2010 7.4L HP Questions

[FreeBeeTony]

I'm a SBC guy........looking at a boat advertised as being repowered in 2010 w/ a 7.4L Mercruiser and is being quoted as having 350HP.
I need to be educated.......boat is a 1992. I believe the 7.4L was rated at 310HP. Wondering if the long block was replaced? Maybe it was pre-Vortec (if that's applicable to a BBC). Looks like it has the Thunderbolt Ignition module on the exhaust riser. Does this indicate it's not a MPI engine?
Boat is a 25' Grady White Sailfish........~6000lbs w/ engine.
I guess a 7.4L could be bored & stroked?
Any/all input is welcome....

 

[alldodge]

In short, without a dyno sheet from a local dyno shop, this is just someone saying what it produces.

Easy way to see if its MPI, is the plenum and injectors

This is the brake down so far as 454

carb was 300 hp
carb HO was 350
mpi 310 L29
mpi LX 330
mpi HO Mag 385

The L29 has the throttle body in the middle of the motor, all others have the TB at the front end of the plenum

Get some casting numbers

 

[Scott Danforth]

the 7.4 liter was available as 310hp, 330hp, 350hp, 385hp, 420hp, etc.

Im pumping about 550 out of mine with a mild over-bore (.060 over or 468 cubes)

AD is getting 640hp out of his bored out 502 (509)

depends on the heads that are on it and the cam.

most likely they repowered it with a L29 (Gen 6 with vortec heads) or even square port heads. that motor makes 385hp at the crank in stock trim with the L29 vortec heads. with only a cam change to a comp cam XM284HR (Mild Marine Cam) it makes 428hp http://www.superchevy.com/how-to/en...power-on-a-junkyard-454-with-simple-cam-swap/

so 350 hp from 454 cubes is entirely within the realm of a stock motor

 

[FreeBeeTony]

Thanks for the beginning of an education.
Right now, I'm just looking at a pic on a website......can't tell what under the cover!

 

[FreeBeeTony]

What about the fact that I see the Thunderbolt Ignition Module on the exhaust riser?
Is that an indication that it's a carb'd engine?
I may see another engine project in my future if the price is right!

 

[alldodge]

Yes, TB 4 or 5 where not used on TBI or MPI's only carb

 

[FreeBeeTony]

That's what I thought............thanks.

 

[QBhoy]

A 2010 7.4 carb would be a rare thing maybe ? Just a guess. Is it maybe just been rebuilt ?

 

[FreeBeeTony]

So............still considering this boat.
Haven't seen it yet.......

How can I determine what version of BBC is installed? L29; GEN V; GEN VI; ??? I need to be schooled on BBC's.

Is a Gen VI a L29 w/ Vortec heads? What's the difference between the versions?

Any info/help is appreciated.

 

[alldodge]

So............still considering this boat.
Haven't seen it yet.......

How can I determine what version of BBC is installed? L29; GEN V; GEN VI; ??? I need to be schooled on BBC's.

Is a Gen VI a L29 w/ Vortec heads? What's the difference between the versions?

Any info/help is appreciated.

post 2

his is the brake down so far as 454

carb was 300 hp
carb HO was 350
mpi 310 L29
mpi LX 330
mpi HO Mag 385

The L29 has the throttle body in the middle of the motor, all others have the TB at the front end of the plenum

First two are carb and look for serial numbers

L29 throttle body in the middle of the manifold

LX is MPI with plenum and does not list as MAG and has VST

The 385hp shows MPI and MAG and is cool fuel not VST and has 502 heads

 

[FreeBeeTony]

Yes, I saw the info in post #2.
I am asking for info on the differences between the versions of the BBC's.......not necessarily Mercruisers,

The S/N for the orig engine was:OC769887.
It is being advertised as being replaced in 2010, but I still the Thunderbolt ignition module on the exhaust riser which leads me to believe the long block was replaced. (Post 5/6)
Would the original engine have been a GEN IV?
How can I tell which version might be installed now? Are there different intake bolt patterns like on the SBC for Vortec?
Does L29 have anything to do with the heads?
Oval vs square ports? Which are better/newer?
I am BBC ignorant and looking to get educated.......trying to find info online but I'm getting confused.
Think I need to start with the differences between GEN IV/V/VI first. 1pc vs 2pc; roller vs flat; Vortec vs non-Vortec.
If in fact the original was a GEN IV and it was replaced w/ a GEN VI......how can I tell? Block casting #'s? Intake bolt pattern?

Thanks in advance......

 

[alldodge]

Maybe someone like Scott Danforth might know, but I would need to look at casting numbers to verify what is actually there. The 385hp is the only one which used rectangular port heads which were used on 454 and 502. Basically a 502 head on 454, and are known as 088 heads (cast number 14097088)

To know what your looking at find the casting numbers. Blocks are on the rear deck below the distributor, heads are under the valve cover

https://www.mortec.com/bbc.htm

 

[Scott Danforth]

look at the block casting number behind the starboard cylinder head
pull the valve cover and post that casting number

without the casting numbers, we dont know what its made from

the boat originally would have had either a left over MK IV (1965-1990) or a Gen V (1991-1995). Gen VI came out in 1996.

all BBC heads have the same bolt pattern, so you need to look at the casting numbers.


L29 references the RPO code for the motor as it was found in 3/4 ton and 1 ton trucks. the L29 comes with the large oval port vortec heads

generally oval port heads flow better at low to mid range RPM's and rectangular port heads flow better at high RPM's. Oval port heads are better at low to mid-range torque

however with a bit of port work, you can get some of the oval port heads to really flow up to about 6000 RPM.


then there are aftermarket heads (much longer discussion)

however step 1 is to identify the motor

 

[dingbat]

OEM was a 5.7 @260HP

 

[Scott Danforth]

OEM was a 5.7 @260HP

the hull (per the 1992 grady white brochure) is rated at 400hp and was available with Yamaha/OMC/Volvo/Mercury or Mercruiser depending on the rigging

so it could have had an SBC or a BBC or outboards on the OB version

 

[FreeBeeTony]

Thanks guys............starting to get a bit clearer. So, if the longblock was replaced in 2010, chances are it's a Gen V1 (guessing).
Is it a correct assumption/statement that the L29/Vortec heads are preferable (like on a SBC)?
Possibly going to look at the boat this w/e. Will be able to get block casting number but not from the heads

 

[Scott Danforth]

Thanks guys............starting to get a bit clearer. So, if the longblock was replaced in 2010, chances are it's a Gen V1 (guessing).
Is it a correct assumption/statement that the L29/Vortec heads are preferable (like on a SBC)?
Possibly going to look at the boat this w/e. Will be able to get block casting number but not from the heads

in 2010, the 7.4 and 8.1 went way of the dodo bird, so it was a reman or old stock.

need the casting numbers, and you will need the casting numbers of the heads as well.

the vortec heads are ok on the BBC, however there are many many many many more head choices for the BBC than for the SBC. depends on what you want.

 

[scoflaw]

Which BBC heads are you calling vortec ? I refer to them as peanut port, oval port or rectangular port.

 

[alldodge]

Manis this forum messed up, started last night

I don't see anyone looking for the L29 (TB is in center of intake), probably not a bad motor, but very few in boats. Look for the LX or Mag for MPI, or go carb

 

[FreeBeeTony]

Which BBC heads are you calling vortec ? I refer to them as peanut port, oval port or rectangular port.

If you're asking me this question............I have no idea.
Do the BBC heads have Vortec shaped combustion chambers?
I'm still not sure which BBC heads are "optimal" for a boat........
This is part of my BBC education!