Offy 250 intake - Quad jet adapter - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Blue71LWB · 10-19-2007, 09:34 PM

I just received my Offy intake and Edelbrock performer 500 from Summit today , but they do not match up. Do they make an adapter for this combo and if so who sells them?

Thanks,

dh81k30 · 10-19-2007, 10:46 PM

Quote:

Originally Posted by Blue71LWB

I just received my Offy intake and Edelbrock performer 500 from Summit today , but they do not match up. Do they make an adapter for this combo and if so who sells them?

Thanks,

Blue71LWB,

Did you try with the carb sideways?

chvtrkman · 10-19-2007, 11:00 PM

Blue71LWB,
Don is correct. You have to turn your carb sideways and it will bolt right on. I've got the Offy intake with an Edelbrock 500 cfm also.. I turned it so the primaries are forward, and the secondaries are toward the firewall.

syncrov69 · 10-19-2007, 11:35 PM

I'm curious but how much hp you add with this manifold?

chvtrkman · 10-20-2007, 12:01 AM

I'm no expert, and I haven't dyno-ed it, but I would guess from stock 170 hp, it may have a gain of 25 hp....????This is without increasing compression or doing anything internally.Basically just a stock 292 with the 4bbl setup, headers, and an Accel supercoil.If you have some serious $$$$ to dump into a motor rebuild you can easily attain 250-275 hp on a normally aspirated engine.That's on the 292,I'm not sure what guys are getting from their 250s. Others who have put on a 4bbl setup may have a better idea. I'm sure someone will chime in.

syncrov69 · 10-20-2007, 07:12 AM

Do you have a picture of this engine with the modifications done.

*1972Ryan* · 10-20-2007, 08:01 AM

what about putting a 194 head on a 250...how much more horse power does that add?

Blue71LWB · 10-20-2007, 09:56 AM

Quote:

Originally Posted by chvtrkman

Blue71LWB,
Don is correct. You have to turn your carb sideways and it will bolt right on. I've got the Offy intake with an Edelbrock 500 cfm also.. I turned it so the primaries are forward, and the secondaries are toward the firewall.

chvtrkman,
Does your linkage touch the manifold on the firewall side?

chvtrkman · 10-20-2007, 07:31 PM

Blue71LWB,
No, my throttle linkage doesn't touch the manifold at all. I should have mentioned that I have a 1" phenolic spacer between carb and manifold. Also, I had to fab up a bracket and bolt it to the firewall to hold the "homemade" cable I'm using. I have to go to work now, but when I get back home (Sunday afternoon) I will see if I can post a picture of it for you.

chvtrkman · 10-20-2007, 07:36 PM

Quote:

Originally Posted by 1972Ryan

what about putting a 194 head on a 250...how much more horse power does that add?

1972Ryan,
I don't know how much of an increase in power you will get using a 194 head, but the smaller combustion chambers will definately give you a modest increase in compression.Again, I'm no mechanic, just a hobbyist. Someone may be able to give you more precise figures.

**slomotion** · 10-20-2007, 10:16 PM

Here's a pic of the 500 CFM/Offy/292 set-up. I used a 43" cable from NAPA for the throttle with a couple of home made brackets. Works good. There is a phenolic spacer and an insulating gasket, but they were primarily for the Holly I had on it before. I much prefer the Edelbrock because there's no gasket line below the fuel level in the carb.

**slomotion** · 10-20-2007, 10:22 PM

BTW, the primarys go outboard (to the left) and the secondarys go towards the engine. The adjustment screws should be faceing the steering column.

JAKES 68GMC · 10-20-2007, 11:15 PM

Nice looking 292 slomotion.

**'68OrangeSunshine** · 10-21-2007, 04:02 AM

Slomotion: Are those Tom Langdon's cast iron headers? Do you like them?

**slomotion** · 10-21-2007, 07:15 AM

68Orange, you're right, they're Toms, and I do like them because they're thick-walled and don't "hammer" like the pipe headers do. There's just a little interference problem with the intake, but a hack saw fixes that. The only other thing, was the manifolds were just a little (<1/8") different in thickness.I made up a stepped washer to accomodate that and haven't had a bit of problem since the install.

