Author Topic: 1975 Pontiac 350  (Read 4804 times)

0 Members and 1 Guest are viewing this topic.

Offline Erwin

  • Jr. Member
  • *
  • Posts: 62
  • Referrals: 0
1975 Pontiac 350
« on: July 28, 2009, 07:19:38 PM »
Hi. I have a 1975 Pontiac 350 engine, how much horse power i can get out of it ? Is it going to cost more rebuilding the 350 than the 400?  is it worth rebuilding it? and can i use the cranckshaft from 400 to 350? Thanks!!

Offline deadfish

  • Member
  • **
  • Posts: 493
  • Referrals: 0
Re: 1975 Pontiac 350
« Reply #1 on: July 29, 2009, 07:18:36 AM »
I'm running a 350P and I love it! The heads will be the biggest pain...the exhaust side is narrow and has "EGR bumps" cast into them back part. My block is a 1970...the heads came off a 72 (unleaded gas heads...hardened valve seats) and the manifold off a 1975. I did all the porting myself as I needed to learn and I still had the 70 heads if I screwed up the 72's. I then sent the heads to a machine shop in town that specialized in Pontiac motors. He did a 3 angle and radius job, plus some extras and told me the my port job was excellent and the heads would "flow like gangbusters" (his words). There are a lot of extra castings that can be taken out as well. (I got a smokin deal on the valve work too cuz I gave him the shortblock that the heads came off of!) I then matched the gaskets to the porting and matched the manifold ports as well. Engine runs fantastic with a mild cam, new springs and liftgers. It is still a 350 ci because no bore work was needed except honing for the rings.
Other than the heads...the rest of the build is as straightforward as an SBC...cost is about the same as well.

oops...sorry for the paragraph ;)

Rick C.

Offline Mr. P-Body

  • Sr. Member
  • ***
  • Posts: 692
  • Referrals: 0
Re: 1975 Pontiac 350
« Reply #2 on: July 29, 2009, 09:54:44 AM »


   The cost to build a 350P is a bit higher than the 400 simply because of volume. There are 20 400s being built for every 350, so pistons and rings are less expensive. The rest of the parts are not only similar, they are the SAME.  For dollars spent versus power gained, no comparison between 350 and 400. The 350 cranks DOES "fit" in the 400, but balancing IS required.

   If you have "small valve" heads, and really want to stick with the smaller engine, it can be made to run VERY well.  many will use "large valve" heads because Pontiac did on some engines. This is not the best way too make power with the small bore. The small valve heads will flow better under these conditions, especially if proper porting procedures are followed.

   To make "real" power with it, you're going to need to "rev" it high, as with any smaller cubed engine. This calls for high qual;ity rods and pistons, in particular, and good valves and springs, as well. A solid lifter cam will go a long way to producing really good power numbers.

Rick C.,

   For clarity only, I must point out a couple of misconceptions you appear to display.  First, catalytic conveters, mandating "unleaded fuel" first appeared in 1975, under EPA laws.  Unleaded fuel doesn't "clog" the converter, where lead does.  Initial EPA rules for EGR (exhaust gas recirculation) were for '72, but many manufacturers weren't "ready" so they pushed it back to '73.  Pontiac WAS "ready", and the '72 intake is unique because of it. It's a sort of a "cross' between the '71 (non-EGR, early crossover)  and the '73 (EGR, "later" crossover). The '72 has the later crossover, but not the EGR provisioin.  Good intake...  Anyway, the induction-hardened exhaust seats were first found in SOME of the '72 heads. ALL for '73. It was felt the added heat from leaning the idle could harm the exhaust seats (correct assumption). While to a degree, it WAS about "unleaded fuel", mostly it's for longevity in a higher heat environment than originally designed for.  Adding the converter compounded the problem.

   Lastly, a 350 Pontiac isn't REALLY 350 CID. It's 354, but GM didn't want any one division "stepping on the toes" of other GM divisions, so they ALL were called "350".  Each division except Caddy, had their own "350", unique from the others, until around '77, when "corporate" engines became the rule.

FWIW

Jim

Offline deadfish

  • Member
  • **
  • Posts: 493
  • Referrals: 0
Re: 1975 Pontiac 350
« Reply #3 on: July 29, 2009, 11:00:57 AM »


   The cost to build a 350P is a bit higher than the 400 simply because of volume. There are 20 400s being built for every 350, so pistons and rings are less expensive. The rest of the parts are not only similar, they are the SAME.  For dollars spent versus power gained, no comparison between 350 and 400. The 350 cranks DOES "fit" in the 400, but balancing IS required.

