Replacing engine, what will fif?

[JimN]

Originally Posted by Surfer

Hi,

JimN, thanks a lot!
Yes, the engine is non-Vortec.

Ok, I might ask for price of roller rocker arms for the base engine, if it is an option and maybe for newer TBI manifold. But MC did this type of engine only 1995 - 1997, after that MPI?

So EFI computer just "puts gas in", when crackshaft position sensor says so? When and how fast the valve is opening, fully open, closing and closed, does not matter?
Craph for roller cam vent opening is more rectangular, as flat tapped cam craph is more parabolic, as in time vs. vent opening x-y scale.


BR, Pasi

They won't have the same intake MC put(s) on the newer TBI and the one used on the Vortec won't work because of the way the bolts go in.

TBI engines, especially from the '90s, don't have a crank position sensor, they use the can on the distributor shaft and, unlike crank sensors, that doesn't tell the ECM which direction it's turning. The ECM uses the MAP sensor to detect engine load (uses barometric pressure and engine-induced vacuum relativee to RPM and throttle position), TPS detects idle throttle position (</= 2%) run throttle position (>2%) and fast throttle position changes (delta ±>20°) for acceleration enrichment or deceleration enleanment, and coolant temoerature to determine whether to add or remove fuel when it compares its state, relative to the fuel mapping tables in the program. These run rich enough that changing the lobe shape won't cause the engine to experience problems unless it's run really hard and something is outside of the normal ranges.

[Surfer]

Hi,

so driving for barefoot, there is a slight change of experience problems with roller cam and original EFI computer? Ok, nothing should be out of normal range, except the cam (the not original roller cam was included in your reasoning). Also cooler air temp. in Finland, but this EFI does not straigth take that into account?

Or, as you said rich enough; If we know the max. output of the original EFI, we could calculate what is the base GM engine's max. requirement?
Or are these specifications publicly available? Something should exist at least.


BR,

Pasi

[JimN]

Originally Posted by Surfer

Hi,

so driving for barefoot, there is a slight change of experience problems with roller cam and original EFI computer? Ok, nothing should be out of normal range, except the cam (the not original roller cam was included in your reasoning). Also cooler air temp. in Finland, but this EFI does not straigth take that into account?

Or, as you said rich enough; If we know the max. output of the original EFI, we could calculate what is the base GM engine's max. requirement?
Or are these specifications publicly available? Something should exist at least.


BR,

Pasi

The intake air temp isn't monitored on older models. The only time I saw people having problems barefooting with a TBI engine was when they had small feet and were relatively heavy. With cooler air temp, the extra power wouldn't hurt (it's always nice to have a little extra)- what is the elevation where you'll be skiing?

[Rossterman]

Originally Posted by Surfer

Hi,

thanks for the answers!



Rossterman, you meant in comparison to vortech car engine cam is different in marine engine?
JimN, yes I just need basic replacement, no customization.

If so, the GM base marine engine will do ok? Even the replacement has got a roller cam,
as the original engine has got flat tappet cam.
Ok, flat tappet cam is maybe an option, but roller cam would be better I understand; E.g. a bit more power.

The valve timings seem to be different with different cams, that is why I am wondering if the original EFI computer would do ok with roller cam?

I do not know EFI working principles yet so closely, and I am not able to tune EFI computer, and don't want to buy a new one.


Thanks!

Pasi

Roller cam in the vortech truck could be the same as marine as i have never seen anyone publish the lift and duration numbers of either. I suspect they are identical but cant prove. You will get more power using the roller cam vortech motor as much superior cylinder heads to non vortech motors and the roller cam has better performance with quicker opening/closing ramps

[Surfer]

Originally Posted by JimN

The intake air temp isn't monitored on older models. The only time I saw people having problems barefooting with a TBI engine was when they had small feet and were relatively heavy. With cooler air temp, the extra power wouldn't hurt (it's always nice to have a little extra)- what is the elevation where you'll be skiing?

Hi,

my barefooting driving is rarely 38 mph (US nautical miles), more likely in 35 -36 mph range at the highest.
By the way the old engine (ca. 2100 h) still this summer took close to 38 mph, before it broke down.

Cooler air is more packed, i.e. more oxygen in smaller space, you get more power then actually?

Maybe with TBI, high revs and constant resistance for the engine with previously described barefooter causes something? Though I understand no major problems.

My altitude where I normally ski would be ca. 102 feet above sea level. Occasionally at around 246 feet.


BR,

Pasi

[JimN]

Originally Posted by Surfer

Hi,

my barefooting driving is rarely 38 mph (US nautical miles), more likely in 35 -36 mph range at the highest.
By the way the old engine (ca. 2100 h) still this summer took close to 38 mph, before it broke down.

Cooler air is more packed, i.e. more oxygen in smaller space, you get more power then actually?

Maybe with TBI, high revs and constant resistance for the engine with previously described barefooter causes something? Though I understand no major problems.

My altitude where I normally ski would be ca. 102 feet above sea level. Occasionally at around 246 feet.


BR,

Pasi

It's less a matter of more power and more about whether the air/fuel ratio is correct and while using an intake air temperature is more accurate, these run just fine in cooler weather. The first thing that happens when the key is turned on is the ECM uses the MAP sensor to check the barometric pressure. You should be fine.

[Surfer]

Hi,

any estimate, how much base engine with roller parts and new intake manifold would increase fuel consumption? Likely to be not less consumption.
I mean more hp, vents longer time open, but less friction, newer engine. + / - = 0?


BR,

Pasi

[Rossterman]

Dont think you will see much change. Tbi predator engine is essentially what you would have and they are very good on gas. Better combustion and less friction with roller cam and rockers = better fuel economy.

[Surfer]

Hi,

any idea what exactly is the ECM on this original engine?
Maybe some codes on the ECM will tell.

I have replaced that many years ago, as the original broke itself, had to order a new one from MC UK.

The boat with original ECM had starting problems with warm engine since new, I experienced that a couple of times, but not anymore after replacing the ECM.


BR,

Pasi

[Surfer]

Hi,

Roger from Michigan Motorz told me not to take an engine with a roller cam.

"TBI 5.7L engines and the ECMs are very finicky and do not like any changes or modifications. We know from experience." The engine might not run properly.