How many RPM's do you lose?

[kevnmcd]

Just curious has to how many rpm's everyone else loses in the heat. In April I was able to get 5400 out of my 502 Mag...this past weekend at Mohave I was only able to get 4600 out of it. :cry: It wasn't that hot either cuz the cloud cover from the thunderstorms...+/- 90-95° Anyone else having this much loss? :notam:

[Infomaniac]

I bet the valve springs are going dead. Do a compression test. If OK a valve job will probably take care of it.
Unless it has a ton of hours.

[djunkie]

The last couple trips out in the heat I couldn't get it over 4800. Usually see around 5200-5300. I think i've got some carb issues though now since I fouled a couple plugs this last weekend.

[CrazyHippy]

i go from 8700 w/ a 32" to 8300 w/ a 32"
or 8600 w/ a 30"
Lose alot fo the mid range punch in the heat too
BJH

[kevnmcd]

I bet the valve springs are going dead. Do a compression test. If OK a valve job will probably take care of it.
Unless it has a ton of hours.
Ron - I have 416 hours on it. I was planning on doing a compression check this weekend to see what was going on. How would the valve springs going dead effect it? :confused: When they go dead are they just not able to close the valve fast enough at the higher rpm's thus losing HP?? If that is the case then I shouldn't see a loss of power out of the hole which I am? :(

[SmokinLowriderSS]

400+ hours is a lot on a boat engine from what I have been hearing. Maybe rings loosing their seal as well. Do compression check and see if basic engine health is OK. At that kind of hours, may be all sorts of worn parts inside.
Rebuilt my 454 last winter, estimate about 300 hours (meter broke long ago & not replaced), rings were stil great but timing chain was thrashed to within an inch of it's life and all the factory A-400 big-end bearings were washed out. Upgrade I did necessitated rod work so rebuild happened from scratch.

[jbone]

I have 30 hours on my engine. I don't notice very much rpm loss at all.
But my engine is a stock 502 carb turning only 4800.
J

[Squirtin Thunder]

I bet the distributor is going bad. The 502's have a habit of eating the cast gear on the distributor. Also the bushings inside the distributor go to shit too. Check it out !!! Cheap quick fix !!!

[OMEGA_BUBBLE_JET]

maybe 200 rpm difference. Have seen as high as 5400 in cool weather and as low as 5200 in HOT weather.
Omega

[SmokinLowriderSS]

In Kansas here (only 1400' elevation on average) I've only noticed about 50RPM drop from a cool morning first blast to the rest of the 100+ degree day. Most of my loss is my covered engine retaining a good deal of heat in the air the rest of the day.

[77charger]

in hot heat my stock 350 mag loses power too.Feels little sluggish compared to mornin.Drop about 3 mph from the big top speed of 59-60 mph too.
Also at powell i drop power too usually about 2-300 rpm.
With the race boat i was driving 110 deg humid i went 9.60s in nov same year cold low to mid 60s,perfect air went 9.30s in the 1/4