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-   -   '76 sbc build , need more head advice (http://www.hotrodders.com/forum/76-sbc-build-need-more-head-advice-134084.html)

TheCiscoKid 02-25-2008 08:09 PM

'76 sbc build , need more head advice
 
I'm not a mechanic, I'm building a 38 Chev,have it running,but it's not running as strong as I hoped.I have a 350 trany (I like them),a 2:73 10 bolt posi,finding an axle in the right width took some time,never found anything else.I know some of you told me this is tall ,but final drive is less than a 700r with 3;73 or 3;42.From my driveway it's at least 10 miles to any stop sign.This car will mostly be highway driven, maybe pass.Someday I'd like to put in a 383sbc.
I have a good 76 4bolt sbc, I know it's low compression year.I used a RV cam 204/214 ,same as Performer stat, Performer intake and carb, shortie headers.I haven't recurved the distributor yet.
If I keep my heads, is there a better cam choice?
If I change to 64cc heads,choices SR torquer $800, S&D has vortec kits with intake for $1000, but I'm thinking if I have to spend this much ,I should look at aluminum heads.Whats good? I've asked about Patriot or Pro comp and been told they'r junk,but why? Are Edelbrock Etec heads a good choice?I'm leaning more to the vortex style as I'm reading they should help mileage.
Cisco

barnym17 02-25-2008 09:02 PM

true the final drive in high gear is close but the over drives have the advantage of deep gears off the line. I beleive you can get what you are looking for with a gear change. I would go to a 3.42 or 3.73. an example would be if your engine makes 200 ft.lbs of touque the 2.73 gears would multiply this into 546 ft.lbs of tourque. a 3.73 at the same speed would be 746 ft.lbs at the rear wheels.Now this is just an example using a easy number to work with but you see the point. No head change by itself will give you anywhere near an extra 200 ftlbs at the rear wheels at the same speed.

techinspector1 02-26-2008 10:18 AM

"it's not running as strong as I hoped"

You may not have enough static compression ratio to run even that relatively mild cam. The cam calls for a s.c.r. of 8:1 to 9.5:1, with good middle ground being 8.75:1 to 9.00:1 and I'll bet your motor is lower than that. The advanced intake closing point of the cam over the stock one is bleeding off too much compression, resulting in low cylinder pressure. Have you done a compression test on the motor? If not, warm the motor, pull all the plugs, disconnect the coil, wire the throttle blades wide open and test each cylinder through four or five revolutions (until the gauge won't climb any higher). Then report back here.
http://www.volvoadventures.com/howto...ompression.htm
http://www.valvoline.com/carcare/art...cid=5&scccid=5
http://64.78.42.182/sweethaven/MechT...Num=7&modNum=6
http://www.misterfixit.com/dyncompr.htm

firestone 02-26-2008 10:49 AM

In order to get a head that will perform significantly better than the vortecs in your application, you will probably be spending ~$1500-$2000. Even then, you will probably only be looking at a ~30 hp difference assuming you will have a somewhat low lift cam. `

I had a vortec headed 355 (listed below) that ran awsome once I threw some gear at it. I originally had a 700R4 with a 2:73 rear gear. I switched to a 3.90 and noticed more of a performance difference than I did when I switched from a 30 year old stock 307 to the new 355. If you are going to keep your gear, I would recommend a 2200 stall at least. I had a 1900 at it was not enough with the 2:73 gears. With the 3.90's it was about perfect though.

355
10:1 compression
xe268h cam (224 230 @.050 .477 .480 lift)
performer RPM intake
650 holley DP
1 5/8th inch headers

It got ~18 mpg on the highway.

Adam

TheCiscoKid 03-10-2008 09:19 PM

'76 sbc build , need more head advice
 
Sorry ,I took awhile to borrow a compression tester.I just took readings, and put the car back together,what a pain getting plugs back in.It's fricking freezing in the garage too, -30 outside.Now I re-read the instructions posted here on how to do it.Sorry,I did not warm up the car, been sitting for months, didn't open the trottle.The compresion was 80 -85 on 6 cylinders, maybe 65 lbs on 2.
My cam is a Summit 1102, same as performer.I don't have an adjustable timing chain.I've been looking a heads and mine are 487, large chamber but should be a good head. Cisco

TorkMonster400 03-10-2008 11:09 PM

I was impressed with GM fastburn heads there not that expensive either maybe even ported L98 heads they can be had real cheep, but it has 58 cc chambers. With it being a truck motor lots of torque would be good.

opelitis5 03-11-2008 05:59 AM

You HAVE to do your CR test over. Bring it up to operating temp. then pull all the plugs and block the throttle OPEN... Get someone to turn the engine over with the key and you hold the CR guage. Count 5 - 6 hits on the guage until the CR does not go up any more. Record your numbers on each cylinder and get back here with your results.. If you have a vaccum guage do that test also and record the number and if the needle is jumping arround on the guage and between what numbers is it moving arround..
Don't put ANY bux on the engine until you test the engine as much as you possibly can!!!! Very IMP... Where is Picton??? Get back with the numbers B 4 U do anything else...

DoubleVision 03-11-2008 06:14 AM

I agree, do the test over, if the readings are still that low, it's no wonder the engine doesnt have any power.