TP from Cntl PA · 10-21-2007, 02:08 PM

I put a Clifford 4 brl heated intake on the 250 I dropped in my K-20 along with a set of there truck headers I got cheap(I'd have prefered to use Tom's cast jobs, but I couldn't pass up the bargain on the Clifford's). I put a 500 CFM Edelbrock on top of it and fought it for awhile tuning it. I have it dialed in now and it runs like a raped ape and does awesome on fuel. I hauled 2 ton home on the stakebody the other day and the engine didn't even know it was back there.

I just wanted to bring it up, because a few on here know I am itching to try a Q-Jet on it but haven't got around to it yet.

Brad · 10-21-2007, 02:45 PM

Yep, I'm still waitin'!

I bought a Q-Jet and have the adaptor to mount it on the Clifford, but I probably won't be able to get to it until spring.

Just curious TP, what jets & rods are you using? I tried several of each and found that the stock ones worked best for me.

BCOWANWHEELS · 10-21-2007, 07:17 PM

YOU NEED TO REMOVE THE PHOLIC SPACER, ALL I-6 engines need the manifold heated by water or exhaust. all the serious i-6 guys acnolage this. also hp increase is smaller and not noticeable except at higher rpm,s. from my sperience. 194 head equaly 1 point increase in compressin ratio. it needs 1.94-1.60 valves to utilize the increase compression though. also hard exh. valve seats.

**slomotion** · 10-21-2007, 08:59 PM

The manifold is heated. 1st by the radiation of the headers, then second, when the ambient temp. gets lower, the manifold has a provision for water heat which I hook up.
I understand the principle of keeping the fuel/air mixture a vapor in the runners with the heated manifold, but I also understand that I want to keep the incoming air as cool as I can, and I don't need to heat the fuel in the fuel bowls.

10-19-2007, 09:34 PM	#1
Blue71LWB Registered User Join Date: Nov 2006 Location: Alabama Posts: 120	Offy 250 intake - Quad jet adapter I just received my Offy intake and Edelbrock performer 500 from Summit today , but they do not match up. Do they make an adapter for this combo and if so who sells them? Thanks, __________________ Working on my first 1,000 post. I'm sure I'll get there before this project is over .

10-19-2007, 11:00 PM	#3
chvtrkman Registered User Join Date: Sep 2007 Location: PA. Posts: 178	Re: Offy 250 intake - Quad jet adapter Blue71LWB, Don is correct. You have to turn your carb sideways and it will bolt right on. I've got the Offy intake with an Edelbrock 500 cfm also.. I turned it so the primaries are forward, and the secondaries are toward the firewall. __________________ _____________________________________________ 69 C-20 292, 4 spd O/D, 4:56 rears. No a/c p/s p/b p/w......restoration project,"Operation:Stovebolt" 78 C-10 305 TH350 new (old) daily driver 02 Suburban Z71 a.k.a. the family truckster 99 Silverado 1500 Z71

10-19-2007, 11:35 PM	#4
syncrov69 Registered User Join Date: Aug 2007 Location: Laval, Québec, Canada Posts: 175	Re: Offy 250 intake - Quad jet adapter I'm curious but how much hp you add with this manifold? __________________ '71 Custom/10 Deluxe LWB '71 Custom/30 Deluxe Dually

10-20-2007, 12:01 AM	#5
chvtrkman Registered User Join Date: Sep 2007 Location: PA. Posts: 178	Re: Offy 250 intake - Quad jet adapter I'm no expert, and I haven't dyno-ed it, but I would guess from stock 170 hp, it may have a gain of 25 hp....????This is without increasing compression or doing anything internally.Basically just a stock 292 with the 4bbl setup, headers, and an Accel supercoil.If you have some serious $$$$ to dump into a motor rebuild you can easily attain 250-275 hp on a normally aspirated engine.That's on the 292,I'm not sure what guys are getting from their 250s. Others who have put on a 4bbl setup may have a better idea. I'm sure someone will chime in. __________________ _____________________________________________ 69 C-20 292, 4 spd O/D, 4:56 rears. No a/c p/s p/b p/w......restoration project,"Operation:Stovebolt" 78 C-10 305 TH350 new (old) daily driver 02 Suburban Z71 a.k.a. the family truckster 99 Silverado 1500 Z71

