BBC performance intake manifolds

[Erland Cox]

https://www.facebook.com/peter.karlsson ... 619&type=3









He has an cold air induction plate but I will talk to him about a plate under the carb.
By the way, the suction for the vacupan does not work, any suggestions?

Erland

[F-BIRD'88]

Your second test is under "hot soak". You get that when you make a pull, make power and heat and then sit without moving (the car). Thats why it "hot soaks". You don;t get that when the car is moving.
(Airflow). You are testing in a closed garage. Your 2nd test is "re-Breathing" its own air.
It is breathing exhaust gas. Invalid test method. Bad test setup.

[Erland Cox]

I have a big fan in front of the car blowing lots of cold air and another door open so the garage is completely wented before the next pull.
My own car draws curve in curve no matter how many pulls but the intake system stays cold there.

Erland

[F-BIRD'88]

Why not retest it using a Edelbrock Performer RPM air gap intake manifold
to see if it actually the GM intake that is the problem?

[Erland Cox]

We will probably test it again with other manifolds.
But performance wise it is a lot of engine in that car with historically corecct tires.
I do not think that he ever can use WOT under 3:rd gear.
He has a lot of chassis adjustment and driver training to do,

Erland

[F-BIRD'88]

Then really you are chasing a problem that is not the problem. Would be real interesting to see how the Eddy Perf RPM air gap intake stacks up to that OEM GM intake. Is that intake fully ported etc? I'd be testing for lap times not chassis dyno power numbers at this point. (including dialing in the carb.) Maybe get some very sticky tires to test with too to see the potential of the car.
Are all the cars running these greasy (period correct) tires? Is there a big difference between those tires and a modern current road racing tire?

Maybe gets some heat probes and probe the intake manifold actual intake temps while out and running on the course.
Your second test is still a "hot soak" ed test. You need to stablize the test conditions to emulate whats going on out on the course. What happens if you run the car on the dyno at a good clip at part throttle to first eat up some of that intake heat... then make a pull.

When air and fuel is passing thru the intake ( when the car is running and moving on the course all that fuel EATS HEAT as it vapourizes. Then as soon as you stop the car the intake hot soaks quickly.
It will re-cool off relatively quickly again once running around the course.
Remember all the cars see the same conditions as yours.

A radar gun may be useful for on course performance testing. Its where "the rubber meets the road"

Very cool car. Interesting.

[F-BIRD'88]

On all my old BBC cars with a holley carb adding a under carb heat insulator plate as sold by holley that keeps heat off the carb fuel bowls made BIG difference. GM used to sell this carb heat plate at the dealer
as this was a drivability issue on all the GM BBC cars with that intake and a holley carb.

The shield plate should be 2 ply ( 2 layers of sheet metal) with either a small air gap between the plys
or a wood or paper layer between. Separate the plys with rivets with washers between.
Paint it white. The Holley shield is not bad but a 2 ply with air gap is better.
Add a small wood carb spacer too. Wood ( and paper) are excellent heat isolators.

Further does this engine have a engine mounted mechanical fuel pump?
This is a big source of heat soak. A heat isolator mounting gasket on the fuel pump
with shield also is a big help. Seals It sells the gasket plate. GM cars origionally had a similar thingy.

You can buy the gasket but you have to make the fuel pump heat shield.
Shields from headers heat and engine block radiated heat. pay attention to the fuel lines too.

Remembering re-calling all the things I did back in the day to deal with heat and hot soak on my BBC cars.
My 70 Firebird with 454 chev motor was real bad for hot soak.

You can buy the Holley carb heat shield and make it a 2 ply better heat shield by adding another layer ( with air gap) that is under the carbs bowls. The part that is on the carb flange is single layer but the parts that are under the carb bowls are 2 ply with air gap.
The fuel bowls really get hot soaked with that intake without the shield and wood carb spacer.

[SupStk]

Nice car! Reducing heat in all the places suggested earlier will pay dividends, all in small amounts. Wonder if the heat soak and subsquent HP loss is more related to carb heat soak/ percolating rather than intake heat? I would try an intake like an Air Gap just to satisfy myself whether or not it an intake issue.

[F-BIRD'88]

Polishing the outer surface of the intake makes it RETAIN HEAT.
That thing is a heat sink. Never polish the surface of something you want to radiate off its hot soak.
You need to fix that. Polished surfaces is a no-no. Especially the intake manifold.
If the inside is polished or too fine surface it is very bad too. You need to remove all that smooth shiny polish surface inside and out. Has that intake been extrude honed or otherwise polished inner runners?

Rough as cast is best. That polished surface intake manifold is a very bad HEAT SINK.

[SupStk]

On your pan-evac, they are position sensitive. I've tried some rather unorthodox moves trying to get more pull. Most of them didn't work well as hitting that magic spot, where ever it is.

[pamotorman]

i have use power steering coolers as a fuel cooler on the block mounted fuel pump outlet

[Schurkey]

With a splash pan under and closed off heating.

By the way, the suction for the vacupan does not work, any suggestions?

I'm curious if the two issues--hot manifold and no suction at the Vac-U-Pan--are related. HOW is the "heating" to the manifold "closed off"?

If one side of a dual exhaust has restriction, the exhaust will tend to flow through the exhaust crossover in the intake manifold. This is the operating process behind having a heat-riser valve.


As said, the tubes in the headers for the Vac-U-Pan are position-sensitive. Maybe they're just not at the right angle/position.

[Erland Cox]

Polishing the outer surface of the intake makes it RETAIN HEAT.
That thing is a heat sink. Never polish the surface of something you want to radiate off its hot soak.
You need to fix that. Polished surfaces is a no-no. Especially the intake manifold.
If the inside is polished or too fine surface it is very bad too. You need to remove all that smooth shiny polish surface inside and out. Has that intake been extrude honed or otherwise polished inner runners?

Rough as cast is best. That polished surface intake manifold is a very bad HEAT SINK.

The manifold inside is rough cut with a burr and the floor of the runners is epoxy filled just like the heads.
Only a bit in to make the runners taper.
The exhaust cross over is plugged and there is a splash shield in the lifter valley.

Erland

[gnicholson]

Like allready said an old moroso cool can and dry ice would be something easy to try.

[MadBill]

... By the way, the suction for the vacupan does not work, any suggestions?

Erland

Is there any back pressure to speak of from the side pipes? (mufflers?) It doesn't take much to choke off an exhaust-driven pan evacuation system. Of course ring seal is also critical and pressure/vacuum testing the crankcase to ensure no leakage paths are overlooked, but given the evident quality of the engine and car build I don't expect these are an issue.

DV in his new edition BBC book devotes a page to exhaust-driven pan evacuation. His tests show anywhere from 28" H2O to 120", depending on design.

Re manifold finish, the needs depend on the relative temperatures involved. Again the road leads to DV, who has found polishing to be worthwhile, as in most vehicles the underhood temps are much higher than the stabilized fuel-cooled manifold's.

Another thermal isolation move is thick intake gaskets and non-metallic 'top hat' washer/inserts for the fasteners.