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Old 09-02-2012, 10:18 AM
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this could get ugly. pontiac/frankenstein

well, i just got a 69 t/a clone. previous owner claims the engine is a 70 455 h.o. and the casting numbers on the heads verifies that. the stamp on the front of the block says it's a 67 400 ram air block. edelbrock intake, holley carb.
the engine needs to be pulled and gone through. he claimed bottom end noise but i'm hearing top end for sure bottom maybe.
i can't see any actual casting numbers for the block only the stamp on the front passenger side. would those heads bolt on that engine with no modifications? this is the first pontiac i've ever owned and there is less information out there than on old ford stuff or i haven't come across it yet.
how big of a mess could i be in here? not planning on racing the car it'll just be a cruiser. won't be pulling the motor for a few days and it's driving me crazy.

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Old 09-02-2012, 10:38 AM
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sorry, i'm old and my eyes have really gone down hill. with reading glasses on i see that the stamp is xf not xr. so, it is a '70 455 h.o.
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Old 09-02-2012, 01:59 PM
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First, you need to sort through the ambiguousness of what you actually have so here is a link to go to that will help you understand and ID your engine.
How to identify your Pontiac engine
Then , once you have your engine size year etc nailed down , we will try to figure out what its doing and go from there.

Hint: the block casting number and the date code is what you want to go by. The engine code on the front tells what horsepower and carb and such that it was built with.Many engine codes are used from year to year and the description changes, so you have to know the date code and block casting number to CORRECTLY ID the engine code.
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Old 09-02-2012, 04:19 PM
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according to poniacation.com the xf stamp was only used on the 1970 455. until i get the engine pulled that's all i've got to go on. found another site that went as far as to break it down to the h.o. specifically. i'm going to assume i'm working with a 1970 455 h.o. until i get the engine out. not planning on ordering any parts until i see what's wrong. i was more concerned that i had 455 heads on a 400 block and i didn't know if that was just a "bolt on" modification. thanks for the link, i may be able to get back there with a flashlight and see some of the casting numbers with the engine in.
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Old 09-02-2012, 04:26 PM
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according to poniacation.com the xf stamp was only used on the 1970 455. until i get the engine pulled that's all i've got to go on. found another site that went as far as to break it down to the h.o. specifically. i'm going to assume i'm working with a 1970 455 h.o. until i get the engine out. not planning on ordering any parts until i see what's wrong. i was more concerned that i had 455 heads on a 400 block and i didn't know if that was just a "bolt on" modification. thanks for the link, i may be able to get back there with a flashlight and see some of the casting numbers with the engine in.
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Old 09-02-2012, 05:20 PM
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455 heads will have large CC chambers. Bolting them on a 400 will be a performance downgrade.
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Old 09-02-2012, 05:28 PM
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XF designation was also used on a 1977 400 180 horsepower and on the 1978 301 Ci 150 horse engine.
Also used on the 1969 428 Ci 370 horsepower, and the 1966 and 1967 -326.
Casting number and date code is very important. Engine codes are not reliable without casting numbers and date codes to correlate by.
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Old 09-02-2012, 07:40 PM
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well, if that's all right i stand corrected. again my question really is that if what i have turns out to be a 400 with 455 heads would that have been a simple "bolt on" change? i know the 455 and 428 have bigger journals than the 400. what about bolt patterns, water channels etc. then what about moving parts? again, i understand that the casting numbers will let me know what exactly is there. for now, i'm just trying to look ahead if it turns out to be a mess and i can't really find very much by doing general searches. if i were checking on differences between windsor blocks there would be a ton of information out there. i thought going into gm stuff would be simple since the sbc is so popular.
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Old 09-03-2012, 06:03 AM
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350 through 455 heads will interchange on 350-455 blocks. Heads with large valve will be problematic on 350 blocks due to the bore being smaller
causing clearance issues and valve shrouding (350 only)
455 heads have larger chambers so putting them on a 400 would lower compression, causing some loss of performance
I hope you have a 455 as that would be an street motor (lots of power) that could be had with minimal funds
A 400 is a great engine and can be stroked to 462. They can be made to run like a striped *** ape.
Remember a pontiac allready has a 3.75 inch stroke , those chevy guys spend big bucks and time to stroke their 383 motors. 400 poncho is allready there. and has a stronger bottom end. onnecting rods are the weak link, but decent forgings are readily available for very little $$$.
Plenty of stuff around to make the pontiac a real runner. Stick around here, and ask questions.There is lots of help here for you. LA
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Old 09-04-2012, 08:55 AM
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Lynn (LATECH) knows his Pontiacs.

If the heads are "64" castings (the only casting on '70 455 "HO" engines), they were quite populaqr to use on 400s , as they drop compression to about 9.2:1, ideal for modern gas.

NOTE: '71 and '72 "HO" engines had round exhaust ports. The '70 did not.

