carbs for 420 mega

[offshoreed]

ha blower guys got a question. i just got a 420 b&m had it rebuilt by the blower shop. i have been running a 250 b&m with two 750's holleys that have been worked over last summer. can i use the same carbs on the 420. this will be going on a 540 cu in. top pulley is a 5.4 , 16 rib. 6000 rpm max per my engine builder that most of you guys know on this thread. this will be in a AO cat.

[ghittner]

I'm running twin 750's on a 420 rebuilt by TBS as well w/ 8pds boost and 498 C.I. 6000 RPM ++ Plenty of fuel, I'm jetted at 78's and 91's, plenty of color on the plugs. Should be fine for you. Try it and see how she runs.

[Daytona100]

I'm running twin 750's on a 420 rebuilt by TBS as well w/ 8pds boost and 498 C.I. 6000 RPM ++ Plenty of fuel, I'm jetted at 78's and 91's, plenty of color on the plugs. Should be fine for you. Try it and see how she runs.
Are you boost referenced on the primary?

[offshoreed]

thanks for the reply. i am hoping that with the 420 it will get me over the 100mph mark and keeping the oil from getting to hot. after talking to alot of people the 250 was spinning so much that it made to much heat even with the superchiller.

[ghittner]

Are you boost referenced on the primary?
No, after EXTENSIVE reading on the subject of boost referencing, I decided to run non boost referenced and see what was up. The primary concern was that I made sure I had NO vacuum at WOT. As I suspected, I did not have vacuum at WOT so all is well. Idles great and runs as intended, plenty of fuel full out.

[ghittner]

thanks for the reply. i am hoping that with the 420 it will get me over the 100mph mark and keeping the oil from getting to hot. after talking to alot of people the 250 was spinning so much that it made to much heat even with the superchiller.
I'm running a 23" X3" oil/PS cooler w/ no intercooler and that seems to keep things cool enough. around 215 to 230 deg. or so. What do you run for cooling?

[offshoreed]

i am running a olson oil cooler thats placed betweened the oil filter and the block. the water comes straight from the outdrive threw the oil cooler to the sea water pump. then out of there threw the power steering cooler then to the crossover and in to the engine with no thermastat to restriction.
my temp gauge never shows to hot except when running hard and slowing down to idle.

[DMOORE]

OFFSHORE,
I too am running the 420's on my motors. I have 750carbs and superchillers running 10PSI. Motors run GREAT on 91 octane. Sorry but I don't know the pulley sizes, but I too am running a serpantine belt system.
Darrell.

[offshoreed]

ha dmoore
i sure wish you knew what size top pully you had because the blower shop said mine will be about a 7 . do you know the numbers on the belt. thats something i have to get also.

[ghittner]

On the 420 you can swap top and bottom pulleys. I started with 3 pds boost, swapped and got 8 pds. Neat deal! I run a 16 rib 59 3/4" belt with no intercooler.

[DMOORE]

ha dmoore
i sure wish you knew what size top pully you had because the blower shop said mine will be about a 7 . do you know the numbers on the belt. thats something i have to get also.
Yeah, sorry about that. The boat is not at my house here.
Darrell.

[Craig]

I ran a 250 on a 454 with two 750's. When I switched to a 509 with a 420 I kept the carbs. On the dyno the motor made 878 hp, but the shop said I could use bigger carbs. They could see the carbs starting to be a restriction on the top end. I said, 878 is more than enough to break my drive :D and just kept them. Runs fine.