Formula311-SR1

Over the winter I added lightning header and crane gold roller rockers to my Formula 242 that was fitted with a ZZ502 motor last year. Motor is basically as it came in crate form except with a 750 vacuum secondary carb, MSD 6AL box and matching distributer. before adding the headers and rockers I was running 62.8 with a 25 mirage plus at 4850 RPMs or 61.9 with a 23 mirage plus at 5300 RPMs. Now with the headers I only see 58.8 with the 25 at 4600 RPMs. Had to put the 23 back on to get it to plane out correctly, but did not get to do a top end test on the GPS to verify the speed. Seems to pull 4900 RPMs with the 23.
When we put the headers on the marina took the thermostat out so the motor now runs between 120 and 130 degrees all the time. Is the temp to low to make the HP or is the carb to small or jetted to lean to run properly? Maybe both temp and jetting is what I have been guessing?

powerguy

Carb might be a little small for you application..... check your timing...... a friend of mine has same boat with very similar power( 525 hp on dyno) and runs close to 70mph. Why did they take the thermostat out?????

Formula311-SR1

Timing is 36 degrees right now.
I forgot to mention the boat has a crossover kit also, that was on last year.
Would that have anything to do why he took the thermostat out? I truely don't know why he took it out. I'll have to do some more invetigating this week. Maybe a more constant temp or it was just to get me through the holiday weekend because he possibly didn't have the right one? It had a 140 in it with 1 hole drilled. What temp thermostat should it have?

Kidnova

formula242 - Anyone who has read my ramblings on the site will tell you I'm not a mechanic...still on the learning curve. But I'll give you some info on what I have for comparison purposes...hope it will be of some help to you.

I also have a ZZ502/502 in my boat, 23 Nova. The engine was installed last spring. The 23 Nova {25' loa} weighs in at about 4100 lbs. I expect your Formula would be close to the same weight.

Usually my ZZ runs at 175*. However, I recently put in a 140* tstat to help with oil temps until I get time to put in the bigger oil cooler I got from TooOld last week. With the 140* tstat the engine runs around 160+,- now. No noticeable change in performance with the cooler tstat/water temp. But, I was told by a guru that running an engine too cold will, or can affect performance. Might be your 120 - 130* is too cool.

Powerguy might have a point regarding the carb. My ZZ came with a Holly 850 vac secondaries. The ZZ ran great with that carb. This spring, because it was/is an automotive carb I sent it to Nickersons to have it marinized. Nickersons sent it back to me reworked. I also chitt canned the Merc exhaust and put on a set of after market manifolds {Revolution Marine}.

Last season with no carb work, and running the stock Merc exhaust the ZZ turned a 25 Mirage Plus at 4850 rpms and speed was 68.5 gps. It turned a 25 Mirage {not a Plus} at 5050 and top speed was about 69.5 to 70 gps.

With the carb work and exhaust change, the engine turns a labbed 25 Mirage Plus at 5100 - 5150 rpms. Top speed is 70.7 gps. With a 25 Mirage regular {not a Plus}, and not labbed, rpms are about 5050 -5100 and speed is 70 gps.

I still have to do some tweaking on the carb, which may result in a little better performance. The exhaust change did not offer much gain at WOT. But made a huge improvement in low to mid range. However, some of the improvement may be due to Nickerson's carb work. The exhaust and carb were both installed at the same time so it's difficult to tell where the low/mid range came from.

Like Powerguy mentioned a carb change may be in order, you don't want to run the engine lean! Also a higher temp tstat might help. Headers....who knows. Sometimes headers will cause a loss in power. I think headers are a science all to themselves.

Hope this helps.

Bill

cuda

I wouldn't think the low temps would cause the lack of performance. In salt water, it's best to keep temps below 140 to keep the salt from crystallizing. I know you are probably in fresh water, but the engine doesn't know fresh from salt, and if they run that way in salt, it should run ok in fresh too.

articfriends

iTrader: (1)

I don't believe all the print on headers either. 3 years ago i bought lightning headers expecting a big 400-600 rpm gain on my supercharger motor over stock but didn't gain anything on top but did notice more midrange,just my 2 cents

articfriends

iTrader: (1)

that is stock mercruiser exhaust i meant

Kanookstr

He took the Stat out because with the crossover you would get way to much water pressure. You want to put the 140° stat back in and install a Merc pressure bypass. Part number 863208A-3.

Lee

iTrader: (4)

What boost were you running with stock exhaust?
and what is the boost now with the headers?

An example of a typical scenerio would see 5-6 lbs with the stock exhaust and adding the headers with no other changes, boost would typically drop to 3-4 lbs, add a smaller pulley to bring the boost back up to the level it had with the stock exhaust and you will see the gains you were looking for.

jspeeddemon

Did you rejet the carb after you added the headers? This can serve for a significant power loss.
I would run a compression test and make sure that something coincidental didn't happen to the motor at the time you added the headers and roller rockers.
Make sure that your rockers are adjusted correctly, a tight lifter can hold a valve off the seat and kill power by decreasing cylinder pressure. The compression test will verify this as well.
I have built many big blocks and have never seen headers kill power on a motor, that is unusual, something has happened or changed with this motor for that to happen. Look thru any dyno test in any magazine, boat or automotive and verify that motor always make more power with headers. As well the Mercury marine manifold is a poor example, for performance, for a log manifold. Keep searching, your answer will be evident if you dig.