I want to upgrade my engine. I have a 350 engine in my 71 Firebird. I want a 400 engine instead. Can i convert my existing engine to a 400 or i it easier/cheaper to buy a original 400 engine?

Asked by Sep 07, 2010 at 12:50 AM about the 1971 Pontiac Firebird

Question type: Car Customization

30 Answers

8,600

You can't Convert a 350 to a 400. To get a larger displacement engine you can stroke it out to 355ci or 383ci but not 400ci. Swapping in a 400 would probably be less work if you can find a cheap original 400.

1 out of 1 people think this is helpful.
6,675

the 400 from these cars specifically was a dog. you dont want it. make your 350 into a 383 stroker.

3 out of 3 people think this is helpful.
25

If you realy want something fun i would go for the 455 big block .Alittle bit more work but its wort it .Specialy in a 1971 Pontiac Firebird.Of course swapping a 400 is nice to but you cannot bore a 350 cc inot a 400 cc motor its not gona happen .383 is the limit of your existing motor .SO its up to yuo swap a 455 or 400 and last but not least bore the 350 tio a 383 stroker .But i would go for the 400 swap more power than you alredy have of course the 455 would be really coll more hp and alot of torque were talking about roughly 300 hp stock if my memory serves m right .so I would chose the 455 .Good luck and have fun .

Thank you all for the help. Unfortunatly the 455 is hard to find in Sweden but I´m going to see a guy with a 400 tomorrow. I´ts a motor that I can work with and make ready then change easily with my 350. Again, THANKS ALL. Pelle

225

some of the 400 Pontiac engines had an oilling problem,,That is why I now have a 455 in my car,,stock they are about 335 hp, 250 net,,and mine has a bunch of aftermarket parts to make about 525 hp,,good luck finding one in sweden,,even here, they are not plentiful,,Jim

2 out of 2 people think this is helpful.

I bought the 400. It´s a 1971 and it dosent look like much. Now i have taken it apart and going to drill the cylinder tunnels and paint it with Bill Hirsch lightblue metallic. I´m also going to buy a stroker kit from the US to get 468 ci. About the oil problem, I´m going to put in a high flowing oilpump and hope that it is enough.

6,675

make sure you put a very good cooling system in it. and i suggest a lower temp t-stat. these engines have thinner cylinder walls between the two middle cylinders. my 400 overheated once while i had it and the cylinder wall cracked. needless to say i was extremely pissed off.

1 out of 1 people think this is helpful.

I am going to put in a better then stock water pump. Summit racing have one with a better flow. In the car there is also an existing extra electric fan that i can switch on if I´m crusing on slow speed and after racing. I hope this should be enough. Please correct me if you think I´m wrong

100

Hi, If i recall right,350 Pontiac doesen't use same block as 400.455 and 400 does.Outer dimensions are the same but bore and stroke aren't. 400 has 4.12" bore and 350 has smaller 3.875,so 350 can't be bored to 400 dimension. It will be cheaper and easier to find 400 or 455.

100

And those who replied that 350 can be bored and stroked to 383,,,,thats chevy small block engine,not Pontiac.It's not the same.Pontiac,Olds and chvy made all 350 motors,but they are not the same.All differen't And the one guy who talked 350cc and 400cc,,,these are MAN motors,those 350cc and 400cc are for bikes.350 is 5700cc and 400 is about 6600cc.Get facts right next time,please.

3 out of 3 people think this is helpful.
6,675

Yeah I'd say that should be sufficient. Will you be upgrading the radiator?

Haven´t checked it out yet. I watched a DVD where they were talking about 2 or 3 "line" (swenglish, don´t know the correct english word) radiators. If i have the one with 3 I´m going to stick with it and maybe just to good flush of the inside.

