49 replies to this topic

[ljmate]

G, day fellas , I would really appreciate some advice on which direction to go with on the exhaust system in my LJ . its got a186- 236 stroker engine M 21 box 3.55 diff ,the head is a yella terra cast 12 port [cast iron] with extensive port work apparently flowing 120 cfm and the biggest valves that can be fitted. This is feed by a set off triple Webbers . the cam is a hydraulic roller cam with 580 lift and 330 adv duration . currently this is attached to a set of 20 yr old genie extractors 1,1/2 inch not mandrel bent 6 into 2 into 1 then into a 2,1/2 inch system .on the dyno the rear wheel hp at 5600 rpm reachs 230 but then run out of puff the torque is 1250 lb . the thinking at the moment is to go 1,3/4 primarys 6 into 1 collector then to a 3 inch system , would it work better with 6 into 2? 1,5/6 or 1,3/4 ? thanks in advance for any advice, especially a calculation for the lenth of the primarys. cheers

[Rockoz]

Really wouldnt go more than 2 1/2 for the system. Would slow the gas speed down too much, then the extractors wouldnt flow so well. From memory I wouldnt get too hung up about primary and secondary lengths, cause this is somewhat dependent on the rev range that you want your max power at. And if you can manage to get a tuned length set built and fitted you would be doing well.
Maybe a set of Pacies and a nice free flowing 2 1/2 mandrel bent system.
By having a stroker fitted, the revability of the motor is reduced too.
Has the distributor been regraphed to suit the motor?

[ljmate]

Really wouldnt go more than 2 1/2 for the system. Would slow the gas speed down too much, then the extractors wouldnt flow so well. From memory I wouldnt get too hung up about primary and secondary lengths, cause this is somewhat dependent on the rev range that you want your max power at. And if you can manage to get a tuned length set built and fitted you would be doing well.
Maybe a set of Pacies and a nice free flowing 2 1/2 mandrel bent system.
By having a stroker fitted, the revability of the motor is reduced too.
Has the distributor been regraphed to suit the motor?

g, day mate , the distributor has been regraphed to suit the motor , the engine was built to do 7000rpm and has been there , the rev range id wont max power would be between 6- 7000 rpm. its definitely going to be a complete custom system. thanks.

[warrenm]

Use 1.5" primary pipes 28" to 30" long.I think 1.75" will be to big & lose to much flow, bigger isn't always better.
Warren

[ljmate]

what size fuel line and fuel pump are you running? also what valve spring pressures are you running open and closed?

Thanks for replying at the moment its just got standard fuel lines and a chevy mechanical pump so far it hasnt run out of fuel. i dont know the spring presures , but it was put together by a reputable engine builder.

[ljmate]

I could probably run some rough simulations thru Engine Analyzer if you like. Would need a bit more info though - ie. is the 120cfm figure at 20"? Also, do you know what the exhaust port flows, and what size carbs, 48s? CR etc. would also help. It sounds like a pretty serious engine to put it mildly, my gut feeling is that you'd get away with the 1-3/4" primaries and 3" pipe downstream..

G , day unfortunitly i dont have any more info on the head flow . the carbs are 45 s the ventures are 36 that iv been told will need to go to 38s . im not shore what you mean by CR . i would appreiate any info you could give from an engine analyzer like primary lengths and how much touque lose 1 5/8 to 2 1/2 vs 1 3/4 to 3inch there would be down low if it can do that. cheers.

[ljmate]

CR = compression ratio. Also need to know lobe centreline angle of cam and approximate length of intake manifold runners. As for head flow etc. I'll just use estimates and it will be close enough for comparison purposes. I'll run some simulations for different pipe sizes and carby choke sizes and post up the numbers in a couple of days.

Hi , the cr is 10 to 1 . the inlet runners are 18 cm, i dont know the cam centerline angle. thanks

[ljmate]

OK ran a few sims based on the info given plus a little guesswork. The baseline run matches reasonably well with your dyno numbers so hopefully these will be reasonably accurate - I think they'll be good enough to be useful anyway. Remember these are flywheel HP numbers. Basically there is a jump of 50 odd horsepower going from 1-1/2" to 1-5/8" primaries. The 1-3/4" pipes gave a further small increase but at the expense of a torque dip around 4000rpm, so it looks like 1-5/8" O.D. primaries are the go. The best primary length turned out to be 28". The collector needs to be around 2-3/4" to 3" dia. as does the muffler and pipework.


