Hi Turbosport. Before I explain my dilemma, I firstly wanted to say thanks for all the valuable information on this site. I’ve been a lurker here for a while and have benefited significantly from numerous posts and topics where forum members are very generous with their time, knowledge, and experience.
I’ve owned pinto Capri’s for 20 years and have always wanted to build and install a mildly tuned pinto engine.
Finally finding myself in a position to undertake the project, I bought a 2L injection head pinto (from a reputable seller), set up a nice workshop in my shed, and started planning the project. I should also mention that I read the Des Hammill book (How to Power Tune For SOHC), and already had both the Ford Workshop and Haynes manuals for reference.
After researching various camshaft options, I settled on a FR30 as I was particularly keen on having a drivable road car, initially on a 32/36 carb, with increased torque lower down the rev range.
After disassembling and inspecting the engine, I sent it off to machine shop for:With the machining complete and components returned, I measured up to verify what had been done.
- +1mm rebore to suit KS pistons
- Fit new KS pistons to conrods
- Crankshaft journey regrind and polish
- Light skim of block and head
- Balanced rotating assembly
- Thorough clean including oilways, and paint.
Without giving a blow-by-blow account, I really took my time with the block and head build, ensuring that reassembly was carried out with measurements, clearances, torque all to specified values/tolerances.
Towards the end of the build process work and life challenges meant that I needed to get the project completed, which lead me to bolting down the head without being fully confident of compression volumes…. (Something that would come back to bite). Based on my assumption that the engine was previously unmodified, I assumed that the light skim of block and head would pep-up my compression ratio by 0.5 to perhaps just under 10:1, ideal for an FR30.
After finally arranging some time off work, I swapped out the Capri’s original 1.6 for my freshly built 2.0.
The reproduction alloy sump and 2L clutch assembly created some challenges but I manged to resolve.
With oil system primed I fired up the engine…
Turn over speed was extremely slow. I was aware of the high dynamic compression caused by the FR30 cam, but the starter was really struggling and occasional kick-back made the situation worse.
I reset static ignition timing from approximately 8 degrees down to 4 degrees and tried again.
She fired up, oil pressure was good, so I ran it at over 2k revs to bed in the cam.
After carrying out post run-in checks and adjustments it was time for a gentle test drive up the road and back.
The Problems Begin
At 2k revs the engine was severely pinking, so to avoid any potential detonation damage I backed right off and limped home.
Clearly something wasn’t right, most likely compression given that I’d deliberately set static timing fairly retarded.
Armed with all the information regarding standard and modified volumes from both the Ford manual and Des Hammill book I set up a spreadsheet to firstly prove standard engine compression ratios based on all possible contributing measurements (displacement volume, head combustion chamber volume range 48.60 – 51.60cm3, gasket thickness, and squish/quench), and test out various modifications to try and approximate my compression ratio before taking off the head.
Getting to the point, my initial calculations showed that compression ratio was potentially somewhere around 11:1 given the felpro head gasket and skims from block/head.
I decided to remove the head so I could CC it and properly measure piston to deck clearance.
Results were as follows.
Head combustion chamber: 40cm3 (Ford spec standard is 48.60 – 51.60cm3)
Piston crown to block deck: 0.15mm (standard is characteristically 0.5mm)
Felpro gasket crushed thickness: 1.0mm
Note, +1mm piston bore giving bore diameter 91.83mm
The head had clearly been skimmed multiple times to a total cut of over 1.5mm (Des H book).
The block had also had a substantial total cut.
Having now suffered the consequences of not checking my volumes properly during the original build I calculated my actual compression ratio to be 11.8:1, and most likely over compressed for the FR30, leading to the detonation experienced on road test.
Searching for options of how to get the compression down I decided to try a thicker head gasket. I was aware of the importance of correct squish/quench and that although a thicker head gasket would reduce compression it would also reduce the engines resistance to detonation. I decided to give it a shot and ordered a 75thou Cometic gasket to achieve a total squish of 2mm, which I understand is the standard engine squish (Des H book). This would give me a CR of 10.6:1, still on the high side for an FR30 but perhaps much better than the previous CR.
Last weekend I refitted the head, re-primed oil system, and fired up the engine.
Turn over was again a real struggle but eventually she fired up.
Aside from an exhaust manifold leak, the test drive seemed mush better although there was slight pinking when I dumped the throttle from low revs.
I’m planning to determine the current ignition advance curve this weekend and potentially try to modify the distributor to help reduce detonation risk.
However, at this stage I feel a bit disheartened and unsure of how best to resolve the situation, with many questions going around my head:Apologies for the lengthy post but I wanted to try and explain the situation as much as possible.
- Is 10.6:1 CR to high for an FR30 cam?
- Is a squish of 2mm to low and risking detonation?
- Should I splash out on a high torque starter motor?
- Should I just bite the bullet and get the head back off again and consider trying to increase head combustion chamber volume?
- Change the cam for something else or even standard?
I would be very grateful for any advice.
Reply With Quote
202mph standing mile
Bookmarks