25

well exuse me for geting it wrong mr i know evrything try being nice too people wo get something wrong now ok ? mabey i will be nicer to you to

100

You mean 3-row radiator?Well for my experience,Pontiac 400 ain't so sensitive about overheating.Someone said something that these engines overheat easily,well i think that they are talking about chevy 400 small block,wich has "siamese" cylinders.It means that water cannot go between two cylinders.That's why it overheats easily. If you don't try tweak more than 400hp,youl do fine with solid radiator,good pump and thermostat.How i know? Well i live in Finland so i know what kind of weather we have(same as in Sweden:)),and i helped my buddy to build his 71 gto with 400 engine,bored to 408,Edelbrock rpm cam,ram air head's with some pro porting.Even with 4.11 gears,it barely overheats,and it has electric waterpump.With regular pump,it would not have this little problem. And yes,it's really fast.I'm talking about low 12 or high 11sec car on Q-mile. What makes Pontiac great is the torque,it's hard to tweak 400-450-500hp on these babies but even with factory settings,on 300 to 350hp range,it will put about 500footpounds on torq.And this is about 2-3000rpm.Can you spell burn-out?

100

To Antoine: If you wan't to help and don't know anything about the topic,don't type anything.It's so easy.Sit back and learn.Or move to the next topic. Don't try to guide anyone if you really don't know it for a fact. You call me "know it all"?Well kiddo,you put bananas in your nose at the same seccond when i corrected you.So who is the big baby? Yes,i do know little bit more than you,"know it all on theory and internet",but only because i've worked with these cars and engines on street and racetrack about 10-15years now. That includes Chevy small and bigblock,Mopar small and big,Fords and yes,on Pontiac's and even on Olds. No hard feelings, take it easy and don't stres about when you don't know something and you get corrected.

2 out of 2 people think this is helpful.

Vatanen what do you think about this setup. Edelbrock 60579 alu heads (Cylinder Head, Performer, Aluminum, Assembled, 87cc Chamber, 215cc Intake Runner, Pontiac, 289-455). Edelbrock 7157 cam and lifter (Cam and Lifters, Hydraulic Flat Tappet, Advertised Duration 308/320, Lift .470/.470, Pontiac, V8, Kit) Edelbrock 1407 carb(Carburetor, Performer, 750 cfm, 4-Barrel, Square Bore, Manual Choke, Single Inlet, Silver, Each) Eagle Specialty Products B51400064 (Actual Engine CID 468 Bore (in) 4.190 in. Bore (mm) 106.426mm Engine Stroke (in) 4.250 in. Piston Material Forged aluminum Piston Style Flat top, with two valve reliefs Piston Head Volume (cc) +5.00cc Wrist Pin Style Floating Piston Ring Facing Material Plasmamoly Crankshaft Included Yes Crankshaft Material Cast steel Rear Main Seal Style 2-piece Balanced Yes Engine Balance Internal Connecting Rods Included Yes Connecting Rod Material Forged 4340 steel Connecting Rod Beam Style H-beam). I´m also going to change intake manifold, a new set of headers that fits the heads, i`m going to change the gear ratio to about 3,50-3,70 somewhere (going to let a pro advice me and let him do the work) my transmission is a 350 not ideal but going to reinforce it and in the future change to a th400 transmission.

