Re: 4.0 heads and turbos

["Brien Tourville" <hh7x@xxxx>]

1. 4.0 heads and turbos
From: "Rj Strong" <rj@xxxx>


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Message: 1
Date: Fri, 8 Nov 2002 23:30:54 -0600
From: "Rj Strong" <rj@xxxx>
Subject: 4.0 heads and turbos



could some one shed some light on the 4.0 head swapp on a 258 for me 
i
was also reading on a forum about turbos any info or opinions would 
be
great if i was to do either of these what do i need and need to look
for and what can i expect as for performance results rj also ........


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OK - 

The 258 in the Grems have a 12 counterweight crankshaft - which
is preferred . Last year for this crank is 1980 .

Depending on your year engine - your compression ratio should be
in the 8 / 8.2 / 8.5 to 1 ratio .

Again the year matters. 

The cylinder head from a late 74 - 76 is what you want to 
Turbo with - not the 4.0 .

4.0 heads are semi-closed combustion chambers - 56.8cc units
which would put your comp. ratio above Street Turbo use - read
ping and knock .

The claims of HP increases with these heads are NOT due to the
raised port design - which was built in starting in 1971 when AMC 
spent $$ on bench flowing the heads. The increase is from the raised 
compression ratio .

The Turbos run best with Open Chamber cylinder heads .

Stock size valves are plenty. 

The 4.0 have larger valves which create shrouding - which impedes
air flow.

The 74 - 75 year heads are 62cc combustion chambers.

You can go with a blow thru carb set up using a 390 mechanical
secondary carb....not vacume secondaries.

If this is you - join the yahoo group : 
www.blowthruturbo@xxxxxxxxxxxxxxx

You can go with EFI from a 1987 - 1990 Cherokee 4.0 as these
have the wide band O2 sensor and a knock sensor.

Grab everything from the Cherokee including harness - sensors
etc. distributor ......

You'll need get a CPS - KIT . Crank position on these Renix
(Renault - Bendix) Fuel injection units are measured at the 
flywheel . The kit will move the sensor to the crank dampner
on the snout of the crank.

A Grand National Turbo from a Buick will set you back $275.00 
off the Internet and will work well with your set-up.

Use a 1981 - 1986 Aluminum intake manifold with a 4bbl. adapter.

These intakes are preferred by Moab race engine builders .

Your exhuast header is from the Cherokee as well.

4 to 7 lbs boost on the street is fine. No need for an 
intercooler.

Replace your cam with the Crane H-260-2 unit.

Get new valve springs and locks and retainers from
Crane . Use new lifters as well.

Harland Sharp has nice roller rockers for $220.00 
complete for the AMC 6 .

Use Teflon valve seals with bronze wall valve guides .

If you care to - have the combustion chambers and 
exhaust ports ceramic coated to keep in heat.

If your 'building' the engine - run forged pistons with 
Teflon buttons instead of clips to hold the wrist pin in place.

Keith Black 'Silvolite' rep - John Erb - is the man to 
speak with on pistons here . KB have the Open Chamber
cyl. head for AMC spec . as they worked with Chris Morrison
- another Engineer - on his Race AMC 6 .

Have the pistons and valve faces ceramic coated .

HP coatings does nice work.

Read up on Coatings @ : www.hotrod.com in their Articles 
Archive. Interesting and good info.

Above the 'street boost' 7lbs. you'll need an intercooler.

Ford Trucks have these - you can get one off the net.

You'll need an enrichment source as well when in the 
12 - 18lbs. boost area.

I'd start with a 30lb injector set & see where your at with
lean / rich mixture.

The AMC Turbo AMX was 258 and ran 450HP.

The 'Indy' car was a 232 and ran 640HP.

The 'Indy' is what prompted AMC to redesign their cyl. heads
to Open Chamber style.

If you plan an all out killer - let me know as the computer choice
then changes .


All Turbo 6 owners I've spoken with rave on the thing.

Low end torque is all there and the engine 'wakes right up'
with the Turbo unit.


Good so far ?


Brien 'milners coupe'


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