compression numbers

[twbowhunter]

i just got my sons 68 bronco with a 170 put back togeather after a frame off resto and i can not get this thing over 50mph,i am running 33inch tires with 411 gears. i pulled the plugs and did a compression check and came up with this 125,120,115,115,105,110. i am not really sure how this is for a stock 170? thanks for any input

 

[fordconvert]

For a used stock motor that looks all right to me. Was that hot and dry? Or cold? Could be a little closer but that shouldnt be your biggest problem. How is the rest of the system? Ignition and carb? What RPM is it turning at 50?

 

[twbowhunter]

it was hot and dry, just put the pretronix on it and had the carb rebuilt,it seamed to help a little when i opened the plug gap to 45 but still cant get 50 mph, i took it to a guys house that has the same motor carb ect and wanted him to drive it as soon as he started it he said he could tell it was not near as peppy as his,im woundering if i could have a valve adj problem or a blown head gasket cause i do have a slight oil leek at the head gasket on the dist side

 

[rbohm]

8) while you have two cylinders that are a bit low, they are with in spec. try advancing your timing several degrees, since the six can usually use more timing than stock. also check the action of the vacuum diaphrams in the dist for proper operation. check the points for proper gap, and check the coil for proper output. i would run a duraspark ignition system and get rid of the ponts by the way.

one more thing, you may not have enough gear to deal with the large tires with the small engine. i think a 4.30 gear might work better.

 

[Lazy JW]

8) while you have two cylinders that are a bit low, they are with in spec. try advancing your timing several degrees, since the six can usually use more timing than stock. also check the action of the vacuum diaphrams in the dist for proper operation. check the points for proper gap, and check the coil for proper output. i would run a duraspark ignition system and get rid of the ponts by the way.

one more thing, you may not have enough gear to deal with the large tires with the small engine. i think a 4.30 gear might work better.

I agree. Your engine is a bit weak, the tires are too big, and the gearing a bit tall. Still, it should hit 50 no problem. I suspect that your ignition advance isn't getting enough advance at speed. Easy way to check is to keep adding more initial advance and test driving.

A DS2 with a hot coil would be a good plan.
Have fun,
Joe

 

[twbowhunter]

thanks for all the input im going to check on some of these today,also i stumbled on what i think is a 200 (it has 5 freeze plugs ) my next question is would a 200 make a noticable difference ?and will my 170 dist go in the 200?also are all 200 the same or could i run into problems with this swap because of different years ect?

 

[rbohm]

8) the 200 will make ia difference, and yes your 170 dist will fit the 200.

 

[twbowhunter]

i just got back from checking the compression on the 200 it had 175 with two comeing in at 150,dose this sound like it might be a better motor for me? also while i was there a couple guys were looking at the motor that is in the bronco now and you can turn it over by grabing the fan blade and all the plugs were in it thanks again for the imput

 

[rbohm]

8) i would go for the 200.

 

[250mav]

you getting enough fule?

whenever i cant get a car over a low mph like that its usually time for a new fule filter

 

[mugsy]

105 to 125 sounds too low to me. You might want to invest in a leak down tester. The other thing would be to raise the piston to TDC and then hit that cylinder with compressed air. Listen to the intake thru the carb, exhaust/tail pipe and oil breather cap. Where you hear the hiss will tell you if the intake valve, exhaust valves or the rings leak. I don't have my FSM with me but I think the spec for a 200 is 150 plus/minus 15 psi.

 

[addo]

If you use the "Bowling and Grippo" calculator it gives about 2125RPM at 50MPH, with the present setup. It should hit 82MPH at 3500RPM.

While gearing may not be ideal, I don't see it as the main issue. I'd be looking at the advance curve, and also checking cam timing/lift.

 

[fordconvert]

The 170's would have had Load O's wouldnt they? I wonder if he has a miss mash for dizzy control? Even with the right combo of parts I suppose the extra load of his setup would make the vacuum weak and knock the advance down before the R's get it back in. Maybe an adjustable vac can would help. I have also heard that buying an inline valve at the fish tank store can help regulate vacuum to the dizzy.

Another thought, what transmission you running? If its an auto is the downshift cable and vacuum modulator working right? I had a 1 ton dually with a 11" dump box and 8' snow plow that had a 305 in it. As long as I kept my foot on the floor (down shift engaged) the thing would keep up with average traffic. When the downshift switch was not working (THM400's were electric) the thing had a tough time getting out of its own way. With all the transmission stuff hooked up and working it kept the R's up high enough for the smaller motor to stay in its peak output areas.

 

[twbowhunter]

im running a np435 4 speed, is there a way i can tell what dist i have? also i checked the vacume and its at 14#and a little shakey

 

[fordconvert]

Im not an expert on the dizzys. The load o's dont have any advance springs or weights. They also tend to have fairly flat vacuum canisters with a treaded fitting. The regular have the springs and weights. Do you have a timing light? Should be easy to figure out with a timing light. With that setup you are going to need everything to be just right.

 

[Harte3]

14hg at idle? I think 17 hg would be minimum acceptable at idle. I can see 14 hg possibly at hwy cruise speed...maybe a little less with your tall ratio but certainly not at idle.

 

[twbowhunter]

just finished adj the valves they were all a little snug seams to idle smoother and the vacume now is 20 and steady also i ran it down the road and it hit 52 mph i still have an oil leek and maybe a bit of water comeing out of the head gasket on the driver side could this possible be a huge horsepower gainwen the head gasket is changed

 

[addo]

Hey, if you're going to pull the head - a few things:

Measure and calculate the compression ratio.

Skim cut the head if needed/affordable.

Check both the block and head for true before refitting.

Clean the block threads and oil or grease all head bolts.

When torquing, after the first torque wait 20-40 minutes.

After the second torque, wait a couple hours, or overnight if possible.

Don't use inhibitors for the first week of running. Just pure water.

 

[Mercury Mike]

For the record, the 170 and the 200 Dizzy are different! While they're both load-o's, the 170 will have a smaller gear (hex bar) to the oil pump. =)

 

[rbohm]

For the record, the 170 and the 200 Dizzy are different! While they're both load-o's, the 170 will have a smaller gear (hex bar) to the oil pump. =)

8) only through early 64. after that they changed to the same dist as the 200's. i know this because i have an early production 64 falcon with the 170.