engine rpm question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

galoolie · 11-10-2002, 02:52 AM

When I blip the throttle, the engine in my 71 burb is very slow to come back down
to idle.
The engine is an 85 305 with a rebuilt 71 quadrajet and I'm using an HEI ignition.
Anyone have an idea regarding this? Also, someone told me this engine has a very
low compression ratio (8:1), is this true?
thanks

crazy longhorn · 11-10-2002, 10:55 AM

You might check/replace the throttle return springs, & check that the throttle cable doesnt have a kink spot causing it to bind. New springs can be found on the help rack at most auto parts stores. as far as comp on the 305......yes most of them were pretty low, in the 8 or 8.25 to 1 range.

Longhorn Man · 11-11-2002, 12:33 AM

The 305 would not really bennifet from a higher compression ratio...it doesn't really have the heart to make any real power...not without some real good heads with tiny valves.
As for the slow return to idle deal...remove the air filter assembly and disconnect the throttle cable, and the kick down cable. With the engine warmed up and idling, blip it by hand from under the hood and see what happens. Some '80's smoggers had a solenoid that kept the door from snapping shut while the RPM's were still high.

galoolie · 11-12-2002, 01:16 AM

I don't think there are any solenoids in play here (I"m using the 71 carb), and
I am bliping the throtle at the carb, and the throtle seem to return to it's resting
position before the engine winds down. Could this be related to advance weights?
Regarding the compression on a 305: can I run more initial advance due to the
low compression?
Can anyone explain why a 305 would not benefit from higher compression?
Thanks.

Longhorn Man · 11-13-2002, 01:22 AM

Titming being off could make it return to idle slowly too, but it'd have to be retarded too much, and that'd make it a true dog to drive.
The 305 has such a tiny bore, that you can not run good sized valves. I think 194 intake valves would fit, but most got heads with 185 (I think that's the size) intake valves, and they were installed in heads that just don't flow.
While it is true that you can make some power, most ppl will say (and I agree with them) that it is not worth the time.

11-10-2002, 02:52 AM	#1
galoolie Registered User Join Date: Jan 2000 Location: Bend, Oregon Posts: 127	engine rpm question When I blip the throttle, the engine in my 71 burb is very slow to come back down to idle. The engine is an 85 305 with a rebuilt 71 quadrajet and I'm using an HEI ignition. Anyone have an idea regarding this? Also, someone told me this engine has a very low compression ratio (8:1), is this true? thanks __________________ Galoolie

11-10-2002, 10:55 AM	#2
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	You might check/replace the throttle return springs, & check that the throttle cable doesnt have a kink spot causing it to bind. New springs can be found on the help rack at most auto parts stores. as far as comp on the 305......yes most of them were pretty low, in the 8 or 8.25 to 1 range. __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

11-12-2002, 01:16 AM	#4
galoolie Registered User Join Date: Jan 2000 Location: Bend, Oregon Posts: 127	I don't think there are any solenoids in play here (I"m using the 71 carb), and I am bliping the throtle at the carb, and the throtle seem to return to it's resting position before the engine winds down. Could this be related to advance weights? Regarding the compression on a 305: can I run more initial advance due to the low compression? Can anyone explain why a 305 would not benefit from higher compression? Thanks. __________________ Galoolie

11-11-2002, 12:33 AM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	The 305 would not really bennifet from a higher compression ratio...it doesn't really have the heart to make any real power...not without some real good heads with tiny valves. As for the slow return to idle deal...remove the air filter assembly and disconnect the throttle cable, and the kick down cable. With the engine warmed up and idling, blip it by hand from under the hood and see what happens. Some '80's smoggers had a solenoid that kept the door from snapping shut while the RPM's were still high.

11-13-2002, 01:22 AM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Titming being off could make it return to idle slowly too, but it'd have to be retarded too much, and that'd make it a true dog to drive. The 305 has such a tiny bore, that you can not run good sized valves. I think 194 intake valves would fit, but most got heads with 185 (I think that's the size) intake valves, and they were installed in heads that just don't flow. While it is true that you can make some power, most ppl will say (and I agree with them) that it is not worth the time.



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