New domain: www.Speed-Talk.com

The forum is currently running on the new domain and server. The old domain will remain active for a short while to forward any (less frequent) visitors.
IMPORTANT: Update your bookmarks to https://www.speed-talk.com/forum/

Search found 11781 matches

by MadBill
Fri Sep 20, 2019 9:33 pm
Forum: Engine Tech
Topic: Sizing IR Carbs
Replies: 4
Views: 267

Re: Sizing IR Carbs

In How to Build Horsepower; Vol. 2, David Vizard gave an IR sizing formula that determines the ideal choke size, which he says should be 72-80% of the butterfly diameter, preferably the latter: choke in mm = √ (CV x RPM/2600) , where CV is cylinder volume in cc and RPM is that of peak power. So for ...
by MadBill
Thu Sep 19, 2019 9:40 am
Forum: Engine Tech
Topic: Are Exh pushrods more stressed even in NA applications?
Replies: 35
Views: 1120

Re: Are Exh pushrods more stressed even in NA applications?

Yes, it's easy to view any pressure above atmospheric at EVO as 'lost potential work', but a percentage of it returns during overlap in the form of the negative scavenging pulse.
by MadBill
Tue Sep 17, 2019 8:58 pm
Forum: Engine Tech
Topic: Are Exh pushrods more stressed even in NA applications?
Replies: 35
Views: 1120

Re: Are Exh pushrods more stressed even in NA applications?

Why is the exhaust valve lifted less than the intake? I can't speak to why, but a number of mid range and better software programs I've used all show a fairly flat optimum lift range for the exhaust valve, as opposed to the intake, where diminishing returns continue up to impractical heights. Catal...
by MadBill
Tue Sep 17, 2019 8:44 pm
Forum: Engine Tech
Topic: Are Exh pushrods more stressed even in NA applications?
Replies: 35
Views: 1120

Re: Are Exh pushrods more stressed even in NA applications?

Bill, With the smaller diameter and less weight, and often less lift than the intake in the newer lobe designs, do you find that the two factors end up cancelling each other out, By cancelling, do you mean because with the same spring and seat load the open force will be less on the lower lift exha...
by MadBill
Tue Sep 17, 2019 9:15 am
Forum: Engine Tech
Topic: Are Exh pushrods more stressed even in NA applications?
Replies: 35
Views: 1120

Re: Are Exh pushrods more stressed even in NA applications?

A realistic example would be a 1.60" valve (2.0 ²") opening against 100 psi and thus adding 200# to the perhaps 200# seat load plus whatever the inertia force. Reputedly, for a TF engine the cylinder pressure on a ~2.0" (3.14²") ex. valve is over 1,000 psi at EVO and the valve opens not when the lif...
by MadBill
Mon Sep 16, 2019 9:39 pm
Forum: Engine Tech
Topic: Bench Data
Replies: 47
Views: 2651

Re: Bench Data

Be interesting to test-glue in a turning vane down the centerline. In the stock elbows of a 1988 Firebird system I tested, they added ~ 4% each.
by MadBill
Mon Sep 16, 2019 8:51 pm
Forum: Engine Tech
Topic: Nickel Fix
Replies: 7
Views: 667

Re: Nickel Fix

mag2555 wrote:
Mon Sep 16, 2019 12:10 pm
Was the broken rocker just a fluke,or are they on the edge?
Well, they had four seasons of 8,000 RPM shifts with 240# seat load on them but passed visual inspection shortly before the failure. Afterwards, the other 15 Zyglowed OK, but I'd have to say they are on borrowed time at this point.
by MadBill
Mon Sep 16, 2019 10:11 am
Forum: Engine Tech
Topic: Nickel Fix
Replies: 7
Views: 667

Nickel Fix

Probably the wrong section, but oh well...: Setting the scene, our SBF Merkur road racer has had a troubled season. Early on, a cracked rocker caused a pushrod to wear through a paper-thin intake port wall and blanket the track in smoke. After a lot of unrelated distractions, got the hole epoxied up...
by MadBill
Sat Sep 14, 2019 10:47 pm
Forum: Engine Tech
Topic: Pan vacuum issue
Replies: 7
Views: 416

Re: Pan vacuum issue

What do you see for vac. if you slowly rev it up out of gear? A 380" SBF with a 5 stage Aviaid pump I consult on pulls as much as 18" with the check valve cranked right down. (we usually run ~ 12") You can test for leakage by sealing up all external ports and connecting a gauge to manifold vac, teed...
by MadBill
Sat Sep 14, 2019 6:04 pm
Forum: Engine Tech
Topic: Air/ fuel ratio data logger
Replies: 26
Views: 1120

Re: Air/ fuel ratio data logger

A common poor boy data logger is a video recorder pointed at the instruments. I believe capturing readable data requires analog gauges.. (or maybe a Super 8 camera)
by MadBill
Sat Sep 14, 2019 1:06 pm
Forum: Engine Tech
Topic: Low speed (1500-1800 RPM) driveability issue
Replies: 115
Views: 2648

Re: Low speed (1500-1800 RPM) driveability issue

Status update... the combination of the divider filler and the 4 hole space is the hot ticket. The car is running smooth in the range where I was having the problem, and the low speed cruise afr is stable right at 14:1. Also, I am having the reduce the main jet sizes and the PVRC restrictor jets to...
by MadBill
Fri Sep 13, 2019 10:57 pm
Forum: Engine Tech
Topic: Low speed (1500-1800 RPM) driveability issue
Replies: 115
Views: 2648

Re: Low speed (1500-1800 RPM) driveability issue

About 40 years ago I made an insert like that for an Edelbrock C454 intake by filing the three sides of the notch in the plenum divider, both ends and the bottom, to a sharp edge on a 90 deg. angle (each 45 deg. from the manifold divider axis) and fabbing a 3/8" aluminum plate with sharp 90 deg. sl...
by MadBill
Fri Sep 13, 2019 10:49 pm
Forum: Engine Tech
Topic: Chamber mod intended to improve combustion
Replies: 6
Views: 688

Re: Chamber mod intended to improve combustion

Vizard has been making that cut on BBC heads for awhile now and I want to say he says it's good for something like 10-15 hp. He lays them back quite a ways, too. Probably about the extent that you did. Yes, he said it eliminates the reverse flow at the bottom of the exhaust port. (which apparently ...
by MadBill
Fri Sep 13, 2019 10:30 pm
Forum: Engine Tech
Topic: 14044862 aluminum heads?!? Are they to much for street application?!?
Replies: 4
Views: 516

Re: 14044862 aluminum heads?!? Are they to much for street application?!?

Looks suspicious certainly, but would anyone be trolling to shill factory GM parts?
by MadBill
Thu Sep 12, 2019 9:46 am
Forum: Engine Tech
Topic: accurately measuring port cross section area
Replies: 26
Views: 967

Re: accurately measuring port cross section area

Could you use the solder method on an odd shape and then just reshape it to a triangle for normal measurement as long as the solder is formed with ends butted?.. No. The shape affects the area. E.g. a 6" length of solder will enclosed a circle of 1.9" diameter with an area of 2.84"² or a 0.001" x 3...