bbc. vs sbc. HEI diff's? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

C10N.UT · 12-31-2002, 12:29 AM

Hi all,

I was wondering if it is possible to swap out the hei out of my 86' 305 for one out of a 77' 454?I dont know if there are diff's in the shaft length or if its a direct swap?

any input would be great!

bigblock73 · 12-31-2002, 12:32 AM

I believe they are the same, not sure on the wiring though.

-Jeff

79BIG10 · 12-31-2002, 04:08 AM

It should be a direct swap. The crate engines from GM use the same HEI on both BB and SB.
One thing that may be different is the wiring like Jeff mentioned.

GMC Jim · 12-31-2002, 04:44 AM

I purchased an H.E.I dist thru a distributor rebuild firm....The dist.
was calibrated to meet the specified advance curves for the 402 engine ( '71 GMC). Weights and
springs were selected to match factory centrifugal advance curves at 930, 1260, 2400 and 4400 per GM Service manual. Also a new vacuum advance to meet specs of 0 degrees @ 8" hg. and 20 degrees. Spark plugs were re-gapped to .045.

GM specs for the '77 454 specifies ....At 2000 RPM; 5 to 9 degrees centrifugal advance; total of 18-26 degrees ( Cent & Vac)

I would imagine the specs for the '86 305 to be different than the '77 454.......

I have been very satisfied with the H.E.I.. increased gas mileage, better starting... and engine seems more peppy.... maybe because dist was calibrated to GM specs.... as compared to the old dist and vac advance.. . which probably were proper due to wear, etc....

12-31-2002, 12:29 AM	#1
C10N.UT Registered User Join Date: Oct 2001 Location: Ogden Utah Posts: 64	bbc. vs sbc. HEI diff's? Hi all, I was wondering if it is possible to swap out the hei out of my 86' 305 for one out of a 77' 454?I dont know if there are diff's in the shaft length or if its a direct swap? any input would be great!

12-31-2002, 04:08 AM	#3
79BIG10 I'm back with 2nd truck! Join Date: Feb 2002 Location: Texas Posts: 3,774	It should be a direct swap. The crate engines from GM use the same HEI on both BB and SB. One thing that may be different is the wiring like Jeff mentioned. __________________ 1979 Chevrolet Bonanza Big10 "Tootsie Roll" 1985 Chevrolet Silverado (wife's) Member of the Southern Bowties Club "Don't underestimate how sexy a fat man who drinks to excess can be." Homer Simpson

12-31-2002, 04:44 AM	#4
GMC Jim Senior Member Join Date: Dec 2002 Location: Portland, Oregon Posts: 901	Advance curves I purchased an H.E.I dist thru a distributor rebuild firm....The dist. was calibrated to meet the specified advance curves for the 402 engine ( '71 GMC). Weights and springs were selected to match factory centrifugal advance curves at 930, 1260, 2400 and 4400 per GM Service manual. Also a new vacuum advance to meet specs of 0 degrees @ 8" hg. and 20 degrees. Spark plugs were re-gapped to .045. GM specs for the '77 454 specifies ....At 2000 RPM; 5 to 9 degrees centrifugal advance; total of 18-26 degrees ( Cent & Vac) I would imagine the specs for the '86 305 to be different than the '77 454....... I have been very satisfied with the H.E.I.. increased gas mileage, better starting... and engine seems more peppy.... maybe because dist was calibrated to GM specs.... as compared to the old dist and vac advance.. . which probably were proper due to wear, etc.... __________________ '71 GMC;fleetside;PB/PS/AC/CC/402 Eng./Custom Paint/110,000act miles/3 fuel tanks(52gal).

12-31-2002, 12:32 AM	#2
bigblock73 yeller Join Date: Oct 2001 Location: Twin Cities Posts: 13,824	I believe they are the same, not sure on the wiring though. -Jeff



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