Data crunching: But will a lot of data.
There are very few dynos that will read below 2500, most are built for hot rodders.
I did find a dyno test of the TPI systems on a rare dyno that did indeed read at 2000, and they made a fuss over getting to use such a engine dyno.
I also had to go with factory ratings...
Reports like:
The 400 was never built as a performance engine. It was a work engine used in heavy trucks, bus, vans, dump trucks etc.
HP is low stock in the 150-185 HP but had a lot of torque.
1976 400 R4carb, 8.5:1 compression, 175HP @ 3600 rpm, 305 lbs ft torque @ 2000
The corvette 350 for that year
1976 350 R4carb, 9:1 compression, 210HP @ 5200 , 255 ft lbs @ 3600
'76 350 for like the camaro
1976 350 R4carb, 8.5:1 compression, 185HP @ 4000 , 270 ft lbs @ 2400
Also the OLDS 403 with a torque peak of 2000 as well.
I then got the specs as best i could of these cams..the best i found was a 2200 RPM Chevy cam:
The choice of a Cam was become a nightmare obsession. The cam is THE MOST IMPORTANT part of a engine. The cam controls what kind of an engine you building. Cam grinders and makers’ 90% of the time give more power by shifting the power band up. So a mild stock engine can run from 1500 to 5000. Move that to 2000 and 5500 more power, move it to 2500 and 6500 MUCH more power.
BUT to get that power costs fuel, more is needed with each power shift.
To get better Miles per Gallon, the idea is to keep the low RPMs power band by not shifting the power curve upward, and setting the whole car/truck up to cruse near your engines torque peak.
I have been working on getting an engine set up to run at a torque peek of 2000RPMs. Sadly it seems this will limit other factors as passing and mountain climbing.
Here is what I think will give me the best set up:
I found this article: How to build a budget 383:
From
https://itstillruns.com/build-chevy-...rque-7988109.…
I combined the notes to what I am doing.
A 383 alone is good for an instant 10 percent increase in horsepower and torque from idle to redline over the same engine as a 350.
“It Still Runs” said to use L31 GM Vortec cylinder heads. (I believed these are known as 193 swirl port heads) These first-generation Vortec heads flow about 239/147 cubic feet per minute of air at 0.50 inch lift, (which is about their max lift) which will support about 490 horsepower in completely stock form, and are a direct bolt-on for any small-block.
You can find L31 heads in 1996-1999 GM full-sized trucks, 93 Vans etc.
I mistakenly thought this was talking about the first swirl port heads known as 193, L05 heads. Flow rate for 193 iron LO5 head: 178 intake; 146 exh (Dyno Don) VS the L31 heads 239/147 Close!!
With these 64CC heads and my pistons I will have 9.3/9.5 Compression.
“It Still Runs” originally suggested: Using a stock 1988 to 1989 Corvette L98 camshaft designed for the tuned-port injected (TPI) 350. They say that this cam is actually far too tame for a 383, but installing a set of 1.7-to-one roller-tipped rocker arms will open the valves about 6.5 percent further. This will almost compensate for the 9.5 percent increase in engine displacement.
It gave me a base line.
Instead: I matched their specs to
orcam@pacifier.com # 806 cam, nearly this same profile as called for with 1.7 Rockers BUT now using milder 1.6 Rockers:
The L98 specs: 207/213 @.050 114 .442/458 with 1.7 rockers
#806 cam’s Specs; 207/214 @.050 117 440/454 lift with 1.6 Rockers (milder rockers)
That WAS my plan until my latest findings:
When I was forced to remove all head bolts and add a sealer I also had to remove the roller rocker as well. Doing so made me see that their adjustment nuts were not using very much stud thread, only a hair over ¼ an inch. I contacted the manufactory about this and was informed that with a 3/8 stud I really should be at least 3/8 an inch of thread to hold.
I then discovered NO ONE Makes a full roller rocker for stock heads, that every build for a hot rodder set of heads with longer screw in studs. My heads are stock.
So I was then facing buying a set of stamped 1.6 rockers to correct this problem…
At this point I was also in deep talks with a number of people about this engine, and decided to reevaluate the rockers.
I dug out the cam specs for the cams: Cams are listed duration and lift Intake then Exhaust.
I will be running Rhoads V-Max roller lifters, and with Rhoads Lifters running at 10% reduction the cam will be listed as well.
WAS My Power Cam: 231/206 424/452 With 1.6 Rockers
With Rhoads Lifers: Less 10% + 180/192 115 .396/408
Now Power cam: 206/ 213 143/428 With 1.5 Rockers
With Rhoads Lifers: Less 10% 185.4/191.7 .371.7/385.2
Low RPM 350 Cam: 179.5/192.2 .350/381
So NOW I am very close to the low RPM cam I modeled this from.
So at 1500 to 2500 My new cam’s intake valve will be opened a just little longer from 179 to 185 and open slightly more from .350 to .371 and the Exhaust Valve will be 192.2 to 191.7 and opened a little more at .381 to .385.2.
This should give me the MAX Torque at 1500 to 2500 RPMs which should product enough power to easily pull the van at 75MPH.
Whereas at 2500 RPMs the Rhoads Lifters will start to pump up and cut in my hotter part of the cams profile so instead of a drop in power my engine should just keep on making more torque and HP all the way to 4500 RPMs.
This will give me a variable cam, mild at low RPMS and HOT at higher RPMs.
I think such a set up should lower the torque peak near 2000RPMs at low RPMs and open up the cam around 2500 RPMs which will give me a big power boost.
“It Still Runs” said an engine built to this spec (minus the Rhoads Lifters) should produce about 300 to 340 horsepower at a usable 4,800 rpm and an Earth-moving 425 to 450 ft-lb of torque at around 3,000 rpm. As I am NOT running the modified heads they called for I figure to get a little less.
As I am not doing the porting work called for, because everything I read about ports has said for MPG leave the intake stock, porting is needed only for MAX HP, so I figure a small lost say 10% BUT I WILL be running a TPI system next year that is reported to add 20/30% more torque, HP and MPG…
Due to so many delays getting my machine work done I will be lucky to do a straight engine swap before the AZ Summer puts a stop to any work.
Now I am thinking I really lucked out with these SLP runners and now will be feeding and replacing that lost power right at the point the cam comes alive…
They say that this fairly mild engine's fat power-band, efficient combustion, glass-smooth idle make it a perfect fit for a daily-driven car or truck.
So this is my calculations.
Rich
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