[actmobmar]

i want it to be a fun street car that will go to the track a couple of times a year, i will put drag radials on the back, just in case i run into a new mustang or camaro on the street, the new cars are pretty quick, and i want this to at least be able to run w/ some of them. i know goals need to be kept realistic, though. incidentally, the tremec resides behind this engine in my '69 camaro convertible, i built everything rite down to the headers, all the turbo parts are based off an ebay kit, did it 3 years ago, car runs low 10's fairly easily, i am putting a 4l80e in the camaro and putting the tremec in the gto. it is nice to know that there are people out there willing to help w/ this project, as i am a lil lost w/ the pontiac- i've worked on chevys for a long time, so thank you all. i think i am going to keep the stock crank, put a good set of rods in it, and figure out the pistons/compression/heads with help from you guys. is there any info available on porting #48 heads? here is a pic of the camaro engine

[WDCreech]

Originally Posted by actmobmar

is there any info available on porting #48 heads? here is a pic of the camaro engine

Craig Hendrickson and Kern Osterstock published a couple of books that were available through H-O Racing Specialties, one of which was "Pontiac High Performance Engine Design & Blueprint Assembly". It had a section, with illustrations, on porting Pontiac heads. Very informative reading. I had to replace my origional copies and found both this and their "Pontiac Heavy Duty Parts & Specs" at one of the book clubs, but if all else fails, I see Craig post on the PY forums website, once in a while.

Bill

[cobalt327]

Originally Posted by actmobmar

hello, i'm new on here and looking to build up a 1968 gto convertible that i inherited when a good friend of mine passed away too soon. the car has a ys code block(400) in it that appears to match the car, along w/ #48 ram air 3 heads. the car has a 4 speed in it, and i am looking at taking the tremec 600 that is currently in my '69 camaro, and has a .6 overdrive, so i am considering 3.73 gears. i'd like the car to run mid 12's as most production cars these days do, and i want to keep the factory block and heads so it appears original. the car currently has headers, performer intake, demon 650, and hei ignition. any help to guide me in the rite direction in this build would be great, as i am not familiar w/ pontiacs! thanks!!

I ran mid 12's using a Holley 4777 and a Performer intake on a 455 w/6X heads in an all steel '81 Camaro, and went quicker than that using a 428 in a '68 LeMans (also all steel), so I see no reason you can't get into the 12's w/your 400 using a decent cam and the '69 #48 heads you have. I'd clean the bowls and give them a good valve job. No harm in port matching the intake and heads (not gasket matching, BTW), but full-on porting isn't necessary to run high 12's.

Whether your idea of stock appearing includes headers I don't know, but using long tube headers will make running 12's a lot easier unless you use the good manifolds- the low-po manifolds hurt power too much. The 400 spins higher than a 455 all else being equal, so using a bigger carb certainly won't hurt.

I'm guessing the pistons aren't flat tops, else the compression would be higher than 9.5:1.

Some reading if you're in the mood:

• Engine info
• Info/sites

[actmobmar]

thanks for the info! i've been looking for the jim hand book as well

[actmobmar]

here is the cam that is in the car, it is a crower solid pn 60310, duration at .050 is 240 int, 248 exh, lift .477/.501) power is from 2800 to 6k rpm, what do you guys think?

[cobalt327]

Personally I like that cam. It has a powerband that compliments a stick shift 400 Pontiac, especially w/freer flowing heads. Not to say your 48's won't be a good match, but if ported the cam can make more power.

This cam in a 400 should make just enough vacuum (11-13 in.) for power brakes, but if it was a problem I'd expect you'd have said so already. Do you know if it was installed at 108 degree ICL? You might try advancing it a little but that's something for the fine tuning stage.

BTW, do you know what pistons (description or part number) are in your engine? At some stage it would be good to CC the heads and measure the piston deck clearance to get the exact compression ratio. Your heads (assuming they're 400 heads and not the 350 heads, which I seem to remember had smaller chambers but you'd need to verify that) are listed as 72cc in most places, but they usually measure somewhat higher than that if they're unmilled.

In any event, running the numbers through a calculator using 72cc chamber volume, a 0.041" quench distance, a 5cc valve relieve volume and a 0.030" over bore, I get a little more than 10.5:1 CR.

Using a wider 0.061" quench (unmilled block and 0.041" head gasket thickness), it's a little more than 10.1:1.

It would take a dish of about 15cc to get you to 9.5:1, using the tighter 0.041" quench, or a 12cc dish using the wider 0.061" quench. Note- All these figures use an arbitrary gasket bore diameter of 4.2", and a flat top piston valve relief of 5cc. Adjust this as needed for the parts being used.

[actmobmar]

i've never driven it so i don't know how much vacuum it has, and the car itself hasn't been driven since 1988. when i broke the cam in i ran it on an external fuel source, and the car wouldn't idle-the carb was dirty from all the years sitting, and i didn't want to rebuild it at the time because i still have alot of work to do on the car-suspension, brakes,etc. i'm stiil on the fence about stroking it, it sounds as though i can meet my goals without doing it. i plan on pulling the heads this weekend, but at a minimum i will replace the rods w/ eagles and port the heads.

[vinniekq2]

If the engine has sat many years,consider freshen ing the engine and cleaning the gas tank

[cobalt327]

There are guys who are already experts and others who need a little help, so it's hard to know where everyone fits at first. So if this is old news, just disregard it.

