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Organized Drag Racing and AutocrossDrag racing and autocross discussions and questions. Techniques, tips, suggestions, and "what will I run?" questions.
Some of you may know my setup. Nothing special. Certainly a compromise between reasonably fast in any one discipline while still keeping the driveability and economy of the current combination.
It's basically a solid 12 second street car that can be a daily driver and not kill you in fuel.
What I've got is:
Carbed 355 with decent heads and small cam.
700R4 w/TCI 10" converter.
3.73 rear and 10.5 x 26 ET Streets.
Nothing special in suspension aside from air bags. OEM spec shocks.
3600 lbs.
I've managed a DA corrected 12.45 at 109. Best 60`was 1.71 but usually 1.8x.
I can also get 20+ mpg on the highway.
I`d like to go 11`s.
Quarter mile simulation show the need for another 50 hp.
What are our resident racer's thoughts?
From what we've discussed in the past:
A better converter.
Suspension to suit the converter.
How about more cam?
I want to keep the heads.
Carb and ignition are up to the task too.
Need much better heads and intake to match and it would pick up. Cam wont need to get to much bigger, it should be enough to get there with heads like afr 195's or equal
I'm a little disappointed to hear that in I that I was hoping the current heads could support north of 450 hp. It's difficult to get an accurate number on the cfm as RHS quotes the heads at flowing x with a 4.200 bore.
From what I've been able to find, the RHS Pro Torker do a pretty good job.
That said, a cam that moves the peak torque up another 500-1000 rpm and a converter that would work better than my TCI might make the difference.
I've thought about that. It's not the way I'd like to go but I have given it some thought. I'm somewhat concerned that I'd get caught up in the " if a little is good, then a lot must be better " way of thinking. Not sure my short block could stand too much nitrous!
Originally Posted by Orr89RocZ
You could keep the heads then but the cam and converter has to get much bigger to work
It's how much cam I would need and then there's the compression ratio to consider. At just under 10:1 now, I'm a little short of what I would consider optimal but I went through a tuning nightmare with nearly 10.5:1 and 200+ cranking pressure (and iron heads).
I have a XR288HR (288/294, 236/242. 520/540) on the shelf, but it's certainly not enough to add 50 hp compared to my little custom grind (274/282, 224/230, .574/569, XFI lobes).
A better converter is on my list (and has been for a while) as I know from previous experience how much of a difference a Yank spec'd to my combination makes compared to the off the shelf TCI 10" I using now.
At this point I have to get the heads refreshed. Probably to the tune of about $600. Any decent head here in Canada will run more than 2 grand ( AFR 195s are $2250 plus tax and shipping) but that's money I'd consider putting towards newer technology (as in LS). But that's down the road. For now, I just want to go little bit faster. But it doesn't look to be an inexpensive thing to do.
You'd be surprised... That 288hr has put stock long block l31's and lt1's into 11's but you need gear and alot of stall.
4000-4200 and atleast 3.73 to start. It may not give 50 peak hp but the cam will force hp to hold at higher rpms before falling off so it may make 50 more well beyond peak. Its power under the curve that makes it go.
Driveability goes down. And you will not have a tuning issue with that comp and cam. Cranking will be alot lower and it wont make low rpm cyl fill to worry about like current small cam does
Yeah. More gear and a better converter. I understand that. Reminds me of how the Super Stock guys achieve what they do with their "limited" horsepower.
I've got the 3.73 rear gear and combine that with the 3.06 first gear of the 700R4, it's not unlike a TH350 with a 4.5x gear set. My thinking is that might be enough for a decent 60' (personal best of 1.71) provided the converter is up to the task (which obviously mine isn't).
Interesting observation regarding the 288 in the L31. I can see that but my guess is those 11 second combinations must be pretty light. I'm a tank relatively speaking at 3650 lbs.
Still, you may be onto something. With the heads I have fresh out of the machine shop and the 288 cam (plus a little more compression with a head mill and a thinner head gasket) I might be able to position myself for a converter upgrade later in the season. It's better to have the engine combination dialed in before I call a converter supplier and get something specific to my ride.
