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Discussion Starter #1
A little background first. 1996 Bronco 302 (MAF).

I pulled a 302 from a mustang and rebuild the block .030 over with hyper pistons. Crank is cut .010/.010, rods are stock, new bearings [obviously]. I used stock pushrods and rockers but stuffed them into iron GT40's from a lightning (with stepped washers on the new head bolts). New oil pan, pickup, pump. New timing cover (built the motor then did the swap because we wanted downtime to be limited) and new water pump. New distributor, cap/rotor/wires/plugs. New double roller timing set.

Edelbrock truck upper and Mustang lower (a screw up from the guy I bought the parts from nearly a decade ago). Tapped the EGR port for the truck and closed the port in the rear center from the car. Ignition timing (spark) is set to 10 degrees BTC as a start.

I used the mustang cam as many others here have said it gives more than the truck cam does.

The problem is low vacuum. It is steady and not erratic, but at idle gives my 12". If I tip the throttle in slowly, it increases to 15, then decreases to 5 quickly. Anything from 3/4 throttle and up and I have good power, but anything less and it is a dog.

I pulled and capped all the vacuum lines from the intake after checking for leaks (as best as possible) around the intake, and that did not change anything. Pulling the y-pipe off let's it come up to about 15", but that is still low (the cats are 14 years and 225,000 miles old so I expect them to be a little plugged anyway).

http://www.classictruckshop.com/clubs/earlyburbs/projects/vac/uum.htm indicates late valve timing. I have the adjustable timing set, but swear I set it up straight up. There are different marks to indicate straight up, +2 and -2.

ANY other thoughts before I tear into the front of this new engine?????

:banghead :banghead :banghead
 

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Satyr of the Midwest
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Was that baseline ignition timing set with the SPOUT connector removed? Have you done a compression test yet? How do the spark plugs look?

I think you meant GT40 heads, not GT30. ;)
 

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Yeah Sig, 40. I didn't catch the typo, I'll fix that in the original. :D

Plugs are new and look it, and yeah, with the spout out. I actually brought it up to 1500 or so to seat the rings and left the spout out and the headers got really hot, prompting me to recall the spout plug, put it back in and let it calm down. Dummy.

I did compression and five were at 125 and the remaining three at 120. The "lower" ones were not adjacent cylinders either.
 

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Discussion Starter #4
Well, the bad news is that the cam IS installed straight up.

The good news? There isn't any. Guess I try to advance the cam 2 degrees and see what happens. :banghead
 

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Satyr of the Midwest
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Those compression numbers are pretty low, like normal for an engine with 300,000 miles on it maybe. It should be up in the 160 to 180 psig range, for a healthy or fresh-rebuilt engine, IME. Were all of the plugs removed and the throttle propped wide-open? Did you try squirting engine oil into the spark plug bores to see if compression would change (to verify either bad rings or bad valve sealing)?

The only other ideas I have for suspects to investigate would be the PCV system, and the EGR modification. First, make certain the PCV valve is functioning properly, and that the fresh air inlet path is clear; having a crankcase at the wrong pressure level can be very detrimental to performance. Second, regarding the drilling for the EGR port, I'd go back in and verify there aren't any cracks or holes where there shouldn't be.

Oh, one more idea: on those GT40 heads, were the valves seated properly?
 

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Discussion Starter #6
Sig, I had run the compression numbers by just removing one plug at a time. I just removed them all and opened the throttle all the way. #1 went to 130. I added some oil and it went to 160. :banghead

These are new rings, not file-fit, and the end gaps measured out properly. I installed them staggering the openings.

Am I looking at pulling this apart to put in new rings?
 

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I wouldn't get too excited about the rings just yet.
Dig up and review the instructions that came in the box then try and remember if you installed them on the pistons correctly. There IS a top and bottom for the top and center rings. Aside from that, you might have broken one accidently, or maybe even two. But breaking all 8 top rings without knowing?....naw, that aint likely.
You said that the end-gaps were right but how about side clearance inside the piston lands? You should be able to insert a .001 feeler gauge between the ring and the land, but a .002 should not fit on a new Ass'y.

Personaly, next thing I'd do is a simple leak test. All you need is an adapter that allows you to introduce shop air into the cylinder. I made mine by breaking all the guts out of an old spark plug and welding a steel fitting onto the threaded shell. If you don't have the means to do that, you can buy a "tool kit" that does the same thing.
Turn the crank untill the piston of the cylinder you want to check is at BDC, loosen/remove the rocker arms on the same cylinder and introduce 100 PSI of air through the spark plug hole. You'll know real quick whether that particular cylinder is sealing. If there's a leak past a valve, you'll know that real quick too.

Other thoughts;
I bought a new TC set once that had the crank gear "dot" stamped-in in the wrong place. Stuff happens.
A dial indicator can be used to possatively identify #1 TDC....and a dial indicator plus timing-tape on the balancer will show if your cam is out of sink with the crank. Both of those things are essential to know and checking them first sure beats multiple tear downs while guessing where to install your "adjustable" TC set.
If the shop you used put too coarse of a cylinder finish for the type of rings you used, it is possable that you've wore the sharp edge of the top ring off while trying to seat them. Particularly if your rods are of the variety that do not have "squirt holes" and/or if you ran the engine at a constant RPM for a long time.......I've seen it happen.

The gist of what I'm saying here is that as-of your last post, you haven't done enough thinking/checking yet. It's better to check stuff than randomly start tearing stuff down.

Hope something here helps.

DGW
 
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