G1 low vs. high compression engines

Topangasmith · 04-28-2010, 11:03 PM

I have a 1982 G1 J17 engine in a cart I recently bought. I understand that this is a low compression engine compared to the other year G1's. Does anyone know what the specifics differences are? i.e. different piston or head or barrel? As I am going to rebuild the top end is there a simple way to increase the compression, say by using a piston from a high compression engine? Thanks in advance.

smallblock450sl · 04-29-2010, 06:07 PM

I'll try to help. The bottom ends are the same on all G1's. The pistons are also the same (you can get oversized piston and rings). The differance is the cylinder/reed assy/intake manifold/carberator/oil pump and muffler on the J17. The cylinder openings for the reed/manifold/carb is way smaller than the other G1'. I'd recommend having the J17 cylinder bored and get the oversized piston and rings, It would cost alot less money then to buy all the parts needed to change out everything. PS...you would not gain much if any power anyway. Good luck.

Topangasmith · 04-30-2010, 09:29 AM

That makes a lot of sense. Thanks a lot. Just curious - does that mean that the port openings are in a different location altering and lowering the effective compression ratio, or is the head combustion chamber volume different as well?

smallblock450sl · 04-30-2010, 09:35 AM

Quote:

Originally Posted by Topangasmith

That makes a lot of sense. Thanks a lot. Just curious - does that mean that the port openings are in a different location altering and lowering the effective compression ratio, or is the head combustion chamber volume different as well?

Both really, the cylinder has a smaller port for the reed assy and the cylinder head is also special to that J17 engine.

sho305 · 04-30-2010, 12:56 PM

IIRC the best thing is to deck the top of the cylinder as (IIRC) the piston does not reach the top of the bore, and if you cut the head very far you lose the squish band though it helps a little by itself. Then advance the timing so it goes faster in forward and slower in reverse. You can raise the exhaust port a hair. Again as I recall, they had 6:1 comp don't recall the 82 comp being different but don't know.

Topangasmith · 05-02-2010, 09:30 AM

Thanks for all the info. I assume the cylinder is decked to bring the piston just flush with the top. Also , what is a reasonable value for the advance?

04-28-2010, 11:03 PM	#1
Topangasmith Not Yet Wild Join Date: Apr 2010 Posts: 3	G1 low vs. high compression engines I have a 1982 G1 J17 engine in a cart I recently bought. I understand that this is a low compression engine compared to the other year G1's. Does anyone know what the specifics differences are? i.e. different piston or head or barrel? As I am going to rebuild the top end is there a simple way to increase the compression, say by using a piston from a high compression engine? Thanks in advance.
Topangasmith Not Yet Wild Join Date: Apr 2010 Posts: 3

04-29-2010, 06:07 PM	#2
smallblock450sl Sometime's............ Join Date: Oct 2007 Location: Tacoma Washington Posts: 11,875	Re: G1 low vs. high compression engines I'll try to help. The bottom ends are the same on all G1's. The pistons are also the same (you can get oversized piston and rings). The differance is the cylinder/reed assy/intake manifold/carberator/oil pump and muffler on the J17. The cylinder openings for the reed/manifold/carb is way smaller than the other G1'. I'd recommend having the J17 cylinder bored and get the oversized piston and rings, It would cost alot less money then to buy all the parts needed to change out everything. PS...you would not gain much if any power anyway. Good luck.

04-30-2010, 09:29 AM	#3
Topangasmith Not Yet Wild Join Date: Apr 2010 Posts: 3	Re: G1 low vs. high compression engines That makes a lot of sense. Thanks a lot. Just curious - does that mean that the port openings are in a different location altering and lowering the effective compression ratio, or is the head combustion chamber volume different as well?
Topangasmith Not Yet Wild Join Date: Apr 2010 Posts: 3

04-30-2010, 12:56 PM	#5
sho305 Vegas modded 420 Join Date: Jun 2009 Location: West MI Posts: 15,445	Re: G1 low vs. high compression engines IIRC the best thing is to deck the top of the cylinder as (IIRC) the piston does not reach the top of the bore, and if you cut the head very far you lose the squish band though it helps a little by itself. Then advance the timing so it goes faster in forward and slower in reverse. You can raise the exhaust port a hair. Again as I recall, they had 6:1 comp don't recall the 82 comp being different but don't know.

05-02-2010, 09:30 AM	#6
Topangasmith Not Yet Wild Join Date: Apr 2010 Posts: 3	Re: G1 low vs. high compression engines Thanks for all the info. I assume the cylinder is decked to bring the piston just flush with the top. Also , what is a reasonable value for the advance?
Topangasmith Not Yet Wild Join Date: Apr 2010 Posts: 3

Today
BGW	Sponsored Links __________________ This advertising will not be shown in this way to registered members. Register your free account today and become a member on Buggies Gone Wild Golf Cart Forum

Similar Threads
Thread	Forum
Swapping engines/G2/G9/G8/G14	Gas Yamaha
Engines for the G9	Big Block Talk!
Header on V engines	Big Block Talk!
Plowmans High Performance Engines/Parts	Golf Cart Parts