'76 GTB engine rebuild - Ferrari Life
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post #1 of 118 Old 07-06-2010, 07:24 AM Thread Starter
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'76 GTB engine rebuild

Hey all,

This is my documented engine rebuild of my steel GTB engine. The engine had 83k miles and still ran very strong, but was burning a little more oil then I was comfortable with which was about a quart every couple hundred miles depending on how hard I drove. The engine dyno'd last before the rebuild at 199.7bhp at the wheels which I definitely classify as a very strong 308. Have not completed enough tuning to know the final outcome of this engine, but I suspect it will be around 215 at the wheels. Entire process took about two months, but I am still not anywhere near completed tuning the thing.

New Ferrea SS valves
New SSi guides
10.5:1 cpr pistons
new everything else


The guides had a good .010-.012 clearance in them and the stem seals were of course shot. Piston rings had about a .027-.029 gap. The main and rod bearings all measured well within spec and had about .001 clearance with all of them. The main especially looked really good, but all were of course replaced.


There were all kinds of issues with the machine shop who had the heads. In short, they sucked. Make sure you use a very good machine shop that stands by their work. If possible, use a shop that knows Ferrari or Porsche or the like.

The pistons are an old Borgo forged piston Ferrari made in what they called a 'sprint pack' which was essentially a factory kit which included these pistons, factory P6 cams, different carb jetting etc. For some reason, the factory quoted these pistons as being 9.7:1 compression, but the dome is a giant 15cc compared to the stock 6cc dome. With the 38cc combustion chamber my chamber cc'd to be, this puts compression well over 10.5:1 by my math. I do not know the original cost of this kit, but I know it was a very pricey procedure as the engine had to come out and be rebuilt from the ground up to do it. The factory quoted around 300bhp with this kit, but 275-280bhp is the realistic figure. I have P6 cams coming to me, but for now I am using the stock early US/Euro cams which I will set up and am expecting 260bhp once done tuning. The original piston rings with this kit were a hulking piece of kit and were very very tight. I substituded those rings for a much more easy going set of NPR piston rings which just happen to fit a '85 Toyota Corolla engine. The giant 5mm oil ring was the only odd-ball which I located with Total Seal rings.


The cams were timed to 105 degree lobe centers as opposed to the factory 96 degree intake center and 91 degree exhaust center. Power is up in the rpm band a few hundred rpm.

Jetting in the new engine started out with 145 mains 190 a/c with F24 tubes but I am still really lean.

The first dyno session pegs me at 202bhp at the wheels, but the spark plugs had detonation over 6500rpm AND the mixture is 15:1. Current spark plugs are BP9ES which are pretty cool, but I am going for the non-projected insulator setup which will keep things really cool. I have a very strong set of Mallory ignition boxes firing things but I will still keep the gaps set to a reasonable .025 until I have things figured out a bit more.

Prior ignition timing was about 39 degree total. Needless to say I can't get anywhere near that at the moment. 35 degrees is the only setting where I don't get any detonation due to the hot plugs. I suspect once I fatten up the mixture and cool the plugs a shade more I will be able to get some more timing in there. I will have this figured out soon.

I remember when I first started tuning this engine a few years ago how awful my first dyno session was. I had just serviced the engine and set the timing spot on, but was still lean and came up with something like 177bhp at the wheels, which is actually pretty typical for one of these engines.

Just goes to show you how much bhp is left on the table for proper tuning.

The engine already driving much better due to a stronger torque curve.

Will keep everyone posted and if there are any tuning suggestions, please comment and let me know!
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post #2 of 118 Old 07-06-2010, 07:27 AM Thread Starter
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http://www.youtube.com/watch?v=UPSjhCYgoFg


first start of engine a couple weeks back



Last edited by Andrew; 07-06-2010 at 12:19 PM. Reason: embedded YouTube
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post #3 of 118 Old 07-06-2010, 07:40 AM
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Nice job John.

Even with all the BS you had to go threw, you got it done.
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post #4 of 118 Old 07-06-2010, 08:21 AM
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Terrific thread and great pictures, thank you. Am hoping to collect my re-fettled 308 GTB later this month to enjoy the sound and power of that wonderful V8 quad cam. Sounds like a F1 Cosworth V8 from the seventies from 6000rpm and up!
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post #5 of 118 Old 07-06-2010, 08:51 AM
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Very cool, well done
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post #6 of 118 Old 07-06-2010, 09:35 AM Thread Starter
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Still LOTS of tuning to go. Jetting/timing/plugs are all over the place. Mark offered me some insight to get the jetting correct first, and then get on with the other stuff
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post #7 of 118 Old 07-06-2010, 09:42 AM Thread Starter
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Purely for documentation purposes, these early US cars had emissions air injection equipment which I weighed out to 27lbs (pic above). I removed all this garbage as well as the US bumpers which were replaced with very lightweight fiberglass bumpers which saves another 82lbs. The 120lbs thermal reactor US muffler on this car had been removed quite some time ago with a 20lbs Ansa Sport unit. Altogether we have 210lbs shaved from a US car which puts it into Euro spec.......thank God! Car weighs in at Euro weight which is in the low 2900lbs area depending on fuel.
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post #8 of 118 Old 07-06-2010, 09:58 AM
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Ahhhh...the classic tune for top end or tune for bottom end dilemma with the choice made even harder by a relatively small 3.0 liter engine......you need a bigger engine I think







Looking good John!
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post #9 of 118 Old 07-06-2010, 10:04 AM
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Quote:
Originally Posted by mk e View Post
you need a bigger engine I think
John, don't listen to him. He doesn't know what he's talking about.
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post #10 of 118 Old 07-06-2010, 11:37 AM Thread Starter
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Just to anger Mark, I am going to build a motor with 13.5:1 compression and use P6 cams with some serious heavy duty valve springs and spin it to 11k.