Pontiacs with stock "cast" connecting rods will sound like a "tap" when a rod bearing is knocking. It can be deceiving. When you put your list of parts together, be certain to include new connecting rods (RPM forgings are the best buy, IMO) and a balance job.

To learn more about the ol' Injun, get Jim Hand's "How to Build Max-performance Pontiac V8s" published by SA Designs. Though a bit dated, it is the most current and accurate information available at this time.

Jim
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Old 09-04-2012, 11:35 PM
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yes they are the 64 castings, so they are d ports. i'm pretty confident about what the heads are. it's got anedelbrock torquer intake. that seems right for a 455, builds power up to 5500 rpm.
i was thinking it was a 455 after checking the compression we got a high of 188 and a low of 168. that seems pretty high. stock it should have had 10.25:1 if i remember right. with the valve covers off it turns out a previous owner out roller rockers on it. it sounds like it has a mild cam. just a little lope at idle.
the guy that yanks my engines for me sys the heads look too clean to have 5000 miles on them. he thinks somebody missed something when they built it that hasn't completely broken. the plugs were all clean as well, but the piston top look dirty. i told him to go ahead and yank it.
i'll feel better knowing what's going on from top to bottom anyway. hopefully the crank is good and know cylinder wall are fried (compression makes me think not) new rod and main bearings and lifters might do it wonders. the high compression has me a little worried that they may have faced off the heads. if that's the case i'll have to figure out how much stock was removed. would you definitely have hardened exhaust seat and guides put in?
anyway, i'm hoping it is the 455 it was sold as. thanks that answered a few of the questions i had.
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Old 09-05-2012, 07:09 AM
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It cannot be emphasized enough: REPLACE THE CONNECTING RODS. Not just the bearings. The cast rods were junk the day they were made, and that was over 40 years ago. For $279, don't "cheap out" on the most important change you can make to the Pontiac. Don't let a shop convince you they'll (cast rods) be "alright". They (shops) make more money rebuilding stock rods with new bolts, than selling GOOD rods. At $20 each for resizing, and $65 for new bolts, you're just about at the same expense as new rods. Be smart.

Cranking compression in the high 160s-low 180s indicates it probably still has flat-top pistons in it, and an original type (if not the "real deal") cam. The solution is to turn a "dish" in the top of the piston about 12-14 CCs. Since you're going to have the pistons off the rods anyway, a good time for that. Rebalance woiuld be called for.

DO NOT install new lifters on a "used" camshaft. It WILL fail. While it used to be a fairly common practice in repair shops, we don't do it anymore due to the changes in oils and metalurgy. Good time to install a new, more modern cam grind, though! We use Comp XE grinds in virtually everything today. Remember, this is NOT a "Chevy", and reacts to input differently than the Chevy. What this means is, pay little heed to complaints about Comp. Leading edge and VERY good. Their solid rollers for street are the s**t... (:-

Jim
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Old 09-05-2012, 08:26 AM
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thanks,
i picked up a 67 cougar about a year ago that the guy claimed he e-built the engine then just parked it for four years.
he had installed the two front cam bearings wrong he also had a cam with less lift than a stock cam.
i used a comp ex256 and was happy enough with it. it wasn't quite as "lopey" as i would have wanted.
larry should have the motor out today. i'm lucky, i work about 70 hours a week but i'm kind of my own boss. i can get by once he has it out and see what's really going on.
previous owner claims 5000 miles on the build but larry says less. i'm thinking that the "build" may have just been a valve job or something.
from what history i do have on the car it has a 400 tranny from a 76 trans am.
no indication that an aftermarket stall was put in it.
so, what cam would you suggest? i think i've read ex274 is good.
i'm not planning on doing any racing or any burn outs. i'm fine with a stock stall. the engine has a decent lope now and i'd like to keep that sound.
idles around 650 rpm if i remember right and doesn't struggle at a red light.
i'm going to get off topic. coming back home with it i was going what i think was around 70 and truning almost 3000 rpm. supposedly this thing has 293 gears. that doesn't sound right to me. is it just because i'm forgetting it's a 3 speed transmission making me think those rpm's are high?
thanks for the good information. keep it coming. i ordered the book, by the way.
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Old 09-05-2012, 08:31 AM
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you can tell i posted after i took my ambien last night.
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Old 09-05-2012, 11:39 AM
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TH400 was dscontinued in F-bodies after '74 because it wouldn't "fit" with the catalyst installed. TH350 (M38) was the trans installed in '76 T/As no matter what engine they came with. If the trans pan is a rectangle with one corner "lopped", it's TH350. If it sorta looks like "Texas", it's TH400 (M40 in a Pontiac).

We use XE262H for the level of engine you describe. XE274H needs at least a 2,400 RPM "stall" and works better with 2,800.

3,000 RPM @ 70 usually means 3.55 gears. If a "big 10 bolt", 3.42s.

Jim
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