10-20-2007, 07:12 AM	#6
syncrov69 Registered User Join Date: Aug 2007 Location: Laval, Québec, Canada Posts: 175	Re: Offy 250 intake - Quad jet adapter Do you have a picture of this engine with the modifications done. __________________ '71 Custom/10 Deluxe LWB '71 Custom/30 Deluxe Dually

10-20-2007, 08:01 AM	#7
1972Ryan Account Suspended Join Date: Mar 2006 Location: Weaverville, NC Posts: 718	Re: Offy 250 intake - Quad jet adapter what about putting a 194 head on a 250...how much more horse power does that add?

10-20-2007, 07:31 PM	#9
chvtrkman Registered User Join Date: Sep 2007 Location: PA. Posts: 178	Re: Offy 250 intake - Quad jet adapter Blue71LWB, No, my throttle linkage doesn't touch the manifold at all. I should have mentioned that I have a 1" phenolic spacer between carb and manifold. Also, I had to fab up a bracket and bolt it to the firewall to hold the "homemade" cable I'm using. I have to go to work now, but when I get back home (Sunday afternoon) I will see if I can post a picture of it for you. __________________ _____________________________________________ 69 C-20 292, 4 spd O/D, 4:56 rears. No a/c p/s p/b p/w......restoration project,"Operation:Stovebolt" 78 C-10 305 TH350 new (old) daily driver 02 Suburban Z71 a.k.a. the family truckster 99 Silverado 1500 Z71

10-20-2007, 10:16 PM	#11
slomotion Old Duffer Join Date: Mar 2003 Location: Maine Posts: 1,822	Re: Offy 250 intake - Quad jet adapter Here's a pic of the 500 CFM/Offy/292 set-up. I used a 43" cable from NAPA for the throttle with a couple of home made brackets. Works good. There is a phenolic spacer and an insulating gasket, but they were primarily for the Holly I had on it before. I much prefer the Edelbrock because there's no gasket line below the fuel level in the carb. Attached Images __________________ '68 Short C20 Flatbed Dually w/ 292 4bbl, Langdon cast headers, and WC T5 trans. '81 G10 Shorty Van "Good judgement comes from experience, and a lot of that comes from bad judgement." Will Rogers "Under promise, then over achieve."

10-20-2007, 10:22 PM	#12
slomotion Old Duffer Join Date: Mar 2003 Location: Maine Posts: 1,822	Re: Offy 250 intake - Quad jet adapter BTW, the primarys go outboard (to the left) and the secondarys go towards the engine. The adjustment screws should be faceing the steering column. __________________ '68 Short C20 Flatbed Dually w/ 292 4bbl, Langdon cast headers, and WC T5 trans. '81 G10 Shorty Van "Good judgement comes from experience, and a lot of that comes from bad judgement." Will Rogers "Under promise, then over achieve."

10-20-2007, 11:15 PM	#13
JAKES 68GMC Aluminum slot wheels rule... Join Date: Jan 2006 Location: Maine Posts: 6,211	Re: Offy 250 intake - Quad jet adapter Nice looking 292 slomotion.

10-21-2007, 04:02 AM	#14
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,504	Re: Offy 250 intake - Quad jet adapter Slomotion: Are those Tom Langdon's cast iron headers? Do you like them? __________________ Every 25 years I like to rebuild that 292, whether it needs it or not.