100

Thi sound decen't combination,but be carefull with compression.Long stroke and hydraulic tappet cam can cause cylinder pressures to go way up.This is made with the closing degrees of intake valve.It's called dynamic compression.Static compression is what you hear all the cat's talking,like "i have 10 to 1 compression. Hyd tappet(flat or roller) cams may have really low closing degrees to create enough pressure on the cylinder to create power=you don't need to have so much static compression. mechanical cams have more degrees on closing angle=they need more static comp to create enough dynamic to make good compustion. I't all about cylinder pressure and how to create it.Too much and you will hear knocking inside your motor.Too little and your engine will be sluggish. But back to your combo: -Heads are good -Cam seems to be ok(i don't know how much compression you will have,calculate it carefully to see if you have the right cam).If you have the money,go with roller cam.It will give you more "rumpety rump"-sound and more gut's on low rpm. Calculate compression and check some cam-books to find good cam for your engine.Make sure that if cam company suggest 9-10 compression,and you have 9.7:1,go with it. -Carb is ok,if you are plannig to drive it more than hammer it.If you want hammer power,and better response on starts,go with Holley vac or db.750 to 850 will work but i'll suggest that you go to 750size.Holley has more agressive acclerator pump than Edelbrock.They will make same power when tuned corrctly,but Holley will be faster. On the other hand,if you drive only on street tires,Edelbrock might be faster because Holley will spin tires more at start and will be harder to launch... But with slicks,Holley will be faster. This i have tested this few times. Th350 will hold if it will be re-built with added cluches and good shift kit and converter that maches to your cam specs.This is REALLY important.Wrong stall on converter and Toyota Prius will kick your ass at stop light:) Correct converter and Toyota won't know what it was... th400 will hold even with litle hop-ups.But remember that if you try to find th400,it must be B-O-P type.Buick-Oldsmobile-Pontiac.Chevy th400 has different bolt circle on bellhousing. Gear ratio with this cam,assuming you run something like 27" tall tires out back,3,5-3,7 sounds good. 27" tall tires,3.73 gears at 60mph(96km/h) will rpm at 2400-2700. My car (-57 chevy with 350 and 6-71 blower) runs on these specs.That's why i knew:) But remember: These Pontiacs don't like to scream high,they are low on power but high on low rpm grunt!ANd block will crack if you try to go past 7000rpm.This is problem with Pontiacs. When i plan street motor with little or moderate strip use,i'll try to remember this: Horsepower indicates how fast you will hit the wall Torque indicates how far you will push the wall. And talk some guys at your homeland,there are plenty of fast car's around.Try to find out someone who races a vintage pontiac(modern ones have chevy engines) and go talk to him.

1 out of 1 people think this is helpful.

You are spot on about the rear tires. I´m going to drive the car during the summer with a couple of trips to the dragstrip. I´m going to get a couple of street legal slicks so I think the Holley carb is for me. I am really thankfull for your advices. Have a guy that I think can help me calculate the compression. About the RPM, I love torque, no plans of over revving it.

100

Mickey Thompson street radials are great tires,good to drive all around and really fast on strip if you have done your homework on chassis tune-up;) But they wear pretty fast if you do burn out on normal street.At drag strip burn out box,theres water and rubber on top of asfalt so tires don't really wear so much. When i had DOT slicks,i clicked down 10.91 with th350 tranny on my 57.Tranny could not hold so i got th400 with some searious mod's and those drag radials.Before when i had DOT slicks,i had to have 2 set of rear tires when i go to races.With drag radials,i could drove to to the strip,got my tools out,lowered air from rear tires(drag radials like to have 10-14psi of pressure.Anything less than 10psi an your chassis ain't working) and clicked down a 10.93-11.07 all day..And loaded my tols back on and got some air on tires and drove home. Magic was done with suspension so i could get these tires to "hook".Car weighs about 1500kg so it's not lightweight,pretty much same weight as you Pontiac. BUt i estimate that you will have pretty stout 400 soon,something like 350-375hp range and +500 on torq.I think converter could be in 2200-3000rpm range on 3.50-3.73 gears.With this kind of numbers you will buy few set of tires:)

I drove on teh strip for the first time this summer. 14.73 and 144 km/h end speed with 350 engine an street tires. I stalled around 2400 rpm and drove on automatic all the way. I cant slam the gears on manuel. I think the shifter is a bit worn. So I have set my eyes on a B&M shifter. I am going to get a second set of rear rims to put on street legal slicks. Not allowed to have full slicks on the open trackdays I´ve heard. So next year i will do better i think. And the year after that i will do more improvements i hope. And maybe i pick up some experience on suspension and road handling on the way.

