LP 1500 Spitfire

J

Jerry Lee Oleson

Well-known member
I have a friend here in Colorado building a LP1500 Spitfire. Any of you Spitfire guys got a recommendation for cam,piston,connecting rod ? Experienced LBC guy just not looking to reinvent the wheel. Feller, Criseberry(sp), Sargis, etc.
 
Jerry
I have been trying for over a year to successfully build a LP 1296 Spitfire. I have found little information and so far trial and error has produced some mixed results. I can suggest that if you use stock rods with ARP bolts that you check the threads in the rods to insure the bolts have threads deep enough so that the bolts do not bind and give a false reading. The ARP bolts are a bit longer than the stock bolts and can bottom out. I found this out the expensive way.
Most of the cams on the market seem to have too much lift for a LP motor. Rockers are always an issue in Spitfires and getting the geometry correct is very important. When my wife ran a Spitfire in the 80s we found that to keep the bottom end alive in the 1500 we had to turn down the rod journals and use the 1300 rods. Others may have other thoughts but that's my two cents worth. Good luck.
 
Yes I mean a 1296. We had problems with quickly wearing the rod bearings if we ran the motor above 6500. The experienced Triumph guys at the time advised cutting the size of the rod bearing journals to the 1296/1147 size so there was less surface area to keep oiled. I believe we just went back to the 1296 motor.
 
Im not sure that you can change Rod end sizes in LP.
If you cant find a good template for a build;
We know that you need all of the compression. Mill the block to get the pistons to 040 Piston to deck.
The Chinese rods have been very good and I think that they make the TR sizes.
Dish the pistons a bit , maybe gas port the top ring. Gapless second ring. The stock pistons have the top ring pretty low on the bore. The ring guys say to move the ring near the top for more power .
For a cam , you need the max torque at the shift point. So , work from a gear chart and determine the needed RPM range. Call some grinders and talk to an engineer that can help you hit the tq range that you will need. I would think that about 260 @ 050 on lobe centers to match your RPM range. Would get you started. Then, you will need to lighten everything that spins .... A racer with a lathe, add beer and free time .
If you can use the Baby Weber, they ran very strong on the street on the 1500 and MGB.
The Spit has good numbers. Way lighter than my Toyota 1600.
 
Jerry, is your friend just getting started or planning for the Runoffs? There are some things that can be run on the cheep side while a car is sorted.

The 1500 can be run on a budget build for mild use or an expensive build for competitive use but little in between. The 1295 with the small crank journals can be prepped with a very linear reliability and performance graph from mild to top performance. And the GCR does now specify a maximum crank undersize so that the 1500 journals cannot be undersized to the 1296 rods like people did in the past.

The 1500 has two main faults, the oiling passages to the mains were no longer circle cut in the block like the 1296 and many other cars. They have a channel on the block side but not the cap side. The oil feed to the center main passage that supplied the #2 and #3 rod had poor oiling. This can be overcome by cross-drilled cranks which should be legal for limited prep which allows lightening and balancing.

The second fault is the crank has bad harmonics above 7000 RPM. I ran a heavily lightened 1500 crank and light rods in FP before switching to HP and could turn over 7000 RPM without bearing issues. A close to stock weight crank has harmonic issues at lower RPM closer to 7000 and wears bearings as a result-which has a predictable bad effect. That is why I say a lower prep motor with restricted low RPM and taking advantage of the torque can actually work and be fun to drive on a moderate performance level.

I think APT has a LP cam that should be fine but I have not run it. Their lifters are the only economical ones to use and Moss and other outlets seem to sell the same part they source from APT. ARP fasteners are good and should avoid the need to drill for oversized like some of the full prep used to do. Standard racing oil pan technology applies which does mean don't run stock. I would keep the stock 1500 head gasket with the recess in the block for the compression ring. A good Payen gasket in that configuration does work well for LP compared to the flat block configuration that was popular for full prep.
Hope that helps -Tom
 
Do the 1500 center main shells have an oil feed groove all the way around? Or just half or none at all?
 
Al, the shells have a grove all the way around but they do better if they are fed through the holes on both side of the shell. That said they increased the rod and main circumference on the late 1296 and all 1500 so that they could use the same rods and main bearings as the TR6. British call it rationalization of parts supply. The speed of the rotating crank surface against the stationary bearing surface increased for the same RPM because of this, so the oil film becomes way more critical. Add vibration at speed and there is a good chance things will go down the toilet.

Jerry, problem at the Runoffs ended up being ignition. Antique MSD went bad and was overheating the coil after about half a lap. Hard to diagnose at home. Replaced the coil twice thinking the first bad just bad. Still acting up with the second then I replaced the MSD. Still acting up and I found I melted the new coil tower when I shocked myself when my hand was close to the coil. If we ran more last year would have been sorted out before the Runoffs but didn't get the chance.
 
The engineer in me can't help suggesting ideas:

Any reason you can't get a machine shop to use a boring bar to groove the main bearing bores to feed the lower shell?

In my old 3 main bearing Datsun 1600 that had similar issues, I increased to ID of the oil feed drilling to the center main, and decreased the cam bearing clearances that were stealing oil from the mains. The cam bearing clearances were surprisingly large, so I had a shop flame spray the cam bearing journals and regrind bigger. And crossdrilled the crank.

Something in all of that worked.

Anybody try a harmonic damper?
 
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