INFO ON HEAD WORK

Birko · tinkerer Joined: 03 Apr 2002 Posts: 180

hey,
after a few phone calls around the place to get some info/prices on gem heads i am confused..(nobody deals with 4 cyl (esp gems) in perth)

If any one doesnt no i am building an engine like so..
1600 bored to fit either 1800/2000 slugs, 3000-7000 crow cam,10.5:1 comp, running either a gas system or if my money runs out a weber or two, and a worked head
ok

Well my questions are:

1) I have been told to get a 1800 head as it will be cheaper as i it flows beter and i wont need oversize valves(wont this drop comp? if right couldnt i just put in higher comp pistons to compensate???)

2) Is this right or do i want a 1600 head with big valves?? or is a small valve head ok if i i fit oversize valves??? (as i have two good small valves heads??)

3) i have been quoted from $550 to $1300 to do the head with porting and oversize valve? what is a good price???

4) Will i be able to run on bp 98 oct fuel with 10.5:1 comp if need be?

5) what valves should i use if i go a 1600 head? The guy that qouted $550 was the only guy that sounded like he new what he was talking about said hell use manga valves? I no EVLGEM used sigma valves? any suggestions?

cheers..

maxpower · tinkerer Joined: 14 Jun 2002 Posts: 58

gemini performance head vgc, with new crow cam 3000-7000rpm, new crow double valve springs, top end set, incl valve stem seals, all parts still in boxes $280 ono lockridge w.a. 9279 4338.

found this in the quaka if i didn't already have 2 twin cam heads i might of had a look at it my self. good luck.

Birko · tinkerer Joined: 03 Apr 2002 Posts: 180

yer i bought it, the head had no work done to it yet, but the parts where all brand new so i bought it.

Mooch · backyard mechanic Joined: 17 Oct 2001 Posts: 573

1)I have been told to get a 1800 head as it will be cheaper as i it flows beter and i wont need oversize valves(wont this drop comp? if right couldnt i just put in higher comp pistons to compensate???)

Ok, I was in the same boat as you about 12 months ago. I picked up a big valve 1800 head from a rodeo for 175 bucks. I don’t know if all 1800 heads have the bigger valves than the pollution 1600 heads. The valve sizes where from memory 42mm and 40mm or something like that. The ones in my 1600 head where around 38 & 34mm (this is from memory so I could be slightly out)

This will save you money as these valves are ample in size to produce reasonably good power. The 1600 and 1800 heads have the same chamber size so your compression ratio will be the same.

I’m not sure if you can get high comp pistons for a 1600, but the cost of obtaining a G200 bottom end may offset the cost of machining your 1600 block. The extra torque will be noticeable from the longer stroke.

2) Is this right or do i want a 1600 head with big valves?? or is a small valve head ok if i i fit oversize valves??? (as i have two good small valves heads??)

1600 head with big valves is quite rare. Then again any big valve head here in SA is rare lol. You would have to get a quote on the machining of the head and fitment of larger valves to determine if this is a viable option.

3) i have been quoted from $550 to $1300 to do the head with porting and oversize valve? what is a good price???

The price usually depends on how good the head is and how much hp and air speed you want it to flow. A good head shop will match port the manifolds to suit the head and flow them all together on a flow bench. When I had my 1800 head done it needed some minor repairs – bent studs, stripped spark plug threads etc etc. It ended up flowing 160 odd hp with an air speed of around 301. Air speed from what I understand is actually more important. All up cost was around the $1100 mark.

4) Will i be able to run on bp 98 oct fuel with 10.5:1 comp if need be?

Im running 10.8:1 comp and it runs like shit on premium. To be honest with you I wouldn’t go over 10.1 if you can help it. I have actually organized a decomp plate thru og speed shop for 112 bucks to get it to 9.8:1. Means I‘ll drop a bit of torque but I can live with it if it means I don’t have to run avgas on the street. Too risky. The timing is advanced 12 degrees and I guess if it backed it off it’d be better with premium but it’d be pretty lazy.

5) what valves should i use if i go a 1600 head? The guy that qouted $550 was the only guy that sounded like he new what he was talking about said hell use manga valves? I no EVLGEM used sigma valves? any suggestions?

Can’t help much with this one. My advice though is to just find a bigger valve head to start with – there must be a couple around.

For other details of what I had done go here:

http://www.geocities.com/mygemi/gemi_build_9

Sorry for the longish post but I guess its something to read as most other posts here a shit anyway.

Cheers
Mooch

Birko · tinkerer Joined: 03 Apr 2002 Posts: 180

Hey thanks mooch,
Ars you positive about the 1800/1600 head having the same chamber volume? cause in the worshop it says that if you put a 1800 head on a 2000 you get 9.25:1 comp? so wouldnt this mean it has a bigger chamber then a 1600 as this gives 10:1 comp? did you use the standard size valves in your 1800 head??
thanx

spud · petrol head Joined: 05 Apr 2002 Posts: 1106

you can get valves from the 2.6 l isuzu engine put onto you head if you want. not sure on prices but it is meant to be a good upgrade.
spud

TXcoupe · petrol head Joined: 05 Oct 2001 Posts: 1675

hey ross

depending on wat happens with my 1800 i might have another gemini head already ported and fitted with big sigma valves. it nees repairs and new springs and shit. but for $200 if the builder doesnt use it u can have it