the lvferraripilot engine rebuild thread

In the seemingly endless labirynth of spark pluggery, I have deduced a few things regarding the needs of these motors.

A spark plug heat range for NGK standards is each number is 70-100C colder/hotter according to the numerical direction they have assigned (higher # is colder). Should a 70-100C be too large a jump then is required, a non-projected insulator plug can be used which is a 20-30C heat change.

For example: a BP8ES compared to a non-projected racing R5671A-8 (8 being the heat range) is 20-30C colder than the BP8ES while retaining the '8' as the assigned heat range.

Boost, nitrous, hard racing typically use a non-projected tip for their obviously stout running applications.

Should 9s not work out and be too cold, I will go for the racing plug route with R5671A-8.

 

Read the ground strap. There should be 'color' or annealing on the strap to the corner of the strap and no further. Check it after a WOT run. I found BP6ES to be too hot for high rpm driving when ignition timing is set correctly. BP7ES are perfect.

 

Spark plugs, timing, and jetting were my focus thus far over the weekend. Between the stints of rain, I managed to rack up a good number of miles, say about 100 making the new engine have a total of about 150 miles.

I am certain the rings have seated and performed the first oil change. The oil was still very clean, but I could tell the viscosity had taken a hit.

Spark plugs! wow, these things are making me batty. I went up to BP9ES, backed off the ignition timing quite a bit, added more main jet and they are still a shade too hot. I have changed again to B9ES which is a noon-projected insulator version of the BP (the P means projected) and backs heat down another 20-30C. These have been working out well so far.

Timing seems to be sitting best at 10 degrees idle and 37 total. The dyno will tell for sure.

Jets are up to 145 mains with F24 tubes and 190 air correctors. I think I have it spot on, but again this will all have to be confirmed on the dyno which will be the week I come back from Chicago (July 17th ish)

 

yup. stock early cams.

 

Hey guys. Had a chance to get the car to the dyno today for a couple baselines. Power was a little 200bhp at the wheels, and torque was 179lbs. I only did one run because the engine is still very lean and I need to find the balance between plug heat ranges and ignition timing. a/f ratio was 15:1 through the power band and that was with about 35 degrees total ignition timing with idle sitting at 5 degrees. Jets are up to 145 mains with F24 tubes and 190 air correctors. Any more timing and I was getting light detonation over 6500rpm due to plug heat ranges and timing. Also, peak torque was at about 4k rpm which tells me I need to up the cam centerlines a bit further to maybe 110. I want peak torque to be around 5-5k and peak bhp around 7-7.5k.


Game plan is to fatten up the mixture a bit more, alter cam timing a bit, close the plug gaps a bit, and go one step colder to race plugs which will give me a few more timing degrees to work with up top. There is 215bhp at the wheels with this engine, I just need to milk it out.........

 

Old motor was 199.7bhp with 174lbs torque. Mixture and timing was just about perfect. The very first time I put that engine on a dyno (dynojet) it made something awful like 177bhp. Jetting was lean, timing was a bit off, plugs were wrong. Just goes to show you how much power is on the table when jetting and timing are incorrect.

Now the hard part of tuning this thing correctly begins! It's all part of the hobby

 

Some carb jetting/tuning updates.

The 5-8 bank intake cam timing was off a degree or so making cranking compression a little higher than the 1-4 bank. I corrected this last night. All cylinders are now cranking about 160lbs.

Jetting is being radically fattened up with 150 mains 170 air correctors on F24 tubes. I am thinking a lot of the light detonation above 6500 rpm is caused by the mixture being so lean causing the plugs to overheat etc. BP9ES for this compression and application is plenty cold. Until I have the mixture where I want it, I will not mess with the plugs.

The dyno showed peak torque coming in around 4100rpm which is very low, then I figured out why....... The dyno run began with me stabbing the throttle in 4th gear at about 3500rpm. The pump jet squirting in fuel temporarily fattened up the mixture to around 13.4:1 making the mixture good all for that brief moment from 3500 to around 4200 and then things got lean again bouncing back to 14.9:1. The radical jetting change should hammer out these issues. I still cant believe how radically different jetting is with this setup. Prior to this modified engine build I was using F36 tubes with 140 mains and 190 air correctors and that was just about perfect.

 

F36 was essentially the US emission tube which I believe were used on all 308s after 1977 regardless of market with the only difference between the various markets being the air correctors and main jets. The F24 tube is the performance tube used on all Euro engines '76 and before on GT4s too (I think). If one were to change to F24 tubes and keep the same mains and air correctors as with the F36, then the a/f typically goes down a little over a full point. So if you were 14:1 with F36 140 mains and 200 a/c, you will be about 13:1 with F24 tubes. F24 tubes are available all over the place and are about $20 each, just make sure you get tubes for DCNF carbs.

And yes, I will probably have to go through this in some shape or form with P6.

I was carousing the Porsche 911 engine rebuilding threads as I have been doing forever now and am always amazed at the cams those guys regularly use on street cars. They make P6 cams look like *****cats with their .485 lift 269 dur @ .050 monsters. Used on smaller carbureted engines no less!

 

Thanks Geno! Take me to Italy next time!

 

202bhp is hardly a stretch lol. I have sheets posted showing my "before" run where she made 199.7bhp. I will post a sheet once she tuning is completely done. It's the 215bhp at th wheels sheet that I want to post. Getting there......

I am ot of town until next week so everyone is gong to have to sit tight!

 

More on spark plugs. I was reviewing the lemans spec sheet with jetting and spark plug recomendations which suggest a champion n60yc is the plug to use with this setup. I searched a bit and found this to be the ngk equivalent to a 10 heat range with an e tended tip. That's right, 10! How 700bhp supercharged chevy engines get away with 8s is beyond me. Must be a European thing. Anyhoo racing plugs are on their way.

 

I have heard of doing this bit I am not too concerned. I just now getting into testing projected tip racing plugs and even with 10s I remain in the middle of warm and hot for racing plug standards. I was very close with 9s and have no doubt 10s will work fine. Ngk gets frigid cold with their non projected and practically buried tip heat range 11 plugs and I doubt I will need to get that cold.

 

Forgot to mention this. The autolite ar50 racing plug is essentially a plug with every corner rounded off and the ground strap sits right at the center of the plug tip. Popular with the gokart racing crowd and are the ngk 10 equivalent