i have a 144 street blower good comp cam, timing gears, 110 wet shot, compleat msd, 650 edl, with complete exhaust. i have a new 400 sb and dont have the knowlage to dicide what i should do to work with my set up. should i destroke for low compreshion or go for big block? need help all opinoins are welcom thank you.

 

Destroking doesn't lower compression, it reduces the stroke and therefore the engine displacement. If you want to reduce the compression, put in dish pistons or put on heads with larger chambers.

I can't imagine a 650 Performer being able to properly feed a huffed 400. Perhaps I'm short on imagination.

I realize the 144 isn't what would be considered a "serious" blower, but it with the 110 shot is going to break things. I don't think I'd supercharge a factory 400 block, but I can be a bit skiddish. If I were doing this, first I'd have to greatly increase my available play money. Then, I'd go with a Motown or Dart block, forged crank, some sort of healthy rod, and forged pistons. Either AFR or Dart heads, maybe Sportsman II's. The Comp cam would have to be one they specifically recommended for the combination, not just a "good" one. A carb that is set up specifically for a blower application.

I'd probably also frequent the Power Adder forum to get ideas from those who have gone before me.

 

Need more detail on what you have.

A generic rebuild 400 will probabily have weak cast pistons and not enough ring end gap for a blower application.

Basic street blower motors need stronger pistons than "stock cast pistons" ( forged or Hi perf hypereutectic. are best)
larger than stock top piston ring end gap. ( avoid ring butting under supercharged power) ( more power = more heat= more ring expansion)
A low compression ratio. 7.5:1 best ( allows most Boost on pump gas) 10PSI
8.5:1 ok for 6/7psi. (with retard)

A blower friendly cam ( dual pattern wide LSA 112/114 best--- 110 ok on 400)

What is the compression ratio on your "new 400"?
what pistons what heads???? etc etc what cam?

A 650 will work but a 750 to 850 is best.

What is the blower drive ratio of the pulleys you have now?
(Diameter of top and bottom pulleys in inches)

If your 400 is a short rod 400 then all you need to destroke it is a 350 crank, 5.7" 350 rods and special main bearing spacers and a crank balance job assuming the pistons are up to the task. A stock replacement cheapy rebuild piston is not going to cut it.

you'll need a improved fuel system ( high volume) to supply the blown engine.

You'll need high octane pump gas ( 92 or more)
You'll need some kind of boost referenced ignition retard.
( available from Holley or MSD.

 

thank you for all your help so far. i built my set up for my 350 "not a stock part in it" and dont have alot of experiance building a bottom end. the 400 is just sitting on my eng stand bare. i am going all out on this bottom end and them i will make the necesary ajustments to my uper set up. i prity much know what i need "ex 750" i just dont know if i should destroke with reversed dome pistons it or beef it up and go for big block cubes.

 

I still don't understand why you keep mentioning destroking and compression control in the same sentence. They are two completely different things.

 

Decreasing the displacement while keeping the combustion chamber volume the same will decrease compression, but it would be a silly way to do it.

 

Well I'd advice taking the 400 apart and at least setting up the ring gaps properly. stock type cast pistons can handle 4 to 5psi boost if detonation is avoided. Detonation will kill them. If you already have a suitable heavy duty built 350 ready to go then use it. You'll make more power with a properly prepared 350 blower motor then trying to crutch fix a 400 that is not up to the task.

The blower will make the power. Concentrate on getting the compression ratio right and useing good heads or improving the heads you have to work with to make horsepower. the cubes of the motor is secondary.
a 350 with good heads, the right cr and lots of usable boost will make much more power than a 400 that is limited to the amount of usable boost cause the cr is too high.

Again, need details on what you have to advise specifily.

A supercharged 400 make a nice street motor, but a blown up 400 sucks. It's all in the details.

 

thanks for the advice you saved me a real head ache. sorry for my inexperance. would i be better taking my 350 to a 383 i am still trying to get more. should i just stop where i am what would you recomend?

comp cam pt number 12-246-3

duration at .050 int/230 ex/236
lobe lift int/.3270 ex/.3270
rocker arm ratio int/.00 ex/.00
lobe seperation 110.0

 

That cam will work in a pinch if you own it already. Ideally you want one ground on wider LSA ( reduced over lap but that one is ok.
On the 400, its fine. For the 350 (if possible) I would sell it off and get a simular cam ground on 112/114 LSA.
But the basic duration and lift is right on for a blower motor.

You have to get over the nessessity to build a larger cubic inch motor to get power. (Stroking to 383) On a blower motor the blower makes the power ( more boost= more power) therefore you want to concentrate your mods in getting a boost friendly compression ratio. This will allow mouch more boost, therefore more power than the gain from increased displacement. The blower makes the motor act as if it is bigger. *Eg: a 350ci motor supercharged with 10lbs of boost pulls like a 450+ci motor does.