100

Focus on 60ft times on strip.60ft time indicates how good your start was.Top end speed will allways be the same.I don't matter did you got 2.5sec or 1.9 60ft.Et will change but top end speed stays the same. Top speed tell's the power engine is making,60ft tell's how good your car hook's at the line. Few tips: -Front end should have 4-5"(10cm-12.5cm) off freelift before front tires come off the ground.Let the car stand on level surface,measure from center of wheel to fenderwell lip.Then use jack to lift the car,and as soon as front tires lift from ground,measure again.Diffrence in these number's should be 4"-5".Remove bump stops if you can to achieve this.You can test this method on track. And get a set 90/10 drag shocks.They are easy to replace on these cars.Even at the track. -If you have the chance,buy CalTracks and Rancho9000 adjustable shocks.Or even the Rancho shocks. And loosen shocks at track.They are 9 point adjustable and on street i use nro 4 and 5,and on strip i use 1 and 2. Rear end should squat little and front end should rise really easy.You can even try to disconnets stabilaiser bar and see what happens.On street tires,try differen't pressures.On front,have something like 3-3.5 bars(easy rolling),and rear 2.5 to 1bar and notise how your 60ft times chance. Allways see 60ft times when you change something.If you improve 60ft by 0.1sec and have same top speed,you will improve your Et by 0.15-0.2sec. -If you are able,leave at idle.If you can leave foot braking at 2400rpm,your suspension will be at partial bind,and it will not hit the tires at line.If you leave at idle,your suspension will be loose,and will "shock" tires more when you drop the hammer.This "shock" is neccesary to gain traction on leaf spring car's. I assume your car is doing 2.1 to 2.4sec 60ft right now?Based on the times you have driven. Chancing rear gears to 3.73 will improve it. But remember:What ever you try with your car,whatever you chance(timing,jet's,shock settings,tire pressure, etc) keep going the same direction until nothing improves.On timing and jet's you can do small changes but better is if you do big changes.Minium of 2-4degrees or 2-3 sizes on jet's.You will see better how your engine is responding. If you change jet's 2sizes bigger(always try bigger jet's if you don't know how you fuel-air ratio is) and car catches 2kmh at top end,try another 2sizes.If car get's slower decrease 4 sizes(2 past your starting point size) to see how that effect's. Long time ago,i raced friend's Duster with 340 engine,727trans and 3.23 gear and stock converter.Best time was 14.5 and 147 or 150kmh. I left at idle and "baby pedal" it of the line.Chassis was more road than strip. With 2500stall car bested high 13sec range.Even on street tires.Funny thing was that when my buddy tried slick's,car improved only 0.2sec!Too much traction caused it to droppdead at the line. Basic rule is:If you can't do a burnout with DOT-slicks easily,you don't need them to go fast. Drive thru the water box,stop at the point where wet and dry area mix.Do burn out,and when smoke is white,pull the car out and same time shift to 2nd or 3rd gear.This will be easier on tranny when traction bites when you leave at the waterbox. And if you have 12-14sec car,you don't need long burn out.But you should try to differen't styles to see what is best for your style of driving.And stick with it:) When you have high staal,it makes street tire racing easier because it's like slipping clutch at start if you baby pedal it.You can get the car moving before full power will come to the tires.With stock converter you can easily apply too much power to the tires. Sorry to write so long story but i get carried away sometimes:)

1 out of 1 people think this is helpful.

I really appretiate you taking the time to share tour knowledge. I have saved all of your replies in my pc. As i said before this could take a couple of winters to get where I want to go. This winter I´m putting all my money inte the engine and rear axel. Different gear ratio and fix the diff so I get power on both rear wheels when I do burnouts. By the way. Today I ordered engine parts from Summit. 4500$, pfffff. Still havent ordered a stroker kit. There are two sets. The cheaper one is not yet balanced and is 200$ cheaper. I´m thinking that there i a guy nearby who has a motor shop. I want to visit him first to see what he can do. If he has the equipment for the job maybe he will be more meticulous and precise. Again I am really thankful for the time you put into youre replies. Pelle

75

Are you talking about a chevy 400 or a pontiac 400. I've never heard of a 400 having cooling problems like that. That sounds just like the chevy 400

25

i only type the word wrong dont get piss dude i know for a fact that a 350 is 350 cubbic inches and that you can only bore a 350 to a 383 stroker longer stroke if i remember right . I did not know you work whit tese cars for 10 + years sorry for getting it wrong .

