Advice on 2.4 cis top end rebuild

ezraman · 01-28-2008, 10:57 AM

I am sending heads to Ollie's for rebuild. My plan is to replace rings (smoke on start up). Should I consider new P&C's for horse power consideration and overall performance upgrade? Which one's? I have a stock cis system. I have stock exhaust with early heat exchangers, My heat exchangers are allowing smoke inside of the car considering changing them to new ssi's. would exhaust upgrade be a better option?

Thanks

HarryD · 01-28-2008, 08:18 PM

Without knowing your budget it is hard to say what you should do. With CIS, you are limited in the mods you can do to your cams and going to a larger bore may require changes tothe CIS as well (unless you go to Carbs or EFI). SSI's are the same as your early HE's so just replace them with the most cost effective choice.

If you are consdiering new P&C's you may want to just do an engine swap to a 3.0 or 3.2.

gumby · 01-29-2008, 03:28 AM

I saw somewhere here what up grades you can do to a CIS with out busting the bank, Do a search

timatt · 01-29-2008, 06:43 AM

I have a 73.5 T with CIS and went through this same scenario last spring. My car had approximately 75k miles on it at the time. I was tired of all the oil leaks. I am located in Indiana and had Bob Farmer near Indy provide the advice and do the wrenching. The most significant mods were as follows. Replaced stock intake with a '74 2.7L airbox, fuel distributor and intake runners to improve breathing. Also installed new valve guides exhaust valves and upgraded springs. Re-ringed and freshened all seals in the bottom end and tranny. New mains were not needed. Installed MSD ignition. I kept the stock heat exchangers and exhaust setup.

These mods made for a big difference in power without increasing displacement. The engine dyno-ed at 157 HP with a much wider power band than the stock setup. Peak power band extends to nearly 7000 RPM before noticeable dropoff.

I'd bet that your smoke problem is due to oil leaking onto your heat exchangers. If so, this can be corrected by replacing your lower valve covers with later style valve covers that are ribbed and therefore more rigid than the original stock covers.

I am very happy with the results. If you're interested I can scan the dyno traces...let me know.

Tim
'73.5 T

Jay Laifman · 01-30-2008, 07:14 AM

Or, you can end up like me, with my 73.5 that I had the head rebuilt and OEM P&Cs replaced and four years later, three mechanics and taking the engine part two more times and it still isn't running well.

Jay Laifman · 10:13 AM

Oh, and don't use Deves rings if you want the smoke to go away. Also, I understand from some places, includings the highly regarded Competition Engineering, that you should use a bare minimum of oil on the top of the pistons, but not on the rings, to get them to seat right. Others have said that is absurd and a quick way to break them.

timatt · 01-30-2008, 08:27 AM

Another footnote to my reply above:

As I understand it, OEM rings for the CIS 2.4L are difficult and expensive to come by. My mechanic was able to find a set of off the shelf rings from a reputable supplier, except that he had to cut (widen) the lands for the oil ring to accommodate the off the shelf oil ring. He assured me that there is plenty of meat in the piston to accommodate this cut. By doing this, I was able to re-use my pistons and cylinders which were still in good shape.

tim