Q-Jet question
 

Can anyone tell me what CFM the Quadra-jet carb is on a stock Merc. 7.4L. (330) If I change intakes to a Edelbrock performer RPM, should I buy their marine carb or will the Q-jet be good enough? Thanks

I think it's 750 cfm. For a stock motor, I'd stick with the quad.

Stick with the Q Jet merc uses them to 400hp should be a 750 parts are easy to get easy to tune it is a better carb than the edelbrock the small primary helps also.

Thanks for the info, could you guys make a suggestion on what intake to buy for the 330. I understand that the stock intake is not of very good quality performance wise. Note that I have upgraded the exhaust already. I am hopeing to gain 4-500 rpm's with the exhaust and intake combination upgrades. I have seen good results from someone using the performer rpm duel plane but is there something better. How about the performer air gap?

Thanks

If you are running in salt water and don't have closed cooling it's hard to beat the stock Mercruiser Highrise that came on the carburated magnums. The one I had was aluminum but had brass inserts to resist corrosion.

Square peg and round hole?
 

I think you would have an issue with the intake ports not matching up if you use a stock magnum intake. Magnums have the larger rectangular port heads, whereas the 7.4's have the small round ports. Not saying the engine wouldn't run, but you probably wouldn't see any gain and you might hurt your performance. But you could go ahead and switch to the square port magnum heads while you are at it, and see some real gains! :D

Edelbrock Performer RPM or RPM air Gap. Quite a few car magazines have written this one up as making as much power on the low end as the regular Performer, with more up top. I've got one on my 330, works great. Clearance was fine also...;)

Must be a morning thing. Didn't even think about oval ports on the 330 hp. If you do run in salt water, just remember all the manifolds mentioned are aluminum. I run an aluminum manifold in salt water and only hope to get 2-3 years out of it.

Scott-I believe that the corrosion would start around the thermostat. Perhaps you could try a stainless one instead of the brass one. I'm not sure, but I believe the stanless is closer to aluminum in terms of dissimular metals. If nothing else, put some never-seize or a o-ring below it to keep the metals apart.

Thanks for the advice, Cord. I have installed a flush kit on the new motor. Hopefully that will help. Salt water is amazing compared to fresh. My old boat was a fresh water boat for 10 years. Pulled a riser and they looked brand new. Three years in salt water (without flushing the motor) and the risers basically crumbled in my hands. I had to replace the thermostat housing due to corrosion and the intake manifold was almost due.

World Products makes the Merlin Marine intake with brass inserts all the way around. P/N 063034. Link Might need a Q-jet to square bore Holley adapter.

DJW
i took off my stock q- jets last year and am much happier with the edelbrocks. i may have a manifold for you too. if you want to see the edelbrocks or the manifold, i live in deepwater.
Fran

excaleagle,

What is it that you like about the Edelbrock carbs over the Q-jets?
What intake manifold do you have and do you have two? Thanks

I have the 330's in my boat (twins)
I bought these intakes (large oval)
Not exact match to small oval but better than the rectangle
I have NOT installed them as of yet but if you call Greenwood, you can pick them up for 150 each plus shipping no hassles
Had them in my hands in 5 days from order date.
Nice that they are polished
They are the exact mold of the performer but nicer attention to detail

Might as well get the same manifold cheaper and polished!!!!
http://www.greenwoodchevy.com/after.htm

Im going to keep my q-jets for now as well but if I switch i was contemplating the 750 edelbrock marine carb == problem is it seems like a rebuilt q-jet so what is the point?
Then Someone told me about the holley and they are good but the Deamon comes highly recommended
You can drop to a 700 deamon and get same perf out of it that you can out of a 750 q-jet or holley
(deamon little more expensive though but dig, might find one used)

Im hoping to gain about 20 hp out of engine with this manifold and new flame arrestor setup.

I cant not answer about the perf gain as of yet cause they are sitting on my work bench waiting for the boat to be finished at the marina and returned so in a few weeks they will be installed and done, Ill let you all know how they do, but for now at least they look nice
lol
Anyway they come with the adapter plate and gasket for the holley conversion and are setup for q-jet so either carb wont be a problem and no goofy spacer deal you have to buy at pep boys or wherever
Give green wood a call, they were cool with me
and the product is really nicely done
Jason

DJW

you just asked me to open a can of worms. ok. i will give you my opinion. i am in the great minority on the board. lots of people on this board like holleys. few like edelbrocks. the general thinking is, that you get more power out of a holley than an edelbrock or quadrajet. you may see a few hp on the dyno, i don't know. in the real world there is no difference. i have two boats, same engines in each with a spare. i have a holley on the little boat, edelbrocks on the big boat. i have switched carbs and saw no difference in engine rpm's. i like both kinds of carbs. stock holley marine carbs are close to twice as expensive as edelbrocks though. edelbrocks are easier to tune, no power valve to fail. there is a check valve you can put in a holley in case you backfire to prevent powervalve failure. my opinion is that the edelbrocks idle better on stock engines. if you have a big cam you need to have a four corner idle system on that is on a modified holley. holleys do have more to work with for more CFM's later if you need it. edelbrocks you can't get much more than stock if you need it. remove the choke and open the barrels a little.
for stock or slightly modified engines, i would run edelbrock for the ease of tuning and for the price. for high hp engines that would make the battleship new jersey chinewalk, i would use a modified holley or similar version like the demon with a four corner idle system, milled choke tower, and all the other goodies but they get expensive.
again, this is just my opinion. both holley and edelbrock have their good and bad points. and for the price of getting a stock Q-jet rebuilt, i'd buy a new carb. i only have one edelbrock torquer single intake manifold by the way and two rebuilt Q-jets for sale.

Try to find an Iron late 60's Hi Rise Manifold. Add the exhaust crossover restrictors and you will gain HP. It would be easier to go spreadbore. If you used a squarebore manifold, The throttle would have to be enlarged 1/8" to use a 750 or larger Holley. I just went through this. By the time I bought the carb and the $117 throttle bracket kit, I realized this was too much time and money spent for not too much better results. The rochester carb works well and is easy to take on and off, easy to work with, and will be fine for a 330hp motor. If you are looking for more power maybe you should go large oval port heads bigger valves, Increased compression etc... Big Block Billy :)