Help me plan my engine!!!!!!!!

[82SC]

okay I think some of you may have heard me talking about my engine plans and I have slowly amassed parts...let me run down my initial plans...then my concerns....and future options....

start with a 3.2L
add 98mm or 100mm p/c 10.3:1 CR
double plug heads
MFI setup
GE-80 cams...maybe 906

but as I plan the project I realize I will have a real gas guzzler...it will be a very smelly car...and I may be pushing the limits of reliability...plus I will prob need to run headers..no heat...and it will be obnoxiously loud to everyone except me....

I already have 3.2L crank, conrods, heads...I can sell if necessary...also a guy has a 3.5 MFI setup fresh rebuild...bored out stacks that I may buy...

but now I am thinking maybe sticking with a smaller displacement engine...something more akin to the RS and the ST cars...I have a good S MFI setup in my garage...

I think budget wise I will save substantially on the smaller displacement...like a 2.7 or 2.9 upgrade...maybe just stick with 3.0 but raise CR, double plug and MFI...

I really want to have an engine with an MFI setup...and one that is not a bear to drive around town...

what do you guys think????

From more knowledgable poeple on this board I know driver skill and suspension is where the car is fastest...I don't want to build a monster that will may be fun REALLY fun 50% of the time...but may be bothersome and be unpleasent to drive the other 50%
I plan to track it...but I want a car that I can drive on the weekends, and occasionally to work...I can pull up to valet without killing everyone with gas fumes..

I realize the pursuit of HP is #1 to some...but I am trying to stay away from that and trying to build something that will put a smile on my face without it being too overkill

and all the proponenets of EFI...NO...I know it can solve alot of my problems...be...ENNN...OHHH

hmmmm....

MJ

[dd74]

It'll be good for you. It's the least radical of your choices and probably more bang for your buck, I think.

[CamB]

No 3.2 high c/r???

Also, everyone tells me wilder cams are less wild in bigger engines. I mean, what is your definition of gas guzzling?

The chap who has sold me/built my engine has a 3.6 with bigger high c/r p&c to make 3.8l with (old, cheapish) MoTeC running injectors mated to genuine early RSR 50mm throttle bodies, and he gets ~27mpg on the highway... He gets about 7 or 8mpg on the race track though

Actually, for your benefit he has about 350hp at ~6500rpm from the 3.8 litres and has GE-80 cams and, I think, 11.3:1 c/r. This should give you a rough idea of the sort of power to expect (eg, if 3.4, hp = 350/3.8*3.4 = 313hp, give or take depending on a bunch of factors).

I can't decide how to vote... yes I can - GE80 cams with a 3.4 twin plug. No replacement for displacement but I understand 100mm p&c are more expensive (buy and install???).

MFI - I suppose so, but I bet trying to buy and get a pump calibrated for a 3.4 costs more than converting the same throttle bodies to EFI...

[jluetjen]

Also, everyone tells me wilder cams are less wild in bigger engines. I mean, what is your definition of gas guzzling?

I'm not sure that I agree with conventional wisdom on this one. As far as I can tell, a wild cam is a wild cam (unless the porting isn't opened to match in which case moving a given cam to a larger motor will make the cam act milder. But that's a function of the porting, not the capacity or the cam). A case in point is the 906 cam which was used in the 2.0 906, 2.3 and 2.4 911ST and the 2.8 and 3.0 RSR's. The peak HP came at about the same point in each engine: 8000 RPM while the peak torque was also at the same point in each engine: 6500+/- RPM. The engine size grew by 50% but the "wildness" of the cam didn't seem to change.

I doubt that lots of overlap (ie: a "wild" cam) has lots to do with decent MPG. Why? Engine's develop their best milage just below or around their torque peak. It also helps that in general street engines (especially those with Webers) are running "choked" on the idle circuit using low RPM's. Race cam's on the other hand give away low RPM performance because of their overlap in order to get the ram affect at higher RPM's. Using a high CR helps to offset this somewhat, but at low RPM's engines with race cam's are not running that well. As a result they don't get very good combustion and a lot of unburnt fuel is going out the exhaust pipes. This is why a sniffer will flunk an engine with a race cam in notime - it will fail at least the Hydrocarbon test. And when that much fuel is going out the exhaust, you are not getting good HP.

If you want decent milage and a street engine, then you should be running something like a Solex or E cam with fairly high compression. Your milage will go up further if you use a T cam with it is optomised for the rev range where the engine will develop the best HP. If you want a lot of HP out of a given engine size, you'll need to spin the engine faster. To do that you'll need a "wilder" cam. Unfortunately you'll need to pick which is most important, or how much of a compromise you want to live with.

The only other option would be to come up with a way to retrofit Porsche's "Verioram" and variable cam timing onto your engine. THAT will provide great HP and milage all in the same package.

[CamB]

My post was half uneducated and half unclear

I agree with the stuff about MPG and camshaft choice. With older engines and technology especially, you need more fuel to make more power (as a general statement) and more aggressive cams mull in more air and fuel (inefficiently). My question was actually what 82SC meant by bad mileage (I personally don't car until it gets below about 15).

I showed my ignorance with the comment on different camshafts in different engines. What you say makes sense - a 911S cam in a bigger engine probably feels less peaky because the bigger engine is more torquey 'cause it is... bigger.