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Low Compression Street Engine's & Tuning Techniques Idea's...How Too's on low compression Engines.

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Old 08-04-14, 01:04PM   #1
nap
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Default Need opinions of engine combinations for 1969 GTO

Guys,
I need some opinions on three different engine builds Iím pondering for my 1969 GTO.

What I have right now is a completely stock engine that is drinking a quart of oil every 300 to 400 miles and has a coolant leak. Details are a WT 400 with a 4spd (M-20) with 3.55 (will be retained) gears out back and has 119,000 miles on it. The heads are number 48ís and will be reused in the rebuild. The RARE D-port 2.5 inch manifolds will also be used along with the 2.5 inch pipes going into the Flowmaster 50-series mufflers and 2.25 inch tail pipes.

1st combination Ė Get a street port and polish for the 48 heads and a 5 angle valve job. Get compression down to 9.8 and use a never used Crane Ram Air IV cam I have from the early 2000ís. Upgrade the pistons and connecting rods with forged replacements and keep the total size of the engine to 406 or 408.

2nd combination - Get a street port and polish for the 48 heads and a 5 angle valve job. Get compression down to 9.8 and use a Comp Cam XR276HR (Duration 276/282 @50 224/230, Lift 502/510). Stroke the engine to 461 and upgrade the pistons and connecting rods to forged units.

3rd combination Ė same as #2 except use the Crane Ram Air IV cam I already have.

Iím thinking that combination #2 will be the most expensive and #1 will be the least expensive. Combination #3 will fall somewhere in between #1 & #2, but maybe closer to the cost of #2.

Power #ís Iím looking for are 450hp and 500tq at the flywheel. I donít think combination #1 will get me there, maybe 425hp at the most. Combination #2 & #3 should be able to hit the 450hp range with little trouble.

Let me know what you think.

Thanks,
Jim
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Old 08-04-14, 04:05PM   #2
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Definitely combination #2.

Combination #1 won't get you 425 hp. A Ram IV motor only made 370 hp.

The 461 will need less gear and less convertor and be a nice driver. 3:55 gear is almost perfect. with a nice 3500 stall convertor. Easy 450 hp.
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Old 08-05-14, 09:04PM   #3
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Ditto, #2.

If you're REALLY gonna port those 48s (I hate to see it..), be sure ONLY a qualified Pontiac guy gets them. Beware the sales pitch or the "CNC" trap. CNC is only "better" if what was "mapped" was really good. And next month? It will be obsolete. 48s are getting rare and valuable to collectors. 62s would be less valuable and still '69. Once porting begins, they're "the same".

FWIW, Dave just finished a set of E-heads that go 380 @ .720 lift, and still maintain 300 at .300. NOT "wide", either. Standard pushrod/lifter. Be sure you understand, "average" (across the lift range) flow is far more important to actual power produced than "peak" flow. The more sales-oriented shops may dispute that.

Jim
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Old 08-05-14, 10:36PM   #4
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Went pretty darn fast with un ported 48's with good valves
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Old 08-17-14, 08:14AM   #5
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Always a debate but many might suggest you take further consideration with 9.8 compression using iron heads and pump gas in all kinds of weather and driving conditions. Especially with a XE lobe.
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Old 08-18-14, 02:39AM   #6
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Cooling , lots and lots of cooling.
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Old 08-18-14, 11:42AM   #7
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Or I'll trade a set of 1971 #96 d ports for those #48's
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Old 08-18-14, 12:22PM   #8
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Not a recommendation, just for interest and discussion.....

The 276HR hyd roller cam using lobe 3314 with 276 rated duration at .006" tappet lift and 0.502" valve lift on the intake. And lobe 3315 rated with 282 duration at .006" tappet lift and 0.510" valve lift on the exhaust.

Take a look at the Comp Magnum High Lift hyd roller lobe 3119 with 280 rated duration at .006" tappet lift and 0.525" valve lift for the intake. And lobe 3111 rated with 286 duration at .006" tappet lift and 0.566" valve lift for the exhaust ( if the lift doesn't look right on the 3111 lobe some catalogs state the lobe lift at .3730", but it is actually .3770")

Both have the same 224/230 degrees duration at 0.050" tappet lift. But note the Magnum lobes have higher valve lift. If the heads in use have a installed height that will accomodate additional valve lift that will have a positive effect as a typical 2-valve engine responds to high valve lift (this is well documented).

Also note the Magnum lobes have additional seat duration.