100

When you make 383 from 350 chevy you will have to bore block to 4.030" (0.030"overbore) AND change crank from 400cid chevy small block to increace stroke from 3.48"(350chevy) to 3.75"(400chevy).You can bore 350 (4.000"stock bore) to 4.060"(0.060" over) safely and still put 3.75" stroke crank in it to make as big as 396 SmallBlock or stay with stock stroke and have 360chevy smallblock. AND these are Chevrolet engines and this guy is asking about Pontiac engines.They aren't at the same ball court.They are totally different engines like Toyota and Ford. So do you now understand that there was more error's than fact in your messsages? Peace out.

100

Yeah i think these guys have mixed chevys with Pontiacs...Orginal Q was about Pontiacs.Check answers from below at topic.

25

how could i forget something like taht of course you have too change the crank . i didnot know you could make it a 396 learn something evryday i am currently taking a class in automotive mecanics so good start . i know stuff about cars but not as much as you doo 10 years thats alot of automobile anyway just too let you know no hearts feeling take care now

2500 IS A LITTLE LITE ON A 340.3500 WOULD PUT IT NEARER THE VERY LIMITED POINT WHERE THEY MAKE POWER OFF THE LINE(60')4500-5500 BECAUSE OF THAT GODDAM DOGLEG CENTER EXHAUST PORT. THE TRANS AM HEAD HELPED A LITTLE DUE TO THE OFFSET PUSHROD LETTING YOU PORT THEM A BIT MORE BUT THE KILLER WAS THE W-2 HEAD.mY 70' 340 (ACTUALLY 348) WAS GOOD FOR 11:88 WITH THE 3500 STALL AND A 3;91 REAR.FORGET CALTRAX ON A MOPAR.GET THE SUPER STOCK FACTORY SPRINGS AND USE THE CHRYSLER IMPERIAL LONG SHOCKS WITH A PINION SNUBBER.GOOGLE THAT.ALSO WE USED TO LOVE THE OLD 6 CYLINDER TAXICAB TORSION BARS.THE ONES THAT WERE SO OLD THEY WOULD HAVE A SLIGHT BOW OUTWARD.GOOD FOR WAY OVER 6" LIFT ON ACCELERATION.WITH A MOPAR IF ITS SET UP RIGHT THE WHOLE CAR SHOULD JUST LIFT STRAIGHT UP.WITH THE FRONT MAYBE TWO INCHES MORE.THAT AND THE HEMI IS HOW THEY MURDERED EVERYTHING IN SS/AA,SS/BA,SS/CA,SS/DA. THATS WHEN THE CHEVY GUYS CRIED AND PRO WAS BORN.THEY CRIED AGAIN WHEN THE HEMI'S WON EVERYTHING SO THEY WEIGHT BREAKED THEM AND FINALLY TOOK CUBES AWAY.BY THE END A HEMI WAS 383 CUBES DESTROKED AND HAD TO RUN A 427 CAMARO.IN THE (JOKE) HEADS UP PRO CLASS.FACT'S!!!!. LOOK EM UP.

dear pontiac 350 guy(origional poster) get your turbo 350 rebuilt by a trans specialty shop.don't pinch pennies,they are marginal on a good day unlike a torqueflite.at least a 3:55 gear and a good 3000 stall converter with all the bolt on standard bullshit.headers,aluminum manifold,holley carb,msd,good wires and at least pull the heads and do a valve job with a cam and kit maybe 284 duration at 470 lift and guides n cut for teflon seals.I have a 69 firebird 350 setup like this that can almost beat my buds 69' 396 71 nova so it's makin bacon.only diff is i'm runnin pontiac #48 heads with ferrea stainless 2.11 intake and 1.77 exhausts with lunati 1.65 roller rockers for about 510 lift. it screams.A melling hi flow oil pump and a canton racing pan to finish it off.contrary to popular belief they run very good with a single plane manifold too. so ditch the stock anchor cast iron intake!!revs to about 6200. F;',# it, live dangerously.you don't always want to be the guy in the rearview mirror,do you?

by the way a stock 340 converter was 2400-2600.just like the roadrunner converter.wanna talk conveters? do you know where the origional A-990 Hemi 68 dart and cuda converters came from? what car?Here's a hint. it was called the "F" converter.what replaced it for the 69 season,straight from chrysler! don't mess with me and mopar.

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