jon8christine wrote:Looks great. I'll be starting something similar this winter. Anything you would do differently? That dual carb setup looks expensive, where did you get it? How much do you think the dual carb setup contributed to the power increase vs HC pistons, cams and head work? Looking for the best "recipe" for a hot street / autocross setup to get mid range power.
I think I built this just about the way I wanted to, other than wanting more cam. I had bought and ran a rad cam that was very powerful but very noisy, no decel ramps. Wanted to finish the build so put the old 40/80-80/40 cams back in. I did not have the rod big ends checked out by a machine shop, probably should have had.
As to what makes power - that's hard. I would recommend the Guy Croft Fiat Twincam book if you can find it on the used book market.
This what I'm thinking based on having tried quite a few things, just my opinions:
- CR alone does not do much at all but will allow other mods to yield better results. Need to be in the 9's and not higher than 10.5.
- A good header is a must if you plan on a bigger cam. I would recommend a 4-2-1 style header with long primaries. Or at least a stock manifold with two long secondaries. I cannot remember what these came with from the factory. A single downpipe results in inlet flow reversal with any kind of a performance cam.
- I would consider 2" exhaust all the way.
- The 40/80 cams run nice. Not too rad.
- Factory heads have the seats cut too small, even for Factory valve size. Open up seat to max allowed by insert and match valve diam to seat. In general the heads (ports) are very good as is until ultimate street or race spec.
- The twin webers are cool and the sound is awesome, but are not easy to set up. I'm not aware of a ready to bolt-on IDF kit. I bough the manifold, had to massively port it to enlarge for 44mm IDFs. Was made for 40s. Had to do some serious engineering, testing to fabricate the carb linkage, levers. IDFs can be had for about $350 ea.
- I hear that single carb engines can be pretty powerful if the rest of the stuff is done right.
- Modern HP and period (-70s) reported HP do not seem to be the same. Modern HP seems to be at least 10% more powerful. I'm thinking my car has 135-140 period HP but only about 120 modern HP.
- Head porting is likely the last mod and not worth it unless seeking ultimate HP.
- Cam and ignition timing is important and should be carefully checked, adjusted. Need an electronic ign, no gaps.
- Modifications generally do not increase peak torque but instead allow the engine to produce the torque at a higher RPM thus increasing HP. What follows is that unless you spin the engine faster, there is no gain. 4.30 rear makes this easier than the 3.90 while making highway cruising less enjoyable. My engine turns at 4000+ rpm at highway speeds.
- Good machine shops are hard to find anymore. Or they are too busy with your one off project.