Originally Posted by actmobmar

i've never driven it so i don't know how much vacuum it has, and the car itself hasn't been driven since 1988. when i broke the cam in i ran it on an external fuel source, and the car wouldn't idle-the carb was dirty from all the years sitting, and i didn't want to rebuild it at the time because i still have alot of work to do on the car-suspension, brakes,etc. i'm stiil on the fence about stroking it, it sounds as though i can meet my goals without doing it.

You can run 12's at 400 ci providing you can get enough traction, the gear ratio is aggressive enough to get the car off the line good, and you are good at shifting the manual box. The first 60' mean a lot when talking about drag racing ET, so you're right on target w/a 3.73 rear gear combined w/the Tremec 600 transmission.

Stroking it would be great if it's in the budget.

i plan on pulling the heads this weekend, but at a minimum i will replace the rods w/ eagles and port the heads.

Good deal. This will give you the opportunity to measure how far down the cylinder the pistons are at TDC (piston deck clearance), as well as to see what the piston type (forged or cast), and design (flat top/dished) is as well as the number of valve reliefs (some rebuilder-type pistons have 8 valve reliefs to accommodate both early and later valve angle, this adds volume to the piston "dish" over what a 4 valve relief piston has). Obviously this will be the time to CC the combustion chambers as well.

The reason for all this measuring is to know what the static and dynamic compression ratio is, as well as the quench distance. A page w/links to dynamic CR calculators is here. Other areas of the valve train that need to be verified can be found at the links below.

The following may be putting the cart before the horse, but if you're considering swapping to 1.6:1 or 1.65:1 ratio rocker arms, check the fit/relieve the pushrod holes to allow the pushrods to fit correctly while you have the heads off. Not necessarily that I think you need more lift, but just in case.

• Valve train points to check
• Valve train geometry
• Valve spring installed height
• Adjusting solid lifters

[actmobmar]

would the additional lift be of any benefit? also, what is an easy way to check how far the pistons are down in the bores(deck height), as i've never checked that, w/ the chevies the machinist always checked. i have dial indicators and calipers, i was thinking a straight edge over the deck w/ a depth caliper over it, get the number, subtract the thickness of the straightedge and that would be my measurement?

[cobalt327]

Originally Posted by actmobmar

would the additional lift be of any benefit? also, what is an easy way to check how far the pistons are down in the bores(deck height), as i've never checked that, w/ the chevies the machinist always checked. i have dial indicators and calipers, i was thinking a straight edge over the deck w/ a depth caliper over it, get the number, subtract the thickness of the straightedge and that would be my measurement?

I have found that unported D-port Pontiac heads (like your #48's) work well w/around 0.480"-0.500" lift. If the heads were ported you would see more benefit from more lift.

What rockers are on it now? The stock Pontiac rockers will spec slightly less ratio than advertised, but aren't as bad as most stock Chevy rockers. If you have stock rockers you'll pick up a little lift just having an accurate 1.5:1 ratio.

Using higher ratio rockers will require the springs be checked for coil bind, along w/the other clearances mentioned in the previous links like piston to valve clearance, rocker to retainer, retainer to seal/valve guide boss, etc. Good pushrods should be used.

Even w/stock rocker arms/ratio you should use straight wall studs (as opposed to the stock bottleneck studs). ARP p/n 190-4003 or BBC studs will work.

You can use a straightedge like you described. Measure to the piston's 'quench band' (top image) if the piston has a dish or dome. Do not measure to the bottom of the dish/valve relief or the top of the dome, in other words. Take the measurement directly over the wrist pin (red arrows bottom image). Measuring over the wrist pin will keep the piston rocking in the bore from skewing the measurement.

[actmobmar]

thanks for the input! i currently have harland sharp 1.5"s on it, and also have harland 1.65's as well, so i do have both

[cobalt327]

Originally Posted by actmobmar

thanks for the input! i currently have harland sharp 1.5"s on it, and also have harland 1.65's as well, so i do have both

Good rockers. If you think there's any chance you might want to run the 1.65's, go ahead and open the pushrod holes up now, while the heads are off. I'd go ahead and check all the clearances, too just to be sure. That way all you'd need to do is swap rockers and lash the valves.

In my experience changing only the rocker ratio hasn't required a different p-rod length, but it never hurts to check to be positive. You can check for the correct p-rod length during the mock-up phase or even when the 1.65 rockers are installed by using an adjustable pushrod.

Click on image for details on making this tool:


Other homemade pushrod length checking tools at HomemadeTools.net

[actmobmar]

i pulled the head off the pass side, piston to deck is .006-.008, so block has been decked. there are no numbers on the pistons, i think they are kb hypereutectics? they have a dish w/ 2 valve reliefs. i am thinking about porting the heads and putting the engine back together- everything inside looks perfect. what do you guys think? i just have alot of money to spend on other parts of the car

[LATECH]

Get a positive ID on those pistons so you can determine the CCs of the reliefs. That way you can figure your CR.
Porting ....yes...mild.
Clean up inside the bowls (behind the valves) and the runners. Clear any flashing from the port openings and gasket match the openings.
Dont go whole hog in the runners. Hogging them out will not improve street performance.Stock runners perform well with just a smoothing and some short turn radius work . Lower the port floor a little at the short turn radius ...a little. Take a little of the bend out of it.
Any bumps in the runners should be removed. Myheads had some wierd little bumps in a few of the ports. I suspect they were ID marks on the original casting mold to ID them, and the marks just transfered to the part when it was cast. look in there, you will see em.
Keep it simple when porting and dont over do it. When porting , imagine water flowing through the heads and how it would flow better. Air will act similar. Not sure if you can picture that but it was put to me that way, I think I kinda get it.