Single Plane vs Dual Plane Intake

**350yj** · 12-16-2015

Hello all,

I am chasing down an issue after performing a TBI conversion on a 350 Gen 1 Small block with a 4 bolt main. I have Summit Racing aluminum heads and a hot cam. I purchased this as a kit from them (SME-K-355-400). I did not purchase the intake and opted to stay with what came with the motor, an Edelbrock RPM air gap. This intake is a dual plane, very similar to the one pictured here: http://www.edelbrock.com/automotive/mc/manifolds/sb/7501.jpg

I also have an upgrade TBI unit from SPR performance. It includes an 18 psi spring and 65lb flow-matched injectors. The TBI unit was spec'd by SPR to flow 650 CFM after machining.

My question is, are the dual plane intakes not recommended for TBI? Should I add/replace the spacer to allow crossflow? Should I grind away the intake to allow crossflow? Or should I install a single-plane intake?I believe the overheating could be caused by a lean condition on some cylinders. I do have a wide band installed downstream from the o2 used for the TBI, the readings are perfect once the engine is warm.

This overheating has long been troubling me. I have installed a 3 row radiator, new standard direction water pump and Flex-A-Lite black magic shroud/fan.

Kris

**Jim_Rockford** · 12-16-2015

Several folks have swapped out the factory dual plane for a 2 brl victor jr single plane intake with great results. and the vortec patterned one is a few bucks cheaper than the traditional intake pattern. Attachment 10002

**1project2many** · 12-17-2015

I have used dual plane intakes successfully in the past with TBI swaps. I would not attribute overheating to a few lean cylinders without doing multiple checks to confirm lean operation. Plug cuts and exhaust port temp are two good indicators of lean operation. I don't want to re-hash everything you've already done but if there's a thread somewhere detailing all you've tried I'll be glad to read the history.

**350yj** · 12-17-2015

A thread for my build does not exist yet. I purchased a 1990 Jeep Wrangler YJ with a 1986 small block 350 installed. This is mated to the factory five-speed, an AX-15. I also have 4.10 gears and 35 inch tires for the warmer months and 31 inch tires for the winter. It came with a 500cfm Holley carb, stock cam, stock heads.

A friend installed a GM TBI system from a 1987 Chevrolet K1500. I wanted more power, so I purchased a top end kit from Summit Racing. Its the SME-K-355-400 kit, seen here: http://www.summitracing.com/parts/sme-k-355-400. I did not purchase the intake from Summit as the motor came with an Edelbrock RPM air gap, which is a dual plane intake.

Attached is a picture of the cylinders, you can also make out the casting marks. I believe the previous owner installed new connecting rods and pistons and had the cylinder walls honed/cleaned. There is no stamp on the cylinders indicating its bored over, however.

Cooling has always been an issue, regardless of the setup. I recently installed a 3 row core radiator to replace the 2 row core that was swapped in, likely during the engine swap. That can be seen here: http://www.amazon.com/gp/product/B000FQ20QQ

I have also installed a new water pump, also from Summit. http://www.summitracing.com/parts/pro-67265

I have also installed a Flex-A-Lite Blackmagic fan, seen here: http://www.amazon.com/gp/product/B000CNHFNA

I am running a 180 degree thermostat, Prestone 50/50 GM coolant and a bottle and a half of Water Wetter. I have run the system with the cap off to ensure there are no bubbles. I have a wide band in the same exhaust header as the o2 for the TBI, readings are spot-on.

I may remove the winch, as when I stare at the front of the Jeep it looks to be blocking some airflow. Pictures of the front and fan+shroud are attached.

The overheating issue that I am seeing is the Jeep will drive around fine, but the temperature will slowly creep up as I get closer into town after a 15-20 minute drive. While sitting at a stoplight, the gauge read 220 degrees. This was on a day where the ambient air temperature was 45 degrees. I am concerned about driving in the summer.

Kris

**1project2many** · 12-17-2015

Sounds like you've been fighting this for some time. What controls the fan on/off operation? Is it an automatic thermostst? Is the temperature adjustable? When the fan is on, is it able to cool the engine at idle or does engine temperature continue to climb?

One thing that's easy to miss is that any coolant which flows through the heater core bypasses the radiator. OEM, GM uses hose nipples with about a 3/8" ID to restrict flow. If you haven't already done this, you can pinch off a heater hose to see if the engine runs cooler. If yes, check the nipples at the manifold and water pump to see if one has this restriction. If both are wide open you can braze a washer to the top of the upper hose nipple to create the right restriction.

I don't believe the winch is a problem. Can you feel the fan drawing air through the radiator at idle?

