1990 365 hp mag adding 250 blower Help!!

[BadCompany]

I finally landed a 250 B&M blower with 2 750's. I have 350 well maintained hrs on the motor. I plan to do a valve job,use a MSD analog boost timing master,cometic head gaskets,ARP head bolts,Ultra gold roller rockers,and ARP intake bolts.I have a 3.5 inch top pulley and a 5.5 inch bottom pulley.What boost will this combo give me? I know from info. from OSO members not to exceed 5 psi. I am open for all suggestions and info. I do not want to overlook something and end up with damage. Appreciate it. Gus

[Back4More]

http://www.holley.com/data/TechServi...ech%20Info.pdf

Happy reading Gus.

[Griff]

The 3.5 and 5.5 pulleys figgure out to 1.57 overdriven and according to the chart, on a 454, you would be at about 7.5 of boost. I think you will want about 4.25-4.5 top pulley to bring boost down.

Other people have 454's with 250's. Hopefully they will chime in with there pulley sizes and boost numbers.

The stuff you posted that you ar egoing to do, all sounds good. I don't think you'll need the MSD boost timing controller though. Just run the V6 module and set max timing at around 30* and you should be fine.

[blue thunder]

You should open up the lines/fittings on the fuel system and a higher volume pump would be wise. Also adding boost/fuel pressure gages is a must to see whats going on. Good luck!

Dave

[GO4BROKE]

Make sure the valve job includes inconnel exhaust and stainless intake valves.

[picklenjim]

Second that on the Inconel exhaust valves. Their a must. 2-750's sound like a lot of carburation on 454 cubic inches.

[Uncle Dave]

Originally Posted by BadCompany

I finally landed a 250 B&M blower with 2 750's. I have 350 well maintained hrs on the motor. I plan to do a valve job,use a MSD analog boost timing master,cometic head gaskets,ARP head bolts,Ultra gold roller rockers,and ARP intake bolts.I have a 3.5 inch top pulley and a 5.5 inch bottom pulley.What boost will this combo give me? I know from info. from OSO members not to exceed 5 psi. I am open for all suggestions and info. I do not want to overlook something and end up with damage. Appreciate it. Gus

Not to rain on your project, but I had that same blower hooked up to a large 406 small block and I chased that combo for years and never got it right. 2 smaller carbs/ one big one/ 2 medium ones jetted all over the place on all of them I could never could stay consistent.

That blower has only 2 lobe non-helixed paddles, it stops making boost and makes a lot of heat early in the boost game.

Id never build another engine with one.

Sell it and get a real 6-71 at minimum or a whipple at best and start over with something that doesn't have to spin as hard to provide some air.

UD

[Griff]

There are lots of people running 250 blowers on 454's and 502's. Merc did it just fine on the 600SC. On a 454, it would probably be easier to go with a single dominator carb, you should be able to make the 750 carbs work.

[Strip Poker 388]

I would get the head studs,the gen 4 the threads are open to the water,eventually the threads in the block will rust and go away,I could go 2 seasons on the studs,the replace them,it eats the stud threads on the water side.It got so bad the hime/heli coils pulled out,block not useable.The block was fresh water with around 1-2 trips to the coast,it had 500 something hours before the threads pulled out.

I built a 1989 365 mag,I put the merlin heads,cam ext.innercooler pfm and a 8/71 1 to 1ratio with 2 barry grant gold claw 775,flow was 925 each.the stock bottom end held up fine,Remember to seal the head bolts.


Rob

[mrfixxall]

+2 on the head studs and single dominator carb!