Speaking of P6 cams, Dave just sent them from South Africa this morning.
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post #11 of 118 Old 07-06-2010, 12:38 PM
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Quote:
Originally Posted by ferraripilot View Post
Just to anger Mark, I am going to build a motor with 13.5:1 compression and use P6 cams with some serious heavy duty valve springs and spin it to 11k.

Speaking of P6 cams, Dave just sent them from South Africa this morning.

It wont anger me and Im looking forward to it.

My point with the bigger engine is that while making more hp is relatively straight forward, there is very little you can do to improve torque, particularly low end torque short of boost or a larger engine. You are doing all the right things, compression, more LSA (lobe separation angle, ect) but you are limited to a 10% gain at most and it will cost you top end. Boost or a bigger engine are about the only way to add bottom end without harming top end.
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post #12 of 118 Old 07-06-2010, 01:08 PM
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excellent write up and pics. thanks alot. i enjoyed reading it. Please keep us updated. You guys are making me want to hot rod my 328. thanks.



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post #13 of 118 Old 07-06-2010, 01:48 PM
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excellent write up and pics. thanks alot. i enjoyed reading it. Please keep us updated. You guys are making me want to hot rod my 328. thanks.
+1 ...really impressive.
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post #14 of 118 Old 07-08-2010, 06:48 AM Thread Starter
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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 radical 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 200 air correctors and that was just about perfect.
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post #15 of 118 Old 07-08-2010, 08:17 AM
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Impressive stuff...

Ferrari's: 360 Modena, 550 Maranello
Ex's: Dino 308 GT4, 612 Scaglietti
The Rest: Rolls Royce Silver Shadow, Porsche 911 2.7s, Porsche 911 3.2 Carerra, Ducati 916... and the Land Rovers
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post #16 of 118 Old 07-08-2010, 12:57 PM
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Im surprised a degree or 2 made such a bit difference I cranking compression. wow.

You are going to pick up quite a bit of power and response once you get the mixture sorted Id think.
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post #17 of 118 Old 07-08-2010, 01:50 PM Thread Starter
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Too right Mark. This is exactly like my very first trip to the dyno with this car. It yielded an ugly 177bhp at the wheels on a dynojet. Proper tuning yielded 23bhp at the wheels. Power is hides very sneakily in carburetors
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post #18 of 118 Old 07-08-2010, 02:22 PM Thread Starter
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Any frequent the Porsche engine building forums? Those guys run some serious cams on the streets. A common cam used the PMO carbs is a DC62 which is .495 lift with 268 dur @ .050. I heard a couple of them on the dyno via various vids floating around. What a sound!

Anyway, compared to P6 cams I would think the substantial extra lift of a DC62 would help where the P6 lacks, which is the low end. Interesting
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post #19 of 118 Old 07-20-2010, 05:03 AM Thread Starter
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Update:

I installed autolite AR50 race plugs which are fantastic btw and rejetted the carbs again. I fire the engine and go through my usual warm up process and proceed to go for a drive. The engine is running substantially better.

I noticed above 4k rpm ish under load the engine cut out as if the ignition system cut things off or jetting was far too fat etc. First thing I do is check the plugs. All looks right. Second, I check the ignition at various rpms while not under any load. All is right. After much head scratching, I peered down below my distributor and noticed the rather low-tech solid-state square box fuel pump taking up space in my high performance engine compartment.

The fuel pump is a facet unit the PO must have installed at some time due to the OEM unit dying. I searched for a receipt for this service but could not locate one. No worries, I looked up the specs and found this to be a 30GPH unit with about 6psi max. This may have been enough for my previous engine but this is not even to OEM standards. Matter of fact, I am surprised the engine ran so well prior to this rebuild with this anemic little pump barely fit for a stock alfa engine.

Replacement will be one of these nifty 110gph capable Holley blue fuel pumps. They are set to about 8psi stock. Well, they used to be blue, now they are just called 'blue'. I used one of these in the past when I had an identical issue with a Maserati Merak ss engine I rebuilt. Worked beautifully.
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post #20 of 118 Old 07-27-2010, 09:07 AM Thread Starter
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P6 cams pinned with appropriate cam extensions. These cams came with the old style extensions which havea larger OD than the splined extensions. I made a sleeve on a lathe to make up the difference in diameter, pushed in the sleeve, then drilled the cam and inserted a super high strength roll pin. Ferrari's method which was a solid pin with the tips on either end mushroomed was convoluted and involving to reproduce and not as tight as a good roll pin.
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