For interest go to the various calculators and note the differance using these differant lobes. For example you can use calculators to detemine, in theory, the dynamic compression ratio, overlap, etc.
For a formula that requires where the intake closes in degrees that can be determined on the Kelley program.

http://www.wallaceracing.com/dynamic-cr.php
http://cochise.uia.net/pkelley2/DynamicCR.html
http://www.wallaceracing.com/overlap-calc.ph

High compression ? The more "overlap" your cam has, the lower your "actual" as opposed to your static compression ratio will be. This is one area you can easily change. Also note any cam can be ordered with a differant lobe separation than the comps typical 110.
A wider lobe separation reduces overlap and will reduce cranking compression.
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Old 08-21-14, 05:45AM   #9
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Quote:
Originally Posted by nap View Post
Guys,
I need some opinions on three different engine builds I’m pondering for my 1969 GTO.

What I have right now is a completely stock engine that is drinking a quart of oil every 300 to 400 miles and has a coolant leak. Details are a WT 400 with a 4spd (M-20) with 3.55 (will be retained) gears out back and has 119,000 miles on it. The heads are number 48’s and will be reused in the rebuild. The RARE D-port 2.5 inch manifolds will also be used along with the 2.5 inch pipes going into the Flowmaster 50-series mufflers and 2.25 inch tail pipes.

1st combination – Get a street port and polish for the 48 heads and a 5 angle valve job. Get compression down to 9.8 and use a never used Crane Ram Air IV cam I have from the early 2000’s. Upgrade the pistons and connecting rods with forged replacements and keep the total size of the engine to 406 or 408.

2nd combination - Get a street port and polish for the 48 heads and a 5 angle valve job. Get compression down to 9.8 and use a Comp Cam XR276HR (Duration 276/282 @50 224/230, Lift 502/510). Stroke the engine to 461 and upgrade the pistons and connecting rods to forged units.

3rd combination – same as #2 except use the Crane Ram Air IV cam I already have.

I’m thinking that combination #2 will be the most expensive and #1 will be the least expensive. Combination #3 will fall somewhere in between #1 & #2, but maybe closer to the cost of #2.

Power #’s I’m looking for are 450hp and 500tq at the flywheel. I don’t think combination #1 will get me there, maybe 425hp at the most. Combination #2 & #3 should be able to hit the 450hp range with little trouble.

Let me know what you think.

Thanks,
Jim
mornin'....
the RA IV cam has no power under 3000 rpm in a 400, you'd need at least 3.90 gears to make it work right with an M-20. many decades ago we had a 72 GTO with a 455 auto and 3.70 gears. It was a real tire burner on the street, tore the road up. I converted it over to stick and M-21 and it had less low end torque and slowed down. lost all the torque multiplication from the converter, and the solid sync of the stick lowered the rpm, even though the gear multiplication on paper was the same. my point is with a stick, you need more gear, because in reality an automatic gives the effect of a deeper gear via the converter.

Pontiacs, esp. original GTO's, are taking on an almost reverent collectability among intelligent people, who realize what they really are. an original survivor numbers matching should be preserved down to the nuts and bolts. I'm talking taking the bolts out of the fender, numbering them, and cleaning them, and putting them back in the same holes - a museum piece.

that's what they have become. just the dummies out there don't realize it yet. they're still defacing the mona lisa as a hobby, in poor taste, thinking it's cool. DeLorean and MacKellar were more than engineers, they were automotive engineering artists. There's a reason why all the cars made since then, look schitty and pale in comparison. It boils down to the guys who designed them in the first place, were highly talented, and gifted.

would you take a rare, valuable old historic painting, done by some famous artist, and start painting over it in a vain attempt to improve it ? see most people don't realize what a big mistake they are making now, modifying or hacking up these cars. but that is the truth of the matter.

keep your cylinder heads bone stock, only do changes that can be easily undone, such as bolting on headers, intake, carb, cam. don't port the heads. don't even bore it out unless it really needs it.
if you want to make more HP, get a pair of schitt lower CR smog heads and port those- or get aluminum heads. or buy heads someone else already ported and devalued. but if you have virgin castings now, don't grind on them. there's just so sane or intelligent reason to do that.

if you were digging in a mummie's tomb and found an ancient gold relic, would you grind on it and repaint it ? hell no...it should not be touched or altered in any way.

same goes for original Pontiac hipo parts and cars now. the hacking days are over.
the Pontiac 400 is easily capable of making 450 HP without porting the heads. the stock RA IV's highly tuned would make 450 flywheel, and 400 rear wheel. there's a few chassis dyno RA IV tests on youtube proving it. I posted it here in an older thread.

porting on the heads will only devalue them, and probably slow the car down for street daily driving part throttle. and give lousier gas mileage, if you really want to enjoy the car and drive it a lot.

there's 3 old Pontiacs in our family, and I can proudly say, there isn't a single non-USA made part on them. Not one Chinese casting, forging, fender washer, door panel, or window knob. You should strive to keep it that way if possible. don't bastardize your car with foreign parts. not even one bolt or washer.

the original GM stuff of the time was far superior to anything you can buy now easily to replace it with.

