo friendly, if you have a stock 1600 big valve head, you may want to put the valves into a later pollution head, giving you a compression ratio in the 9's.

If you currently have a decent cam, and flycut pistons, you may want to consider sticking on a ported 1600 pollution head for extra grunt due to the compression increase, and try a little porting yourself to save dollars. If your cam, exhaust and induction setup are good (big!) enough, you should be able to get close to 150hp.

If you haven't invested in a cam and decent carb(s), then you could definitely put on a turbo, and run 7psi comfortably with mid 9's compression ratio. My g200 made 90hp at the wheels on 7psi, and 8:1 compression ratio, a compression icrease to say 9.5:1 should give about 110hp at wheels, meaning you will have about 150 at the flywheel.

One thing I would advise against is a decomp plate. I have never used one, but I have researched the theory of 'squish'. Squish helps an engine avoid detonation, and a decompression plate reduces the amount of squish that occurs in a combustion chamber. I have read about an engine that detonated worse when it had lower compression with a decomp plate, than it did without. To decompress an engine properly, you should shape the combustion chambers and dish the pistons.

Thinking about it another way, my engine made 196 at the wheels, on 18psi before it blew a couple of weeks ago. So if you want more power in the future, which I am sure you will, a lower compression engine is probably a better starting point. I keep having trouble at around the 200hp@wheels level, which is why I am chasing forged pistons. Cast pistons seem to handle lower power levels fine, and should handle my power levels, but I keep having trouble.

In short, a cast piston should handle almost the same power levels as a forged piston as long as the engine doesn't detonate. If detonation occurs, a forged piston is a bit more resiliant to detonation. But then again, they cost a shit load more.

A turbo setup can be a pain in the ass to install, but if you perservere, the power increase is well worth it.
If you go a turbo, one last piece of advice, get the thing dyno tuned as soon as its running. dont rev it and dont boost it unless you have an idea of the tune, being both fuel and ignition.

Ben Wight

[Mooch]

Thanx Mate,

probably should have given you some more info, The head has been ported and flows 160 hp, it is an 1800 rodeo head, with the larger valves and the chambers are 47.5 cc a piece. The head has been shaved 40thou, the block also decked and the compression ratio with a normal gasket, is 10.52:1.

The cam is a crow, 425 thou lift, 284 duration - with the double valve springs etc etc. Like i said, the head alone owes me over a grand, and the bottom end about 3 and a half. I'd like to retain as much of my stuff as possible. Its running a 34ADM and makes 147hp @ 5500rpm on the dyno at the fly. Or rather was.....

Thanx again mate.
Mooch

[IDAREU2]

Mooch

didnt you say your head was throw away? that meens you can start again, but if you can try to minimize the head shaving
and open your chambers up a little to lower the comp ratio no need to go ballistic with the exh and inlet ports, just get your trusty little dremmal and clean them up yourself then take them to a machine shop to flow them.. If you like mooch you let me know when you get your head mate and i'll come through and give you a hand.. did mine cant see yours being any different.. and mine flowed 474 hp @ 536"lift

cheers mate
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