Still thinking and running through more iterations on Dyno and Drag Sim.
Oh yeah, I need a better exhaust too....at least cutouts at the right length for race days.
I'm assuming your take on that would be to increase the overlap. Yes?
One thing I've found is that I'm suffering from a miserable exhaust. By that I mean, with a single 3 inch pipe to a poor flowing muffler, back pressure I'm sure is quite high. Evidence of this is the marked improvement in my 1/8 mile ET and MPH when I open the cutout I installed just upstream of the muffler. 8.124 @ 83.82 vs 8.070 @ 85.14 . A little tuning to correct AFRs would have netted better results still.
Trying to take advantage of more overlap (by way of pulse tuning/exhaust induced intake charge) is pointless with this exhaust. As it is there's evidence of reversion in the intake. I do have plans for collector length cutouts though.
That said, since we're taking about LSA, my understanding is that the novice builder (and I won't pretend to be anything but) most often makes the mistake of using too big a cam. One with duration numbers that result in too much overlap, killing driveability and low speed torque. Isn't this why (and I'm discussing the Gen 1 SBC here) the major cam manufacturers open up the LSA to 110 from (for a 350) a more optimal 108-106? To protect the engine assembler from himself.
I had thought the one change I should have made when I spec'd my current cam was to tighten up the LSA as you suggest, thereby getting a little more overlap (because truthfully the cam I have is tiny) while keeping the duration values in check. Note: At the time of this build, which was several years ago, I was quite happy to have a mid 12 second street car while achieving my target of 20+ MPG on the highway. I did that but now I want more!
Your comment about the L31 guys using the 288 cam has me intrigued. As you've pointed out, with a better converter, it's not so much a question of peak horsepower but rather the average power delivered to the rear tires. Even if the 288 results in another 15-20 hp, that combined with something like Vigilante, Yank, etc might get the results I'm looking for.
The converter is key.
Yeah most sbc setups seem to like 106-108 lsa. Better heads may like wider 110-112's.
But you do bring up good point, more duration has more overlap to begin with. And that wont be happy on a poor exhaust system.
Fix that, and try more cam and converter. Up the shifts. See how it goes.
Only other way to go faster using your current technique of trying to get good performance while keepin drivability and mileage is to go better head like a 195 afr or profiler and intake to match. Turn more rpm but cam is still small ish.
Yeah most sbc setups seem to like 106-108 lsa. Better heads may like wider 110-112's.
But you do bring up good point, more duration has more overlap to begin with. And that wont be happy on a poor exhaust system.
Fix that, and try more cam and converter. Up the shifts. See how it goes.
Only other way to go faster using your current technique of trying to get good performance while keepin drivability and mileage is to go better head like a 195 afr or profiler and intake to match. Turn more rpm but cam is still small ish.
That's about it in a nutshell. I have found some independent builds with these heads, and a few flow bench analysis that say they're capable of better than 450 chp. A basic ported Vortec is the best way to describe them so the potential is there in stock form. 1986Z28OWNER ( you know Charlie with the other 8 sec Camaro!) works in a local machine shop and I'll approach him about maybe getting a little head work done along with the refresh.
I'd go with the 288 cam but I'd feel better about it if I could get the DCR to were I would like it. As is, I'd be less than 7.5:1. Somewhere north of 8:1 would be better. That would help make up for some of low engine speed torque loss I'd see otherwise.
As for replacement heads, I've seen you mention the Profilers before and I've looked into them. Looks to be about the best bang for the buck. Certainly more economical than the AFRs. But for now, I'll work with what I've got.
Carbed. 20 mpg, 12 sec timeslips. Man that's a great setup you have going I would love to build one just like it!
It was my intention all along and I assembled the 1st version of this combination before EFI became even remotely affordable. I kept the intake runners small (170 cc Vortecs) and the cam on the milder side (XR276HR). The thing that made the carbed approach workable was the wide band O2 sensor and dash mounted vacuum gauge. I tuned the original 670 vacuum secondary to run lean cruise. Combine that with an OD trans with lockup converter and there you have it.
