Flopped Straight....how much to raise Flop?

UTG and MP2 are loose/passive as is table.

Party Poker No-Limit Hold'em, $ BB (10 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

saw flop|saw showdown

Hero ($30.83)
Button ($67.72)
SB ($3.92)
BB ($23.75)
UTG ($43.13)
UTG+1 ($16.01)
UTG+2 ($10.65)
MP1 ($25.35)
MP2 ($24.38)
MP3 ($25.25)

Preflop: Hero is CO with 6http://www.flopturnriver.com/phpBB2/...iles/heart.gif, 5http://www.flopturnriver.com/phpBB2/...iles/spade.gif. SB posts a blind of $0.10.
UTG calls $0.25, UTG+1 calls $0.25, UTG+2 calls $0.25, 1 fold, MP2 calls $0.25, 1 fold, Hero calls $0.25, 1 fold, SB (poster) completes, BB checks.

I've been trying to open up my range of hands in LP so with multiple limpers at a loose passive table I make the call with position.

Flop: ($1.75) 4http://www.flopturnriver.com/phpBB2/...es/diamond.gif, 7http://www.flopturnriver.com/phpBB2/...iles/spade.gif, 3http://www.flopturnriver.com/phpBB2/...iles/heart.gif (7 players)
SB checks, BB checks, UTG bets $1, UTG+1 folds, UTG+2 calls $1, MP2 calls $1

How much to raise in order to make it +EV longterm?

rephrase your questions! all raises are +ev long term. you want the most +EV. raise this to 4 or so. if there were draws i'd make it more.

Seeing as you flopped a hidden straight and there are no flush draws you only have to fear someone with a set filling up. There was no PF raise so I imagine you have a smattering of draws and pairs and overcards. I would raise it to 4.50 or so here. You don't want to get counterfeited and if anyone has a real hand (like a set) they will probably reraise you here in which case you can just call and take a card off. If you take the pot down awesome there is already $5.50 in it. I bet you'd get at least 1 caller and you could bet 3/4 of the pot on the turn depending on the card