I need race engine overhead cam help 2

[red4re]

I am restoring a 1974 Lancia Stratos factory race engine based on a Ferrari V6 engine. This engine has 4 valves/cylinder and 4 overhead cams. Displacement 2470cc with 10.5 compression. Horsepower around 300 at 8,700 RPM.

My question is this, the original cams the intake opened at 38 degrees BTDC, close at 74 degrees ABDC. Exhaust open 74 degrees BBDC and close 38 degrees ABDC, duration 292 degrees with overlap of 76 degrees. The cams were damaged and were sent to a cam specialist to repair and they changed the values to the following: Int open 21 BTDC, close 51 ABDC. Exh open 53 BBDC, close 19 ATDC. Duration 274 both intake and exhaust. Overlap 40 degrees. How will this change effect the performance of this engine?

 

[evelrod]

Just from a casual observation I'd say you will most likely pick up a bit in the lower mid range and lose a lot at the top end. If the "292" really made 300hp at 8700 rpm, the "274" will probably make less hp at a lower rpm. A guess---250 to 275 at 7500 or so. All this depends greatly on getting the fuel mixture, choke sizes, exhaust and, ign. compatible with the "new" camshaft timing events.
From my point of view, the change would make the engine much more "streetable" if that is what your after. It's the wrong direction for a race engine, IMO.

Rod

 

[RossABQ]

Agree with the previous comments; but I'm more curious if the changes are the result of re-grinding on a new base circle (i.e., grinding off damaged matgerial), or was it a copy of some other profile available for this engine?

 

[tbuelna]

A 1974 vintage engine running at 8700 rpm? I'd seriously consider a new set of valve springs with that new cam.

 

[allmotor8v]

Im usually a lurker, but i wanted put my 2 cents in...

292*
38/74 - 74/38
106* LSA
108* IN CL
104* EX CL

252*
21/51 - 53/19
106* LSA
105* IN CL
104* EX CL

These two cam profiles are worlds apart. The new 252* profile (not 274*) will produce massive low end and give you no reason to rev past 4000 rpms. IMHO, those cams are junk now with the regrind. Even if you could put adjustable cam gears onto adjust your center lines, it still wouldn't perform like the original lobe grinds.

 

[patprimmer]

This is a 4 valve per cylinder, low displacement per cylinder probably very short stroke motor. It will not need "American V8" type duration to rev high, however I agree, maximum rpm, and points at which maximum torque and power are developed will be reduced markedly. If that is of concern, the cams are junk, but if this is being restored as a weekend show car/cruiser, with no real interest in exploring performance in the over 6000 rpm range, they might be fine.

It also depends a lot on what minimum lift the cams are measured from.

The earlier closing of the intake might induce detonation.

Lift was not specified, but will have a significant effect depending on the flow of the heads at original and reground lifts.

Regards

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[modesign]

The standard Dino 246 (2.4 litre 6 cylinder) engine is 92.5x60 with a cam timing of 40-52/53-31 lift 36.7mm inlet and 36mm exhaust. Power 195bhp.The standard engine revs to 7800rpm. The engine has a rep for wearing the camshafts if not allowed to warm up for a minute at low revs. I always allow the oil temperature to come up before reving the engine.The standard engine has two valves and only a few 4 valve engines were manufactured for the Stratos. The works 4 valve engine gave about 300bhp.Works two valve about 260+bhp.A turbo 4 valve gave a claimed 500BHP!The 4 valve was banned.If this is a 4 valve then the cams are special to that engine.If it is a two valve then hot cams are still available but are reduced base circle ground.

Regards, Sandy Cormack.

 

[red4re]

This engine is made up of parts I bought that were from a factory Stratos 4 valve rally race engine. Most of the parts had never been used, the cams and the 44 IDF-27 Webers had been used. My problems started when the cam carriers, which were new, had an oil hole in the wrong location at one of the exhaust cams. I went to Web Cam in California to have the cams repaired and wound up with the mess I have detailed. My quandary is what to do now. These engines are very rare. I'm sick to death about this as I have spent a considerable amount of money trying to get this project completed. I appreciate all of the feed back.

 

[patprimmer]

You can tolerate the performance decrease.

You can buy new cams.

You can have a competent cam grinder build up your cams with Stellite then regrind to your spec.

You can have steel billet made into new cams to your spec

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[modesign]

If it is any help all the spares, part engines, gearboxes etc for this project were purchased from Italy a few years back (5?) by an active US Stratos racer. He had spares such as cams.Maybe you could trace him.

Regards