Background
The SRF has a 1994/5 Mexican, Ford Escort 1.9L engine with a hemi head, a custom Rousch ECU and a 1995 Ford Ranger MAF. This engine was not sold in the USA and SCCA has purchased all of them from Ford. The engine is a sealed unit ,used in SCCA racing, producing 108 Hp at the flywheel.
I removed the spec engine and replaced it with a 1997 2.0L SHOC SPI. I chose the 1997 because it has a dual line fuel rail. Any year engine will work but I required this fuel rail for my system.
I have run a junkyard engine for two years against other SRF's with their custom engines and found the SPI to be dead even in power. We run bumper to bumper at the tracks and neither car, SPI or Rousch, can pull away from the other. The SPI may have just a little more torque in the very low end of the RPM band, but otherwise it is an even match.
New Engine and head re-work
This new engine has a ported and flow matched SPI head. It also started from the junkyard and was warped as seen in the pictures. The first step in deciding to invest in the porting is to check the head to see how much it is warped. If it is out more than 0.020" get another head. If it is less than 0.020" it can be fixed but it requires line boring with a special tool. The only outfit I found to do that work was Dover Heads. They cleaned the head up, did a pressure check, line bored, resurfaced and a valve job for $265 total. The head looks like new. An easy way to tell if the head is OK is to remove the lifters and if you can turn the cam by hand it is good. If not the head is warped and will require measurement to determine if it can be repaired.
Porting
This is the first SPI head I have done and it took about 40-50 hours total. Now, with that experience, it can probably be done in 15-20 hours. Porting is an EXACT process and not a DIY venture. To do it right you must have a flow bench. It takes a lot of time, about $25 of expendables and you have to go pretty slow. I flowed the head occasionally to monitor the progress. I also had a junk head that I experimented on with different cuts before cutting on the one I intended to keep. The final data is here:
In the combustion chamber under the valves (not shown) there is a divider for the two intake ports. I guess it is there to increase the velocity or swirl when only the primary port is open (under 3000 RPM). What I discovered was that by removing most of that divider down to the valve guide and back into the ports about 1/4" that it dramatically increased the heads flow while maintaining the velocity.
There is a major modification to the dome area. The normal SPI head is straight on one side. I opened up just a little around the valves to provide more flow on the back side. Also, around each valve the sides were undercut just a little to make the walls naturally cup and guide the air in/out to the valve's port. This made a lot of difference in the flow as well. All of the raised surfaces, bumps and ridges in the dome were smoothed out as well.
The actual ports were enlarged just slightly. Enlarging the port is not nearly as important as removing every sharp edge and every edge where air flows past it creating a back eddy (drift). Think of it as a berm on a road and the wind is blowing the snow across it. Pretty soon you have a huge drift on the downwind side. The same applies in the head; this creates turbulence and reduces the flow. All of the sharp edges that are thicker than a dime on edge need to be smoothed out and transitioned too. These faces are like a wall and air hitting them starts a lot of turbulence resulting in lower flow.
Using the correct gaskets, and comparing those to the mating parts, the final step is to match the port entry/exit to the gasket surfaces. You can't (and don't want to) enlarge the entire port to the gasket size because you will probably get into the water jacket. As a final step, after you have opened them up to the maximum you need, bevel the edges to make the match up pretty close to the gaskets and to provide a smooth transition.
Be mindful about getting the exhaust too big and creating the snow drift problem we discussed. If the port is too big then the exhaust manifold will be smaller and the exhaust gas will see the manifold edges as a wall. Ideally the exhaust port should only flow 75-85% of the intake port. Any more than that will create an undesirable scavenge effect. In this case too big is not better. You will find that matching the port to the gasket is very close on the SPI engine but check it against your header or manifold first..
The intake SPI Runner just needs a little matching to the gasket as seen in the pictures. The actual intake manifold needs a little more work to get it matched up nicely with the gasket.
The throttle body hole is already very close. All that is needed here is to smooth the inside of the round opening in the manifold so it transitions nicely to the side walls of the manifold (eliminating our snow berm example).
Turbo
At some time in the future the engine will get the turbo fitted and tuned. I have a basic tune completed using the J3 Port on the ECU.
