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Gains porting afr195 on sbc 388

General engine tech -- Drag Racing to Circle Track

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68corvette
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Re: Gains porting afr195 on sbc 388

Post by 68corvette » Sun Feb 09, 2020 5:02 am

Here is dyno graph from 1st posts configuration:
Image

PRH
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Re: Gains porting afr195 on sbc 388

Post by PRH » Sun Feb 09, 2020 12:01 pm

Did you have an air flow sensor on the carb?
Was the airflow still rising steadily after peak hp?

Basically I’m asking if you feel the peak was occurring where it did, and fell off at the rate it did because of a lack of flow/cross section........ or might there have been some valvetrain stability issues that were contributing to where it peaked and how it fell off?
Somewhat handy with a die grinder.

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Re: Gains porting afr195 on sbc 388

Post by steve cowan » Sun Feb 09, 2020 12:17 pm

I think that is where that size engine would peak especially with airgap, it will really choke it down as in available airflow.
Looking at the reworked numbers, seems like going in the right direction, I am curious how the exhaust port sounds on the bench as I see a slight dip in the high lift numbers.
I am interested as well in your valve seat profile change you made if you are willing to expand on it :D
Overall I think the engine will gain across the board especially with a nice single plane intake
steve c

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Re: Gains porting afr195 on sbc 388

Post by Orr89rocz » Sun Feb 09, 2020 12:39 pm

I think a better intake or single plane would do better, atleast help feed past peak rpm to hang onto power longer

I had a 230/245 .603/.613 hyd roller make peak at 6250 rpm and hold to 6600. Box stock street afr 195’s. Intake was a tunnel ram style holley/weiand stealth ram efi setup

68corvette
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Re: Gains porting afr195 on sbc 388

Post by 68corvette » Mon Feb 10, 2020 12:23 pm

There was not airflow meter used at dyno.
It could be also that there is hydraulic pump up, or valve bounce.
I did not measure the cam profile and valvetrain weights to calculate required spring forces, just checked that springs were within specs.
I would had expected that with this much cam the power should had been hanging there up to 6500rpm, but thought that maby intake manifold and cylinder head made it to dive.

Exhaust sounded smooth.
It was measured without pipe, so flow separated at high lift.

I have 388 with XE274H camshaft (230/236-110-.500"),RPM intake, Dart 180cc platinums and it peaks also at 6000rpm.

So definitely something is holding this beast at peaking higher :D

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Re: Gains porting afr195 on sbc 388

Post by steve cowan » Mon Feb 10, 2020 12:51 pm

68corvette wrote:
Mon Feb 10, 2020 12:23 pm
There was not airflow meter used at dyno.
It could be also that there is hydraulic pump up, or valve bounce.
I did not measure the cam profile and valvetrain weights to calculate required spring forces, just checked that springs were within specs.
I would had expected that with this much cam the power should had been hanging there up to 6500rpm, but thought that maby intake manifold and cylinder head made it to dive.

Exhaust sounded smooth.
It was measured without pipe, so flow separated at high lift.

I have 388 with XE274H camshaft (230/236-110-.500"),RPM intake, Dart 180cc platinums and it peaks also at 6000rpm.

So definitely something is holding this beast at peaking higher :D
Wondering if you would share more information on the 180 cc combination as in cylinder head average CSA etc.
I am in the process of doing a set of dart 180 for a new combination 383 sbc 4.030" bore.
I want to peak around 6500
I am working on an average CSA of 2.2" and approx 200 cc
2.02" valve I think needs duration in the 240s
Cam not purchased yet but will be Comp solid roller.
At a guess you're 180 cc combination makes around 470 hp
Pretty small cam and lift limited but would be a great street engine for sure :D
steve c

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