351 to 302 swap

djmikel · 11-11-2008, 05:43 PM

hello i have a 1990 gt

i installed a 351 w crate engine in my car back in 1998 after destroying the stock 302 so i went with a 351 the cam went in the 351 so i put in a bigger cam for that nice sound but the car has never run consistent some days it runs great no problems then it runs like @#$% so my question should i just go back to a 302 or should i try and figure out the right size solution like mass air meter throttle body and i still have the stock computer, and no oxy sensors which the car does not have. the car does run but it has been sitting since june of this year i started it up so it just needs to be taking on the road and ran all day but then after all the gunk is run out the idle is up and down which has been the problem
the idle is bad ,up and down so guys what the best bet to get this car back in tip top shape ? the car has stock mass air and stock throttle body
with gt 40 upper and lower intake
and no 0xy sensors. or just do the swap and move on and where can i swap a great running race ready 351 w with a big cam for a good 302

86nu · 11-11-2008, 06:48 PM

check the idle air control valve for the idle problem. You might need a bigger maf, Not sure on those, ive delt mostly in carbs.

QWKSNKE · 11-11-2008, 07:37 PM

you need the 02 sensors installed, at least a 70mm t/b, a 80mm MAF, and some type of EEC tuner to fine tune everything. After that it should run like a sewing machine

04 Mach1 · 11-11-2008, 07:43 PM

I Agree YOU NEED THE O2

banditmwp · 11-11-2008, 08:44 PM

EHardy1971 · 11-11-2008, 09:18 PM

x3 on the O2's.I also agree you definately need a bigger TB like QWKSNKE stated. The stockers are only 60mm,and the GT40 upper already has a 70mm opening.

militarymustang88gt · 11-11-2008, 11:25 PM

what size inj are you running?

Italian LX · 11-12-2008, 05:18 AM

I agree with the comments above. How many miles have you put on the motor?

I'm curious... you've had this set-up for ten year, so why did you wait this long to finally try to get it running right?

11-11-2008, 05:43 PM	#1
djmikel Junior Member Join Date: Nov 2008 Location: florida Posts: 1	351 to 302 swap hello i have a 1990 gt i installed a 351 w crate engine in my car back in 1998 after destroying the stock 302 so i went with a 351 the cam went in the 351 so i put in a bigger cam for that nice sound but the car has never run consistent some days it runs great no problems then it runs like @#$% so my question should i just go back to a 302 or should i try and figure out the right size solution like mass air meter throttle body and i still have the stock computer, and no oxy sensors which the car does not have. the car does run but it has been sitting since june of this year i started it up so it just needs to be taking on the road and ran all day but then after all the gunk is run out the idle is up and down which has been the problem the idle is bad ,up and down so guys what the best bet to get this car back in tip top shape ? the car has stock mass air and stock throttle body with gt 40 upper and lower intake and no 0xy sensors. or just do the swap and move on and where can i swap a great running race ready 351 w with a big cam for a good 302 Last edited by djmikel; 11-11-2008 at 05:45 PM. Reason: change words

11-11-2008, 06:48 PM	#2
86nu Senior Member Join Date: May 2007 Location: orlando florida Posts: 165	check the idle air control valve for the idle problem. You might need a bigger maf, Not sure on those, ive delt mostly in carbs. __________________ 86 Coupe aka the battle ship H/C/I, Nitrous, bla bla bla all on a 351

11-11-2008, 07:37 PM	#3
QWKSNKE 3v's are slow Join Date: Dec 2004 Location: Here and There Posts: 17,152	you need the 02 sensors installed, at least a 70mm t/b, a 80mm MAF, and some type of EEC tuner to fine tune everything. After that it should run like a sewing machine __________________ 2009 Porsche Carrera S 2008 ///AMG C63.. Eurocharge Tune. RIP 2019 AMG GLC43..wife's 03 F250 SD.. Edge Evo, AFE Stage 1 CAI 08 GT. JBA axle back, FRPP springs, FRPP swaybars.. daughter's 01 Cobra vert... wife's I need a new toy

11-11-2008, 07:43 PM	#4
04 Mach1 Bet I red light B4U Join Date: Aug 2005 Location: ANNISTON, AL Posts: 975	I Agree YOU NEED THE O2 __________________ 89 gt 2.3 stroked holley head with n12n port high flow intake with great big fart can skunk 2 seat belts with kool glow water squirters and new light up shift knob basically everything from wal-mart art carr C4 10.53@127.3 w/ 1.53 60' 89 gt vert 347 eldebrock heads and intake AOD w/3000 stall unknown with 5spd went 12.7 on steet tires 04 Mach1 automatic flowmaster K+N drop in 13.9

11-11-2008, 08:44 PM	#5
banditmwp Welcome to America! Join Date: Dec 2004 Location: in the 11's Posts: 4,501	__________________ 91 GT Convertible 2006 Nissan Titan LE Crew Cab 2014 Peterbilt 337/Marion 22' box

11-11-2008, 09:18 PM	#6
EHardy1971 Trunk Monkey Join Date: Jun 2007 Location: Home Posts: 5,708	x3 on the O2's.I also agree you definately need a bigger TB like QWKSNKE stated. The stockers are only 60mm,and the GT40 upper already has a 70mm opening. __________________ Eric 89 LX Coupe-Juiced 01 Lightning-Boost 06 TBSS

11-11-2008, 11:25 PM	#7
militarymustang88gt Senior Member Join Date: Jun 2007 Location: bham and auburn Posts: 337	what size inj are you running? __________________ finally got my avatar. it is the white one.

11-12-2008, 05:18 AM	#8
Italian LX Daddy x4 ...we're done Join Date: Dec 2004 Location: Oxford, AL Posts: 11,551	I agree with the comments above. How many miles have you put on the motor? I'm curious... you've had this set-up for ten year, so why did you wait this long to finally try to get it running right? __________________ -Brian '86 Mustang GT Convertible '88 Mustang LX coupe '11 Odyssey TE '21 Insight Touring