10-21-2007, 07:15 AM	#15
slomotion Old Duffer Join Date: Mar 2003 Location: Maine Posts: 1,822	Re: Offy 250 intake - Quad jet adapter 68Orange, you're right, they're Toms, and I do like them because they're thick-walled and don't "hammer" like the pipe headers do. There's just a little interference problem with the intake, but a hack saw fixes that. The only other thing, was the manifolds were just a little (<1/8") different in thickness.I made up a stepped washer to accomodate that and haven't had a bit of problem since the install. Attached Images __________________ '68 Short C20 Flatbed Dually w/ 292 4bbl, Langdon cast headers, and WC T5 trans. '81 G10 Shorty Van "Good judgement comes from experience, and a lot of that comes from bad judgement." Will Rogers "Under promise, then over achieve."

10-21-2007, 02:08 PM	#16
TP from Cntl PA Registered User Join Date: Apr 2003 Location: Central PA....In the Berg of Nisbet Posts: 790	Re: Offy 250 intake - Quad jet adapter I put a Clifford 4 brl heated intake on the 250 I dropped in my K-20 along with a set of there truck headers I got cheap(I'd have prefered to use Tom's cast jobs, but I couldn't pass up the bargain on the Clifford's). I put a 500 CFM Edelbrock on top of it and fought it for awhile tuning it. I have it dialed in now and it runs like a raped ape and does awesome on fuel. I hauled 2 ton home on the stakebody the other day and the engine didn't even know it was back there. I just wanted to bring it up, because a few on here know I am itching to try a Q-Jet on it but haven't got around to it yet. __________________ '72 K-20 EFI'ed 250 Inline/4spd stake body, Farm Truck '71 C-20 Cummins Diesel Powered, In storage thanks to $5.00 diesel! '69 3500 GMC 305V-6/4spd, Still under reconstruction.......... Inlines Rule! 6 soldiers standing is better than 8 laying down!!!!!!!!

10-21-2007, 02:45 PM	#17
Brad Out of the carpool lane. Join Date: Jan 2000 Location: Clark Co, WA Posts: 5,672	Re: Offy 250 intake - Quad jet adapter Yep, I'm still waitin'! I bought a Q-Jet and have the adaptor to mount it on the Clifford, but I probably won't be able to get to it until spring. Just curious TP, what jets & rods are you using? I tried several of each and found that the stock ones worked best for me. __________________ 1968 C-10 SWB, 5.7 Vortec/700R4/3.73 posi, Torch Red 1968 Camaro, 250/Powerglide, all original (No, I'm not gonna drop a 350 in it!...Jeez!) 2000 Honda VFR in the faster yellow! 2008 Husqvarna TE-610 1967 C-10 SWB 'Six Appeal'-Gone but not forgotten... Last edited by Brad; 10-21-2007 at 02:46 PM.

10-21-2007, 07:17 PM	#18
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	Re: Offy 250 intake - Quad jet adapter YOU NEED TO REMOVE THE PHOLIC SPACER, ALL I-6 engines need the manifold heated by water or exhaust. all the serious i-6 guys acnolage this. also hp increase is smaller and not noticeable except at higher rpm,s. from my sperience. 194 head equaly 1 point increase in compressin ratio. it needs 1.94-1.60 valves to utilize the increase compression though. also hard exh. valve seats. __________________ I BELIEVE IN JOHN 3:16



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10-21-2007, 08:59 PM	#19
slomotion Old Duffer Join Date: Mar 2003 Location: Maine Posts: 1,822	Re: Offy 250 intake - Quad jet adapter The manifold is heated. 1st by the radiation of the headers, then second, when the ambient temp. gets lower, the manifold has a provision for water heat which I hook up. I understand the principle of keeping the fuel/air mixture a vapor in the runners with the heated manifold, but I also understand that I want to keep the incoming air as cool as I can, and I don't need to heat the fuel in the fuel bowls. __________________ '68 Short C20 Flatbed Dually w/ 292 4bbl, Langdon cast headers, and WC T5 trans. '81 G10 Shorty Van "Good judgement comes from experience, and a lot of that comes from bad judgement." Will Rogers "Under promise, then over achieve."

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