Heres the short summary copy/pasted from the baseline run (I previewed this post and noticed the columns are all out of whack but hopefully it'll still make sense):

RPM 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000
Brake_Tq 226 264 257 255 221 218 178 128 80.0 34.4
Brake_HP 150 201 220 243 231 249 220 170 114 52.4
Exh_Pres .6 1.0 1.3 1.7 1.9 2.4 2.5 2.5 2.5 2.4
Int_Vacuum .2 .3 .4 .5 .6 .8 .8 .8 .8 .8
Vol_Eff_% 82.9 96.1 99.1 103.4 98.9 102.5 97.4 90.3 83.7 77.7
Actual_CFM 213 283 327 379 399 451 464 463 460 456
Fuel_Flow 73.9 98.2 114 132 139 157 161 161 160 158
A/F_Mix_Qal 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
BSFC .491 .488 .516 .542 .599 .628 .733 .944 1.399 3.022
BSAC 6.213 6.167 6.522 6.853 7.579 7.949 9.270 11.937 17.699 38.220
Friction_HP 32 46 64 85 109 138 173 215 260 310
Mach_# .288 .329 .370 .411 .452 .493 .534 .575 .617 .658
Piston_Spd 2129 2433 2738 3042 3346 3650 3954 4258 4563 4867
Piston_Gs 856 1118 1415 1747 2113 2515 2952 3423 3930 4471
Overlap_%VE -1.9 2.8 -1.4 -1.8 -5.7 -3.0 -4.9 -5.4 -4.7 -4.0
Int_AvgVel 171 195 219 244 268 293 317 341 366 390
In_InertiaPrs 2.5 3.6 4.6 5.0 4.8 4.5 3.9 3.3 2.5 1.7
In_ResTunPrs 0.0 0.0 -.1 .4 -.7 1.0 .1 -.6 -.2 .4
Ex_AvgVel 248 283 319 354 389 425 460 496 531 567
ExTun_Prs -.6 -1.2 -1.6 -1.5 -1.3 -1.3 -1.2 -1.1 -1.0 -.8
Valve_Toss None None None None None None None None None None
Spark_Adv 27 28 29 29 30 30 31 32 32 33



This run is with the 1-5/8 primaries with 2-3/4" collector and a race-type muffler and system:

RPM 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000
Brake_Tq 258 277 291 294 245 263 218 149 105 70.0
Brake_HP 172 211 249 280 257 300 270 199 149 107
Exh_Pres .2 .3 .5 .6 .6 .9 .9 .8 .8 .9
Int_Vacuum .2 .3 .5 .6 .7 .9 1.0 .9 .9 .9
Vol_Eff_% 90.4 98.5 106.1 111.4 103.8 111.7 105.8 94.0 88.2 84.8
Actual_CFM 235 292 355 415 419 499 506 482 485 499
Fuel_Flow 81.8 101 123 144 145 173 176 167 168 173
A/F_Mix_Qal 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
BSFC .475 .481 .496 .516 .566 .577 .651 .843 1.126 1.625
BSAC 6.008 6.079 6.270 6.521 7.160 7.295 8.232 10.663 14.247 20.552
Friction_HP 33 45 62 84 106 135 170 210 255 306
Mach_# .288 .329 .370 .411 .452 .493 .534 .575 .617 .658
Piston_Spd 2129 2433 2738 3042 3346 3650 3954 4258 4563 4867
Piston_Gs 856 1118 1415 1747 2113 2515 2952 3423 3930 4471
Overlap_%VE 5.2 5.0 5.3 5.7 -1.5 5.7 3.3 -2.3 -.8 2.6
Int_AvgVel 171 195 219 244 268 293 317 341 366 390
In_InertiaPrs 2.5 3.6 4.6 5.0 4.8 4.5 3.9 3.3 2.5 1.7
In_ResTunPrs 0.0 0.0 -.1 .4 -.7 1.0 .1 -.6 -.2 .4
Ex_AvgVel 209 239 269 298 328 358 388 418 448 477
ExTun_Prs -.6 -.8 -1.4 -1.4 -1.5 -1.5 -1.6 -1.5 -1.4 -1.2
Valve_Toss None None None None None None None None None None
Spark_Adv 27 28 27 29 30 30 30 31 32 32


This last one is with the 1-3/4" primaries and a race type 3" collector muffler:

