Turbo cam question

64-5mustang

Well-known member
Having deciding to put a turbo on a 200 i built a while ago. Ford 200 77 head ported direct 2 bbl mount 8.6 cr. The current cam is a vi 264-264 110. With it running it has crazy vacume at idle. And it is requiring race fuel or I have to lean it out a fair bit. What cam have you guys used that's more turbo friendly. And pump fuel r
Friendly. Also there like no turbo lag at all.
 

pmuller9

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Here come the questions all at once.
This info is important.

Is the cam still installed straight up?

Are you retarding the ignition timing as the boost increases?

Are you also boost regulating the fuel pressure?

How much boost?

Intercooler?
 

64-5mustang

Well-known member
Cam is straight up and any adjustment and valves hit. Its draw threw so no inner cooler or need to change fuel pressure. The timing is locked now as I can't get much advance out of it
 

pmuller9

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You need both mechanical advance and boost retard in order to run on the street.
How much boost are you running?
What is the ignition timing locked at?

When you do a draw through you need to modify the carb so the power valve is referenced to the intake manifold.
Was that modification done?
 

64-5mustang

Well-known member
The timing like around 12. And boost I've only done 3 driving 5 when I got on it once. The max I would do is 10
 

pmuller9

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So when is it detonating?

When you do a draw through you need to modify the carb so the power valve is referenced to the intake manifold.
Was that modification done?
 

pmuller9

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The power valve chamber normally has a small hole that gets vacuum from under the carburetor.
When the carburetor is sitting in front of a turbocharger the power valve chamber will always be under a high vacuum and the power valve will never open and the engine will run lean at any boost level.

Your dynamic compression ratio with the 264 cam at straight up is about 7.1 and you shouldn't be having a problem especially at high elevation.
What are the air fuel ratios from idle to WOT?
 

64-5mustang

Well-known member
On good mix it was 12 idle and I couldn't get wot. On lean it was 14 to 15 never went for much boost 3 or run time due to it being lean.

And on the power valve, the port is the small hole between the berrals? Would a valve for a much higher vacume be the awnsers or not?
 

64-5mustang

Well-known member
Did some resurch and found the way is to block the hole, still threw the side and install a nipple to manifold vacume. Read it from a blower form, but I beleave that's what's needed
 

drag-200stang

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If the carb is before the turbo you need a mechanical seal on the compressor side or you will suck oil from the center section and that can cause detonation ... What turbo did you get and do you know if it has the right seal?
 

64-5mustang

Well-known member
It's from the buick grand national 3.8 my father had he was going to put in a jeep but never happened. And it's supposed to have the carbon seal.
 

drag-200stang

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64-5mustang":30xmpuma said:
It's from the buick grand national 3.8 my father had he was going to put in a jeep but never happened. And it's supposed to have the carbon seal.
Good (y) I wondered because it is not done much anymore.
 

powerband

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Draw-thru turbos were the cutting edge of big HP gains on existing engines from VW's to Big Blocks'.

With the Draw-Thru (sp) setup, high vacuum at the carb will keep PV closed at all throttle positions. Carb'd draw-thru turbo's typically have a way to get the Power Valve Circuit to OPEN when the Intake manifold transitions to positive boost pressure .
GM-BOP V6's and V8' draw-thru turbo's used a specifically built Quadrajet that simply ran the PV vacuum circuit externally and used a proprietary vacuum switch mounted on the intake manifold to 'switch' the carbs PV circuit to open under boost. ONLY the BOP draw-thru Quadrajet has the external port. I used a generic vacuum-dependent small engine safety fuel line shutoff to 'switch' the Qjet's PV circuit on my Draw-Thru BOP setup.


==
. . . .


Draw-thru setups require huge CFM increase as boost-RPM increases. the proprietary external PV ported Quadrajet , the BOP system uses is rated at 900 CFM at WOT !. This is the reason for the 'Crutch" or supplemental fuel supplies tied to boost that were often built.


Blow-thru systems actually often need smaller CFM requirementsto maintain optimal AFR ratios. My Bow-thru project had a 2300-500CFM initially but hits better AFR's with a 350CFM and smaller jets. The popular 2300 series 2BBl can be boost modified as per 'hangar 18' mods fairly simply.


I added an external PV port to this blow-thru carb 2300:



With normal NA operation, power valve 'opens' / adds more fuel when vacuum/suction drops as you press the accelerator and the carb throttle plate opens to atmosphere. The PV's are rated in vacuum typically @ 2 to 9 hg. Obviously that is the opposite of what you need when you pressurize / blow-thru a carb.

A new option for Blow-thru forced induction is a proprietary Power Valve (Holley type) made to Open under Boost which basically operates backward from a normal PV. It stays closed until bost and is adjustable. This requires sealing the PV vacuum port and letting fuel bowl pressure (Boost) operate the PV.


have (boosted) fun ...
 

powerband

2K+
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Since 'turbo' postings generate so much interest and contrary opinions I want to add a few more:

Fuel supply conversion for BLOW-THRU usually entails a separate elec. fuel pump and its' safety interlock, return to tank bypass fuel line for boost referenced regulator return , etc. since carb fuel bowl is same as boost. DRAW-THRU conversion can use any pump mechanical or elec that can supply enough volume to carb since carb bowl isn't ever pressurized and doesn't need boost reference.



Ignition timing is the most misunderstood: For high boost - high performance @ $ 500.oo + these days you can control timing, draw your own curve referenced to boost - no problem (MSD etc). For under $100 you can 'lock out' an OEM distributor OR find an emissions years (@71-78) DSII distributor and peek under reluctor plate. Most are already limited to near optimal advance for safe low boost use. The vacuum advance can actually still be used if sourced from intake since vacuum will transition to boost and no vac advance.

This D4xx (1974) DSII distributor has a 13R weight channel meaning at Crank X 2 it equals 26 degrees maximum advance.

.

have (boosted) fun

 
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