TheCiscoKid 03-11-2008 07:41 PM

'76 sbc build , need more head advice
 
warmed up the motor, starts well, runs smooth.Did compression test.Wired trottle open , 6 cylinders were 95-100lbs, one was 85, one was 75lbs.The gauge is Snapon so it's prob OK.Someone else did the tappet adjustments, if the lifters weren't pumped up and the tappets adjusted could the lifters now be taking the valve off the seats or are the heads toast/Or is my cam blowing it all out? thanks guys, Cisco

DoubleVision 03-11-2008 08:12 PM

You got problems somewhere. I think its time for a tear down. A leak down test would tell you where the issues lay.

TheCiscoKid 03-12-2008 04:23 AM

'76 sbc build , need more head advice
 
Crap, just got it together before winter.I'll do a leak down test, I think it's probably valves as motor doesn't smoke.Motor had 70,000 on it.
BTW ....Picton is in Ontario,Canada.I work in the town Avril Lavinge comes from.If it gets much warmer my 30 x 40 igloo garage will melt soon. :oP
Cisco

454C10 03-12-2008 07:20 AM

sounds like the cam is installed wrong. retarded cam timing will cause very low pressures like that.

As for heads......I would use a set of edelbrock heads, 64cc chambers, 170cc intake ports. I would also use the regular performer heads with the exhaust crossover (not the rpm heads). This will come in handy when it is cold outside and -30 is pretty cold.

vortec heads are nice and would match your cam very well. be they need special rocker arms, valve covers, and intake manifold and machine work to run a cam with more than 0.450" lift so it ends up costing the same or more. And they flow terrible on the exhaust side.

you should get fairly good performance even with a 2.73 gear if you can make some more cylinder pressure.

opelitis5 03-12-2008 08:01 AM

Good morning!!! Ask arround to find a trusty engine/machine shop in your area.. Yah gotta be near the Ottawa Valley or close thereabouts... Did you put oil into the cylinders after you had the low readings??? Try and get a spoonful into each spark plug hole and see if your readings go up or if they stay the same... Staying the same means valves and going up readings means rings... Either you do a leakdown test or get the above trusty shop to do it... Make your decision after that as to exactly how much you would spend, what exactLY you want the engine to accomplish... Sit down with the engine shop person of your choice and discuss exactly exactly what you want and how much you want to spend... Keep it all under one roof ... so to speak as if you go to 4 different spots, if something goes astray (wrong) they will have built in excuses as to "well we did not tell you to do that or buy that or go that way". Do it right the first time and yah won't have to go back and do it over... Maybe the shop will have a great deal for you sitting on the shop floor for a great price with a guarantee / warranty???
Lotsa people will give their own ideas and some are great, but yah gotta start with a good base or all the heads / cams / intakes / carbs ain't a gonna do you right if you start off with a "wheezer"
Don't spend a dime until you do the above, for your own sake!!!

red65mustang 03-12-2008 09:39 AM

Cisco,

"if" the rotating assembly is sealing decent and all is ok, your vac guage will tell you....a rv cam motor should read 25Hg+ when decelerating back to idle from about 3k...read this link for diagnosing a motor with a vac guage (kinda cool, the guages are "animated")

http://www.users.bigpond.com/ergoff/vac1.htm

to get a even more accurate reading, rig your vac guage so you can read it while driving (windshield wiper hose and a T in the manifold vacuum advance line and duct tape it to the windshield?)

"if" the rotating assembly is sealing as it should it will read 25Hg+ (28Hg=really good) and steady(!) when down shifted 3rd to second at 3k rpms "with a load on the motor" (which is really what you want to know, how well is it sealing while actually driving)

"ballpark" with a rv cam your comp test readings should be atleast:
8/1+CR=140-150psi
9/1+CR=140-170psi
10/1CR=180+

the specific cam and how it's installed and at what "altitude" are you doing the test does impact the results you see "some" (ex: a motor that tested 180 at sea level will test around 160 at 5,000 ft)

ps: that link points out just some of the reasons you DO want to have a vac guage "in" your car...to see a new problem immediately

TheCiscoKid 03-17-2008 08:53 PM

'76 sbc build , need more head advice
 
OOPS, never done a CR before. I was using a hose with CR tester that had a short male connector at spark plug hole like the sprk plugs, looked at the long connector hose today and tried it.Compression was way up,instead of 95lb was 150-160, but 2 cylinders were still down at 130-135Lb.Oil brought them up to 145lbs.Don't know why 2 cylinders won't be down like that.Guess motor is screwed.
I have a friend that deals and plays with cars.He has a SBC that he had custom built ,took motor out when he sold car and it's been sitting.I know he never drove the car much.He offered the motor to me. It has a good crank and rods,10:1 forged flat top pistons, 461 heads,290*/500" cam.The down side for me is maybe the compression, but for sure the cam.He ran a 3500 stall convertor and I don't want to.
I have a TH350, 2:73 10 bolt, performer intake and carb, shorty headers with 2'' exhaust.I live in the country, no stop and go traffic, so all I want is to cruise in this car. I've spun enough rubber on 2 or 4 wheels in my day.
I have a Summit 1102 cam,(204,214@ 420,442),will this cam work well for me with that compression? Should the valve springs in the new motor be OK with the 1102 cam.Think I can run 87 octane?
Cisco


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