**350yj** · 12-17-2015

I have a Derale adjustable fan controller: http://www.amazon.com/gp/product/B000CN4XZI

I have the controller configured to turn on around 170 degrees. I will try to pinch one of the hoses and drive around this weekend, it is supposed to be a bit warmer. As I recall, the nipple on the water pump (7/8" I believe) was unrestricted.

I also stumbled across some great articles, one on pirate 4x4: http://www.pirate4x4.com/tech/billavista/Cooling/

Also, my thought about single plane versus dual plane came about after David Freiburger test a GM LS motor with a carb and EFI on an engine dyno: https://youtu.be/2sQJPZYSoUI?t=7m42s

I can feel the fan drawing air through the radiator at idle. I typically see the temperature start to climb in stop and go traffic after driving for 20+ minutes or a long uphill on my way back home.

**Nasty-Z** · 12-17-2015

I know this sounds weird but ,,,,, If you have a leaf blower , drive the Jeep until the temp starts to climb , until you feel uncomfortable about the temp , preferably on a back road , when it reaches the temp you are uncomfortable with , pull over and aim the leaf blower at the rad , if it cools down with the added air flow from the leaf blower ,you have an air flow problem. I have never been a fan (no pun intended) of the Flex A Lite black magic fans (or any flex-a-lite fan for that matter).

The YJ SBC conversions I have done have utilized either a mechanical engine driven fan , or a Lincoln MKVIII fan and a good 2 row radiator , these options I found were the best way to maximize airflow through the radiator and keep the engine cool , remember the thicker the rad you have the harder it will be for a fan to pull through it , you need a lot of fan to pull through a 3 row not to mention a 4 row rad. For example , my S10 Blazer uses a single row OE replacement (Chevy Camaro) plastic tank aluminum core radiator and a set of F**d Contour dual fans , it has a 496 BBC / 700R4 and 4.56 gears with 35" tires , fans are controlled by the PCM and it rarely goes above 185* on a warm day here in PA , the rad is able to dissipate heat quickly and the fans move a tremendous amount of air individually and when they are both on (which is a rare occurrence) .

Unless it is an extremely bad tuning issue , I would not suspect overheating being caused by tuning , or single vs dual plane manifold . I believe you either have an airflow problem or a coolant flow problem.

HTH

TOM

**Jim_Rockford** · 12-17-2015

yea a shroud and a good OEM electric fan is the way to go, I have never been a fan of aftermarket fans either, any fan without a shroud is pretty useless.

**350yj** · 12-30-2015

Originally Posted by 1project2many

Sounds like you've been fighting this for some time. What controls the fan on/off operation? Is it an automatic thermostst? Is the temperature adjustable? When the fan is on, is it able to cool the engine at idle or does engine temperature continue to climb?

One thing that's easy to miss is that any coolant which flows through the heater core bypasses the radiator. OEM, GM uses hose nipples with about a 3/8" ID to restrict flow. If you haven't already done this, you can pinch off a heater hose to see if the engine runs cooler. If yes, check the nipples at the manifold and water pump to see if one has this restriction. If both are wide open you can braze a washer to the top of the upper hose nipple to create the right restriction.

I don't believe the winch is a problem. Can you feel the fan drawing air through the radiator at idle?

I welded a washer to the nipple reducing the flow through the heater core to 3/8. Driving it around the temperate now sits at 180*. This was of course after switching back to the 180* thermostat. I am cautiously optimistic that this has fixed the issue, being that the high today is only 39*. Thank you for this tidbit of information.

**350yj** · 12-30-2015

Originally Posted by Nasty-Z

The YJ SBC conversions I have done

Do you have a recommendation for exhaust headers? Mine are dangerously close to the plugs/wires even with shorty accel plugs. I have melted a few plug boots and wires. The plug wires are currently wrapped with Titanium. I would like to swap in some headers that will still fit but are not as "block-hugging" as my current set.

**1project2many** · 12-31-2015

No problem... if it works. But if it doesn't help then it wasn't my idea!

**Nasty-Z** · 01-03-2016

Originally Posted by 350yj

Do you have a recommendation for exhaust headers? Mine are dangerously close to the plugs/wires even with shorty accel plugs. I have melted a few plug boots and wires. The plug wires are currently wrapped with Titanium. I would like to swap in some headers that will still fit but are not as "block-hugging" as my current set.

Hedman P/N 69640 , fit good and plug access isn't terrible , its not great , but tolerable.

http://www.jegs.com/i/Hedman/500/696...DmlxoCKZHw_wcB

TOM