You can make a 350 work. You can make the 400 work.

You can swap in a 350 crank and rods on a short rod 400 getting a 377ci motor that will have lower cr.
You can build a 400 based blower motor that has the right compression ratio by selecting the right pistons and head volume.

Forget the 383 build something with what you have. I would lean toward the 350 as a base for a blower motor.
But you have supply some more specific info on exactly what you have to work with. then I can advise you on whats the best route to go.
Does the 400 have dished pistons or flat tops. Does the 400 have stock 5.565" "400 rods" or was it rebuild with longer 5.7" "350 rods"? What is the head casting numbers? Whats on the 350 for heads?

Need specific info. Preparing a motor as a street blower motor is not difficult but there are key areas that need attention.

The main ones are: stronger than stock pistons Can be high perf cast or forged for a street motor.

a low static compression ratio (7.5:1 best for high boost on 92 octane) Its just easier to build a 350 to that cr than a 383.

increased top piston ring gap

a fuel system that can feed the motor with all the fuel it needs. under boost.

A ignition system that is tailered for boost (boost retard)

Slightly cooler heat range spark plugs.

A good cooling system (radiator, fan)

A high flow exhaust system (the need for strong exhaust scavenging AKA tuned headers is not near as critical on a supercharged motor as it is on a N/A motor but high exhaust flow capability is nessessary to get the exhaust out. ( a blown 350 with 10lbs of boost is going to exhaust like it's a 450 ci motor.

 

the 400 is just a bare block with no pistons rods or crank ecc. if i destroked it to a 377 would that beter fit my my aplacation? if so how do i diside what forged pistons would give me the comp i want what are the best rods, crank, rings barings and soforth sould i have my new heads mach my cam specs? do i need to get a new cam?

would i be better rebuilding another 350 and setting it up specificly for my blower.what do i need to look for in maching heads and cam for proper valvetran. and crank rods and pistons for comprestion and stroke?

thanks for your patients.

i am starting from scratch on the botter end new block and all the only thing i would like to keep is my cam but it can go if nescesary.

 

I recomend building the 400 block as a 406 (.030+)
using KB #KB-753 forged 26cc step d dish low compression pistons and a large chamber (76cc) head deshrouded to 80cc
With a standard 400 head gasket the cr would be 7.9:1 as long as the block is not "decked" more than a clean up cut.
Your cam will work fine in the 400 with the blower.
You can get aftermarket hi perf heads (200,215cc ports and large chambers best) ( dart, protopline world products) or prepare a set of factory 76cc heads with large 2.02x 1.60 valves and porting. Look for 441 487 920 336 76cc castings. Consult comp cams for valve train for your cam. its straight forward. If you go the factory route avoid 882's and 624 castings.

Use factory GM "mag tested" 5.7" rods with arp bolts. get a factory 400 cast crank or a Scat or eagle crank. cast or forged will do.
Follow KB's ring end gap recomendations for a street blower application for their forged pistons.
The bottom end will need to be balanced. The 5.7 rods' bolts will need to be clearanced to clear the cam. (.030-.060")

This combination will allow about 9-10 lbs boost using 92+ octane fuel and modrate boost ignition retard 6-8degrees at full boost. Should make close to 500hp and 500+LBs torque. You'll need about a 2.38:1 blower pulley drive ratio to get the boost on the 400. I think the stock out of the box drive ratio is 2.08:1 a little low for max performance. Holley sells high boost pulleys.

You can substitue another brand of 26-30cc dish forged piston if you wish. ( JE Wiesco, Ross)
Hook up with a good local engine builder/ machinst on this one so it all comes together for ya. its not a hard build but key areas need a experienced pro.
This engine when done right should outlive ya for a reletivley modest price. If you'd like to read up on porting factory heads search my posts and Sitting bulls posts on 305 heads. its the same job.
i recommend a 850 holley DP . Use standard Clevite 77 bearing set.
this engine does not have to rev high so no trick bottom end stuff is nessessary other than and new standard oil pump and a windage tray.

 

i am thouroghly happy with my 406, it has forged crank rods and pistons and a good set of heads, you can step down the compression with some dished pistons and throw that blower on drive that thing all day long on pump gas , and 110 shot is pretty big on a boost application i wouldnt go more than a 75 shot honestly. another think u have to look at as far as cams go, is that the 400 isnt really a high revving engine, i shift mine at 5900 rps where i make about peak hp and tq, so a good blower cam should be on the menu, but all in all a good bottom end, good flowing heads, compatable cam and good fuel system should be the ticket

 

thanks so much for your patients and advice it will all come vary much in handy. this will be a long prcces to get it compleated but i will let you know how it terns out in the end. thanks agen you really were a big help. Tommy