Head CFM and horsepower

[c1500sbc]

Just can’t help but want to swap the cylinder heads on a 385 I built. About 10.5:1 compression with Promaxx maxx series 200 heads and a crower .236/.240 .555/.559 hydraulic roller.

The truck only made like 340 to the wheels. I have since learned a lot about tuning a carb and it feels stronger but I haven’t put it on the dyno since.

The Promaxx 200 heads have a flow rating of 263/195 at .500
The AFR 195 flow at 293/224 at .500 and jumps to 304/229 at .550 (right at the cam specs).
The AFR 210 flow at 296/224 at .500 and jumps to 310/229 at .550

I mean that’s a big cfm jump over the Promaxx heads. Anyone have a guess or experience with how cfm relates to power gains? Even more so what it would improve my current engine?

210’s or 195’s?

[lefty o]

the afr195 is a great head on a 383/385 sized streetable engine. is the money worth the gain, idk. i imagine you'd see a gain across the board, but peak maybe 30hp.

[rustbucket79]

195’s would get my vote, but how much it translates to hp numbers and seat of the pants smiles is up for debate. Posted airflow numbers are really no help, they may or may not be factual.

[KnightEngines]

A little porting on the existing heads will net you an easy 30cfm gain & cost a lot less.
Use the saved $$ to put 1.6 ratio rockers on it

[F-BIRD'88]

I can make more than 340 to the wheels net rwhp with ported 305 heads on a 350 sbc.. You are barking up the wrong tree chasing advertized flow #'s to any corrilation to potential hp #'s. when on a engine that is not even close to optimized (induction, exhaust, valvetrain etc).
You may well be loosing up to 30% power "as installed" inYOUR TRUCK, vs stripped down on a engine dyno.

"It feels stronger". Get some kind of viable tool to allow you to measure real, on road +/- truck acceleration performance changes thru real tuning.

Its a big eye opener and you will get real gaines if you work at it..
Eg: I use a Vericom and back up with a radar gun.
(and also track perf). Just one example.

Never used ghe ProMaxx heads.. Would not have been my first choice... As others have said they can probabily be improved on YOUR COMBO. with real work.
May involve epoxy to make things smaller where sMAller is better on YOUR COMBO.

Think (real tested) truck acceleration performance, not "horsepower"

Your cylinder heads are just one area that needs attention.

[F-BIRD'88]

Question: When you did the 340 rwhp on the chassis dyno what was the max WOT ignition timing?
Your post history shows some mix ups.

[mag2555]

The biggest slice of info that you need to determine which head will perform on average best and across the widest rpm range for that combo you do not have, and this lack of info / detail is typical since hardly any head manufacturer provides it!

You need the very important detail as to what the minimum port area in these heads are.

This determines how fast a given amount of Intake air flow can make it into the chamber and by some math and details of your build allow you to see this factor expressed in fpm .

As many great builders have said, not enough port air speed can ruin a much bigger width of a power curve then too much port air speed, which only effects a much narrower upper portion of a motor's power band!

If your motor rpm wise spends most of its time above 5500 rpm when it's at full throttle then the 210 cc head might be the ticket for you, if not then my lunch time bet would be to go with the 195 cc head,especially if you preform a light bowl blend to them and even just pick up 10 to 12 Intake CFM!

On average I have seen heads that flow in 260 cfm range on a motor built like yours use 240 or so of that 260 cfm to make 480 to 490 hp at the fly wheel .

The Cam does need to have the needed amount of overlap for this and a 10.5 compression is needed.

[Nut124]

"It feels stronger". Get some kind of viable tool to allow you to measure real, on road +/- truck acceleration performance changes thru real tuning.

Its a big eye opener and you will get real gaines if you work at it..
Eg: I use a Vericom and back up with a radar gun.
(and also track perf). Just one example.

Regarding on the road performance testing, I recommend the Dragy GPS based performance device. Costs about $150. Works with an iPhone. The SW is not perfect but workable.

I used it for tuning, testing my project. I set up time-to-speed intervals; 40-50, 50-60, 60-70, 70-80mph. Then made 3rd gear WOT passes from 35 to 80mph thru the power band. Time to speed is very sensitive to power changes, even air temp changes. Need a level road.

[c1500sbc]

I do need to take it up to temple and just run it down the track. If nothing else, it will be fun!

After that I may end up just pulling these heads and doing a little hand porting on them. Installing a better spring package and maybe swapping to some 1.6 rockers. I’m apparently lacking something here as everyone thinks I should be making more power! Timing has been moved around a lot, which is probably why yall have seen the different posts. On the dyno, if I remember right, it was 22 initial and 14 mechanical. All in by 2800.

If I get real antsy I may just pull the motor. Do the head work and then engine dyno it. That will leave me with a real answer on drivetrain loss.

That will be a whole different adventure!! The truck has new bearings, driveshaft, u joint, brakes, everything spins/rolls like you would expect. The new trans/clutch feels a lot less “drag” than the previous one. I wouldn’t even know where to start!

I’ve heard great things about the draggy unit. I’m about to just order one. They seem to be great little tuning tools.

[rustbucket79]

So what tire height, gear ratio, and transmission?

Trucks suck up hp. In my youth I had a lightly modified 79 Camaro running 13.7’s, built a slightly better 350 for my girlfriend’s late 70’s pickup and it ran cool mid 16’s.

[stealth]

agreed.. .get existing heads ported and new valve job.

They will be custom tailored to your exact combination, cam, CI, intake etc...

Spend the money saved on another dyno day.

[BobbyB]

"It feels stronger". Get some kind of viable tool to allow you to measure real, on road +/- truck acceleration performance changes thru real tuning.

Its a big eye opener and you will get real gaines if you work at it..
Eg: I use a Vericom and back up with a radar gun.
(and also track perf). Just one example.

Regarding on the road performance testing, I recommend the Dragy GPS based performance device. Costs about $150. Works with an iPhone. The SW is not perfect but workable.

I used it for tuning, testing my project. I set up time-to-speed intervals; 40-50, 50-60, 60-70, 70-80mph. Then made 3rd gear WOT passes from 35 to 80mph thru the power band. Time to speed is very sensitive to power changes, even air temp changes. Need a level road.

AMEN,!!!

I did essentially the same thing on my project. How can there be anything better than measuring the actual time to travel a known distance or from one know speed to another known speed?

I strongly recommend a Dragy to anyone with a performance car of any kind!

[c1500sbc]

I went ahead and ordered the dragy. Got it in on Saturday. Finally had a little time on my lunch to get out on a safe road to do a couple little test pulls on. My launch is terrible. I mean, terrible lol. 60' foot in 2.5-3 seconds. As you can see, some launches were better than others while some 1/4 mile e.t were better. Obviously a driver/shifting issue on my end. Combine the good launch of the second run with the e.t of the third run and I'd get a rough 13.5 e.t. Anything helpful with this info?

First run:
1/4 mile in 14.33s
1/8 mile 9.41s
0-60 mph 6.01s

Second run
1/4 mile 14.50s
1/8 mile 9.23s
0-60 mph 5.71s

Third run
1/4 mile 14.16s
1/8 mile 9.31s
0-60 mph 6.40s

[mt-engines]

A crappy torque converter can eat a lot of hp.. was the converter locked up during the dyno pulls?

[c1500sbc]

A crappy torque converter can eat a lot of hp.. was the converter locked up during the dyno pulls?

This is actually a 5 speed (AR5) manual transmission. To clarify a little further on the dyno pull, it was in 3rd gear (1.49) instead of fourth (1:1) so I know that can affect numbers as well.