   If you have "small valve" heads, and really want to stick with the smaller engine, it can be made to run VERY well.  many will use "large valve" heads because Pontiac did on some engines. This is not the best way too make power with the small bore. The small valve heads will flow better under these conditions, especially if proper porting procedures are followed.

   To make "real" power with it, you're going to need to "rev" it high, as with any smaller cubed engine. This calls for high qual;ity rods and pistons, in particular, and good valves and springs, as well. A solid lifter cam will go a long way to producing really good power numbers.

Rick C.,

   For clarity only, I must point out a couple of misconceptions you appear to display.  First, catalytic conveters, mandating "unleaded fuel" first appeared in 1975, under EPA laws.  Unleaded fuel doesn't "clog" the converter, where lead does.  Initial EPA rules for EGR (exhaust gas recirculation) were for '72, but many manufacturers weren't "ready" so they pushed it back to '73.  Pontiac WAS "ready", and the '72 intake is unique because of it. It's a sort of a "cross' between the '71 (non-EGR, early crossover)  and the '73 (EGR, "later" crossover). The '72 has the later crossover, but not the EGR provisioin.  Good intake...  Anyway, the induction-hardened exhaust seats were first found in SOME of the '72 heads. ALL for '73. It was felt the added heat from leaning the idle could harm the exhaust seats (correct assumption). While to a degree, it WAS about "unleaded fuel", mostly it's for longevity in a higher heat environment than originally designed for.  Adding the converter compounded the problem.

   Lastly, a 350 Pontiac isn't REALLY 350 CID. It's 354, but GM didn't want any one division "stepping on the toes" of other GM divisions, so they ALL were called "350".  Each division except Caddy, had their own "350", unique from the others, until around '77, when "corporate" engines became the rule.

FWIW

Jim

Thank you for the added info...I am only a "backyard" mechanic of sorts (i do my homework before I wrench). Still learning new things everday...thanks: 0

Rick C.

Offline 72blackbird

  • Adv. Member
  • ****
  • Posts: 2077
  • Old Birds don't die-they get faster, corner harder
  • Referrals: 0
Re: 1975 Pontiac 350
« Reply #4 on: July 29, 2009, 01:55:50 PM »
I'm actually building a 350P to go into my '72 Bird while I overhaul/upgrade the 406 currently in the car now. The original 4c's were cracked, so I'm using a set of ported  no.13's w/ the same e-performer and Holley 750 v/s off the 406- should run very nice. I've already ball honed/re-ringed the block in addition to tearing down, inspecting and cleaning the block, so I'm expecting it to run at least mid 13's, even with the same TH-350 and 3.08 posi in the car now.

Geno

Offline Erwin

  • Jr. Member
  • *
  • Posts: 62
  • Referrals: 0
Re: 1975 Pontiac 350
« Reply #5 on: July 29, 2009, 05:01:02 PM »
THANK YOU GUYS,  I'm not a mechanic,I just love working on my car's, I can rebuilt an engine not a problem.But i dont know anything about number's ("cc",duration,size of valves all those numbers "crap") I'm more of a hands on ,Anyways Can i get the 350 bore to 383? if i can, what size piston and ring can i use? and i have 6x-4 heads i want to get it machine, what kind of intake and exhaust valve you recomend. and  camshaft,lifter, pushrod combo? I know I ask to many question's . I read the article from performance pontiac about building a 350 Pontiac, but to much $$$$  THANKS again for the input.

Offline 72blackbird

  • Adv. Member
  • ****
  • Posts: 2077
  • Old Birds don't die-they get faster, corner harder
  • Referrals: 0
Re: 1975 Pontiac 350
« Reply #6 on: July 30, 2009, 02:32:04 AM »
The 350P/383P expert is arguably Ace Brewer of Pacific Performance racing down in San Pedro, CA- he's got everything you need to turn a 350P into a high-revving 383P stroker. The cost of a full-on 383P stroker kit would no doubt be spendy, but the basic rotating assembly kit is about $1450 and includes lightweight Probe SRS pistons, total seal rings, 5140 forged rods, stroker crank, King bearings, balancing and pit fit- about what you'd spend to stroke a 400.

