Resolved 6 bolt block, 7 bolt head

[Tom Gibbons]

Today I realized that the eclipse I bought recently actually has a 7 bolt head on a 6 bolt block after looking at the exhaust manifold studs (2 on outside are bigger). Are there other things I can check to confirm this? For example the 1g cas works fine on my car but from what I have read, 2g heads can use that no problem.

Is it better to use the 7 bolt intake manifold since it matches up better with the ports on the head? Or is the 1g intake mani still better since its larger?

 

[Cox Abele]

Without getting into the "which head is better" debate, using the generation correct intake is optimal due to port matching.

A 2g head will have additional bolt provisions for the 2g thermostat housing. Both 1g and 2g thermostat housing will bolt to a 2g head. A 2g thermostat housing will not bolt to a 1g head.

The head bolt holes are also a different diameter between the two heads, but that takes a bit too much work if all you are after is identification.

Using the larger port 1g intake on the 2g head will produce poor performance due to the different in port design. The air will not transition smoothly between the intake and the head. The larger port design does allow for more top end power (when paired with the correct head), however the 2g intake on the 2g head will produce better port velocity and torque due to the runner design.

A 2g head on a 6-bolt block also bumps compression a little bit (over the 1g head on a 6-bolt block.) In my opinion, if the ports are left unmodified, the best combination of parts is the 6-bolt block under the 2g head with a 2g intake. Seems to be pretty responsive off boost and makes for great street manner with the additional torque that is made. The only steps necessary to get this working properly is opening up the 2g head bolt holes to the 1g size (1/2" or 13mm) if planning to run studs, otherwise the oil feed to the head can be hindered.

 

[pauleyman]

You cant use terms like 7bolt manifold as there is no such thing. You have 1g and 2g intwke manifolds.
All 1g are big port regardless of year. 1g big port heads are both 6 and 7 bolt. 2g small port heads are all 7 bolt. So....you know the outer two studs are bigger giving you reason to believe its a 7bolt head but I see no reason to suspect why it couldnt be a 1g 7bolt especially if whoever did it used a 1g intake manifold.

 

[Tom Gibbons]

I checked the provisions for the thermostat housing, and I do have a 2g 7 bolt head on 6 bolt block.

http://www.dsmtuners.com/threads/1g-thermostats-housing-and-neck-on-2g-head.430329/
Figured I would post this link in case someone stumbles across this forum one day, and for my own reference too.

And yeah Pauleyman thanks for pointing that out. I mean to say 2g intake mani and 1g big port intake mani.

 

[enriquez2000]

Are the 1g 7bolt head bolts a different size still. Or is it just 2g 7 bolt....

Ive always assumed 7 bolt means smaller head bolts period

 

[19Eclipse90]

All 7-bolt engines use the same head bolts.