RPM 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000
Brake_Tq 259 259 291 296 251 267 225 158 123 79.7
Brake_HP 173 197 249 282 263 305 279 210 176 121
Exh_Pres .2 .2 .3 .5 .5 .7 .7 .6 .7 .7
Int_Vacuum .2 .3 .5 .6 .7 .9 1.0 .9 1.0 1.0
Vol_Eff_% 90.6 94.4 105.9 111.5 104.8 112.0 106.8 95.3 91.9 86.3
Actual_CFM 236 277 354 416 423 502 512 489 507 510
Fuel_Flow 82.1 96.1 123 144 147 174 178 170 176 177
A/F_Mix_Qal 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
BSFC .476 .488 .493 .513 .557 .571 .638 .809 1.000 1.457
BSAC 6.015 6.172 6.234 6.483 7.051 7.228 8.075 10.235 12.649 18.433
Friction_HP 33 44 61 82 105 133 167 207 253 302
Mach_# .288 .329 .370 .411 .452 .493 .534 .575 .617 .658
Piston_Spd 2129 2433 2738 3042 3346 3650 3954 4258 4563 4867
Piston_Gs 856 1118 1415 1747 2113 2515 2952 3423 3930 4471
Overlap_%VE 5.4 1.1 5.1 5.7 -.6 5.9 4.2 -1.1 2.9 3.9
Int_AvgVel 171 195 219 244 268 293 317 341 366 390
In_InertiaPrs 2.5 3.6 4.6 5.0 4.8 4.5 3.9 3.3 2.5 1.7
In_ResTunPrs 0.0 0.0 -.1 .4 -.7 1.0 .1 -.6 -.2 .4
Ex_AvgVel 178 204 229 255 280 306 331 357 382 408
ExTun_Prs -.6 -.4 -1.2 -1.3 -1.5 -1.6 -1.6 -1.6 -1.6 -1.5
Valve_Toss None None None None None None None None None None
Spark_Adv 27 28 28 29 30 30 30 31 32 32

The other things that showed up were minor increases that could be had from using slightly bigger choke tubes, and also the existing intake manifold runners are a bit too long. I was expecting the huge cam to put the powerband higher, I guess the extra cubes balance it out a bit. Anyway, keep in mind these are just rough simulations so don't take the HP numbers as being gospel. Should be useful as a guide though..

Thank you very much for your time and effort it is very much appreciated. all the best.

[ljmate]

I think you are either running out of fuel pressure/volume. Or running short of valve spring pressure.
That is a very serious cam............
That is also a VERY serious output @ only 5600rpm. especially at only 10:1 comp!
I'd check the fuel and the springs.....
THEN. build a set of pipes 1"5/8" stepped to 1"3/4" @ the first merge then 2"1/4"@ 2nd merge to a 3" outlet.

That engine is going to have a LOT of bad breath to get rid of when that cam is on the boil!

Cheers Greg.. G, day Greg , thank for your input . so far it hasn't run out of fuel but yer that could be a problem after the exhaust is done. i remember the engine builder was very particular about the type of spring he was going to use and theres been no valve bounce .the running out of puff is coz of the current exhaust . Thanks

[ljmate]

i now run 1 5/8" H&M's tri Y's on my lj 202 red head and a 3" mandrel system because my old 1 3/4's fell apart from old age (they were gonzo's)... contrary to what every engine builder/dyno tuner said about them being way to big it would fall on its nose but it made truckloads more power thru the range on a dyno than it shouldve in their books... but they said that about me putting 308 valves etc in also... and revving it as hard as i do... i never had any luck with stroker cranks i kept breaking the rear journal off the bloody ford cranks whenever i revved them over 6000... your 230 is that RWHP?? and on whos dyno??

cheers
micko

G, day Micko , The first crank i had in the motor was the Ford 221 and yeah i busted the end of it as well . the crank in it now is a full cast made by a guy in Queensland Cit Cullen ,thats been heat treated . then just about the whole engines including the crank has been cryogenicly tempered ,what they do there is basically put it in a big fridge and freeze every thing down to absolute zero -273 Celsius . this was mainly done to strengthen the block. the 230 hp is at the rear wheels on a dyno dynamics dyno. was there a big drop in touque in the lower revs when you had the 1 3/4 headers? cheers Micko ... Leigh

[ljmate]

yeah bryants engineering used to do most of them up here 20 odd years ago... i believe they were also the pioneers in this technology... good in theory but not in practice... very unreliable... we went as far as getting 244ci out of one but couldnt rev it over about 4000 it used to break a cam almost every month they were only as big as a pencil in diameter where the reliefs for the crank were...

contrary to what everyone said and had me believing the 1 3/4 primaries made truckloads more than all my other combos i have tried... exact words of the dude driving it on the dyno was it pulls like a f%*#ing mack truck... but it was on metho back then also... alot of people these days are running genie tri y 88E's but imo they are a waste of time on a decent engine... these same pipes used to glow red on my engine (speedway) back in the "old" days lol

cheers Scary stuff yeah i remember now they took metal of the cam so the crank will clear.... might have to limit it to 6000 rpm .
micko