My new engine is a dog!!
- Thread starter crushnut
- Start date
-
Sponsors (?)
sounds to me like you have a few problems here;
1: you do have a timing issue be it advance and/or initial timing. check to make sure the vacuum advance is working properly, and that the mech advance springs are not too light, or heavy, and that they control the weights like they should. initial timing should be set at 10-14 initial and total timing should be 36-40.
2: cam timing and compression sound like they are incompatible. you gave some specs for the cam, but what is needed is the valve overlap spec. if it is low(below 30 degrees) then you should be ok as it will add dynamic compression. if it is high(above60 degrees) then you lose dynamic compression. for a low compression engine you need low overlap, and it sounds like you have high overlap, and low compression.
also who's cam did you buy? i usually recomend something like the he260h, or the he268h from comp cams, or the performer or performer rpm cams from edebrock. these cams are designed for low end and mid range performance and are perfect for the daily driver. your carb selection is fine, but you may also have a vacuum issue, but i think that is related to your cam choice, and the lower compression than you expected.
1: you do have a timing issue be it advance and/or initial timing. check to make sure the vacuum advance is working properly, and that the mech advance springs are not too light, or heavy, and that they control the weights like they should. initial timing should be set at 10-14 initial and total timing should be 36-40.
2: cam timing and compression sound like they are incompatible. you gave some specs for the cam, but what is needed is the valve overlap spec. if it is low(below 30 degrees) then you should be ok as it will add dynamic compression. if it is high(above60 degrees) then you lose dynamic compression. for a low compression engine you need low overlap, and it sounds like you have high overlap, and low compression.
also who's cam did you buy? i usually recomend something like the he260h, or the he268h from comp cams, or the performer or performer rpm cams from edebrock. these cams are designed for low end and mid range performance and are perfect for the daily driver. your carb selection is fine, but you may also have a vacuum issue, but i think that is related to your cam choice, and the lower compression than you expected.
jerry S
New Member
I have no informed contribution to make here but I have an observation
and it is that threads like this demonstrate that the collective experience and knowledge of stangers here is top notch. You guys who know and who are willing to share your experience and knowledge make this place a veritable brain trust. Well done all. And in good form too.
and it is that threads like this demonstrate that the collective experience and knowledge of stangers here is top notch. You guys who know and who are willing to share your experience and knowledge make this place a veritable brain trust. Well done all. And in good form too.
rbohm said:
Can you elaborate more on the valve overlap spec. that you were talking about please? The only other specs on the cam card are SAE timing and .050 timing.
SAE Timing- BTDC 27, ABDC 73, BBDC 75, ATDC 34
.050 Timing- BTDC -6, ABDC 30, BBDC 43, ATDC -9
Does that help any
I also was mistaken about it being a RV cam, it actually is a Melling performance torque cam/lifter set. I bought it off a guy on ebay, this is straight from the description he gave in the auction:
"This is a Melling MTF-1 camshaft with lifters. Duration at .050, Int. 204, Exh. 214, Adv. duration Int. 280, Exh. 290. Valve lift Int. .448. Exh. .472, Center lobe Int. 107 Exh. 114. Characteristics-1962-85 CLASS 1, TORQUE CAMSHAFT, GOOD IDLE, GOOD LOW END TORQUE AND PULLING POWER"
ratio411
Founding Member
That is the classic description of "RV" cam.
When folks use the term RV, it means more recreational car, cruiser, nice pick-up, sunday driver... etc.
A smooth cam that makes plenty of torque to move your ride and get you stoplight to stoplight without revving to the moon.
That sounds like a nice street cam. Cams like this are designed to make more vacuum and cylinder pressure. This allows you to run your power accessories and use streetable static compression.
Things that help you with you "recreational" driving.
Dave
When folks use the term RV, it means more recreational car, cruiser, nice pick-up, sunday driver... etc.
A smooth cam that makes plenty of torque to move your ride and get you stoplight to stoplight without revving to the moon.
That sounds like a nice street cam. Cams like this are designed to make more vacuum and cylinder pressure. This allows you to run your power accessories and use streetable static compression.
Things that help you with you "recreational" driving.
Dave
mdjay
Premium Sponsor
IMO I would change the carb, and see how it responds. 625 would be a good place to start. The rv cam may be part of the issue, but I still think she wants a lot more air and fuel.
If possible, just borrow one from a friend to see if it makes a difference.
If possible, just borrow one from a friend to see if it makes a difference.