To do it all again, I could go faster still with a more powerful engine but I'd choose a throttle body style EFI. Then the tune is simpler. Especially the hybrid types that have both a self learn function and laptop accessibility.
Of course, you can buy a LSX454 with 620 hp and get 25 mpg out of it these days.
That's about it in a nutshell. I have found some independent builds with these heads, and a few flow bench analysis that say they're capable of better than 450 chp. A basic ported Vortec is the best way to describe them so the potential is there in stock form. 1986Z28OWNER ( you know Charlie with the other 8 sec Camaro!) works in a local machine shop and I'll approach him about maybe getting a little head work done along with the refresh.
I'd go with the 288 cam but I'd feel better about it if I could get the DCR to were I would like it. As is, I'd be less than 7.5:1. Somewhere north of 8:1 would be better. That would help make up for some of low engine speed torque loss I'd see otherwise.
As for replacement heads, I've seen you mention the Profilers before and I've looked into them. Looks to be about the best bang for the buck. Certainly more economical than the AFRs. But for now, I'll work with what I've got.
Talk to charlie, he posted about a vortec motor that made good steam with a cam similar to what you have now. Abit of minor cleanup will help get 10-15 cfm easily and with proper valve events with converter you can get your goal. Intake and heads work together so have them both looked at and see what it does. May like more carb too
Are you running LCA relocation brackets?
You can check out my sig for my setup. 12.01 at 112.45 mph with 1.62 60ft.
Stock bore L98 with just H/C/I. Im running Comp XE282hr on a 112 lsa.
Race weight with driver 3400. I am at 10.3-1 compression.
Oh yeah, that track is at 1200' elevation. Not sure on that day.
Are you running LCA relocation brackets?
You can check out my sig for my setup. 12.01 at 112.45 mph with 1.62 60ft.
Stock bore L98 with just H/C/I. Im running Comp XE282hr on a 112 lsa.
Race weight with driver 3400. I am at 10.3-1 compression.
Oh yeah, that track is at 1200' elevation. Not sure on that day.
Yes. Relocation brackets and air bags too. Still have a stock style shock/strut arrangement with the Sensatracs but I'll forgo the drag racing 90/10 approach as this is still a cruiser more than anything else. (I just want an 11 second cruiser!).
As for 60' times, this chassis has a PB of 1.71 but that suffers when the track prep isn't the best like opening day this season. I started this year with 2.0 60's but worked my way to 1.8 flat. My old and ancient ET Streets have seen better days.
I carry about 250 lbs over your race weight but your 12.01 is impressive nonetheless. I like the MPH too.
Elevation here is 2100' and DA is typically upwards of 3500' so it kills my time slips.
I will say though my PB at my old near sea level home track (600') was a corrected 12.4x at 109 mph (time slip said 12.6 at 107) and my best here at the elevated track was a 12.9 at 103 which corrected to...12.4x at 109. And that's with zero fuel pressure at the stripe (fueling issues plagued me all year).
By the way, if you give me the track name and the date/time of your PB, I can find the DA that day. Drag Times has an excellent data base.
I'll be checking out your signature for secrets....
...and having done that, I can see that you're ahead of my game with better heads and converter. Precisely what Orr and I have been discussing.
I can see my future now...
And that I did but in a brain fade moment I totally forgot to ask him about a little bowl and port work on these RHS heads. He'll be getting my rebuild business though. Gotta start somewhere.
Sadly, he didn't have a set of AFR 195s sitting on the shelf ready to sell at a discount.
...and having done that, I can see that you're ahead of my game with better heads and converter. Precisely what Orr and I have been discussing.
I can see my future now...
I had my heads and intake ported matched and flowed on a bench also. We also changed the back cut angle on the valves to see what flowed better. We milled the heads from 64cc to 60cc. That helped bump up the compression.
Plus I am running at 40* timing all in by 3k. No vacuum advance. I know the timing may be high, but the car likes it. We kept bumping it up to see what it likes.
I will see if I can find the time slip with my best pass for find the date.