Geno

Offline Erwin

  • Jr. Member
  • *
  • Posts: 62
  • Referrals: 0
Re: 1975 Pontiac 350
« Reply #7 on: July 30, 2009, 08:51:46 AM »
THANKS Gino.

Offline Erwin

  • Jr. Member
  • *
  • Posts: 62
  • Referrals: 0
Re: 1975 Pontiac 350
« Reply #8 on: July 30, 2009, 08:56:28 AM »

Offline Mr. P-Body

  • Sr. Member
  • ***
  • Posts: 692
  • Referrals: 0
Re: 1975 Pontiac 350
« Reply #9 on: July 30, 2009, 10:02:44 AM »
Erwiin,

   All that "number crap" is what makes your car go down the road in the first place. This is where the REAL part of engine building "lies". The guy that shoves the pistons "in the hole" is the assembler. He (or she) may or may NOT be the "builder". The builder is the one that chooses the combination, assigns the clearances and tolerances, and is responsible for the success/failure of that combination.

   IMO, the 383 "stroker" Pontiac is an attempt at finding a way to use otherwise uindesirable parts, like the 350 block. In any "form", it will be no match for either a 383 Chevy OR a 400 Pontiac.  Your money would be better spent on a 400.  Not to worry, Geno, "Ace" sells parts for those, too...

Jim

Offline Erwin

  • Jr. Member
  • *
  • Posts: 62
  • Referrals: 0
Re: 1975 Pontiac 350
« Reply #10 on: July 30, 2009, 10:50:45 PM »
Thanks Jim, I will go for the 400P.

Offline deadfish

  • Member
  • **
  • Posts: 493
  • Referrals: 0
Re: 1975 Pontiac 350
« Reply #11 on: July 31, 2009, 08:11:12 AM »
Erwiin,

   All that "number crap" is what makes your car go down the road in the first place. This is where the REAL part of engine building "lies". The guy that shoves the pistons "in the hole" is the assembler. He (or she) may or may NOT be the "builder". The builder is the one that chooses the combination, assigns the clearances and tolerances, and is responsible for the success/failure of that combination.

   IMO, the 383 "stroker" Pontiac is an attempt at finding a way to use otherwise uindesirable parts, like the 350 block. In any "form", it will be no match for either a 383 Chevy OR a 400 Pontiac.  Your money would be better spent on a 400.  Not to worry, Geno, "Ace" sells parts for those, too...

Jim

Mr. P-Body...not to hijack the thread or anything, but what is the difference between the 350P and 400P block...I thought they might be the same block with different bores...could a 350 be punched to a 400? Or is the 400 a big block like the 455?

Thanks,

Rick C.

Offline brian c

  • Lifetime Member
  • *****
  • Posts: 4880
  • Ohio Firebirds Member
  • Referrals: 0
    • Y88 Resto
Re: 1975 Pontiac 350
« Reply #12 on: July 31, 2009, 08:20:25 AM »
There are no Big Block/Small Block Pontiacs. They are all the same size externally. That's why its such a popular swap to go from a Pontiac 301 or 350 to a 400/455 :)

1978 Y88, '70 455 HO block bored 0.060, TH350, 3.42:1 gears...Oct '08 Fbodywarehouse Calendar - Woot!
1980 Firebird - no engine/tranny... to be pacecar clone

Offline Rick

  • Global Moderator
  • Lifetime Member
  • *****
  • Posts: 7939
  • Referrals: 0
Re: 1975 Pontiac 350
« Reply #13 on: July 31, 2009, 09:48:05 AM »
To follow up on Brian's answer -- while the blocks all have the same external dimensions (no "small" or "big" blocks from 326-455 CID), the castings themselves are different and there are limits to how far they can be bored.  To reliably get the engine displacment you want, you have to start with that size block because there won't be enough material in the sleeves to punch it out.

Offline deadfish

  • Member
  • **
  • Posts: 493
  • Referrals: 0
Re: 1975 Pontiac 350
« Reply #14 on: July 31, 2009, 11:39:01 AM »
To follow up on Brian's answer -- while the blocks all have the same external dimensions (no "small" or "big" blocks from 326-455 CID), the castings themselves are different and there are limits to how far they can be bored.  To reliably get the engine displacment you want, you have to start with that size block because there won't be enough material in the sleeves to punch it out.

Gotcha...thanks!