cam shaft question

[hush777]

Putting a carbed short block in with turbo heads to basically run a car with mpfi.

Car was turbo but the short block is shot and I don't have any extra stuff except the carbed block. So my question is which set of cams would be closest to the cams from a true mpfi engine. Carbed? SPFI? or TURBO?

I can do any one of these (extra sets of cams around), so whats your opinion?

 

Thanks

Hush

[MilesFox]

i would use the spfi or carb cams, as they have valve overlap for scavenging. wheras a turbo cam has little overlap otherwise boost would blow out the exhaust

 

if you used turbo cams for n/a it would lug great pulling trailers at 2000 rpm but would be a dog at higher rpm. it would be ideal for an open header(no y pipe) for lower rpm power

 

carb and spfi would have different rpm curves. right now i am running spfi cams and heads with a carb motor

 

i would say get some numbers betwen carb and spfi cams. i think one is a 4500 rpm cam and one is a 5500 rpm cam, but dont know which is which

 

kep in mind a carb motor has less compression than spfi, so i wonder if that would factor into the cam duration?

 

spfi has 9.5 compression same as n/a mpfi

 

just my suggestions but the turbo cam in a carb motor i know about from my own experimenting

[85Sub4WD]

Putting a carbed short block in with turbo heads to basically run a car with mpfi.

Car was turbo but the short block is shot and I don't have any extra stuff except the carbed block. So my question is which set of cams would be closest to the cams from a true mpfi engine. Carbed? SPFI? or TURBO?

I can do any one of these (extra sets of cams around), so whats your opinion?

I would use carbed cams - lower peak torque and HP

 

I would also go with N/A MPFI - found on many 1985 cars that were non-carb (no SPFI in 1985) and all non-turbo XT4's - more power than SPFI - and if it is an 1987/later XT4, it has the later gen MPFI, which is a lot like SPFI

 

However, SPFI is much easier to find parts for, so you might be just as well off with an SPFI setup.

 

I currently have a carb block and heads, with SPFI intake & exhaust manifolds - very good combination, makes the car run well

 

your compression ratio is 9:1 if it is a carbed block - so I would use a SPFI or N/A MPFI block for a higher ratio (actually all you need is the pistons - they adjust CR for these cars) - higher CR ratio = more power

[calebz]

if it is an 1987/later XT4, it has the later gen MPFI, which is a lot like SPFI

 

Elucidate please.

[85Sub4WD]

if it is an 1987/later XT4, it has the later gen MPFI, which is a lot like SPFI

Elucidate please.

Sorry - that was stupidly vague - what I meant was that it uses a similar engine control system - hot wire MAF (though I think it is different than the SPFI system) and the CAS is the same - so at least a part is interchangeable - also your timing advance is controlled by the computer (like with SPFI), so you get better performance (the advances - mechanical and vacuum used to get stuck all the time on my distibuitor)

 

Basically, if you go MPFI N/A, go with a later version.