1320stang
Founding Member
Sorry, that's CB talk. Your location says something about King Kong. Are you in New York City?
If you're in central Oklahoma, I'd offer to give you a hand. Likewise, if you were somewhere near one of the other members, they might be inclined to give you a hand. Kind of a problem when you don't fill out your profile like it was intended, we have no idea where you are. I've got a 4100 and a Holley 600 we could try out.
If you're in central Oklahoma, I'd offer to give you a hand. Likewise, if you were somewhere near one of the other members, they might be inclined to give you a hand. Kind of a problem when you don't fill out your profile like it was intended, we have no idea where you are. I've got a 4100 and a Holley 600 we could try out.
Im in Oregon, well.... i did some checks today and the compression test turned out good, all the cylinders are firing, spark plugs looked good, no vacuum leaks that i could find. I played around with the carb some more and the timing. Set the intial at 10 and check that my mechanical advance was working and it is. So it has lead me to beleive it is carb related also. It almost feels like i am only using the primaries when i drive, i never feel the secondaries kick in Any ideas?
Thanks
Any ideas?Thanks
ratio411
Founding Member
Crushnut------- what brand & part # pistons did you use ? What is their pin height ( compression height or distance from the pin center to the top of the piston) Do they have two or four valve reliefs? Did you happen to measure how far down the bore they are at TDC? What head gaskets did you use ? Were your rods reconditioned? All these questions need to be answered to accurately determine the comp ratio. Not all flat top 302 pistons actually place the piston tops at or near the block's deck surface. Many so called flat tops end up with a -.020-.040 deck clearance.This makes a huge difference in the comp ratio on a smalll displacement motor like a 289 or 302 Also depends on what year block you have too as the others have mentioned.
brianj5600
Active Member
What timing chain set did you use? Some of the early smog motors like 74s retarded the cam which does nothing for performance.
This discussion about static and dynamic compression is interesting, and it's a great tangent, but I think you have enough cam and compression to run fairly well. I also think you have a timing issue.
Maybe you need to find true TDC and see if your harmonic is lined up to 0 degrees.
Also, (shhhh) I have MS Office on a disk that I might be able to share for a..ahem...trial period, if you really need to get Excel....ahem.
Maybe you need to find true TDC and see if your harmonic is lined up to 0 degrees.
Also, (shhhh) I have MS Office on a disk that I might be able to share for a..ahem...trial period, if you really need to get Excel....ahem.
The Edelbrock/AFB's have mechanical secondaries. There's a linkage on the passenger side that controls them. If you think the secondaries aren't opening check your choke setting. If the choke doesn't open all the way the secodaries won't open up.
ok to determine you valve overlap, the time at which both valves are open at the same time, you will use the sae timing numbers as in this case they are more accurate. take the number at which the intake valve opens, and add the number at which the exhaust valve closes, which in this case the intake opens at 27 btdc, and the exhaust closes at 34 atdc. adding them together gets you 27+34=61 degrees of valve overlap. thids means that this cam was designed to work with an engine that has a compression ratio of 9.5-10.5:1 so you can lower the dynamic compression ratio at low to moderate speeds to reduce or eliminate detonation, while keeping good overall engine power. since it sounds like your compression ratio is much lower, likely closer to 8.0-8.5:1 you need a cam with a shorter overlap period. and lest anyone question why you use the sae(advertised) timing numbers over the .050 timing numbers, remember that when the intake valve opens there is still positive pressure in the cylinder, and this pressure along with piston movement is what is used to bleed off cylinder pressure to lower the dynamic compression pressure at low speeds. at high speed this makes no real difference as everything is moving too quickly for it to.crushnut said:
D.Hearne said:
Not totally sure but i will answer what i can. They are Sealed Power pistons, part# 272AP. They have 4 valve reliefs i think? I didnt measure how far down they were when i installed them, but i remember them coming almost all of the way up at tdc, real close. I used Felpro head gaskets (they were in a full rebuild gasket kit) The rods were checked and magnafluxed. The block is a 74' 302.Now that i think about it, i think they are slightly dished on top. These are the pistons that my machine shop recomended for the rebuild. This is the only info that i could find on the piston box before i threw it away:
skirt size 4.02825 +/- 0.00025 inches
size point 2.30 from top of head
Minimum Clearance .0015
This is my first rebuild and i probably screwed it up by just throwing a whole bunch of parts together and thinking it would work
Man, that ticks me off!! 
Similar threads