Last edited by Zedo : 08-21-14 at 06:07AM.
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Old 09-12-14, 12:15AM   #10
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Get a set of 6X-4 heads (from 350 Pontiac) and get them shaved about .060 to get the CC's down. Have the the bowl work done on intake & exhaust with mild cleanup on the ports.Stay with 2.11 int /1.66 exh valves. Have the high flow valves put in (reduced stem at head). Have the heads pushrod holes clearanced for 1.65 rocker arm use just in case you decide to tune around in that area.
When you get the short block done make sure your engine builder gets the pistons as close to zero deck height as practical.
Only use flat top forged pistons with single valve reliefs.
.030 overbore on the std 400 block will yield 406".
Serious prolonged racing effort?
Use forged I-beam or H-beam stock length connecting rods that use the standard Pontiac rod journal size.
Don't rely on the old stock rods by the time you properly prep them yer getting into the cost of a premium forged rod and what do yo have when you are done? A 45 year old stock rod that is on borrowed time . #'s matching blocks cannot be replaced.
whether its 2 bolt main or four bolt main use studs and nuts on the main caps instead of bolts.It's just better that way if you plan on racing it hard.
Better bet would be to yank the original 400 out, lay it up for long term storage and seek a 400" core block that you can build and beat the crap out of.

Depending on cam selection the above will leave you with an engine that will run reliably on 91 octane pump grade gasoline and have plenty of power on the street. Depending on how it's geared, spark timing, carb set and chassis set up you will have the possibility of an honest 12 second 1/4 mile car if that is what your goal is.
These are changes that can easily be put back to stock that will not de-value the car in anyway.At time of sale you have the original #s matching engine saved for restoration purposes.
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Old 09-17-14, 08:16AM   #11
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very good advice. at this point in time, if you have # match and vin matched parts i.e. block, trans, rear axle, I would not risk breaking them. these cars are worth some money now to restorers and worth saving that stuff. get a 400 2bbl crap block from a 70's full size car and club that instead. if it tosses a rod oh well. these blocks are dirt cheap most times. I got 2 of them for free at the Pontiac race/swap meet/show at Maple Grove years ago. the vendors just left them there in the grass with "free" signs on them. another long block I picked up for only $30 with heads.
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Old 11-11-14, 01:50PM   #12
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Guys,

I should have mentioned that I have another set of 48's that already have some work done to them. The orginal 48's, cam & crank will be put away.

All of the above advice leaves menwith a question. If the block is machined for a roller cam and stroker kit can it be brought back to stock?

Thanks,

Jim
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Old 12-12-14, 12:59AM   #13
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The roller cam is basically drop in so no special block machining needed there. For a stroker, all that needs to be done is a small area of the block, up by the front main, needs to be ground back slightly, or the crank counterweight hits it. The factory crank clears no problem, it was made for it, but the aftermarket cranks hit. It can easily be put back to stock, with the exception of the bore size.
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Old 12-30-14, 07:29PM   #14
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Quote:
Originally Posted by nap View Post
Guys,

I should have mentioned that I have another set of 48's that already have some work done to them. The orginal 48's, cam & crank will be put away.

All of the above advice leaves menwith a question. If the block is machined for a roller cam and stroker kit can it be brought back to stock?

Thanks,

Jim
what he said, ditto...even if you drill/tap lifter feed holes and use restrictors, they can be removed later to go back to a hydro cam. the relief grinding in bottom of bores for stroker crank, can stay there with a shorter stroke crank- no one will see it and it won't hurt anything if you went back to stock crank
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Old 09-02-15, 10:55AM   #15
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Quote:
Originally Posted by Gach View Post
Definitely combination #2.

Combination #1 won't get you 425 hp. A Ram IV motor only made 370 hp.

The 461 will need less gear and less convertor and be a nice driver. 3:55 gear is almost perfect. with a nice 3500 stall convertor. Easy 450 hp.
Lou, not trying to be a nitpicker or ball buster, but they have chassis dynoed oem GTO RA IV cars and they made 400 HP at rear wheels, 425 HP flywheel
they "can" do it but these are knife edge tuned in new condition
there are vids on youtube

this one did 392HP rear wheel
https://www.youtube.com/watch?v=8bMWrwzAsQ0

here's more
https://www.youtube.com/watch?v=iLiXhgPNqKY

at flywheel they were over 400HP
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