For old afr 190 and L98 LT1 heads, 38-40 isnt really too much
We started out about 34*-36*. We bumped it up and the car picked up, so we gave it what it wanted. Ended up at 40* with out any detonation and it started great.
Timing brings up a good point and something I had forgotten.
When I first installed these heads on my short block, compression went to 10.4:1, with a DCR of 8.4:1 and cranking pressure in the 205 PSI range.
I pulled a lot of timing out of it just to keep it from blowing up. With the heads opened up to 66 cc and a .014" thicker head gasket (.026" to .040"), I still dialed the timing back to 34 degrees (which is about right for these heads) but it's not all in until 4000 rpm. If I hadn't been messing with fuel delivery problems most of the racing season (vapour lock or boiling or lack of volume or all of the above) I would have addressed the timing but never did. That's another tuning aid I can pull out once I sort out the heads and cam.
I would agree. I've found that compression isn't nearly as important to engine performance as timing. This is why, (until I started to fixate on this 11 second thing), I was happy to have less compression than I though optimal (I'm in the 9.8 range now) with cranking pressure in the range that you suggest.
With the installation of a bigger cam, there comes a point where some of the compression will have to restored. That's the connection I make with DCR and cranking pressure which are more or less the same thing. Having the value of one allows you to predict the value of another (with the right supporting data). The objective for me then, with the 288, will be to work out how much compression I will need to achieve a 180-190 psi cranking pressure. I see roughly in the area of 10.5:1 (SCR) to get that.
Can play with the icl abit but couple points wont hurt you too much. If it falls to the 170's psi it still can run hard if the valve events are on target to get cylinder fill in the higher rpms. Average power may still be up overall once exhaust is opened up
I had thought about installing the 288 in an advanced position to help with the low rpm torque and cranking pressure if I can't reach my target static compression. That, and seeing as my heads are on the small side, might help in the overall power production as running the engine to 6500 doesn't do much if the heads have given up. The only reason I shift at that RPM now is to get past that miserable 1-2 shift split in the 700R4. Once I have a proper converter, that will no longer be an issue. Or shouldn't be anyway.
I ran a couple of simulations comparing my 274 custom grind cam and 9.9:1 compression ratio with the 288 and increased compression of 10.5:1. That puts both builds with the same DCR and more or less the same cranking pressure which is about 185 on average.
Interesting to see that the 288 doesn't give up anything in torque or horsepower below peak and adds about a dozen HP at the top.
I had thought about installing the 288 in an advanced position to help with the low rpm torque and cranking pressure if I can't reach my target static compression. That, and seeing as my heads are on the small side, might help in the overall power production as running the engine to 6500 doesn't do much if the heads have given up. The only reason I shift at that RPM now is to get past that miserable 1-2 shift split in the 700R4. Once I have a proper converter, that will no longer be an issue. Or shouldn't be anyway.
Even with a higher stall it will still be an issue. I ran a 700 down into the upper tens and it was always an issue.
JMO but I would work on the heads, exhaust, and restall after the first two are done. Should be able to pick up a decent set of heads for not that much scratch. I think you would be shocked at how much you would pick up at the track. Especially if you have a poor exhaust setup.
If you loosen up the converter and start making more power MPG may suffer.
Even with a higher stall it will still be an issue. I ran a 700 down into the upper tens and it was always an issue.
JMO but I would work on the heads, exhaust, and restall after the first two are done. Should be able to pick up a decent set of heads for not that much scratch. I think you would be shocked at how much you would pick up at the track. Especially if you have a poor exhaust setup.
If you loosen up the converter and start making more power MPG may suffer.
My expectations of a properly spec'd converter are to duplicate what we did with the 81 Monte Carlo. It has a small block similar to mine with a 700R4 and 3.73 rear gear too. With the upgrade to a Yank designed for the application from a 10" TCI, out of the box like mine, saw about 2/10ths in a heavy 12 second car with street suspension. A tenth in the 60' but there wasn't much gained in foot braking. Maybe a few hundred rpm extra. 2500? Would my experience be the same? Can't say. What converter(s) were you using?