Images
 Short Block Lower |
 Block Crank Journals |
 Finished Head |
 Runner - to Head Matching |
 Dome Areas to Work |
 Dome Major Mods |
 Exhaust Side |
 Intake Side |
 Full Manifold |
 Manifold Transistion |
 Manifold Smoothing |
 Rod Marking |
 Runner - Head Side |
 Runner - Intake Side |
 Runner - Head Side |
 Intake - Throttle Body |
 Intake - Throttle Body |
 Engine in |
 SRF Engine Bay |
 Flow Bench |
 Original Head |
 Check warpage |
 Measure Here |
 Custom Headers |
 Oil Return for Turbo |
 Oil Pan Internal Baffle |
 SPI Motor |
 SPI Controller |
 Controller Finished in the Box |
 SPI New Dome |
 Head - Block Side |
 SRF Chassis |
 29 On-Track |
 Shop |
 Shop |
 5 Spd. Transmission |
1997 SPI Head Flow Data
| Stock flow at 28 in | |||||
|---|---|---|---|---|---|
| Lift | 0.1 | 0.2 | 0.3 | 0.4 | 0.5 |
| Intake Flow "H20" | 0.09 | 0.26 | 0.42 | 0.53 | 0.68 |
| CFM | 53.87 | 93.4 | 119.1 | 133.9 | 151.9 |
| Exhaust Flow "H20" | 0.06 | 0.19 | 0.29 | 0.35 | 0.39 |
| CFM | 45.28 | 79.4 | 98.54 | 108.55 | 115.55 |
| Exhaust % flow of Intake | 0.84 | 0.85 | 0.83 | 0.81 | 0.76 |
| Flow at 28 in | |||||
| Lift | 0.1 | 0.2 | 0.3 | 0.4 | 0.5 |
| Cylinder 1 | |||||
| Intake | 0.11 | 0.35 | 0.5 | 0.67 | 0.87 |
| CFM | 61.31 | 108.65 | 130.78 | 151.35 | 172.54 |
| Exhaust | 0.08 | 0.23 | 0.33 | 0.4 | 0.45 |
| CFM | 50.56 | 87.8 | 105.37 | 106.2 | 124.11 |
| Exhaust % flow of Intake | 0.82 | 0.81 | 0.81 | 0.7 | 0.72 |
| Improvement vs stock | 0.12 | 0.14 | 0.09 | 0.12 | 0.12 |
| Cylinder 2 | |||||
| Intake | 0.12 | 0.34 | 0.48 | 0.68 | 0.89 |
| CFM | 62.48 | 107.89 | 127.4 | 151.85 | 174.4 |
| Exhaust | 0.06 | 0.21 | 0.31 | 0.39 | 0.45 |
| CFM | 45.28 | 83.9 | 102.15 | 114.65 | 123.3 |
| Exhaust % flow of Intake | 0.72 | 0.78 | 0.8 | 0.76 | 0.71 |
| Improvement vs stock | 0.14 | 0.13 | 0.07 | 0.12 | 0.13 |
| Cylinder 3 | |||||
| Intake | 0.12 | 0.37 | 0.5 | 0.66 | 0.87 |
| CFM | 64.04 | 111.65 | 130.05 | 150.21 | 171.95 |
| Exhaust | 0.06 | 0.22 | 0.33 | 0.41 | 0.47 |
| CFM | 40.4 | 80.54 | 100.3 | 113.2 | 126 |
| Exhaust % flow of Intake | 0.63 | 0.72 | 0.77 | 0.75 | 0.73 |
| Improvement vs stock | 0.16 | 0.16 | 0.08 | 0.11 | 0.12 |
| Cylinder 4 | |||||
| Intake | 0.11 | 0.35 | 0.49 | 0.64 | 0.85 |
| CFM | 59.75 | 108.52 | 128.75 | 147.25 | 170 |
| Exhaust | 0.06 | 0.22 | 0.34 | 0.42 | 0.48 |
| CFM | 40.4 | 80.54 | 106.95 | 119.9 | 128.18 |
| Exhaust % flow of Intake | 0.68 | 0.74 | 0.83 | 0.81 | 0.75 |
| Improvement vs stock | 0.1 | 0.14 | 0.07 | 0.09 | 0.11 |
Data and photographs courtesy of Rexlantz srf-engine.rexlantz.com
Also see
- Ford Escort & ZX2 section for the entire index of all Ford Escort and ZX2 related articles.