Differences in cam timing specs

Road-race engines and ancillaries - general discussion
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csi2000s
Posts: 18
Joined: September 10th, 2008, 9:58 am

Differences in cam timing specs

Post by csi2000s »

Hi,

I am building a new head for my 1974 Fiat spider. It is fitted with a 2 litre engine and already boasts the following upgrades, hi comp domed pistons, twin 40mm DCOE Webers, MSD 6A ignition coupled to a Bosch block mounted electronic distributor and Abarth style headers and exhaust.
I intially purchased a set of Abarth 130TC cams for the head upgrade but have since found out that they are not much better than the 131 cams that the engine is now running. Since I'm hallf way through the rebuild of the new head and have already spent money on new valves, guides etc, I want to buy cams that will make all the work worthwhile.I have an 1800 head for the build which I understand will add a little more compression due to the smaller size of the combustion chambers.

My question concerns the specifications of different cams and what they mean in the real world when you are out on the road. The car is used only on the weekends for spirited driving around the countryside. There is no city driving nor will it be used to participate in any form of motorsport. I've been looking at the specs of two cams and would like to know the difference between them in simple terms. I understand lift and duration but I not not sure exactly what the figures on valve timing mean and what they translate into when driving.

The cams in question have the following specs, the 1st cams are 282 duration, 10.54mm lift, 35/67 67/35...2nd are 280 duration, 10.65mm lift, 12/52 52/12.
What does the difference in these timing figures mean in terms of performance and drivability on the road. Also what he pros and cons of these differences in timing?

Regards
Angelo
TomLouwrier
Posts: 333
Joined: July 28th, 2010, 3:09 pm
Location: Leiden, The Netherlands
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Re: Differences in cam timing specs

Post by TomLouwrier »

hi Angelo,

Unfortunately there is no 'short and easy' answer about cam lift, profile, timing, overlap etc. It's an aspect of engine design and tuning that forms a world of its own and is heavily influenced by inlet and exhaust tracts, carbs etc so pretty complex stuff.

Being on this site, I can only advise you to call Guy, discuss what you wrote here and buy the one from him that he recommends. You'll get all support you need concerning setting up cams, ignition, carb jetting etc.
Do it right first time.

regards
Tom
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nabihelosta
Posts: 94
Joined: December 14th, 2010, 5:37 pm
Location: Lebanon

Re: Differences in cam timing specs

Post by nabihelosta »

Angelo

The first camshaft is a fast road camshaft for sure. Degrees are fairly good (35/67) with a long 282 deg duration, and a moderate lift (10.54mm - .40 valve clearance = 10.14mm).

The second camshaft is an OE one probably. It surely isn't 280 degrees, as 12+180+52=244 degree. I think it's a Fiat OE camshaft, maybe having a back grind at a machinist for more lift (10.65mm).

I would advise the first set of cams (282deg).
OR
As Tom said, just drop Guy a call. He'll be glad to help.

Nabih
HORSEPOWERunlimited
csi2000s
Posts: 18
Joined: September 10th, 2008, 9:58 am

Re: Differences in cam timing specs

Post by csi2000s »

Both cams are brand new and not regrinds. I'm just confused with the specs. All I want to do is to have an understanding about engines so can I can make the right decisions to achieve the results I want.
Guy Croft
Site Admin
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Location: Bedford, UK
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Re: Differences in cam timing specs

Post by Guy Croft »

Publish my email reply here Angelo if you wish,

G
Guy Croft, owner
csi2000s
Posts: 18
Joined: September 10th, 2008, 9:58 am

Re: Differences in cam timing specs

Post by csi2000s »

Hi everyone, I sent Guy the below email and got exactly the answer I needed. I seeked advice from other specialists and was consistently told that I'd wasted money on the 130 TC cams and the only option was to spend big money on new cams which they were willing to sell to me. Guy's reply made it all clear to me that I have the right parts, allowing me to get on with job of finishing the head for my car with confidence.

Hi Guy,

I'm getting down to the business end of my upgraded head rebuild for my Fiat Spider.The 2 litre engine already has hi comp domed Mahle pistons, twin DCOE 40mm Webers, Abarth style headers and exhaust system. The head and cams fitted are from a Mk 1 2 litre Superbrava.

I purchased a pair of Abarth 130 TC cams but I now understand the gains in performance will not be that much higher than the cams already fitted to the engine. Is this correct?

You've seen in my posts under user name csi2000s some of the parts I've purchased for the build including the 1800 head for the slight lift in compression and using your forum to get the best out of it via the porting and polishing section.

I'm spending a lot of time and money to get the new head sorted so I want to make the right decision the first time. Should I just stay with the 130 TC cams or are all my efforts going to waste using these cams because they are similar to the 131 pair already in the car?

At the end of the day I want more performance but nothing too extreme just a nice rapid car for weekend drives. I've been looking at the Kent cams FT10 sports and the Catcams 1900300. The thing that has thrown me off is the differences in valve timing between the two and what it means in laymans terms. I'm keen to find out how your cams compare to the two I've already had a look at. What would you recommend from your range of cams for a fast road motor?


Looking foward to your reply.

Best Regards
Angelo

Hi Angleo

the best TC cams come from me - and I am an agent for Kent!

Catcams I do not recommend at all and will offer no advice at all on their products.

However for what you want the 130 cams are ideal. You will tie yourself in knots changing to comp cams so don't do it.

The thing that is wrong are your carbs they are too small. Sell them and get 45s. I can tell u jetting later on but they come with 36mm choke which is right.

The 1800cc 124 CSA Abarth Spider (not Gp4 of course) had a standard 9.8/1 engine, standard Fiat 132 1800 cams and twin 44IDF on 36mm chokes and gave 128bhp. You will see about 140 if the motor is good with a whopping torque curve ideal for fast road.

Trust me on this.

G
csi2000s
Posts: 18
Joined: September 10th, 2008, 9:58 am

Re: Differences in cam timing specs

Post by csi2000s »

Hi Guy,

My friend and mechanic John who has worked on my car for the last 20 years has a few 45s ripe for rebuilding. They are older made in Italy versions.He has the right 36mm chokes and a box full of jets and most parts to complete the job. John is also doing all the head work using your guidelines from this forum.

There is also the option of buying new 45s. The local importer has the 3 and 4 progression hole versions available for the same price.What do these differences mean? They offer a jetting service as well. I will also be fitting ram tubes, will they and the length of the tubes have any bearing on the jetting requirements? Lastly does it matter in terms of quality, where they were made ie Italy or Spain?

This will all happen in the next couple of weeks. When you have a spare moment later this week to post the jetting requirements for my application and advise on the new and used options I have listed, it would be greatly appreciated.


Thanks again
Angelo
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