As for the heads and cam, the most interesting thing about the dyno simulations I've run (which I don't use for actual output numbers but more for comparisons sake) aren't so much what the new combination makes more power, which it does, but rather that the current setup has given up well before I'm shifting. 6500 rpm shows about a 75 hp difference. The heads I have now have the numbers to support my horsepower target. They're in the shop getting a going over too. I'll see where that takes me.
As for the exhaust, while I'd like to get the new Holley/BlackHeart duals, it's more practical to simply add cutouts in the appropriate place. I can uncork them at the track and that'll solve the exhaust issue.
Like you said, the converter will come after the new engine combination is sorted out.
As for mpg, this 288 cam I have, in the shortblock I have, with AFR 195 Eliminators squeezed out over 20 mpg (Imperial) on the highway. I can live with that.
i'm just a shadetree, but i doubt that mild of a cam change will get 50 HP? it will surely help some though. an so would some exhaust improvements. losing some weight would also help. i dont know what youve done to the heads, but perhaps some port work, spring change, gasket matching, etc., would add? for a gauranteed 50 HP, without the bottle, you cant beat stroking it.
It's not a peak horsepower thing but more power overall past peak torque. That I'm shifting a short cammed engine at an rpm where it's run out of steam, that's where the difference lies. Results from running the parts through DynoSim show that at 6500 with my 274 degree cam, (9.9:1) horsepower (for comparisons sake) is down to about 330 from a peak of nearly 400 at 5500 rpm whereas the 288 with higher compression (10.4 is making 400hp at 6500 from a peak of 420 at 6000. The actual numbers don't mean much but the difference in the numbers does. Even with the same converter as last season, it stands to reason the car will be quicker.
Of course there are always other changes....
50hp can be obtained with a cam change. It really depends on how far "off" the old cam was. My car had a XR288HR cam in it (off the shelf grind) when the original owner had the car. He swapped to a custom grind cam that, on paper, didn't look much different. The car picked up a ton in the 1/4! I just had Mike Jones from Jones racing cams cut me a cam to replace that one. He thinks 30hp is possible with this change...and the existing cam is pretty darn good. The new cam has a tighter LSA and the lobes are different. It will turn more RPM, which is where most of the horsepower increase will come from.
Your heads are probably your biggest bottleneck right now. Not that they wont work. Guys were making plenty of power with stockers and your heads are better than that.
I have no doubt the 288 will make more power. I'm also confident that these heads flow the cfm needed to make power in my target rev range.
My only real concern is whether the slower engine speed torque will be reduced to the point where my 60' time suffers. Something I believe will be taken care of with a different converter. But that's a ways off still.
You probably will suffer some low-end-loss. That is the trade off. With marginal heads, it takes more cam and RPM to make the power. With better cylinder heads, you can make the power with less cam.
I don't know how much you drive the car, but I was daily driving my IROC (except in the winter months) with my "similar to a 288" cam, 10.75:1 compression, 4.10 gears and a 3600 converter. I didn't mind it at all. The best move I made was swapping out the miniram for an air gap and a 750. Once I did that, I didn't even need the vacuum pump for my brakes anymore.
I have that custom Joe Overton cam still. Maybe you want to try it...
These RHS Pro Torker heads have better than average low lift numbers and that certainly helps with the lower rpm torque. Much like the Vortecs they're patterned after. What they have over the Vortecs is better high lift numbers and bigger valves. I could probably stand to add some intake lift which with the 288 is .540" with a 1.6 rocker. That's not going to change seeing that I already have the cam and hope to have it degreed this weekend.
I drive the car a lot. Every day if I can during the season. That was my logic in building with the small heads and cam. But now that I live about 25 minutes from the track, I'm prepared to give up some of that mileage in the pursuit of performance.
Thanks for the offer on the cam though but as I said, I've already got the 288 so I'll work with it.
12-26-2015, 07:09 PM
is making 400hp at 6500 from a peak of 420 at 6000. The actual numbers don't mean much but the difference in the numbers does. Even with the same converter as last season, it stands to reason the car will be quicker.
