DeTomaso Mailing List: July 2001, Message #491

Did a leakdown test today on the left bank, in an attempt to determine the 
problem with the fouling #7 plug.

Let's say I know what the winters project will be...

I built a simple leakdown tester, with a 1mm orifice ane two gauges.

Tomas Gunnarson was kind, and probably curious, enough to help me run the test.

We set the pressure to 5bar (~70psi) and noticed the pressure drop.

cyl	press	leakdown
-----------------------
5	3.4	32%
6	3.8	24%	faint hiss in the exhaust, leaking exhaust valve
7	4.3	14%
8	3.4	32%

The weird thing is that once again is it #7 that shows the best pressure, 
despite it being the cylinder that fouls the plug.

To verify that the tester worked, I tested one of the cylinders in my wifes 
Golf, with five times the km:s on the odo, and it had a pressure of ~4.8, or a 
leakdown of ~4%.

I'm a bit puzzled by the engine apparently being so worn. It has only only 
around 40k km, or 25k mi on the odo.

The car was originally owned by a Saudi prince, and I guess it may have seen 
some rough times in the desert, with sand being drawn in.

The planning has begun for the rebuild and I'm soliciting ideas.

Heads:
I have located a supplier of Aussie 302C heads, and I will likely rebuild a 
pair. Slight porting, stainless valves, maybe hardened exhaust seats as I'm 
running unleaded, new valve guides (bronze inserts?), springs, maybe roller 
rockers.

Block:
Minimum boring.

Pistons:
What kind of pistons are people with 302C heads using? Must run on pump gas.

What are peoples opinion on zero-gap piston rings?

Cam:
I'd like a cam that allows the engine to breathe properly. I have no need to 
putter around town at 40 - 50 kph in 5:th, but I still want a cam that provides 
proper vacuum to the brakes and heater controls.

I'm not particularly interested in a solid lifter cam. I have better things to 
do than adjusting valve lash every 500 miles (hi Charlie!). Are the hydraulic 
rollers good?

Cheers,
Thomas


> From: Thomas Tornblom <Thomas.Tornblom@Sun.COM>
> To: Multiple recipients of list <detomaso@realbig.com>
> Subject: Compression
> 
> How much compression can one use with 302C heads and pump gas?
> 
> I'm planning to replace my open chamber 2V aussie heads with closed chamber 2V 
> 302C heads. AFAIK they have a volume of 58cc vs the 4V closed chamber heads 
> 62cc.
> 
> Using the http://www.waldens.com/calceng.htm calculator with stock bore and 
13cc 
> dished pistons I get a CR of 9.5. Flat top pistons with a 2cc valve depression 
> yield around 10.7. Would that work with 98 octane RON, which I guess is around 
> 90 or so octane MON?
> 
> Thomas
> 
> 

Real life:      Thomas Törnblom             Email:  Thomas.Tornblom@Hax.SE
Snail mail:     HB Hax                      Phone:    +46  18 290 290
                Banvallsvägen 14            Fax:      +46  18 290 291
                S - 754 40 Uppsala, Sweden  Cellular: +46  70 261 1372