low compression on the dyno?

[99 gst spyder]

I have a 1ga stock motor with 272's, mods in profile. Compression is sitting at 130 across the board and was wondering if it can be tuned the way it is being in the lower compression range. Any ups and down if it being on the dyno. I wanted to get it tuned with my mods and be able to just drive it around.

Thanks.

 

[bryanwheat]

With bigger cams that sounds pretty acceptable. IF they are all the same than that is a good indication that there is not a problem.

 

[brian9397gsx]

You will be fine, the larger overlap of the cams cause your cranking compression to go down.

 

[99 gst spyder]

How low of an compression be for my situation for it not to be on the dyno?

 

[Chicken Patty]

Was the compression test done with the car hot or cold? Throttle open or closed?

I have Kelford 272's and I have 185 all across on a 212k mile old stock 7 bolt. Same as I did with stock cams. Although I rather have low but even compression over high but uneven compression, that's still a bit low for my liking. But that's just me.

 

[99 gst spyder]

Was the compression test done with the car hot or cold? Throttle open or closed?

I have Kelford 272's and I have 185 all across on a 212k mile old stock 7 bolt. Same as I did with stock cams. Although I rather have low but even compression over high but uneven compression, that's still a bit low for my liking. But that's just me.

Compression was done with the motor hot at 230* coolant temperatur and wot. Stock radiator only has a small 10" slim fan on maybe that's why it gets a little hotter. I'm waiting to put a new aluminum radiator with two 12" pusher slim fan rated at 1750 cfm so hopefully that'll help the overheated radiator.

 

[JacksonAuto]

All engines that I've done a compression test on that had 272's had at least 165 psi. 130 seems low. Was the battery fully charged? The lower numbers could be a result of the starter not turning the engine over fast enough. If not, I would do a leakdown test and see where the compression is going.

 

[Chicken Patty]

The battery comment is also often overlooked. I even forgot to think of that as well.

 

[91tizzy]

If its even and never smokes run it....130 is fine for an original motor...esp with cams

 

[bryanwheat]

All engines that I've done a compression test on that had 272's had at least 165 psi. 130 seems low. Was the battery fully charged? The lower numbers could be a result of the starter not turning the engine over fast enough. If not, I would do a leakdown test and see where the compression is going.

Stock 6 bolts likely don't have 165 fresh from the factory

 

[99 gst spyder]

Car runs pretty smooth forward. No smoke of any kind at anytime from idling to driving or wot. Still pretty strong. I'm still sure the battery should good. Car turns over normaly no hesitation at all at anytime.

Would some over heating cause it for lower compression. The Stock gauge is right in the middle just kinda hot out in the engine bay and for sure coolant is a little on the high side.

 

[MY1GDSM]

230 is REAL high temps to be running around at IMO... . I'd get your A/c fan going in town if you can and don't have AC any more and did, you can just hit AC the button an you fans will kick full on all the time... .(EDIT) or put one on if you can...

While that's low I'd be more concered about the temps at this point then the comp numbers as they are even and probleably not that far off from what a high mileage cam'd motor is going to be... . I have to argree, while most the motors I've ever put together where built fairly lose to take a beating(and I do more tuning these days then motor building) that's(165) on the high side for 7.8:1 cam'd motor IMO(perfectly good with out (again IMO)) and there are a lot of factor to take into consideration anyway. As said your real concern would be uneven numbers as motors don't play nice when just one cylinder is out of spec and it's a serious sign something isn't right...


OP swap out you T-stat for a 170* one and run a 30/70 mix of coolant/distilled water with a bottol of water wetter when you put the Radiator in or 50/50 if your concered about REAL low temps up there If you don't see TOO SUB zero temps or at least going into summer it should help that is if you don't have a H/g problem... .

Leak-down wouldn't be a bad Idea at all though... .

 

[99 gst spyder]

230 is REAL high temps to be running around at IMO... . I'd get your A/c fan going in town if you can and don't have AC any more and did, you can just hit AC the button an you fans will kick full on all the time... .(EDIT) or put one on if you can...

While that's low I'd be more concered about the temps at this point then the comp numbers as they are even and probleably not that far off from what a high mileage cam'd motor is going to be... . I have to argree, while most the motors I've ever put together where built fairly lose to take a beating(and I do more tuning these days then motor building) that's(165) on the high side for 7.8:1 cam'd motor IMO(perfectly good with out (again IMO)) and there are a lot of factor to take into consideration anyway. As said your real concern would be uneven numbers as motors don't play nice when just one cylinder is out of spec and it's a serious sign something isn't right...


OP swap out you T-stat for a 170* one and run a 30/70 mix of coolant/distilled water with a bottol of water wetter when you put the Radiator in or 50/50 if your concered about REAL low temps up there If you don't see TOO SUB zero temps or at least going into summer it should help that is if you don't have a H/g problem... .

Leak-down wouldn't be a bad Idea at all though... .

Thanks a lot for the information. I really appreciate it and will look more into it.

 

[Chicken Patty]

230 is a bit hot, wouldn't recommend running at that for too long. Aluminum radiator and those two 12" fans should do the trick.